Maha 800s = HOT batteries?

[SangYuP]

I just received my new Maha 800s and some ENELOOPS. My ENELOOPs were dated 05/06 so I decided to charge them right off the bat. It took a little less than an hour to fully charge, but when I took them off the charger, I noticed they were pretty hot. I charged them on the default fast charge. Is this normal? I just reread the 808 review and SilverFox said that his batteries off the charger at the hottest was 96 degrees.

I don't really have a reference to how hot my batteries got, but when I touched them, they were hot, but not uncomfortably hot. I figured since my body is 98 degrees, the batteries shouldn't feel too much warmer than me. Is that a good way to judge the temp?

I figured the 800s would be cooler since the fast charge is equal to the slow charge of the 808. Can someone chime in and let me know if my charger is defective or not? Thank you.

 

[NiOOH]

First think you should do is discharge these cells fully and charge hem again. Most probably, your Eneloops still had 70-75% charge left, so you were merely topping them off. Some charger/cell combinations are heated a bit more when topped off.
Second, we need to get a bit more information about how hot your cells really get. Could you hold them comfortably in your hand for more than few seconds?

 

[SangYuP]

I'm at work right now so I don't have access to the charger. The batteries did not get hot to the point where I couldn't hold them, but they were pretty hot. I was expecting the batteries to be warm and not that hot. Like I said, the batteries were hot but I could hold them until they cooled.

 

[SilverFox]

Hello SangYuP,

People have different impressions of heat. Some people have hot hands with skin temperatures of around 90 F, others have cold hands with temperatures of around 85 F. Of course the skin temperature is influenced by the ambient temperature.

Batteries heat up at the end of the charge cycle. The amount they heat up is dependent on the condition of the cell, the charge rate, the termination method, and the ambient temperature.

You can spend a few hours with a thermometer and gain an appreciation for how hot is HOT and what warm really is. As a point of reference, I believe all battery manufacturers state that 140 F is too hot.

Tom

 

[SangYuP]

SilverFox,

Thank you for the information. As always you are very helpful. What would you say for an average person would be uncomfortably hot(what temp)?

I was just surprised that the batteries felt that hot. I was expecting them to be warm especially since it was the 800s and not the 801d.

 

[SilverFox]

Hello SangYuP,

Unfortunately there is no such thing as an average person...

My hot water out of my kitchen faucet is 140 F. I can not hold my hands under that temperature for any length of time, but have no problems with short term exposure to it. My wife, on the other hand, feels that she is being burned by any exposure to the same hot water.

Tom

 

[NiOOH]

Hello SangYuP,

Unfortunately there is no such thing as an average person...

My hot water out of my kitchen faucet is 140 F. I can not hold my hands under that temperature for any length of time, but have no problems with short term exposure to it. My wife, on the other hand, feels that she is being burned by any exposure to the same hot water.

Tom

Yeah, most people would feel instant pain in contact with 60C liquid, especially a liquid with high heat capacity like water (European=No Fahrenheit for me). Liquids make a large area contact with skin, thus increasing heat transfer.
Back to the cells and charger, I'd recommend to fully discharge your cells and charge them again, while monitoring their temperature. New cells may not display sufficiently high voltage drop at the end of charge for the charger to terminate properly, which may lead to overcharging and high temps. In other cases they may show the so-called false peaking, at the begining of the charge causing premature termination. That's why it is a good idea to do an initial charge at low currents of c/10 ( one tenth of the capacity rating of the cell, in you case 200 mA) for 14-16 hours. This usually solves the problem and the cell can be fast charged from then on. Since your charger cannot do this, just discharge them and try again, I think that the second time the temperatures will be lower.

 

[Turak]

One of the best things I ever bought was one of those little Infra-red temperature sensors. C/F selectable. Uses little 12v battery.

Works GREAT for batteries.

By the way....

Most of the spec. sheets that I have ever seen specify;

53'C or 127.4'F as the MAX temperature for the batteries.

Many chargers also use this as the temperature cut-off point...the BC900 immediately comes to mind.

I have been working with electonics, batteries, chargers, etc for quite a number of years now and one thing still has not changed....

A batteries WORST enemy is HEAT. The next would be FREEZING COLD.

