What is the max safe temperature for a nimh battery???

I have a old school rustler that I have novak 4.5R gtb system in, I use a 8 cell gp3300 nimh battery with and my batteries are getting pretty hot around 160F, if I drain the pack to where the truck gets pretty darn slow I see temps on my battery around 180F.

Is 160F to 180F too hot for a nimh battery, I have run this battery a couple times like this and it seems to be doing allright. If its too hot I will just gear down a tooth or two on the pinion.

I know someone is going to say that your not supposed to run the novak gtb brushless stuff past 6 cells but I have been running a 7 cell pack with this setup for a year. Even with the 8 cells being run the GTB esc only gets to about 115F to 120F max, and the motor stays around 120F to 130F and the darn thing runs great and screams.

[What's_nitro?]

Wow those are some hot cells! Have any of them vented yet? I thought 160*F was the maxximum for all nickel cells??? You could try a higher capacity pack, like a 4600. That should bring the temps down a bit.

Originally Posted by What's_nitro?

Wow those are some hot cells! Have any of them vented yet? I thought 160*F was the maxximum for all nickel cells??? You could try a higher capacity pack, like a 4600. That should bring the temps down a bit.

Vented? I dont know what that means, but they are still taking 3100mah+ of charge and they still have tons of power and good run time. I dont know what the max safe temperature is for a nimh type cell thats why I am asking. I know if I gear down a tooth or two the temps would drop right away on the battery.

[johnrobholmes]

170f would be my limit on good low IR cells. I start a run at 140 to 150f, normally end the run around the same or a bit higher.

To kind of answer my own question.....

After several runs on my 8 cell gp3300 battery its defiantly getting weaker. I mean it still takes almost 3300mah of charge its that its less punchy than my 7 cell gp3300 pack and about the same power as my 6 cell pack. I remeber the first couple of times using the 8 cell pack it was crazy fast.

I think the 170 - 180F+ temps hurt the 8 cell battery and eventually took its punch away. Anyway on the same gearing my 6 cell pack saw temps in the 120F's, 7 cell was in the 140-150F's. I think I am going to lower the pinion gear two teeth and try the 8 cell pack again.

Nimh batt temps were advised to 140F max and preferably below. I think it obvious, but the temps you're seeing is damaging your packs. The life expectancy will go way down.

Its always been said if they are too hot too hold, they are getting too hot! I'm suprised they haven't vented at those kinds of temps.

With your setup, 2s lipo will be a world of difference for you. Obviously you need a higher C rated battery and lipo is where its at. How are your run times with those batteries you're using? I think your batteries are probably starving your motor.

Originally Posted by 1maxdude

With your setup, 2s lipo will be a world of difference for you. Obviously you need a higher C rated battery and lipo is where its at. How are your run times with those batteries you're using? I think your batteries are probably starving your motor.

About 5 minutes full throttle street running and about 10min on dirt track racing conditions.

Wow, whats your gearing? I run a MM 6900 which is probably somewhat similar, and with my 6000mah 2s Lipo, I get way more than that. 20-30 mins worth of bashin. My friend has same battery in T4 with 3.5r. Huge difference lipos made. All of his 6 cell packs ran like crap and would draw way too much off the batteries. And he would get like 5 minutes, then he tried my battery and whoa, that thing just tore up his tires and was a different beast altogether. Same thing with my setup, geared 13/90 I've ran it for 45 minutes off roadin, never dropped off in voltage. 17/83 is a good all around gearing, I've clocked it at 46mph, stock gearing 23 tooth, 55mph. but run times are considerably less when doing the speed runs geared that high. Battery has never seen more than 121 degrees. Your ESC might heat up more, yours has a fan tho right?

[Motoman]

It's funny that I kind-of stumbled upon this thread because I was running my XXX-T MF2 today with a "frankenstein" battery I made out of 5 new cells and 2 old cells(7 cell Ni-Cd 2400). I guess the 2 old cells were bad because I got 1 or both of the old cells to vent. I wasn't even running it hard. I checked the temp on one of the old cells and it was 300+ F. the new cells were only like 130F.

Anyway...yeah I think you either need to lower you gear ratio or get a battery with a higher discharge rate. If you want to stay with Ni-Mh you should probably get the biggest capacity pack you can find. If you want to go with li-pos you'll be impressed with the difference in power throughout the charge. The voltage of Ni-Mh packs tend to sag alot more under load than li-pos.

Yeah, plus the pure amps lipos put out will surely make your motor happy. You'll probably gain a significant amount of watts with a 20c 5 or 6000 mah 2s lipo. 300 deg. ouch, you mixed nicads with nimh? different mah as well??

Oh, I re-read the 7 cell 2400 nicad, my bad, I assumed nobody used nicad or 2400 for that matter anymore.

[Motoman]

Yeah I'm not too happy about using Ni-Cd's but this one will be my last one. I just wanted to squeeze out every charge I could get out of the old cells, and I guess I did it. All of my other batteries are li-pos well, except for transmitter batteries (I'm looking into fixing that soon).

Glad I stumbled onto this thread, because I have the same question. I just bought some new EnerG 4600 7 cell packs for my E-Maxx, and they seem pretty hot compared to what I am used to. I was running it on 6 cell Venom 3000's while I waited (a very LONG wait mind you) for the new batteries, and I don't recall them getting so hot. I've only run the new batteries in the truck once, so before i ruin them, I need to know how high I can go on temps for:

Batteries
Motors
ESC

I can't remember what the readings for each were last night, but I'll run it again tonight and check all three temps. I seem to recall similar temps on my batteries (160F range), a bit higher on batteries, and a bit lower on ESC.

Any suggestions (besides Lipos)?

Here's some guidelines -

http://www.rc-monster.com/forum/showthread.php?t=2200

Besides the obvious - you have the body vented I hope, run a fan of some kind. I run a novak setup on esc and a pr of integy fans on the motor heatsinks.

I run 7 cell paks in my "stock" Emaxx, and only the motors get hot - 7 cell Maxamps 4400s. I'm still running brushed motors in it and they get 160-170F. I have to let it cool down between pacs. Batts are warm - a little cooler that when they come off charger. I asked when I got my 4400s if they needed breakin - Jason said no. Yours may be diff, you might want to run them easy for a few cycles. I've always heard temps like 160F is damaging the cells - that damage appears as shorter batt life.

[ssspconcepts]

LOL....

This post reminds me of the days...."what is the minimum safe distance for a 60lb. charge?"

I think 160 is max...if you want good cells for the long haul.