Battery or Charger problem
 

I have an ImaxRC B6 AC Pro charger and 2 Duratrax Onyx 5000mAh NiMH batteries.

Ever since the first time I charged the batteries with this charger, I get random results. The first time I charged one of the batteries, it only took about 500 mAh then the charger said it was 'FULL'. I ran the battery, and it died after about 5 minutes. I read about 'false peaking' and all kinds of other things and I even went back to the hobby shop to talk to them about it. The guy there basically told me to keep cycling the battery and it should plane out.

The second time I charged the battery, same thing; it took about 4-500 mAh and said it was done. I knew the battery was dead, because I ran it down, so I just charged it for another cycle and it took about 800 mAh this time. Being the astute mathematician that I am, I added the mAh (about 1300) and charged it again, this time it went for about 3200 mAh. I called that good and drove the car with the battery lasting about 30+ minutes.

Both of my batteries act like this with the charger, I charge them at 5.0A for two or three 'charges' all of which add up to 5000 mAh or less.

Yesterday, I was distracted and didn't pull a battery off the charger, expecting it to stop on it's own, and the battery took a bit more than 5000mAh between the three charge cycles. I put the battery in the car and drove it and stopped responding to low-rpm input, but would go fine if you gave it half-to-full throttle, but it was sluggish and the car stopped after about 15 minutes. The battery was pretty hot and it looked like it was bulging, so I took it out of the car.

Questions:
1) Does anyone else have experience with the B6 AC (Pro) charger (it is pretty much the same as every other b6ac out there) doing NiMH batteries and have this problem?

2) Is there any hope of this battery working again, or is it safer to dispose/recycle the battery?

Thanks for any help

Pretty much the reason i went from using NiCd straight to Lipos. the couple of Nimh packs that i did purchase new would only take 400-800mah even after cycling them over 10 times on my duratraxx ice.. Nicd were easy because they came fully discharged and after a few times out, they were getting full capacity. Nimh are a pain in the ***. don't bother with them. the good thing about your charger is its lipo capable.

do your self a favor, go to hobbycity/hobbyking, buy a hard case 4000 or 5000mah 2S lipo for under $20 and never have problems again. just remember to program the charger for lipos, never charge more than 1C rate, and never ever cycle lipos.

I agree about getting yourself some Lipos, but if you cant afford it right now and you have the two Nimh packs you might as well use them to their best capability. If one of your Nimh packs is physically bulging you should discontinue use immediately and find a place to recycle it.

When peak charging Nickle cells, the voltage will peak, then begin to drop as it is over charged very slightly. "Delta Peak" or "Peak Detection mV", are a few names for the setting that adjusts how much the voltage drops before the charger shuts off. Nicds like a pretty heavy over-charge(8-20mV/per cell) and seem to run better, plus the voltage varies so much during the charge that it would false peak with too low of a "peak setting". Nimh, on the other hand, like as little as possible voltage drop upon peaking(3-6mV/per cell). This low of a setting leaves little room for voltage fluctuation during charging and will stop charging anytime the voltage drops that amount. If your cells are not damaged in any way they should come around and begin holding a steady enough voltage during charging to not trip a false peak, after 3-5 cycles maybe more if they have been sitting unused for some time.

Now that I have covered peak detection, Ill tell you how to get the proper setting for your packs. The proper way to monitor the pack is by temperature, terminate charging when pack temp reaches 125F. If the charger shuts off before the pack is 125F, the setting should be turned up. If the charger is still running and the pack exceeds 125F, the setting is too high. To simply eliminate the false peaking, you should try to turn up your peak detection a few mV. But you have to be careful not to overcharge the pack! Packs that have been sitting unused can fluctuate alot during charging and need a higher peak setting to avoid the false peak, but the higher setting can overcharge it in the end when it really does peak. You should be able to find a sweet spot where it will take one charge to get perfectly full. Monitor the cycles closely the first few times to ensure you have it correct and you should get a long happy life out of your pack(s).

New NiMhs seem tpo be prone to false peaking where the charger shuts down early thinking the batt is charged. As long as the battery has not gotten hot, continue to charge it until it does get hot.

If you have a bulged cell, its time for a new one. If your RC is demanding so much current that the pack is getting that hot, maybe you should consider lipo.

Thanks for your replies, guys.

@liquid: I think this is the direction I'm leaning. Thank you for the advice on charging and not cycling, just balance and charge, right?

@burn: I will dispose of that battery, thanks. The temperature you are speaking of, 125F, is that just a NiMH or does that apply to LiPo too?

@duster: I have been feeling them to make sure they are getting warm before I take them off lately, well, the one I have left. Looks like I'm going to the LiPo store.

Thanks again for your advice(s).

temps are definitely just for nimh. lipos during charging should not get any warmer than the ambient temperature.

rgr, ambient temp for LiPo.

I can't post links, but the Turnigy nano-tech 4000mah 2S 25~50C Lipo Pack was what I'm looking at, do you know if that is hard case?


Thanks

This one ?

http://www.hobbycity.com/hobbycity/s...dProduct=11926


That one is not a hard case. I'm not sure, but I don't think any of the nono-techs are hard cased.

Yeah, that was the one.

Can you suggest a hard case one? I know I need 2s and 25C, as far as mAh, I'd like to get 4000 or above.

I appreciate your help.

[edit] I don't have any preference of Turnigy, it just looked OK to me. If you have a brand you like that is decent price, I'm open to suggestions.[/edit]

What about these? They look like they have deans connectors already, and that's what I use.

www cermark dot com/products/Amped-Up-LiPo--2S-7.4V--4000mah dot html

I don't see any 25C in 4000mah.....


http://www.hobbycity.com/hobbycity/s...dProduct=11598


I don't know anything about these, never heard of them before....doesn't say anything about them one way or the other. This one does hav ethe Deans installed, that would be something you'd have to do with the HK hard case.

That looks like a good deal. And 10$ less per pack, I can solder the connectors )).

Sorry for all the questions, but is a 30C going to do anything 'too much' over a 25C rating? I just don't really know what that means.

Thank you for your help.

No, it won't hurt anything. The C rating in this context indicates what the lipo is supposed to be capable of discharging. A 4000mah 25C would be expected to discharge 4000/1000 x 25 = 100amps, similarly, a 30C would be 120amps.

A battery doesn't force current thru a setup - the motor is what sets the amp demand, the esc responds to what the motor needs. A 30C vs a 25C isn't going to hurt anything. The 30C will have a little smaller voltage drop at load than the 25C would. More battery that you need? Probably, but that is how most setups are run. That helps keep things cool.

If you were flying a plane, it would be diff - higher C rated lipos tend to weigh a little more, here is a surface rc is isn't that much of an issue like it is in a elec plane.

Awesome. Thanks for your advice. It's for a drift car so a few more grams wont hurt a thing. I'll just take the deans plugs off the batteries I fried.

And lipo might help the problem w/ my ESC, if it wasn't getting enough juice it might be why it's stuttering.