NiMH Storage Voltage?

[kwe]

I have one of the stock batteries(7.2V 1200MaH) and I had to store it for a week. Before the one week storage period, I charged it at 1 amp how I always do. When I got back, I plugged it in and my MERV was quite sluggish and slow. I drove until the battery was basically dead and then I charged it(@ 1 amp). The car performed as normal- quick acceleration, wheelies, and great power. When I took the battery out after that last drive, the plastic around one of the cells was all cracked and shriveled up due to extreme heat. This has happened to me before, typically due to charging batteries too quickly. This battery is only three weeks old and only has about 30 runs on it. What do you think is causing for the individual cells to die? I think it is either that my cheap $30 charger is not charging at the rate it says it is or I ruined the battery by charging it before storing for a week. What do you think?

I hope that wasn't too wordy or confusing. Any help is appreciated! Thanks.

[jimbo74]

sounds liek you shouldnt have driven it past it being dead....

that battery is trash now


you always charge a nimh before you use it......

dont know what charger you are using, but if it is not a peak charger, then you really shouldnt be using it.... an ac/dc fast cahrger will fry a battery quickly

[Farabomb]

Your charger can be cooking the cells. I've been playing with RCs for a while now and the investment on your charging system pays off in the end. If you're bashing every once and while a cheap charger should do you fine. That said realize you are not being kind to your cells. My charger has a cycle function that has brought friends packs back from the dead. Sounds like you might have a bad cell in the pack.

[JJVeld]

is it better to store nimhs at full or almost empty?

[Wileybrett]

is it better to store nimhs at full or almost empty?

I'm curious about this too. Honestly most of the time mine are dead. But sometimes full and others half. But thats just my nimhs.

[kwe]

I charged and drove my MERV again since the start of this thread and the cell is definitely dead... the battery came out of the compartment smoking- time to trash that battery! I'm not sure when I'll make the switch, but I think I'm going to start the move towards LiPos soon. I currently have a blue universal smart charger(1 or 2 amp charge options). It does have peak detection. I think I will get a Thunder AC6 charger. It seems to be a good charger for NiMH and LiPo(when I'm ready).

[mike-susieq1]

never run a nimh till it dead and always store your nimhs fully peaked charged. if storing even for over night i would stick it back on the charger and repeak it and then let cool and then its safe to run the pack but never run a pack till the car is not moving, run the battery till you see the car slows down a little starting to loose performance. thats when its time to stop kinda like the same thing as Lipos except not by voltage.

[JJVeld]

i know this is off topic but what about storing lipos? cuz i just ordered one today. i heard ur supposed to store them at about 2/3 of the way to minimum voltage so like high 3's or low 4's for a 2s right?

[mike-susieq1]

lipos are suppose to be stored at 3.8-3.85v per cell. a good lipo charger will have that feature, works best i think if the charger has a discharge function as if the pack is higher than 3.85v then you have to use the car to lower instead of using the charger.

[Jimmie Neutron]

lipos are suppose to be stored at 3.8-3.85v per cell. a good lipo charger will have that feature, works best i think if the charger has a discharge function as if the pack is higher than 3.85v then you have to use the car to lower instead of using the charger.

Please notice what I have bolded.

[mike-susieq1]

thanks Jimmie should have bolded that. my lipos are in storage for who knows how long right now during my move so i made sure they were in storage mode at those voltages.

[Farabomb]

Say your charger doesn't have a storage option. How would you go about storing LiPOs?

[Jimmie Neutron]

The only reason I did so is because JJVeld was talking about pack voltage earlier.
With LiPo's cell voltage is more important than pack voltage; way more important.

I always top off my NiMh before storing.
NiMh like to self discharge. They will discharge themselves beyond the point of return... not that they cannot be brought back, but most (if not all) battery cookers... er chargers... cannot perform such a task. It takes sophisticated equipment... more sophisticated than most people realize.

It is also important to go back to that same battery every so often, sometimes weekly, and re-charge it.

Fara:
The goal is 3.85v/cell. If the pack is above voltage discharge it. If the pack is below voltage charge it. There should be a termination voltage setting within the charger. If not, you are going to have to manually end the charge process at 3.85v/cell.

[Farabomb]

I was sitting thinking about setting it for storage voltage but I was going the wrong way. Instead of having it come up to storage I wonder if I can set it to discharge down to 3.85.

[kwe]

So... a 2 cell lipo should be stored at about 7.6Volts total?

[Jimmie Neutron]

No.... 3.85v per cell.
Cell voltage is the only thing that matters with LiPo.

You always want the cells to be very close to each other in voltage.
If one goes above 4.2 during charging or below 3.0 during discharging you have a ticking time bomb on your hands.
Always pay attention to cell voltage, not pack voltage.

[kwe]

Thanks jimmie, that's real helpful.

[EmaxxChris]

I was sitting thinking about setting it for storage voltage but I was going the wrong way. Instead of having it come up to storage I wonder if I can set it to discharge down to 3.85.

If it's a decent charger, with a storage setting, it will either discharge or charge the voltage to 3.85V per cell itself. You may have to set the level you want it to store at, but it should do the thinking for you. At least my Traxxas EZ peak plus does.

[Farabomb]

It's a decent charger but it's probably a gen 1 LiPO charger. Back when I bought it I had to check dimensions of airplane batteries to figure out what ones would work in my RC18. No balancing, no storage setting so I just discharged them to 3.85 per cell. Having it automated would be nice but not the end of the world.