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.

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.

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.

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?

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.:surprised: 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.

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.:lol: All of my other batteries are li-pos well, except for transmitter batteries (I'm looking into fixing that soon).:yes:

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.

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.

wow 300 beats my record. I heated some 3800 tenergies to 210F a couple of times then I went lipo. lipos havent seen more than 107F the whole time I have had them and its nearly 100 here now.

Wow! Either you drive your truck like an old woman, or you need a bigger motor! :lol:

I think my 1515 is big enough. I wouldnt say I drive like an old woman, but I would say im not jumpy. I have finally learned to drive smooth.

Lol... But yes throttle control makes a big difference in battery temps. Especially with Nixx. They'll heat up quickly if they constantly see ~60A sustained loads during acceleration. Most Nixx cells are rated for only ~35A.

Thanks for the link - that's exactly what I am looking for. Guess my "stock" E-Maxx isn't going to be stock much longer. I need to get a fan or two me thinks... :yes: Will adding fans actually draw more current and therefore make the battery temp issue worse though?

I think I will also contact the battery manufacturer, that's a good idea. And I was already thinking I would have to let it cool between runs, so I guess it's a good thing I also have my Revo! It's nitro, so I don't have to worry about recharging it. I'm having a lot of fun with the E-Maxx though, especially for a truck right out of the box.

Someday (in the distant future I am afraid), I'd like to build one (a Revo or E-Maxx) from scratch and do the whole brushless/lipo thing. I don't have the time or moeny to do it now though. Any idea if lipos work in an E-Maxx without replacing motor and ESC?

fans draw a few seconds of runtime, if that.... they contain TINY motors (brushless at that) which draw around .05-0.2 A.


a piece of bark will hurt your runtime more than the small fans.

[QUOTE=Motoman;170803]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.:surprised: the new cells were only like 130F.

I believe the temp record you made was not real temp of the cell. Since you use a temp gun, it has a larger error in shiny metal material. The reflectiveity is hight for the ir temp gun. Try to avoid to measure cells without any cover and stick.

Gallagher:
I know what you mean about measuring the temperature of reflective surfaces, but trust me it wasn't as shiny as it looks in the picture after it overheated. It does have a heatshrink covering on the cells but they are not the labeled kind. Also, the error increases as you move further away from the surface, and as you can see in the picture I had the temp gun touching it. My experience with the error in reading reflective surfaces has been that the temp gun actually reads less than the real temperature and not the other way. So, the cell had to be at least 300 maybe even a little more especially because I took that reading after I came inside my house about 3 or 4 minutes after I stopped running the truck.

dirt101:
I also noticed that a properly sized lipo is less susceptible to overheating. I would rather spend a little more for a lipo than buy another NiXX. There's a lot of people that think that NiXX are still cheaper, but if you compare the price of a decent lipo to that of a good NiXX it's really not a big difference.

Does anyone know at what temperature smoke starts to come out of the vents of the cell??:lol: The bottom line here I think is that the capacity of the cells was way too low and therefore the discharge rate was also too low.

I haven't tried it with my Emaxx. Just concerned about possibly smoking the esc I guess, motors wouldn't worry me at all. In theory, lipos shouldn't be any diff than 7cell pacs and thats all I've ever run in mine.

You would need to have a separate low-voltage cutoff module, because I don't think the EVX has one.

^^Def, there is no lvc in the evx.

I have the side windows cut out, but no fans - yet. I guess that's my next step. What's the best way to connect the fans? Solder them to the battery leads on the ESC? I noticed the reciever has a socket that says Batt on it. Is that to plug a battery into or to draw battery power out of? Could that be used?

Off to order a couple of fans!

Yeah.

That's the easiest - just wire them so you have a plug that'll plugin the batt slot in the rx. This drains a little away from the servos, but unless you get a power draining fan, it shouldn't be noticeable.

If you're runnning nitro, its for a batt. If you have a 3rd channels in the rx you could you use that if you were running nitro - all the slots have power.

Thanks, that helps. I'm getting the Novak fans mentioned, so according to tc3 racer, a piece of bark draws more current! :lol:

I'll just wire them all into one plug ans plug it into the reciever. Here's hoping for cooler runs!