So while you can take any of the more modern batteries and charge them at say .5C or 1C safely. The 1C charge rate is ALWAYS going to generate more heat and therefore, generally speaking, be worse for the battery. Usually resulting in reduced overall number of times that the battery can be cycled in its lifetime.

I have tested this with many of the 1800mAh, 2000 mAh, and a few of the 2500 mAh batteries....still seems to be holding true.

Hehe another little tip...just as the manufacturers tend to be 'generous' in their estimates of a batteries capacity....they tend to do the same with the number of times it can be cycled. Bottom line, don't count on getting a 1000 recharges out of ANY battery you can buy right now.

 

[SilverFox]

Hello Turak,

Check out the Sanyo engineering handbook. Maximum temperature cut off is 60 C or 140 F.

50 C or 122 F is an ideal charge to temperature when charging at 1C in warmer ambient conditions of around 75 - 80 F and when you are looking for maximum performance from your cells. 40 C or 104 F is a target I like to shoot for.

Tom

 

[Turak]

I have noticed that Sanyo is one of the 'exceptions' that specs their upper limit at 60'C.

I tell you though....touch a battery at 60'C. WAY too hot, im my opinion. It is definitely not good to run them that hot. Definitely have to keep in mind that the higher ambient temps, the hotter the cells are going to get too....

Generally speaking the heat causes the insulator and seperator materials to breakdown or in some cases to thin.

I generally go with slow and cool whenever possible and throw in a high rate charge/discharge cycle much the same way you might throw in a conditioning cycle every so many cycles.

 

[III/V]

Just for info:

I've been using a Maha C401FS charger for some time now for my digital camera. I started out using the fast charge whenever I needed to and I ruined two sets of the Powerex batteries.

The batteries were so hot I was afraid to put them in the camera until they cooled off some. The batteries grew in diameter to the point they didn't slide easily into the camera.

Since then I only use the slow charge and have had zero problems with my batteries.

Mark

 

[TPA]

Just for info:

I've been using a Maha C401FS charger for some time now for my digital camera. I started out using the fast charge whenever I needed to and I ruined two sets of the Powerex batteries.

The batteries were so hot I was afraid to put them in the camera until they cooled off some. The batteries grew in diameter to the point they didn't slide easily into the camera.

Since then I only use the slow charge and have had zero problems with my batteries.

Mark

Did you run it with the lid closed on that charge cycle? You're supposed to run that charger with the lid open. I've used a few of them and didn't have any overheating issues like that.

On the 800s, the batteries DO get warm/hot, that's naturally going to happen. It's far less than many other chargers I've used, but it's still noticable. Batteries even get "warm" on a C9000 running at 0.1C. I've found the AAAs get warmer than the AAs, which makes sense. Less surface area to dissipate the heat. Also, battery temps will vary with ambient temperature. It's 80F inside my home right now, so I'd expect the batteries to be warmer than for someone who keeps their bateries & chargers in their basements.

 

[SilverFox]

Hello Turak,

It is interesting to observe the variations in temperature cut off values from the different manufacturers. Sanyo goes with 60 C, Panasonic goes with 55 - 60 C, Harding Energy goes with 55 C, Gold Peak goes with 45 - 50 C, Duracell goes with 60 C, and Energizer seems to suggest around 50 C.

I agree with you on these upper limits being too hot. I believe all of these upper limits are a secondary termination if the primary termination fails.

I also have observed that all of the manufacturers recommend charging at 1C. With proper charge termination, batteries do not get hot when charging at 1C, if they are healthy. As they age, their internal resistance increases, then they start to heat up at higher charge rates. When this happens, I call them "crap" cells and recycle them. I figure that after 300 - 400 cycles I have gotten my moneys worth and I am ready to move on to new ones.

So, when you are charging at slow rates are you doing a "standard" charge?

Tom

 

[SilverFox]

Hello Mark,

The "cooking" of cells in the fast mode of the 401 chargers has been well documented. Maha's response has been that the 401 termination algorithm was developed around 15 years ago and things have improved since then. They chose to come out with the 800 and 9000 series of chargers rather than upgrade the 401.

The fast charge current on the 401 is only 1 amp. It is not the charge current that is causing the batteries to heat up, it is the termination algorithm. In contrast, the 808M keeps cells cool while charging at 2 amps.

