MH-C9000 BREAK-IN not safe? CYCLE or REFRESH instead?

I've recently upgraded to the MH-C9000 for proper charging methods. I began reading the manual regarding the different modes, noticing the implied importance of the BREAK-IN mode, for fresh or old batteries. I recognized it follows a rather basic, unwavering formula, charging any given cell at 10% its capacity per hour for 16 hours (overloading during the final 6), discharging, then charging again. It states overloading cells is "safe" because of the low(er) charge rate, which may contain some truth. Common sense seemed like overloading is generally a bad idea.

Unsurprisingly, the first 4 AA cells (Duracell 2450 mAh) I used BREAK-IN for were popping & venting dozens of time after their rated capacities began to become overloaded. It is my understanding that at no point should a cell have to vent under safe operating conditions, or am I mistaken? Venting also degrades the cell & lowers the capacity as properties escape the cell, no? The ambient room temperature was around 50-60 F, with a fan circulating air directly over; this was not a heat issue. I tried a different model of AA cell, an Energizer, same deal, maybe not as much venting. AAA cells did not readily appear to vent with their lower charging rates, though I couldn't be certain. Before every BREAK-IN, I made sure the cells were fully discharged, as well.

The manual recommends BREAK-IN for fresh cells and once every 30 cycles. I don't trust this based on my experiences. Input? Maybe I just don't understand it, but overloading seems to be doing a lot more harm than good. With a large order of new Imedion cells coming in, I am cautious to use BREAK-IN on them. Rather set a custom & safer CYCLE or REFRESH mode instead for similar effect? Or compensate for the formulaic overloading by inputting a lower capacity?

You should always discharge the cells completely before a break in. If they're already charged or nearly charged, then you add another 1.44 C of charge via the break-in cycle, then you could cause a cell to vent.

EDIT: I just realized that the OP did in fact discharge the cells prior to break-in. My apologies. At this point I would say the likely cause of the problem is a defective charger. To be fair, this would be very rare given Maha's quality control. I have 4 MH-C9000s. The first two have worked flawlessly for over six years. The two new ones are working flawlessly. A friend who has three hasn't had any issues, either.

The Break-In cycle is the same as the IEC capacity analysis cycle so it should be safe if the battery is in good condition and in a discharged state at the beginning. I have never had venting with any brand or model of battery (even old ones that had degraded to 60% of rated capacity).

You say you started with fully discharged cells, so either the batteries or the charger are faulty. Are your batteries relatively new? Have they been performing well with your previous charger?

How far into the charge stage (hours or mAH input) did the batteries start to vent?

Hello Looqs,

Welcome to CPF.

You are correct that something is not working properly.

The break in mode is beneficial to both new and used cells. The process is designed to revive the chemicals within the cell without doing damage to the cell. Venting usually does not occur during this process.

There are several things that can contribute to this problem.

You may have entered the a cell capacity value higher than the actual capacity of the cell.

The charger may be malfunctioning.

The cells may be crap.

Any of these or a combination of them can lead to what you are experiencing. Maha generally produces good chargers but there have been one or two that have malfunctioned. Cells are usually reasonably good but occasionally there are bad batches. Sometimes wrong numbers are entered but the charger displays the charge current so that should be easy to check out.

Venting comes with pressure build up within the cell. This usually occurs during heat build up. Did the cells get hot?

To zero in on this you will need to verify that the charger is operating properly, that the cells have reasonable capacity, and that you entered the correct numbers. If your cells are venting at a low charge rate, charging at a higher rate by using the cycle or refresh mode may make things worse.

Let us know what you discover. You may want to contact Maha for some additional tips on making sure the charger is working properly.

Tom

Thanks for your responses, I appreciate the thoroughness.

Yes, I made sure all cells were discharged. I'm not sure if the manual remarked about prior discharging but my common sense said it should be done. I made sure to double-check all cells' listed capacities & cautiously enter the correct number into the charger. The manual said to "round up" on xx50 mAh cells, and I noted that, as well.

The charger specifies "0M0BA" on the back. Is this the firmware or revision? What is the latest firmware/revision?

Is venting exclusively attributable to heat alone, or will cells vent when cool yet overcharged beyond capacity? I will setup a small cooling fan aimed directly across charging cells from now on. Also, what is the report on heat during BREAK-IN? Do any/all of of you experience warm/hot cells when running BREAK-IN, too?

The venting occurs via BREAK-IN when charging begins to exceed specified capacity e.g. the 6 hours after the normal capacity has been reached. The cells are indeed warm or maybe even hot to touch at this point, regardless of ambient cooling. Is it not normal for cells to become warm, or only during higher charging currents? Is that not a variable for the charger in determining when to terminate?

My most recent issue with the charger is 3 of 4 AAA Energizer cells reported 3999 mAh capacity after BREAK-IN. Obviously, this massive capacity is not (yet) possible with AAA cells. There seems to have been an error occurring during discharging, as that is when I believe the charger determines capacity, so maybe there is something wrong with this charger. How would the cells cause the charger to interpret this if they are faulty, and not the charger? The 4th cell was reported as basically dead & would not accept a charge, so maybe they are a crap batch altogether.

