Range story problem: Parallel vs. separate

I’ll bet this is a electro/physics story problem of some kind, but I’ll also bet the answer is anti-intuitive.

The question is simply: will go you further (better range) with 2 identical packs connected in parallel, or by charging them both to full and running them out individually (ie. run the first down, stop, swap to next batt, keep going…)

Philosophically it sounds like those two options should yield the same result, but the world just doesn’t work like that. It’s never so neat and tidy, so I can’t believe it would really work that way - so does anyone know which one gives better range (and why?)

In my experience, you will loose a little range on the higher voltage pack. Because you can go faster you will go faster, faster uses more voltage so less range. Its not a significant loss though, around 10%…in my experience.

Best guess - parallel will give more range due to voltage sag. By itself -
Once the battery gets to lower charge, it can’t provide the voltage to push the motor. In parallel - However at the same voltage, there would be enough amps to continue farther. Albeit a small amount.

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Very good point @SageTX Range will be better running 2 packs in parallel instead of running them one at a time. Because of reduced voltage sag due to the parallel setup’s higher current capability

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Yeah, that’s a great point. I suppose, for the sake of experimentation, you could run them down individually, then stop and connect them in parallel and see how much extra range you’d get…

The results would vary depending on riding conditions

In real-world practice for sure, but for purposes of the thought experiment we must preface the question with “all things being equal” and also assume we do not give in to temptation to go faster simply because we are able as @mmaner pointed out.

I don’t think you fully understood what I was saying. Even with all things being equal, If you test the 2 setups on flat ground at moderate speed, there will be little difference in range because of minimum current draw which will cause minimum voltage sag. If you test the 2 setups on hills, there will be more substantial difference in range because of high current draw which will cause more voltage sag.

And the 2 packs in parallel will not increase top speed or torque over the single pack because there is no change in voltage, only capacity.

Ahhhhh, indeed. I see what you are saying now. The riding environment will affect the results. Indeed. This little exercise stemmed from my trying to decide if I would run my two 6s batts in parallel, or just carry one around (or leave it disconnected) until needed. A potential advantage is that I could be charging one while riding the other, it I thought there must be some cost to doing that…

its going to be so close to the same… its worth testing in the real world but I predict that the difference in having a parallel pack will be negligable.

It would certainly be negligible if you where just cruising on flat ground. But I’m guessing it would be more noticeable in a situation where continuous high current is drawn like climbing long hills for example.

I would run the two in parallel for convenience (charging both at once).

However, there is something to be said here if you add another small variable…

3 6s batteries ran 1 at a time will significantly outlast 2 in parallel. And putting 2 in the enclosure , but running them only 1 at a time - while carrying a spare to swap out, if you are going on a longer ride (or just 1 in the enclosure , whatevs) would get you easy extra range. Heck, with a easy to make parallel adapter, you could rig the first two batteries together for the best of both worlds. :stuck_out_tongue_winking_eye: But that’s not the question you asked. Just something to think about in this mind experiment.

I even considered wiring them in parallel with a switch between them so that I could switch to the next one, kind of like an extra gas tank in a pick up truck.

a mate of mine who I built a board for specifically asked me for 2 seperate packs mounted no in parallel, with a loop key to switch between them so that he knew when he was “halfway” he could swap the loop key and still get home. well that was his theory. I did it for him and its worked well for a few years now.