Tom

 

[NiOOH]

Just for info:

I've been using a Maha C401FS charger for some time now for my digital camera. I started out using the fast charge whenever I needed to and I ruined two sets of the Powerex batteries.

The batteries were so hot I was afraid to put them in the camera until they cooled off some. The batteries grew in diameter to the point they didn't slide easily into the camera.

Since then I only use the slow charge and have had zero problems with my batteries.

Mark

IMO Maha should revise/improve the fast charging on the 401FS. This is otherwize a very good charger, but the fast charge heats up the cells way too much for the 1000 mA it charges at IMO. I could watch one of these heats the cells to the point I couldn't hold my finger on them for more than a couple of seconds. Didn'measure the temperature, but it must have been close to 60C.
Most manufacturers recommend 55C as the highest temperature during charge. Sanyo decided to go higher. The fact that the manufacturer has specified a max. temp. does not mean that charging to this temperature is healthy for the cells. If your Sanyo cells are heated to 60C during every charge, you won't get much more than 100 cycles. I'd imagine that some lesser quality AA cells may even vent at temperatures close to 60C.
It should also be known that the cell temperature at the end of charge is a sum of the heat generated by the cell and the heat generated by the charger. Most charger designs ignore the latter effect. In order to be compact, the chargers are designed with a minimum space between cells and between cells and charger electronics.

 

[Turak]

So, when you are charging at slow rates are you doing a "standard" charge?

Tom

Hi Tom,

Lately, I have been giving my two BC900's and my MH-C9000 a pretty heavy workout.

I have to say that overall I REALLY like both units, but I find that the BC900 is just a bit more 'user' friendly overall, and the way the BC900 displays the stats for ALL 4 batteries at once only changing when you press a button....just blows away the single item, constantly rotating display on the MH-C9000. Maha needs to change the display to something more like the BC900 displaying all 4 batteries at once, and quit the annoying, constantly rotating single display.

Anyway, as to charging the batteries.... For the cells 2000mAh and above, I have been typically using .5A for charging and .5A for discharging. I do typically run a 1A charge about every 10-20 cycles, similiar to a 'conditioning' cycle....making sure they are fully discharged and then fully charged, typically leaving them on the charger for at least 4-6 hours after they signal ready, to let the trickle charging give them that little extra bit of 'topping' off. Anything longer than that is just uselessly heating the batteries.

Since I have recieved the MH-C9000, I am now ALWAYS running at least 1 and as many as 3 'Break-In' cycles to get the batteries up to their 'maximums' right off the bat.

Another tip that I have noticed and verified via simple testing.....

DO NOT leave your batteries 'trickle' charging for extended amounts of time. It WILL reduce their overall life.

Many of the manufacturers indicate that leaving them on 'extended' tricklle charging should not cause any detrimental effects....I TOTALLY disagree. It causes the separator materials to thin out over time, it causes cell heating (any heat is bad), it literally cooks the electrolyte...do I need to go on?

In the older Nickel Cadmium batteries, the batteries would form what is refferred to as 'whiskers' or 'internal shorts'. Supposedly the Nickel Metal Hydride batteries are not suppose to suffer from this problem.....which IS true, up to a certain point.

What ends up happening is that the separator material which is already MUCH thinner than it used to be......will thin out even more, enhancing the major problem we see with the High capacity batteries.....SELF DISCHARGE.

So while the exact problem is technically different, the end result is the same.....the batteries end up not holding a charge.

Bottom line....just as overheating the batteries during charging/discharging can reduce thier overall capacity and number of cycles, so does extended trickle charging (although usually to a lesser degree).

 

[SilverFox]

Hello Turak,

I also really like the C-9000. It isn't perfect, but I feel it stands head and shoulders above the BC-900 in spite of the way it displays its data. The Break-In function alone is worth the price of the charger.

You have an interesting charging regime... If you want better performance and improved cycle life, I would suggest reversing your charging rates. You are aware that slow charging makes the end of charge termination signal quite small and that slow charging promotes the growth of large crystals. A weak termination signal leads to damage through over charging, and large crystals can be hard on the thin separator used in higher capacity cells.