Another instance is that at certain points, some cells were significantly warmer than others of the same group/model that started BREAK-IN at the same time. Slot 3 seemed to produce the "worst" or lowest final capacities and the cells were always the coolest from that slot during charging and after termination. I'm beginning to wonder if I'm in need of better built charger if this one's not defective... I'm not sure why so many variables are presenting, I thought this MH-C9000 was one of the best options?

It's difficult to say whether the MH-C9000 is acting up or the cells were bad initially or have gone bad, through charging cycles in a fast "30 min." charger (which included a cooling fan) previously, or other reasons. I have ran different models from only Duracell & Energizer through BREAK-IN, and not all of them appeared to have vented, though I did not equally monitor all the same. I know one of the worst venting batches was from cells only 2 years old with light use. If I recall correctly, I think I occasionally heard venting while using the older charger, but with much less frequency. Maybe a single pop here or there, but not frequently & often like the MH-C9000.

At this point, I think my last option is to monitor the last 6 hours of either BREAK-IN charge cycle with the Imedion cells & see what happens. These cells are crucial to an upcoming event & I do not have time to return either them or the charger beforehand, so I might as well give it a go. Right now, I am waiting to observe some older Duracell cells when their final 6 hours comes around.

In the mean time, what's the skinny on BREAK-IN? Could/should I enter a lower capacity to allow a smaller current charge and also less overloading in the 16 hour period? And also, in regards to utilizing REFRESH or CYCLE, I would be entering low charging values, nothing high. I know some La Crosse owners swear by 100 mAh for all cells, though this charger's manual specifically says you should not charge less than 30% capacity per hour for NiMH cells.

Thanks again for your replies! It's takes away a bit of the below feeling...

Hello Looqs,

I am not sure what the latest revision is but in following various revisions there has been no change in the operation of the charger. You should contact Maha to see where yours stands. The revisions seem to be for Maha's benefit rather than changes in the way the charger works. If your revision is a brand new one there is a chance that something went wrong. Call Maha and see where you stand.

Cells barely warm up during the break in. NiMh chemistry allows for gas recombination during an overcharge as long as the charge rate is low. Emergency lighting battery packs are subjected to the 0.1C charge continuously and the packs are still viable after a year of this. 16 hours done twice a year is nothing compared to this. Crap cells warm up more than good cells because of the higher internal resistance, but they still don't get hot.

Another thing to keep in mind is that charge efficiency varies with charge rate. At low charge rates the charge is not efficient. As an example let's look at a 2000 mAh cell charged at 200 mA. To get to a full charge you would expect to put 2800 mAh into the cell giving us a charge time of 14 hours. The 16 hour break in only subjects the cell to an additional 2 hours of overcharge. If your charge rate was 2000 mA (1C) you would expect the charge to finish in 60 minutes but it actually takes around 5 minutes more. As you can see at a charge rate of 0.1C you need 140% of the total capacity put back in order to achieve a full charge. At 1C you only need 105% to achieve the same full charge.

Your experience with the AAA cells is adding fuel to the idea that your charger is malfunctioning.

One way to check the charger is to take some new cells and run them through a charge cycle at the default charge rate. Monitor them and see if the cells heat up and if the charge rate is accurate. Then run a discharge cycle and see what you get. If all that is OK you can then put the cells into a break in cycle and see if the total number you get is close to what you got from the previous discharge cycle.

This will give you a rough idea of how things are going. Beyond this you need to hook up a scope and start measuring specifics. You can also check out other chargers you have provided the discharge function of the Maha is working properly.

Call Maha and tell them to explain to you how AAA cells achieve 3999 mAh during the break in. That may be enough for them to replace your charger.

Tom

Thanks, Tom!

I really can't express enough appreciation for your involved replies & relaying specific knowledge such as NiMH chemical behavior. The information is helping immensely & provides a lot of insight.

I currently have the unit in a window with 50-60F cold air cooling the unit & cells. I have just emailed Maha about the situation & their replacement process.

The latest AA cells I ran through BREAK-IN did not appear to vent, and they were some of my older cells. I discharged the first batch of new Imedion cells @ 800 mAh with normal results. I began the BREAK-IN process 1.5 hours ago, and their temperature is cool & not warm to the touch, though it is early in the cycle & they are receiving deep cooling.

I think you may be referring to an oscilloscope, which I do not have, but I have an average multimeter. Would you recommend checking out the charger with a multimeter, or perhaps not?

I believe I read somewhere that another MH-C9000 owner suspected his malfunctioning unit was not to blame but his AC adapter was. Eventually, the adapter was determined to have been the problem. I will need to find that old post & see if parallels can be drawn.

With cells I have also run an additional REFRESH & ANALYZE process on (normal charge, normal discharge, normal charge), capacity results seemed normal & slightly improved. I will take your advice & keep observing.

I will report back if anything abnormal should arise again or if Maha provides any information on revisions. Thanks again for your time & in-depth thoroughness!