M.L. Toys
M.L. Toys
HobbyMasters M.L. Toys
Anything that doesn't fit somewhere else & general forum updates
I just bought 12v 12ah and 6v 12ah batteries that that I was going to put in the grandsons dune racer, making the "high speed" gear 18v. Then I got to thinking, what if I ran the original PW 12v( 9ah?)and the new 12v 12ah battery parallel to give more run time. I know it's best to keep the ah rating the same, but what are the consequences? Kill the PW battery after the first ride? Kill both batteries after the first ride? Shorten the life of the batteries within the first year?
From what I'm reading from the "experts", it seems mixed 50/50 as to if you can do it or not. At least in parallel. The most common reply when searched seems to be; batteries in parallel: voltage strictly equal, capacity whatever. batteries in series: voltage whatever, capacity strictly equal.

I don't think I'll chance it, but was curious if anyone had done it and what were the results. Seems like it's pretty common to mix ah rated batteries in the solar power house world.
You should be fine running your stock 12v 9.5ah battery in parallel with your 12v 12ah battery. Nothing catastrophic will happen. Just make sure to charge them separately (not in parallel) from time-to-time.
I think the big risk here is the OP's assertion that he was considering this in pursuit of longer runtime. This won't help him, since his runtime will be limited by the *6V* battery that he has in series with the current 12V battery.

I would say it's fine *IF* you have a way to ensure you don't over-discharge the 6V battery (and damage it).

However, the benefits are fairly small:
(A) It will not increase runtime by any substantial amount since you are still limited by the 6V battery
(B) It will increase the lifetime of the 12V batteries since they won't be discharged as far (degradation is lower on an SLA if depth-of-discharge is lower for each cycle).
(C) It will improve the Vdroop some under high loads (unlikely to be noticeable)

I would recommend against it if you are not actively monitoring the 6V battery, because you're more likely to run it very low since the 12V will not be "getting low" around the same time -- therefore the decrease in speed/torque/etc. will be less noticeable than your current setup. Running the 6V too low will at least reduce its lifetime substantially.

Now, you could also go buy another 6V, 12AH battery and wire that in parallel with the current one... :lol:
Thanks all. I'm not sure I understand why this setup will be hurt by the 6v battery. I found a diagram showing how someone else connected a 6v in series to the Dune Racer. Basically, I was going to run the 2 12v batteries parallel to the slow side of the gear selector, then run the 6v in series to the fast side of the gear selector.

Is this not going to work? In my mind, it seems like when on the slow side, it will run 12v at 21.5ah (12+9.5), and the on the fast side it will run the 18v. Now that I think it through, the 6v will only be 12ah, paired with a 12v 21.5ah source...probably not a good idea, huh?
To clarify, My reply was in regards to only running the two 12v batteries in parallel. If you are planning on running the 6v battery in series also then it is a bad combination. Your math on battery voltages and amp hours is correct.
Mixing amp hours in parallel not a hazardous condition. Mixing amp hours in a series circuit can cause multiple problems and not recommended.

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