I believe Mr Al just finished a test where he left some cells on a low trickle charge and they finally died. The only manufacturer that I have seen give a specification on trickle charging is GP. They state that their cells are good for 1 year at a 0.1C rate. One of these days, I will get around to testing this, but I think it is a rather bold statement. Everyone that I know of that leaves cells on extended trickle charging end up with "crap" cells. The exception may be with the Maha 8xx chargers. Their trickle charge just slows down the self discharge rate, but does not try to overcome it. However, you still end up with the problem of large crystal migration so it still is not the best answer.

I wonder how the low self discharge rate cells get around this...

Tom

 

[III/V]

Did you run it with the lid closed on that charge cycle? You're supposed to run that charger with the lid open. I've used a few of them and didn't have any overheating issues like that.

No. I always leave the lid open, even when charging on slow.

The "cooking" of cells in the fast mode of the 401 chargers has been well documented. Maha's response has been that the 401 termination algorithm was developed around 15 years ago and things have improved since then. They chose to come out with the 800 and 9000 series of chargers rather than upgrade the 401.

Thank you very much for letting me know this. I think I will check out these newer chargers.

Do they make a charger with the new algorithm that is as compact as the 401? I only need to charge 4 AA batteries at a time and I want it you control charging on each cell seperately. I also need a cigarette lighter adapter and a power supply that works on 110-220V. I burned up the first 110V power supply and had to order a new one.

Mark

 

[Turak]

Hello Turak,

I also have observed that all of the manufacturers recommend charging at 1C.
Tom

Hi Tom,

Many of the manufacturers indicate that it is 'possible' to charge them at a 1C rate, but.....I have not seen where they 'recommend' that rate. Most of the 'recommended' rates are actually in the 250-500mA range. The one thing most of them do seem to agree on, is that slower is better.....hence the 250-500mA rate seen on almost all the chargers.

MAHA is one of the few that I see recommending the 1A rate and mostly with their newer chargers, probably because of the problem of termination with some of their various chargers (i.e. 401S at 1A rate, early MH-C9000's). Whoops almost forgot about them bending to the marketing hype of the public wanting 'fast' chargers, with the public not really understanding the faster rates are detrimental to the overall life of the battery. The charger manufacturers need to learn to quit depending/doing it the cheap way with -DeltaV termination exclusively. At the 'very least' a charger should terminate using -DeltaV, 0DeltaV, time, and temperature as a last resort.

As for 'recommended' charge rates, take the new Sanyo Eneloops for example....

Their data sheet indicates that they 'can' be fast charged at 1C....but nowhere do they indicate that they 'recommend' that rate.

Actually if you look at the data sheet closely, they indicate that their capacity determinations are made using the standard .1C charge rate (200mA for 16 hours) and .2C discharge rate (400mA) with EV=1.0v and ambient temperature at 25'C.

If you look at ALL the chargers made by Sanyo for the Eneloops, they are either 250mA, 300mA, or 500mA.

Which REALLY puts the 'recommended' charge rates for the Eneloops at 250-500 mA, although it is 'possible' to charge them at 1C.

The discharge rates are shown at .2C, 1C, and 4C (this rate will shorten the batteries life I almost guarantee it).

You want to get your 1000 recharges out of them....you better stick with the 250-500mA rates. You go with the 1A rate all the time and from my previous experiences with ALL other batteries...you WILL get LESS cycles out of them. Probably something in the 400-600 range, unless the newer LSD design has improved this (doubtful).

 

[Anders]

Hello Turak.

"A charge rate of 1C and
a 5 to 10 millivolt per cell drop is recommended for
the nickel-metal hydride battery with a backup temperature
cutoff of 60°C"
http://www.duracell.com/OEM/Pdf/others/TECHBULL.pdf

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"A charge rate of
1C is recommended for restoring a discharge cell to full capacity."
http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf
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"When charging the Twicell, we recommend that you ensure precise charging control, and use constant current charging (quick charging) with a constant current of 0,5 to 1 It"

"If charging is performed at a current less than than 0,5 It, the voltage change and temperature rise that occurs when the battery becomes fully charged will not be sufficiently pronounced, making charging control difficult"
http://us.sanyo.com/batteries/pdfs/twicellT_E.pdf



Anders