MH-C9000 hesitates to cut off with cooling fan ?!

[webfors]

FYI: I'll post my results in the 'Improved c9000' thread:

https://www.candlepowerforums.com/threads/154300&page=4

in order to follow the thread titles more closely

I've got 4 'unhealthy' nexcells charging at 200ma now.

 

[tacoal]

Hi Tom,

You can measure the voltage on the battery in the time of on pulse and off pulse and make the difference, divided by the current through the battery in on pulse period. This is a rough estimation since it is hard to avoid the influence of contact resistence due to the low impedence of battery in practical application.

this charger claims to have the ability to adjust charging current according to the impedence of battery, a nice idea.

Hi Bill,

What I want to say for the example is that the charging wave form, mainly of current play a important role in the charging efficiency, heat generated during the charging and endurance of the battery. Surely, they are related each other. the so called "standard charge" usually means constant current charging, however, most of recent charger uses pulse charging current with different wave form. BC-900 is a square one, C9000 might be sawtooth one(guessed from the PCB photo), ......

Sorry I did quote your post to make the post clear since every time I did, the IE just hung there--it seems I am not welcomed to post here

 

[wptski]

tacoal:

The C9000 does produce a squarewave but it has some hash on it. I posted a waveform in one of these threads and asked William Cheuh about but never receiveed an answer about the hash.

Yeah, quotes are a problem.

 

[tacoal]

Hi Bill,

I didn't said it very clearly.

from the PCB board, there are four inductors, one for each charging channel. This inductor should be the basic part of buck converter. since I only saw three electrolytic capacitor on the PCB board, this means the output of buck converter is not filtered and the wave form is sawtooth during the on period. (as a contrast, BC-900 is flat during on period except the glitch caused by other channel on-off). this is mainly for cost saving. it will cause more noise and inaccuracy when you measure voltage during the on period, like the charging current. it also affect the calculation of charging capacity as a side effect.

 

[SilverFox]

Hello Tacoal,

Do you have that other charger?

Yes, it does sound like a good idea, but I am unclear if the charger does it automatically, or if they are offering several charge rates to accommodate batteries of different states of health.

Tom

 

[wptski]

tacoal:

A bit OT but that's the way these threads go sometimes!

I observed on the BC900's DC input from the wallwart with a current clamp probe a stairstep-like waveform. It conicided with the number of cells charging, one cell had no step, two cells had one step, three cells had two steps and four cells had three steps. I never looked at the C9000's input. I assume that's normal for a multi channel charger?

 

[Mike abcd]

Hello Mike,

It looks like we are actually getting closer on this.

We agree that there are standards in place.

We agree that all of the manufacturers use these standards to determine the capacities of their cells.

Frankly I don't see us "getting closer on this".

You're missing the point and still confusing standards for TESTING batteries that include a charging method with standards for charging batteries for best performance. There is a huge difference and standards for the later don't exist.

Yes, testing standards exist. No, I don't agree that all manufacturers are currently using the existing standards or at least any ones that you've posted or I've read about. As an example, as I previously posted, Sanyo states that they measure cycle life with a 1C charge terminated with a –dV = 10 mV. Is that a standard?

I suspect Sanyo isn't even using the standard for capacity testing to spec their Eneloop line. We're seeing the spec'ed capacity or higher with –dV termination and I'd expect capacity to be higher after a 16 hour .1C charge.

We agree that cycle life is determined by a reduction in capacity.

It appears that our discussion centers on the "best practice" for charging.

I determine cycle life by a reduction in watt-hours at the load of my requirement but otherwise agreed. For the record, I don't formally check watt-hours but I do periodically check run time on regulated lights which is a meaningful approximation. I time every cycle on my r/c heli LiPo packs.

I think I am beginning to understand… If you designed a charger, you would make sure that its performance could be compared using "Standard Practices," but if you are only a user of a charger, you are willing to review it based on what you believe to be information that is more accurate than what the standards offer. Furthermore, since the last revision of this standard seems to have been done in 2003, you believe it to be antiquated, not suitable for current technology, and you are aware that there has been a huge evolution of more accurate information since then.

I won't split hairs here too much so generally agreed. However, as I already said, my only concern in designing a charger would be for the things customers care about; charging time, charge completeness aka capacity, cycle life and of course cost. There are obviously tradeoffs between the features.

I also don't see a "huge evolution of more accurate information since" 2003. Again, the standards being discussed are for testing and the meaningful comparison of testing results on batteries. They're not intended as a guide to "best practice" for charging.

We pretty much agree here, however my main objective in charging is to obtain the highest watt-hours from my cells. I seem to place a higher priority on performance than you do.

I care a lot about real world performance Tom. I just don't view performance as narrowly as you apparently do.

I'm not going to overcharge my NiMh so I can get a better number on a discharge test or a short term higher Lux reading on a flashlight. Much of any overcharge bleeds off quickly and I rarely if ever use NiMH immediately after charging and won't give up usable cycles for it, etc.

My references to cycle testing came from the Handbook of Batteries, and a specification released by Harding Energy. The Handbook of Batteries states that about 500 cycles should be obtained from NiMh cells under the standard charge/discharge conditions of
0.1C charge for 16 hours and 0.2C discharge for 5 hours. The cells should retain 80% of their capacity during this testing.

Upon reviewing the Harding Energy document, I realized that the specification was for several NiCd cells, and the cycle testing was referred to as accelerated cycle life. I noticed an interesting note on the accelerated cycle life testing. They were limiting the charge to 120% of the NiCd cells capacity. I believe this comes from an earlier version of the standard. Perhaps Duracell got their 120% reference from this earlier version of the standard. I agree that a 0.1C charge for 12 hours will give you more than 80% of the batteries capacity.

