Dual battery question.

[Dr.Newb]

I have a traxxas evx2 esc in my new project. My question is i have 2 5000 2s lipos one is a 25c the other is a 30c. Can i run them together even tho the c rating is different????

[MasteroFlego]

I wouldn't. One of them will puff a lot sooner due to being unmatched. If you want to run dual batteries they should be matched, and only run in that specific pairing.

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[Rekreant]

running two batteries at once is already a risk even if they are the exact same battery. The problem is how the current flows through the final battery. SMC recommends if you must do this to rotate which battery is first in series every time you use them. Having different discharge ratings will burn out the lower C battery VERY quickly. You dont want to risk it!

[MasteroFlego]

Note that this is if you run them in series, I'm not sure what would happen if you ran them in parallel.

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[Rekreant]

Very good point.

[Voodoobrew]

I am not 100% but I believe in parallel the higher C rated battery will discharge into the lower C battery till voltage evens out. So Basicaly they will stay close to the same voltage and die at the same time.

But don't try it just because of me, I could be dead wrong, and it's your stuff that burns up.

[Voodoobrew]

Also make sure you know parallel-series wiring! One wire in the wrong spot with a lipo can cause an explosion.

[QuesoDelDiablo]

Originally Posted by Voodoobrew

I am not 100% but I believe in parallel the higher C rated battery will discharge into the lower C battery till voltage evens out. So Basicaly they will stay close to the same voltage and die at the same time.

But don't try it just because of me, I could be dead wrong, and it's your stuff that burns up.

I hate being the guy that tells people they're wrong because I don't like sounding like a know-it-all, but that's mostly/partly wrong, or at least misunderstood a little.

If the voltage levels are different the higher one will instantaneously drain into the lower until they equalize when the system is initially connected. That fast discharge is REALLY bad for the battery. This is the concept that the quoted post refers to I think. In running different discharge rates, it causes this to happen essentially non-stop. Really hard on batteries and potentially very dangerous.

C ratings won't influence the voltage balance, only the discharge rates. Batteries with different internal resistances WILL drain at different rates and die at different times.

Batteries with different C ratings should not be used in a dual set-up.

The C rating on it's own won't cause an imbalance of the batts. BUT the ONLY time you should dual batts is if BOTH batteries are matched - meaning they have endured the same number of usage cycles and the internal resistance of each cell has been tested and balance across the packs.

Originally Posted by Voodoobrew

Also make sure you know parallel-series wiring! One wire in the wrong spot with a lipo can cause an explosion.

This is true, make sure you know what your doing when making a dual battery set-up.

[JennyC6]

Originally Posted by QuesoDelDiablo

BUT the ONLY time you should dual batts is if BOTH batteries are matched - meaning they have endured the same number of usage cycles and the internal resistance of each cell has been tested and balance across the packs.

Been workin' fine for me in my CA-10. Bought a pair of 2s 5000mAh 50c Gens Ace hardcase lipos for it and it's the only truck they ever go in. Have 'em in parallel and every time I recharge them they take within 50mAh of each other.

Also, runtime for dddaaayyyysssss. Somewhere around 6-8 hours I think. Never actually run it from full to LVC in one session before.

[Dr.Newb]

Thanks for all the input. I will pick up a perfect matching pair of 2s

[v33]

i was running parallel 3S 1800 lipos for a few weeks on my 10.2. for crawler, i think it is overkill and adds unecessary weight. i took them out, the punch i get from my 3S 1800's with 50c ratings is more than enough to get me anywhere.



i guess if your running a monter truck for bushing the extra boost in power helps. i think its minimal for my setup and usage.

[JennyC6]

I do it for the increased runtime rather than the increased punch. I love how my CA-10 has so much energy in reserve that I can run it off and on for a couple weeks between charges.

[mewalsh100]

I would not recommend running two packs of different C-ratings. Heck, I'm not a fan of running twin packs of identical C-rating. Theoretically, if you ran them in parallel, you COULD be ok. Stress on the word could. I guess I just wonder what's to be gained. I mean, are you burning through 5,000mah packs? The extra weight of running an additional 5,000 pack is probably more detrimental to a crawling rig any way.

[mewalsh100]

Originally Posted by JennyC6

I do it for the increased runtime rather than the increased punch. I love how my CA-10 has so much energy in reserve that I can run it off and on for a couple weeks between charges.

But, it's not a good idea to keep those packs stored at any more than roughly 33% total charge for any length of time.

[JennyC6]

Originally Posted by mewalsh100

I would not recommend running two packs of different C-ratings. Heck, I'm not a fan of running twin packs of identical C-rating. Theoretically, if you ran them in parallel, you COULD be ok. Stress on the word could. I guess I just wonder what's to be gained. I mean, are you burning through 5,000mah packs? The extra weight of running an additional 5,000 pack is probably more detrimental to a crawling rig any way.

I did it because I hate having to stop mid-run and recharge. I wanted to maximize runtime over all else. It was runtime issues that pushed me to nitro way back in 2003 when I got into RC, after all. 'Course that was before the days of LiPO where if you wanted to run for more than 10 minutes continuously you had no other option, but even today that sticks in my head. Runtime. Punch is irrelevant to me, I have punch control turned down to just 10% to avoid exploding driveline parts. Wheel speed is irrelevant to me, 2s on a 5700kV brushless motor gives me way more wheelspeed than the vehicle has any right to posess. But that sweet sweet runtime....mmm. And I'll be needing the large capacity anyway once my build's done, since I have plans for a pretty potent FPV system in it, winches, lighting, it has a soundkit already...

Lighter weight on this truck? Bad idea. It needs the extra weight. Thing's too light for its own good unladen, somewhere around 6.5lbs and very nose heavy besides. Somewhere around 3-5 pounds in the bed is necessary before itt'l stop unloading a rear tire at random. Which is beautifully realistic and I've no plans to change that, I'll just keep it loaded down whenever it's on the trail!

Originally Posted by mewalsh100

But, it's not a good idea to keep those packs stored at any more than roughly 33% total charge for any length of time.

They're....not stored. I run the thing every day just about. And I'm not about to spend an hour and a half charging it just to drive it ten minutes, then another hour and a half discharging it. I charge it fully and then it sits there on my endtable, never more than 48 hours between runs, until I hit LVC. I love that I can just flick two switches and get right to driving it, so convenient.

[Rekreant]

Originally Posted by mewalsh100

But, it's not a good idea to keep those packs stored at any more than roughly 33% total charge for any length of time.

3.83-3.85 per cell is the safest storage voltages. I often run my batteries till they get there and then charge em for extended life.

[Voodoobrew]

Why not get a 10000 MAh battery and not burn your house down.

[JennyC6]

I'm not going to burn my house down because I have two identical packs wired in parallel. The days where lipos randomly went up in smoke are loooooooooong gone.

[xv-townboy]

I run saddle packs on sliders...My SCX 10.2 is running 2x3's 1300 on a brushed set up and my OG SCX 4 way steer is running 2x2's 1300 on an older Novak 2's brushless system..I love how it balances out both trucks along with the low weight and good run times.Win Win for me