Batteries Getting HOT while Charging.

[Aircraft800]

I'm having trouble charging my FM 2x6AA battery pack with my Universal Smart Charger for RC 7.2-12V NiMH RC Battery,

The batteries ge SO HOT that I need to unplug it. It seems like the charger never shuts off, even after 2 hours.

Is this because this charger is not designed for 3600mAh (2X1800mAh) or something?

I have also tried using my Sanyo 2700 with the same results. I'm now using Titanium 1800, and want to be able to charge all batts at the same time, not remove them from the battery adapter.

FM's 12AA (2X6AA) can be seen HERE or

Maybe someone can recomend another smart charger.

 

[LuxLuthor]

Most of us are either using a hobby charger for the charging plug FM setup (you might try another one if that one is going bad....they are pretty cheap crappy chargers for their price), or individual AA's in the MH-C9000

 

[SilverFox]

Hello Aircraft,

Are all of the cells getting hot, or only some of them?

Tom

 

[rdh226]

What's the actual temperature? Normal charging easily hits 130F and higher (which is pretty
toasty to the touch). I think 140F is considered about the max allowable.

And what's the voltage across the array? *If it's much over 9.0-9.5 volts, I'd be real worried.

-RDH

 

[Aircraft800]

@SilverFox

All of the cells are getting equally hot. They are new Titanium 1800 from Amandotec. I had the same problem with my Sanyo 2700, but not every time. It seemed like I had a sucessful charge one time when I depleted the cells almost fully, but I haven't had more than 3 charges total on either cells, so it's preatty hard to compare, or pinpoint the problem.


@rdh226

I can try checking the actual temperature in a few days, I have access to a temp gun and a high temp thermometer. All I know is they were so hot that I could not hold the pack in my hand, and it happens after 1.5hr. I checked the voltage at 8.9 volts soon after removing the charger.

Is it possible I need to get the Universal Smart Charger for 2-12 cells as seen here?

Mine is the 6-10 cells version.

Or suggest a completely different type, like the digital smart one FM uses.

Thanks guys for all of the help!!

 

[SilverFox]

Hello Aircraft,

I believe your charger is fine. I would suggest using the 1.8 amp charge rate when you use it.

The problem you are having is that the charger is missing the end of charge termination signal. This is a direct result of charging in parallel.

Your set up has two strings of 6 cells in series that are paralleled together. When the cells get out of balance during a discharge, one string may signal the end of charge, but the other string may overcome that signal and the charger continues charging.

Parallel charging is not recommended for NiCd or NiMh batteries.

Now that we have identified the problem, let's see if there is a way to work around this.

The best way is to separate the charge and charge twice with 6 cells in series.

Another was it to manually monitor the temperature of the pack and shut off the charge when the cells start to warm up. The risk in this way is that it will not correct an imbalance between cells.

Although terribly inconvenient, you could also charge all the cells individually and disassemble the pack for charging and reassemble it for use. This would bring all the cells back into balance, but it involves more work.

Tom

 

[Aircraft800]

@SilverFox

I have been doing some reading on a thread you posted Here:

http://www.candlepowerforums.com/vb/showthread.php?t=159764

It looks like you are the authority in charging! Awesome!

Is it possible to trickle charge the cells, or slow charge them so that the pack will equalize naturally? If so, how long can I keep them them on a trickle? The charger I would use is a 7.2 volt correct? (6 cells) Would a trickle be able to essentially charge (2) 7.2 in parallel? I have an old ProTec Super Charger from my RC days, is it safe to use it to trickle charge this pack? The charger does not say it's for Ni-MH, problbly built before they were avaliable. It is a NiCad, but I don't know if the charge rate/amperage would be the same.

I don't need them quick charged, I can plug it into a lamp timer or something, as long as it's ready 12 hr. later when I return to work. Maybe I could find another 2X6 adapter so one is always ready!

Thanks!

 

[SilverFox]

Hello Aircraft,

You can't go wrong with a 0.1C charge. If you run the cells all the way down, it will take 14 - 16 hours to fully charge them back up. If you only partially run them down, it will take less time.

A 0.1C charge on your 1800 mAh Titanium cells would be 180 mA, but you can probably get by with 200 mA.