12 hours at .1C on a fully discharged NiMH cell results in the same charge level as –dV termination. I think it's far more likely that's where Duracell got it from. You insist on calling that less than full capacity. Sanyo and Duracell disagree advising that the optimum charging method of a 1C charge with –dT/dt of 1 deg C followed by a .5 hr .1C top-off charge yields a slightly lower charge and 20% more cycles. A 12 hour .1C charge is fully charged according the battery manufacturers despite your insistence it isn't.

Yes, you can get more charge in the battery Tom, but a lot of that excess will bleed off as the battery exhibits a higher self-discharge than the one charged to a lower state. The difference a couple of days later will be very small and will cost you cycles and a decreased voltage under load earlier in the cycle life. Poor tradeoffs IMHO.

BTW, anything labeled "accelerated cycle life testing" screams "don't do this".

Endurance (cycle life) testing is covered in IEC 61951-2.

The standard no longer calls for the standard 0.1C charge for 16 hours, followed by the standard 0.2C discharge with this cycle repeated until capacity drops. Now you start with a standard charge, followed by a standard discharge to check the actual capacity. This becomes the standard reference capacity and is supposed to match the cells label. Now, moving on to the cycle testing, the cell is charged at 0.1C for 16 hours, followed by a 0.25C discharge for 2 hours and 20 minutes for cycle 1. Cycles 2 – 48 consist of a 0.25C charge for 3 hours 10 minutes, followed by a 0.25C discharge for 2 hours 20 minutes. Cycle 49 involves a 0.25C charge for 3 hours 10 minutes, followed by a 0.25C discharge to 1.0 volts. Cycle 50 is a standard charge of 0.1C for 16 hours, rest for 1 – 4 hours, followed by a standard discharge of 0.2C. If the standard discharge is longer than 3 hours, you gear up for the next 50 cycles. This is repeated until you get less than a 3 hour discharge. Once you get less than 3 hours on the standard discharge, you do another standard charge/discharge to verify your results. The test ends when you have 2 runs in a row with less than a 3 hour discharge. Breaks between 50 cycle runs are allowed "for convenience."

The total number of cycles when the test is completed shall not be less than 500.

It is interesting to note that at the higher charge rate, cycle life is determined utilizing around a 136% charge. Also note that we are still below the 0.3C charge rate where you start to have problems with oxygen recombination.

The standard goes on to state that for cycle testing, the cell temperature should not exceed 95 F. Forced air blowing over the cell is allowed to keep the cell wall temperature down, if needed.

There is an accelerated test procedure that allows 1C charging. Cycle 1 involves a standard 16 hour charge, followed by a 1C discharge to 1.0 volts. There is a 30 minute hold between charge and discharge, and also after the discharge. Cycle 2-48 involve a 1C charge, rest for 30 minutes, followed by a 1C discharge to 1.0 volts, and a rest for 30 minutes. Cycle 49 calls for a 1C charge, rest for 24 hours, followed by a 1C discharge to 1.0 volts and a rest for 30 minutes. Cycle 50 calls for a 1C charge, followed by a 0.1C charge for 2 hours. Rest for from 1 – 4 hours, then discharge at 0.2C to 1.0 volts. At this point you can rest until it is convenient to start another 50 cycles. This is repeated until the 50th cycle discharge is completed in less than 3 hours. Once again you have to verify your results with a repeat of the 50th charge/discharge cycle. The test ends when you have 2 runs with discharge times under 3 hours.

The total number of cycles when the test is completed shall not be less than 500.

Charge termination, when charging at 1C, is recommended by the manufacturer. Examples include negative delta Volts, or delta Temperature with respect to delta time.

Interesting but completely irrelevant to what constitutes "best practice".

It is interesting to note that the accelerated cycle life test involves adding a 2 hour 0.1C top off charge to a properly terminated fully charged battery. Sanyo states that they are charging at 1C, terminating with a negative delta V of 10 mV per cell and that they are getting more 500 cycles following this standard for cycle life.

I guess the 2 hour 100 mA top off feature on the C9000 is a non issue with cycle life.
[\QUOTE]
Wow, where did that conclusion come from???? Sanyo specifies their testing method right down to the rest period duration and test temperature. There is NO mention of a top-off charge. Even the ACCELERATED cycle life test you quoted only does the top off once every 50 cycles.

And you wonder why I think you're showing a positive bias to the C-9000…amazing…

I do stand corrected though… I thought the cycle testing was a series of standard charge/discharge cycles, but it is a little more involved.

Let's take a closer look at that Duracell document section 6.3.2 that you only partially quoted. The full quote is

"Charging at a constant current at the C/10 rate with time-limited charge termination is a convenient method to fully charge nickel-metal hydride batteries. At this current level, the generation of gas will not exceed the oxygen recombination rate. The charge should be terminated after 120 percent charge input, or approximately 12 hours for a fully discharged battery. Excessive overcharging should be avoided, as it can damage the battery."

I would like you to think about "At this current level, the generation of gas will not exceed the oxygen recombination rate."

I can make a good argument that as long as you are not exceeding the oxygen recombination rate, the cell temperature will not rise and although it will eventually lead to reduced cell performance through an eventual drying out of the electrolyte, it may not totally qualify as an "overcharge." It is most definitely not an "excessive overcharge condition."

"the generation of gas will not exceed the oxygen recombination rate" only means that internal pressure will not build and cause the cell to vent which would cause an immediate large and irreversible loss of capacity.

