re Release power

[mikem65d]

Not having much luck looking up power supplies for the re release cars so i thought i'd ask here and hopefully start a good thread to discuss power systems for our re release interests.
Mine at this point consist of the Tomahawk, Scorpion and the Turbo Optima.
Right now i have all 3 built and am trying different motors from brushed to brushless.

I have 3000 and 5000 7.2 nimh batteries that i have for my crawlers.
Nimh and nicads are all i ever used from back in the 80's as that's what we had. I don't remember what mah capacity i used back when i had the Tomahawk.

Lipos on the other hand just seem like the best way to go. More power and less weight.

But what is a starting point?
Obviously a 5000mah lipo is lighter than a 3000mah Nimh, but is 5000mah lipo overkill?

I'm interested in discussing what is the best size for the cars i now have.
Please jump in and share your thoughts.

[XLR8]

Hey Mike,
I really don't think 5000 mah is overkill for any RC, it just requires re-charging less often.
I'm currently running a cheap 3500kV motor with either a 4000 or 5200 mah 2s lipo in a Turbo Scorpion re-release and it seems to handle the power without a problem.
I'm getting around 25 - 30 minutes total run time on the 4000 mah but I don't run it beyond 10 minutes to prevent the motor overheating.
I've retired all my nimh packs about 3 or 4 years ago and have switched to lipo exclusively - more power, longer run time, less hassle overall and they can be recharged multiple times a day without causing any harm.
That said, there's certainly nothing wrong with nimh. Some point to potential safety hazards with lipo batteries and that's a valid concern - especially for the kidos.

[Dadio]

I'm pretty happy to use lipo on my re re and original cars but just remember that old school brushed motors can get very hot , they got hot with 5 min runs on NiMH ! So a 25-30 min run with a brushed motor at high speed can kill the motor , I regularly use a brushed crawler for 30+ min on lipo but its no where near as highly stressed , as long as you time your runs to 5 min and then allow a cool down time for the motor its fine , if you go brushless its fine to run longer as they generate less heat .

[jwscab]

yeah, as far as capacity, you could have a 10000mAh battery and it would be no problem. Just need to watch motor and esc temps. run them and let them cool. the only difference between the 10000mAh battery and a 2000mAh battery for a given car is one has to be recharged 5 times more as the other.

i would say if you aren't racing in a specific class, the trackstar turbo systems are really nice quiet and cool. the 17.5 combo I have isn't the torquiest, or fastest but i bet a 13.5 system would run awesome.

[Coelacanth]

The biggest problem with NiMH batteries is, just like your 3- to 5-year-old cordless drill that only lasts for 30 seconds before it craps out, they stop taking a proper charge when they get old. I had a weird issue several years ago with an ESC that I thought was wonky; the thing would run for a minute or two and just shut off. It turns out it was due to low voltage cut-off, and the 7-cell NiMH battery that I'd just charged a week before, without running it, had already lost most of its charge (or didn't take much of one, anymore). The other issue with NiMHs and NiCads is the voltage output decreases steadily as the battery drains; with LiPos, the voltage stays pretty constant, somewhere between 7.4 and 8.4 volts I believe, for the duration of whatever the mAh battery capacity is. That 6000 mAh number, for example, only refers to a battery's capacity, = run-time in ordinary language, and doesn't have anything to do with a battery's power. A 600 mAh 2S LiPo with run your car just as fast as a 6000 mAh LiPo, it'll just run out of juice 10 times faster.

One final issue with NiMHs, but moreso with NiCads, is that they have a charge memory and if you don't discharge a battery completely before recharging it, the battery doesn't function properly anymore, and will need to run through several charge/recharge cycles to attempt to restore it. That sometimes doesn't work with older batteries and you gotta toss 'em out.

The only downside to LiPos is the need to take care with storage and discharging/charging them; if not done properly, you'll risk having a pretty intense, explosive fire. So like the others said, LiPos aren't great for careless kids.

[mikem65d]

Hey Guys,

Thank you so much for all the info and the way you all put things into perspective for me.
All made so much sense to me now and I do have the Trackstar 13.5 combos. My Turbo Optima has a Reedy 19t brushed motor that scoots. For the Tomahawk i put in my never used Tamiya Technipower. Haven't run it yet.
The other thing i realized with going Lipo is the weight reduction vs the Nimh packs.
Amazing, the 5,000 2s lipos are more than 3 ounces lighter than the 3000mah Nimh batteries i have, so those will be kept in play for the crawlers i have.

You guys rock with the input. I never would have considered how hot the brushed motors would have gotten had it not been mentioned here, and now i know better.