Tom

 

[65535]

If you do decide to do a 0.1C chare for the norm set a lamp timer for 16 hours and make sure you completely drain the cells down to 0.9volts or less. It will overcharge the cells slightly but it's within safe limits, and will hardly notice drop in cycle life.

 

[Aircraft800]

Thanks Guys! All great information.

I've got a questionon, what exactly is a 0.1C charge? What unit is "C"? I have a old RC charger by ProTec, how do I measure the output to make sure it's at 180 mA? Don't I have to run my Multimeter in a series with the battery back to check the draw or amperage? The charger was designed for 6 cell NiCad, so what should the voltage be, aprox. 7.4volts?

Thanks again!

 

[SilverFox]

Hello Aircraft,

Yes, we always get into trouble with our terminology...

C refers to the capacity of the battery. It is actually supposed to be C mA or IsubT, but we get lazy and just call it C.

Your 1800 mAh cells have a C of 1800 mA. A 1C charge would be charging at 1800 mA, a 0.5C charge would be at 900 mA, a 0.1C charge would be at 180 mA.

If your ProTec charger doesn't offer adjustable charge currents, you won't be able to use it with this battery pack. Chargers that have adjustable charge currents probably won't have a setting for 180 mA, but you can use a 200 mA setting without problems.

Does your ProTec charger allow you to choose the charge rate?

Tom

 

[Hondo]

I know my adjustable rate Protec only controls the fast charge when the 15 minute timer is running. But when the timer is off, it is in a fixed rate slow charge mode which should be somewhere around what Aircraft is looking for. I would think even slower than 180 ma could still work, but much over 200 ma would start to warm the cells more significantly and should be stopped fairly soon after full charge is reached. I have also used a car tail lamp bulb on pigtails in series with the charger for smaller numbers of cells to keep the current down.

Aircraft - you will want to measure this, and yes, you put the multimeter leads in series with the charger input. Of course, you need to be in a current measuring mode on a meter capable of this, and the cheaper ones can only reach 200 ma, which may or may not be enough for this job, so hopefully you have a 10 amp current measuring model.

Hondo

 

[Aircraft800]

@SilverFox

My ProTec charger does not allow me to choose the charge rate, just weather I have 6 or 7 cell pack, so this is probably just adjusting the voltage. Thanks for the clarification of the battery capacity.

@Hondo

It sounds like we have the same charger, I can quick charge for 15 min. by setting the timer, and when it's done, it will automaticaly enter the trickle mode. It's probably not the best to use in this situation, but I have no way of getting my Smart Charger to enter trickle charge mode (unless someone knows how to trick it). I'll measure the current with my Fluke 77 multimeter, I believe it can handle a few amps.

Thanks for all of the great info!!

 

[LuxLuthor]

Most of us are either using a hobby charger for the charging plug FM setup (you might try another one if that one is going bad....they are pretty cheap crappy chargers for their price), or individual AA's in the MH-C9000

BTW, when I said that it was based on experience. I had gotten 7 of those exact chargers in various sizes....some I bought from these forums, some came with complete turnkey packages with Mac Torch, and some with other setups from FiveMega, etc.

2 of the 6 did exactly what you described over time, and with all cells. If I used the other 4 units that fit the correct cell number/voltage range, they worked again just fine without the dramatic heat issue. I think they use really low quality components, and have no QC specification....so I retired all of them after getting my Hyperion 1210i charger.

 

[Aircraft800]

Your 1800 mAh cells have a C of 1800 mA. A 1C charge would be charging at 1800 mA, a 0.5C charge would be at 900 mA, a 0.1C charge would be at 180 mA.

I've got a quick question about this part,

My adapter is series/parallel 2X6 12-1800 mAh, so wouldn't my Capacity be 3600 mAh (2X1800 mAh) and the charge rate for a 0.1C be 360 mA?

Just a thought

Thanks Tom.

@LuxLuthor

I'm keeping my eye open for a supernova 250s or Hyperion 1210i. I'd like to be able to give one a try before purchasing one, unless I find a steel on eBay. Congrats on the battery pack welder, let me know when you start offering your services!

Thanks for the help!

 

[SilverFox]

Hello Aircraft,

Oops, I forgot you have two strings in parallel. You are correct.

Tom