Per Sanyo, section 2-4-2 factors Affecting Battery Service Life"
"If a battery is overcharged and the negative electrode consumes oxygen gas formed at the positive electrode, the hydrogen absorbing alloy will become partially oxidized and will deteriorate the performance of the negative electrode. Therefore when charging the Twicell, it is necessary to avoid over-charging as repeated over-charging shortens battery service life."

Sanyo makes it clear that damage still occurs. You can try word dances around it all you want but the only question is not whether it's bad, it's how bad is it.

Now we are back to wondering why there is such an interest in the "standard capacity" of a cell…

Could it be that we are wondering just how long our cells in our application will last?

Or, which combination of cells should we use in a multi cell application?

Or, how do we measure the overall health and condition of our cells?

You may not ponder these questions, in which case your prime concern is with cycle life. If that is the case, the "best practice" for long cycle life is to charge to 95% of full capacity, and only do a 60% depth of discharge. I believe you can attain 1000 – 1500 cycles this way.

I find your condescending simplistic lecturing insulting. I'll try to keep this civil and refrain from anything further. Hopefully anyone else reading this will realize I'm not a simpleton needing childish lecturing who only cares about cycle life.

I have gone even further. I have done some carefully controlled tests comparing 0.1C charging for 12, 16, and 20 hours. Cells charged for 12 hours are not "fully" charged, whereas there is no difference between cells charged at 16 hours or 20 hours. It looks to me that 16 hours gives you a "full" charge. It is possible to get a full charge with a cell that is healthy and has low impedance and low internal resistance. As cells age, both the impedance and internal resistance increase. It is my understanding that the 16 hour charge was set with aged, not totally "healthy" cells in mind.

Are you actually claiming that a "full" charge is determined by charging until no additional charging increases the measured discharge capacity??? If so, you've convinced me I'm wasting my time other than giving the other members a fuller picture of NiMH charging issues and trade-offs.

Thankfully you don't give that advice to Li-On users.

You can only charge for longer amounts of time if the charge rate is below 0.3C. At 0.3C and above, you exceed the oxygen recombination rate of the cell. I wonder if the Swedish study chose 0.3C because they knew that was the lowest limit where damage from slight overcharging shows up. If they had gone lower than that, there is a good chance their 30% overcharge would have had no impact.

Already covered above in my response. According to Sanyo, damage occurs. The Swedish study evidently was just to compare the effect of the same additional percentage overcharge input at different charge rates. I suspect the 30% overcharge was about the highest they could go at 1C without causing cell venting.

I find your assumption that a 30% over charge at .3C can result in a loss of more than 50% cycle life but have no effect at .1C absurd.

In order for a batch of cells to be accepted according to the IEC standard, they must undergo, after determining its "standard capacity," a 0.1C charge for 48 hours, rested for from 1 – 4 hours, then using the standard discharge their capacity should not be less than their original capacity. If one cell fails this test, the batch is rejected.

I am confident that any surplus charge would bleed off during the 1 – 4 hour rest period.

I also need to point out that when using battery packs, it is not unusual for a cell in the pack to get out of balance. If the pack is welded together, your only way to balance the pack is to do a 0.1C charge for an extended period of time. The idea is that you can bring all the cells up to a full charge in the pack without damaging any of them. Some of the cells are at a higher state of charge, but the gentle 0.1C charge is enough to balance the pack without overcharging.

By definition, a full charge takes 16 hours at 0.1C, so there is no overcharge involved. I understand that you can get increased cycle life by undercharging, but you loose performance. Also, I do advise people to start with a discharged cell, but if you are working with a battery pack it is better to just charge it up, rather than trying to do a discharge first.

"By definition, a full charge takes 16 hours at 0.1C, so there is no overcharge involved."

Wow, nice circular reasoning. Start with a fallacy as an assumption and end up with a fallacy as a conclusion. I'm amazed you continue to ignore all the references I've posted.

Pack charging is a whole other topic Tom. If you want to discuss it, start a thread and I'll chime in. I definitely have some opinions that run contrary to yours. In general I avoid serial charging NiCad/NiMH whenever possible but there are things you can do to maximize pack life. When it comes to LiOn/LiPo, I will never use serial charging because of the dangers and all of my 15+ LiPo packs have taps that allow independent charging of each cell.

I do agree that continuous charging at 0.1C is not good for your cells, neither is extended trickle charging. However, I have seen no studies or other information that suggests that a standard charge is detrimental to your cells. As a matter of fact, it usually improves the cells performance. I agree that excessive overcharging is not good for your cells, but I don't consider a "standard" charge as excessive.

You've seen lots of "information that suggests that a standard charge is detrimental to your cells" from the cell manufacturers that I've quoted with references in my posts. You just choose to disregard it.

It would be interesting to do a test to confirm this, but you can only get about 1 cycle a day. The test would run for over 500 days. I found it hard enough to do the 150 cycle testing, I think I will pass on this.

At last, something we agree on.

An interesting observation on your comments about the cycle testing observations, is that even though the Sanyo 2500 mAh cell that was fast charged on the Energizer 15 minute charger has developed a high impedance and can not be charge on the 15 minute charger, it is still above 60% capacity. This means that according to the IEC standard, it still has some cycles left in it.

It seems you mixed up the two different tests. I also tested some Titanium 2000 mAh cells. They are the ones that were still going strong after 150 cycles. Although the Sanyo cells seem to have some cycles left in them, I wouldn't use them, but the Titanium cells are doing quite well.

