need some expert battery advise
 

ok.....here's the situation...i'm running a mmm 2200 combo in my e-maxx and i freakin' love it. there is one problem....my battteries are draining unevenly. I'm running (2) 3S packs in series for 6S total....

2 sets of packs, i've tried have drainded unevenly. first set of packs were a set of maxamps 3s 8000mah batteries with a series harness. one side drained to 3.86, and the other went to 3.11. both batteries were purchased at the exact same time. so i thought maybe i just had a weak pack.......so i try some neu 3S 4100mah i had and i get the same thing.....one pack is 3.77 the other pack is 3.02V. this is too coincindental for me to think each sets of packs have one weaker pack.

what gives?

Have you ever used them individually? Its not good to have some of the cells being more used than others.

Do you charge them as one pack or two?

Your series connecter may have a bad solder. Also, Maxamps isn't the best choice... the Neu is the thing that confuses me though.

If there was a poor series connector, the whole system would act funny, but both packs should still drain by the same amount. Current is the same in a series circuit after all.

Are you by any chance using an external BEC? If so, do you have it hooked up to only one pack?

i'm not using an external BEC, it's a V3 MMM. I don't charge them as one pack though, i hadn't thought about that...does that make a difference? can i charge it as a 6S using the series adapter? how would i balance them then? they only have 3S taps.

Also, i'm going to make another series connector to be on the safe side, it always seems to be the pack on the right side that drains so much faster than the other. keep the ideas flowin guys, any help is greatly appreciated.

Do you always use the packs together or have you run them individually in other vehicles?

It's best to charge them the same as they are used - in your case, in series. Then you can use the diagram below to make an adaptor so that all the cells are balanced together:

http://scriptasylum.com/rc_speed/ima...3s3s_wmain.gif

thanks Brian, i'll try that.

do you think it's worth it to make another series connector for the esc to the battery, or do you think i'm just barking up the wrong tree?

Is the pack that drains quicker always the same one, or just on the right side of the chassis (so it could be either lipo depending on which side you mount each one)?

Label them, run them, check them, charge them, then repaeat, only switching posistions to see if its the same lipo. Weird, but without some external influence they should stay very closely balanced- have you checked the balance tabs are clean so that the cells are being fully charged correctly, and there isnt a false reading on any of the cells cuased by dirt on the pins etc...

that's what i'm going to do tomorrow...i've labeled the weak packs and i'm gonna switch them out for consistency..if they do the same thing, it might very well be the pins or something like that. God knows they've never been cleaned. :whistle:

EDIT: i'm wondering if you're right Neil....my weak pack is doing some crazy stuff. i keep getting "voltage too high" on my hyperion charger with readings of 4.86 3.85 and 4.98...i put the cell spy on it immediately and it's 4.19 4.19 and 4.20. i wonder if the spy is getting some false readings too.

it makes me think you might have hit the nail on the head
i'm definately going to be doing alot of testing tomorrow....and getting some contact cleaner. :lol:

Dirty balance connectors are a pain. That's why I do this: http://rc-monster.com/forum/showpost...9&postcount=40

great idea, thanks!

well guys, it looks like i found the solution. the second mmm V3 i've had in 2 weeks has failed. i plugged it in to get ready to test and it started, went 3 feet and all power was lost. same thing happend to the first one, except the batteries were draining equally.
i tested the switches and it dosen't look like that's it either.

i threw the packs on yet another V3 and they drained equally.

i'm going to call castle with this. two V3 failures with no obvious cause....this sucks. :cry:

I know everything can fail, but having three V3's fail in a row where reports of even two in a row is extremely rare (if any), I would start looking at other things. Maybe there's something you are overlooking? Are you geographically located near someone here that can help you out? Not saying you don't know what you're doing, but sometimes it's nice to get a fresh perspective.

it was the second failure, not third. :lol: as far as overlooking something, maybe....tell me what you think...

setup was:
3905 e-maxx
revo tires
geared 65/18
neu/castle 2200
6.5mm plugs
6S (3) 8000mah maxamps lipos in series ...also 2 neuenergy packs on occassion

drive train was smooth, batteries never got hot, and the motor was as cool as my forehead....nothing sticks out.

yesterday, i was having the best bash session ever...i was out for 45 minutes in my back field..it was running beautifully.

EDIT....also, not to have a big head about myself, but i've been running brushless for a few years now. i really wasn't doing anything out of the ordinary.

Bad juju... :neutral:

the worst part is it's gonna cost me 150 to replace both because i bought them both new on ebay and i don't have a receipt.

Maybe, maybe not- call Castle and explain the issue- they tend to be very good when it comes to warrenty issues (where you got it isnt always such a problem, just so long as its a real castle project and not some dodgy grey import).

I thought I remembered somewhere that castle doesn't like using maxamps with their controllers.... Try running the Neu packs next time for the first 4-5 runs and see if there are any problems.