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

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.

[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. 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.

[Motoman]

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?? 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.