I didn't mix up the tests Tom. They were both in the same thread and I read the whole thing. You portrayed your test as evidence that the cells aren't damaged by charging to a temperature of 140 deg F and were "still going strong after 150 cycles". I simply pointed out that the higher capacity cells had evidently degraded appreciably faster on the Energizer and that the temperature reports in the thread were significantly lower than 140 deg F.

In fairness, you did state it was the "lower capacity cells" still going strong but I still find your portrayal of your test results misleading and largely irrelevant to the current discussion.

I brought up the cycle testing because it offered a look at high temperature versus low temperature charging. It is clouded by the charge rates and 100% depth of discharge, but it is the closest thing I have to a temperature study on cell life. I am sorry that you were unable to understand the point I was trying to make. Just to clarify, the Energizer 15 minute charger heats cells up warmer than the Sanyo charger does. In spite of the extra heat and fast charging rates, the Titanium cell was performing very well after 150 cycles. I am still not at 500, but think it may be attainable. The Sanyo cells died. The lower temperature charging cell did a little bit better, but it is still not fit for service, in my opinion, after 150 cycles.

If you would like to share your cycle testing results indicating the effects of temperature, I am sure we would all like to review it…

I don't have formal test results Tom, just close to two decades of informal "field" testing with a wide assortment of devices with LOTS of batteries and well over a dozen chargers starting with NiCads long before NiMh was available. I realized from experience that over charging and high charge temperatures were hurting my run times and cycle life even with NiCads and far more critical with NiMH. The manufacturer's documents I've since read only confirmed what it took a long time to learn by myself and let me understand the mechanism involved. None of that info was readily available before the web came into being and my experience goes back beyond that.

It sounds like you would like the C808M. It is not compact, but the heat generating components are removed from the cell holder.

From what I've read on CPF of the terminal charge temps folks are seeing on the C808M, I'm sure I'd like its' charging a LOT more than the C-9000!

I agree that the C9000 generates heat when charging 4 cells at 2000 mA, but you are not forced to use that setting. If you want to keep your cells cool, charge at one of the lower rates. Since Maha has improved the charge termination algorithm, we don't seem to have issues with missed terminations, and the cells are running cooler.

I bought the C-9000 for a few reasons in its' specs;

- ability to charge at 2000 mA with four cells

- -dT/dt termination capability which keeps termination temperatures lower and is more reliable than -dV

- large physical size which I expected would mean less battery heating from the charge circuitry waste heat.

- ability to discharge at 1000 mA and not start recharging automatically like the BC-900.

One out of four is not nearly good enough for me. What I'm using already works far better. It's just less convenient. I've seriously considered modding it to minimize cell heating or kludging an external charge setup but the 200 mAH "top off" is a show stopper.

I initially charge on a Lenmar Mach 1 Gamma charger. It uses dT/dt termination and a variable charge rate that averages around 1C. It keeps batteries a LOT cooler, even charging four AA, than anything else I've seen or heard about but significantly under charges batteries on fast charge. I pull the cells after the fast charge and put them in a BC-900 to complete charging.

I never charge more than two batteries at a time over 500 mA to limit waste heat from the charger heating the batteries. Usually it's two AAA at 500 mA or two AA at 1000 mA. Max charge temps in the BC-900 are much lower than they are when doing a full charge on it at the same rate since the charger takes a while to heat up and the batteries have far less time to get heated up by the charger.

One annoyance is that cells come off the Lenmar at very close or just over the cut off voltage of the BC-900 for starting fast charging so sometimes I have to let them sit for a few minutes before the BC-900 will fast charge them.

With a 70 F ambient, none of my batteries ever get over 110 F. They stay below 85 F during the entire Lenmar charge time. They spend less than 30 minutes on the BC-900 with the first 20 minutes at below 95 F and most finishing below 106 F. I always check charge input and it never misses charge termination.

It's the best I've come up with in close to 20 years of trying and far better than the C-9000 IMHO. My oldest batteries charged with this method are over 100 cycles and show less than a 5% capacity loss.

Bill has been logging some impedance measurements during charging. It is very interesting to see that while you would expect some changes during the charge, the are not of the magnitude I expected, and some of them are not in the direction I was expecting. For example, Bill measured the impedance during charging a Duracell cell. It started out up, then dropped as soon as the charge started. It stayed pretty level throughout the charge, then shot back up to where it started as soon as the charge was complete. I would have expected the impedance to gradually drop as the cell temperature heated up, then dropped way down at the termination of the charge. Over the next few minutes, I could see it gradually ramp its way back up as the cell cooled down, but that is not what we observed.

I think I've seen all his posts on CPF about it. From what I remember, the results didn't surprise me as much as you although I think I also expected a larger impedance drop at the end of charge. Frankly, at the risk of upsetting Bill again which I sincerely don't want to do, I wonder about the accuracy of the measurement particularly in the presence of a large PWM charging current. I don't remember reading a description of how it performs the measurement but from what I've read, it's not an easy measurement to make. I just don't know enough to venture opinions or comment but remain interested.

I assume you are joking… First of all, I have no connection, nor do I work for Maha. Secondly, they did not ask me for a set of design features. Finally, you don't charge NiMh cells in parallel.

I wish I was joking about your apparent bias. I don't pretend to understand why and I really hate coming across as bashing the charger. It's just really hard to avoid when you keep posting things like "hot hot is hot?" It's a major disappointment to me but there are lots of chargers that are worse. It's just more expensive, two years late, bigger and not better at charging than the BC-900 IMHO.

I do let them know of problems I am having, and I did send them a couple sets of "problem" cells.

The ability to Break-In and analyze C and D cells is a good feature to have, in my opinion. The quality and consistency of these high capacity cells is poor, and their cost is high. If there was a way to match them up and properly break them in, we would get better performance from them. You are correct, however. This added feature should not come at the expense of charging AA and AAA cells.

I know from experience that new cells usually require conditioning to reach a stable capacity and always condition and capacity match for any batteries used as a "pack" or away from home. I find my method a lot quicker and just as effective as "forming cells" with a 39 hour ICE standard so that's a worthless feature to me and a discussion for another thread.

The ability to charge C/D cells externally by hacking a connecting arrangement and charge cables is useless to me and I suspect the vast majority of Maha's customers. I have one 3 D Dorcy Luxeon flashlight that rarely gets used, a months supply of continuous use of alkaline batteries to feed it in the frig for a (very) long term emergency I hope I never see and 4AA to D cell adapters for it for more serious use when I stop these long replies and get around to putting one of the SSC P4 emitters in it that I have waiting.

The C808M doesn't have problems charging the high capacity C and D cells at 2000 mA, so I wouldn't expect there to be a problem with the C9000 either. 2000 mA is about as fast as you want to charge these cells. If you try to charge them at 0.5C, they get very hot. It seems the larger size does not allow them to dissipate heat as well as the AA cells do.

Interesting… I was beginning to think you worked for Duracell. J

It is my passionate humble opinion that the C9000 is an excellent charger/analyzer. I am also very passionate about my Schulze. Most people aren't interested in the monetary investment required for the Schulze, nor are they willing to spend the time to figure it out. I like the features of the BC-900, but don't trust it. Mine has worked without problems over the last couple of years, but I keep a close eye on it. I also like the added flexibility the C9000 offers.

Your entitled to your opinion, I'm entitled to mine and any folks reading this less than pleasant exchange are entitled to theirs.

I've stopped worrying about my V32 BC-900 after putting so many batteries through it. At worst, it'll ruin a couple of cells and I doubt that will happen as I don't use the 200 mA rate where most of the MOSFET thermal runaways seem to have happened. I completely trust it not to miss termination based on lots of experience. I'll probably spot a bad cell long before it gets bad enough to miss a charge termination in the BC-900. If it died tomorrow, I'd immediately order another. I really wish the C-9000 had let me put it in a closet or give it away like I hoped though.

Is the C9000 perfect? No. It still heats up when charging 4 cells at 2000 mA. However, I think I can live with cell temperatures in the 115 F range when charging AAA cells at 2000 mA, and the highest I have seen with AA cells after Maha improved the charging algorithm has been 137 F, but most have been below 130 F. I consider this warm, and not hot.

I've never seen temps below 130 F on the inner slots when charging 4 AA at 2000 mA including on new Maha Powerex 2700 AA cells that hit over 135 F.

"How hot is hot" again??? I covered that in my last post. The C-9000 is way too hot IMHO and FAR worse than what I'm using.

Getting back to "best practice…"

It seems that the "best practice" for cycle life is to keep cell temperatures below 95 F. The "best practice" for performance is to heat the cells up to around 140 F. The "best practice" for negative delta V termination is to charge at 1C. The "best practice" for delta temperature termination is to have an independent dedicated temperature sensor for each cell and make sure that it is accurately reading the cell temperature. The "best practice" for charger design is to have the heat producing components separate from the cells, but the "best practice" for a compact charger is to have the components combined in the same box. The "best practice" for keeping cells cool is to have a fan blowing air over them, but the "best practice" for reliability is to eliminate moving parts. The "best practice" to break in a new cell or battery pack is the "standard" charge. The "best practice" to balance a battery pack is the "standard" charge. The "best practice" for storing NiMh cells is to store them in a discharged state and cycle them through a charge/discharge cycle every 30 days. The "best practice" for charging is in an ambient temperature of 68 F.

The C9000 package comes closer to the "best practice" in charging than any other consumer charger.

Tom

Let's see, somewhere around 12-15 "best practice" items there. Several completely irrelevant to a charging discussion and/or the C-9000, a couple I disagree with and only one (cycling cells) that the C-9000 actually adheres to and I also agree with. I can make an item by item list on request.

I hope you're not surprised I don't find your conclusion convincing.

Mike

 

[Mike abcd]

Mike my eyes are bleeding from your micro-sized font size in that long post just now. LOL! Great post, but now I'm seeing bleeding elephants wandering around the room.

Hi Mike,
great post!

I just wondered how you guys can post such a long post. The IE always hang there if I did it.

Thanks guys, it's nice to know that at least some folks see some value in my long posts.

tacoal,

I find Firefox a lot more stable than IE which I no longer use. I also learned a long time ago to periodically copy my reply into another program and save it just in case. On really long replies like these, I generally do it all in another program and then just paste the whole reply. MS Word works but will result in lots of extra line spacing unless you manually edit the spacing after pasting into the CPF reply window.

L_L,

Sorry about the small fonts from the reference cut and pastes. I'll try to be more careful to check and reset font sizes when needed.

Mike

 

[Mike abcd]

Tom:

I just remembered that I ran into a similiar situation in one of the other C9000 threads. The same brand and size of cells. Mike abcd suggested that my cells weren't discharged but I know for sure that they were. I repeated the test and all was well! I'm wonder if there's something about discharging 1.8Ah cells at 1A because it was the first charge that was off? I'll have to try again at .5A.

I took four 2,2Ah Energizer cell and did the same 1A discharge but of course I charged at 2A only. They frinished at 78,81,83 and 87 minutes not like the 15-20 minute difference I seen with the PowserEx 1.8Ah cells.

Hi Bill,

I did a poor job of explaining it at the time but I never meant to say you did anything "wrong". It was just that the center cells showed a low lower charge input than the outer ones on that particular test. I thought that explained the lower temps you saw and was just postulating possible reasons for the lower charge input.

Again my apologies. I greatly value the contibutions you made posting your test results with your fancy toys (drool) and hope there are no hard feelings.

Mike

 

[wptski]

Mike:

I think the impedance graphs that Tom is refering to is in this seperate thread:Impedance where I used a Duratrax ICE which uses constant current. I did post a few in whatever thread using the C9000 but like you stated the PWM makes it messy!

The post that I refered back to where you suggested that the cells weren't discharged was actually kind-of good because "something" did happen there. I just seen it happen again with these other 1.8Ah PowerEx cells and just again with some 2.3Ah Duracells. I discharged those alternating between .5A and 1A. The cell that was discharged at 1A finished way early in Slot#2. I discharged them all at .5A and rotated them in slot position. Maybe it's something with Slot#2 only!

In normal usage, when a cell finishes ahead of others I blame SOC or other factors but when their all discharged they should finish fairly close. So they don't, they discharge showing the same spread and after a .1C charge for 16 hours they do discharge close! Something is wrong!!

 

[Bear]

Mike, I really appreciate your posts. They are really informative. Like you I have been involved in standards committees, not directly, but I ran experminents and fed data to people to present at committee meetings. I agree with a lot of what you are saying. I also agree with a lot of what SilverFox has been saying too. More on this in a minute.

First though, I feel bad in a way prolonging this thread. Mike, you seem to be upset in the one post above. Most of us come here as a hobby to fave fun, not get upset or see other people get upset. OK, enough of that.... I hope you're not upset now though

As a new product, I think that most people approach commenting on the C9000 carefully, to be fair. Even more so with the latest improvement. We, and the C9000, are kind of like at stage of "two dogs sniffing each others butts" phase right now, LOL.

I think what we have here is some information that seems to irreconcilable. That is, to what extent is an overcharging bad, or is it really good, and to what extent are high temperatures detrimental, or even beneficial?

A portion of this answer depends on a user's goals, maximizing performance or number of cycles or somewhere in the middle of those extremes.

Another portion of the answer to this depends on whether not a chunk of cathode wants to go into solution or not, or get oxidized, at the end of charge. This depends on the chemistry of the material, the temperature, and also the "energy state" of the material with regard to its "cold work" history, which in turn would depend on the material plus all of the forming steps (bending, stamping, etc.) involved in getting the material to its final form. That is, the manufacturing process itself has an effect. And of course, there are all of the other components of the cell too.

There is no realistic way for a consumer to know all of the precise details of the batteries plus the details of all the manufacturing processes, related quality standards and practices, and the like. So, we are in a position of having to make judgements based on consensus standards, personal experiences, inferences, and performance data from relatively small data sets, etc. Its tough to come to terms with a lot of this. Thanks to a lot of the dedicated people here we do have a lot of insight though.

So, what I am saying is that you and SilverFox are both right. Take the Duracell data as an example. Maybe the 120% is a valid number for that brand. And so on. BTW I am wondering if Duracell really is a bit intolerant to overcharge based on it melting down one LaCrosse charger (mentioned above). Plus my own experience is that Duracells seem to self-discharge quicker than other brands. My only split NiMH cell was a Duracell. BTW#2: I noticed capacity improvement from about 1750 mah to 1950 mah with Eneloops using standard forming charge on the C9000.

Mike, when you get a chance, can you open a thread on your own forming charge technique?

Switching gears... impedance vs. SOC. The data makes sense to me in this way: Fully charged or fully discharged results in the active metal being fully deposited on the cathode or anode. For any other SOC in the middle of those extremes some of the active metal will be in solution and add to the cell's conductivity.

 

[webfors]

I've stopped worrying about my V32 BC-900 after putting so many batteries through it. At worst, it'll ruin a couple of cells and I doubt that will happen as I don't use the 200 mA rate where most of the MOSFET thermal runaways seem to have happened.

My bc900 meltdown happened at 500ma, charging 4 AA 2500mah, relatively new batteries.. maybe 10 cycles on them. And it wasn't just the batteries that were cooked, the charger was destroyed along with the finishing on my brand new PSB hi-fi monitors. I know.. I should never have placed the charger on top of my precious speakers, but I never experienced a charger meltdown before, and was quite naive about the idea.

The charger worked beautifully for almost a year and I thought I would never need another charger. How wrong I was

Mike, have you tried the new 'revision'? If not, I suggest you exchange your current c9000 for the new version. I bet it will resolve a lot of the issues you have with this charger.

Personally, I'm not that involved with my cells. Yes, I agree too much heat is bad. That's why I like my 808M and LP4000N the best. These are the coolest chargers I have used. The new c9000 comes a close 3rd with respect to heat generation and is much better then my first c9000.

 

[coppertrail]

I'm running a set of 4 Sony 2700 mAh cells through a cycle mode on the "new" C9000 using a charge rate of 1400 mA / discharge rate of 500 mA. I'll keep an eye on the heat. Unfortunately, my Raytek MT6 won't arrive until Monday, so I can't get cell temps during charge.

 

[webfors]

I'm running a set of 4 Sony 2700 mAh cells through a cycle mode on the "new" C9000 using a charge rate of 1400 mA / discharge rate of 500 mA. I'll keep an eye on the heat. Unfortunately, my Raytek MT6 won't arrive until Monday, so I can't get cell temps during charge.

Keep us posted. I charged 4 powerex 2700's at 2amps, and the heat generated was low when compared to the first version, and to other chargers like the 204w. I'm very happy with the new version so far.. and am even happier with the way Maha/TD handled it all.

 

[wptski]

In reference to a couple of my posts above refering to the C9000 habit of the center cells, moreso Slot#2 finishing way ahead of the others.

I thought that it was the fact that the cells weren't discharging fully, so I discharged some at .5A and some at 1A, rotated the cells and since I have two chargers, I tried the other one but it always did it!

I finally found "part" of the answer! It's the charging rate. Duracell 2.3Ah discharged at .5A and charged at the 1A default rate. The center slots didn't finish first this time. It appears and just a guess on my part that the at higher rates the center cells pick up more heat from the charger which affects the termination.

It would take more testing to find out at what point heat becomes a factor. It's going to depend on the cells capacity, SOC, impedance, etc.

I should have my C9000 replacements on Monday, it'll be interesting to see if they do the same thing!

 

[dekelsey61]

Webfors,
I also have the newer version of the C9000. Heat on the cells is very low. It is alot better than the 1st version of the C9000. Coppertrail will find this out when he finishes with his charging. Heat is really not a issue that I can see so far. Good luck.
Dan

Keep us posted. I charged 4 powerex 2700's at 2amps, and the heat generated was low when compared to the first version, and to other chargers like the 204w. I'm very happy with the new version so far.. and am even happier with the way Maha/TD handled it all.

 

[SilverFox]

Hello Mike,

You're missing the point and still confusing standards for TESTING batteries that include a charging method with standards for charging batteries for best performance. There is a huge difference and standards for the later don't exist.

I don't think I am missing the point at all.

People complain that they get poor cycle life. I suggest that if we charge according to what the battery manufacturers use when establishing their cycle life, we should get close to their 500 cycles.

You jump in and say that the charging methods used by all of the battery manufacturers to substantiate their 500 cycle life claims are severely damaging the cells. I have to stop and ask "How are they managing to get over 500 cycles if they are severely damaging their cells with their charging methods?"

Yes, testing standards exist. No, I don't agree that all manufacturers are currently using the existing standards or at least any ones that you've posted or I've read about. As an example, as I previously posted, Sanyo states that they measure cycle life with a 1C charge terminated with a –dV = 10 mV. Is that a standard?

Yes. That is exactly what the standard calls for under "Accelerated Life Cycle Testing." If that screams "don't do this," one has to wonder why Sanyo (and others) embrace it.

I also don't see a "huge evolution of more accurate information since" 2003. Again, the standards being discussed are for testing and the meaningful comparison of testing results on batteries. They're not intended as a guide to "best practice" for charging.

I care a lot about real world performance Tom. I just don't view performance as narrowly as you apparently do.

This seems to be the crux of our discussions.

If I were to start from scratch to establish a "best practice" for charging, I would want a method that gives me maximum capacity and long cycle life. This seems to be exactly what the standard practices offer. If I follow them, I can be assured of over 500 cycles, and that is reasonable life for me.

I do narrow things down by demanding voltage retention under load, and I have a lot of multi cell applications, so I don't spend time dealing with "marginally healthy" cells. I tend to recycle my cells when they have reached 80% of their labeled capacity.

I do pay a price for following these narrow guidelines and practices. I find that I replace my cells after 250 – 300 cycles, which is about two years of use for me.

However, the benefits far outweigh the costs. I don't have problems with mismatched cells. I don't have problems with cells in a pack going out of balance, even with hard use. My cells don't heat up while charging. Finally, my discharge performance is very consistent from run to run.

A $2 battery that runs consistently for 250 cycles seems very economical to me.

I understand that some people prefer cycle life to performance. The best study I read on this was an evaluation done by a college class for an electric vehicle. They found that by charging to 90% of full charge (using a timer) and limiting the depth of discharge to 60% (once again using a timer), they were still going strong with their NiMh cells after 3500 cycles.

There was no mention of charge method, charge rates, or discharge rates used during the study.

I have tried this. The Schulze allows you to terminate on capacity and a timer will work for discharge times. This seems to work well for single cell applications, but multi cell packs don't seem to balance well. An individual cell balancer must be required to make this work well. I did not run it long enough to get valid comparison data.

I believe the Toyota Prius uses something similar with their NiMh battery pack.

If you are interested in maximum cycle life, that sounds like the best way to go.

I can see that we are back to the 12 hour 0.1C discussion…

I have been thinking a lot about this, and finally realized that I have also heard of that. I have been trying to remember where and all of the sudden it came to me.

This is a standard reference when charging NiCd cells. Early on, the chargers for NiCd cells used a 12 hour timer and charged at 0.1C. The first IEC standard for NiCd cells that I reviewed had the standard charge as 14 hours at 0.1C. In 2001, the standard charge for NiCd cells was changed to 16 hours at 0.1C to insure uniformity between NiCd and NiMh test methods.

I did find another manufacturer that supported the 120% charge limit. GP did a series of cycle testing exploring some different termination values. Normally, they recommend a limit of 105% when charging at 1C, however for this test, they used a timed charge of 120%. They compared this to two different values of negative delta V, 2 mV per cell and 30 mV per cell.

The cells charged to 120% went for 500 cycles down to 80% of their initial standard capacity. The cells charged to a negative delta V of 30 mV per cell only went for 400 cycles. Finally, the cells that charged to a negative delta V of 2 mV per cell went for 700 cycles.

They recommend using a 2 mV per cell value, but give a range of 0-5 mV. Still, I was impressed with the performance of the 120% cells.

Also, note that this is less than the 130% used in the Swedish study.

Yes, you can get more charge in the battery Tom, but a lot of that excess will bleed off as the battery exhibits a higher self-discharge than the one charged to a lower state. The difference a couple of days later will be very small and will cost you cycles and a decreased voltage under load earlier in the cycle life. Poor tradeoffs IMHO.

I think we almost agree here… Let me expand on your statement a little.

The excess surface charge will bleed off over roughly the first 30 minutes. After that the self discharge rate is pretty uniform over the next 5 days. "Hot off the charger" enhanced performance requires using the cells in less than 10 minutes after the charge completes.

I have found that if you charge a cell at 0.5C with a negative delta V of 3 mV, let it sit for a week and then discharge it. It will have a lower voltage under load, and a lower capacity, then if it is charged at 0.5C and topped off with a 0.1C charge for 4 hours and left to sit for a week. If I do a 16 hour 0.1C charge and compare it with the charge + top off I don't see much difference, so my conclusion is that my charge + top off is fully charging the battery, whereas my charge only is not.

I have some cells that I did a "standard" charge on 3 days ago. Normally, after 3 days, I expect to see a voltage around 1.33 – 1.36 volts when the cells are fast charged. These cells, after 3 days, are at 1.399 volts.

Battery chemistry is a very complex subject, and I am not a chemist. I understand the various phases involved in charging, and I understand the cautions about overcharging. I also understand the concept of equilibrium.

In a cell under charge, it seems that the chemical process remains in equilibrium until the charge rate approaches and exceeds 0.3C. Once you get to 0.3C and above, you need charge termination and need to heed all of the warnings about overcharging. However, below that rate, things seem to pretty much say in equilibrium.

GP states that in mission critical applications such as emergency lighting, you can expect good performance even after 8760 hours of charging at 0.1C. If 16 hours is a full charge, 8760 hours is 547.5 times that. They do refer to this as an extended overcharge condition, and prefer the charge to be terminated at 16 hours.

This is something new that only relates to NiMh cells. You can't do that with NiCd cells because of Cadmium migration.

Sanyo makes it clear that damage still occurs. You can try word dances around it all you want but the only question is not whether it's bad, it's how bad is it.

I will throw the question right back at you. If the cells still work in a mission critical application after 1 year of constant 0.1C charging, how bad is a 16 hour 0.1C charge?

Are you actually claiming that a "full" charge is determined by charging until no additional charging increases the measured discharge capacity??? If so, you've convinced me I'm wasting my time other than giving the other members a fuller picture of NiMH charging issues and trade-offs.

I am sorry I didn't make myself clear. Let me rephrase it this way. If my cell states 2500 mAh capacity with a minimum of 2300 mAh, a "full charge" will give me over 2300 mAh of capacity.

To further clarify, I understand that I have to know the conditions that the rated capacity was derived at, and I will have to follow similar procedures to verify the condition of my cells.

I don't have formal test results Tom, just close to two decades of informal "field" testing with a wide assortment of devices with LOTS of batteries and well over a dozen chargers starting with NiCads long before NiMh was available. I realized from experience that over charging and high charge temperatures were hurting my run times and cycle life even with NiCads and far more critical with NiMH. The manufacturer's documents I've since read only confirmed what it took a long time to learn by myself and let me understand the mechanism involved. None of that info was readily available before the web came into being and my experience goes back beyond that.

Personal experience is very valuable, even without documentation. Thank you for sharing yours. I continue to believe that we are very close in our ideas, even though you disagree.

I didn't get started with rechargeable energy until early in the 1980's. At that time all of my chargers were timed 0.1C chargers. I had really good luck with them back then, and continue to have good luck with slow, timed charges today.

I didn't get into fast charging until early in the 1990's. I got involved in RC cars and wanted to do several runs a day and did not want to have a huge inventory of battery packs.

We blew a few packs up, testing the limits, and settled on a pack temperature that was a balance of cycle life and competitive performance. The frequent failure we had was having a cell go out of balance and drag the whole pack down. I, and my boys, did not understand pack balancing and cell reversal, but we experienced it on occasion. Overall we had a very good experience.

I have a lot of "mission critical" equipment that I use in my work, including flashlights. I spend more time qualifying my replacement batteries now, but also have far fewer issues with my equipment. I walk my talk and have very few battery problems, so I feel I am doing a pretty good job.

It sounds like you are not satisfied with the C9000. I don't know if you have exchanged yours for the improved C9000, but it may be worth checking out. It seems to be unable to miss a termination, even when charging at 200 mA. At 200 mA, the temperatures are barely above ambient.

Tom

 

[LuxLuthor]

More good reading, thanks.

So given the improvement in termination of the revised C9000 with lower charging currents, other than speed, is there any reason to charge NiMH at 0.8 - 1.0C vs. 0.3 to 0.6C

Another thing I have not read much about is the effect of various DISCHARGING rates with this charger.

 

[bp044]

Hello Tom ; Bottom line. If i charge eneloop cells at 0.5c will this give me a reasonable cycle life and decent charge. ? Quantify if possible or suggest alternative chargr rate.Gratefull for your input.

 

[webfors]

My rule is .5c or 1 amp charge rate, whichever is higher. With eneloops .5c is exactly 1 amp charge rate, and would provide a good balance of performance versus cycle life, and would adhere to the .5c charge rate recommendation by Maha. Can't go wrong with that logic