pickworthi said:
Results:
Separately: The packs yielded 9.6ah and 9.2ah.
In Parallel: Packs yielded 17.2ah
If everything was perfect, I should have got at least 18.8ah. So difference (1.6ah) is an 8.5% efficiency loss roughly.
Yes, you should get the same or better. Noticeably better really only happens when there is enough load on a single battery to cause greater voltage sag and thus greater loss to internal heating of the battery, vs paralleled batteries. If there is not enough load on a single battery to create significant voltage sag then there is not significant internal loss of power to heating, etc., and paralleling them wouldn't change that much.
But at the least, you should get the *same* results.
The only things that I can think of to cause different results might be different total conditions causing greater loading, like higher headwinds or more starts from a stop, but those might have to be significant and very noticeable to you to make that kind of a total capacity difference, as they would have to cause significantly higher power usage causing significantly higher voltage sag over enough distance / time to cause that much loss. If both trips are at the same speeds and no pedalling (motor power only, since people don't pedal exactly the same over a trip and thus pedalling can greatly affect actual power usage in a test like this, depending on various conditions), and the same stops, starts, terrain, winds, and throttle usage, then the conditions should be close enough to get the same results from either test at any time the test is done. If conditions and usage aren't the same, then results might vary significantly even between separate trips of the same configuration.
What are the other stats from the wattmeter for each trip? (max and min of Watts, Volts, Amps, total Wh, etc--any info it provides).
I believe that the loss is caused by the cabling - the packs are connected together over the two supply leads that go from each front pannier to the back pannier where the controller connection is. That is around 3 meters of cable battery to battery. Its very high rated (AWG 10 equivalent) but balancing flow over that length of cable must loose energy - at least that's my theory.
Actually, it is *better* to run separate cables for each battery as far as possible, because then there is even less loss in parallel, as there is half the resistance in the wiring for the total.
If they were paralleled closer to the batteries, you would then have a smaller "pipe" for it to flow thru, by half, for more of the length of the path, and there would be higher losses, when used in parallel.
However, if it's 10g, then at the currents you are using them at, there is negligible loss. If you like, you can measure the voltage drop across the length of the cable at the max current you use them at, to see exactly how much it is.
But either way, since almost all the path is separate wiring, then that is identical losses to when using them separately, as well as parallel.
The only thing that is different between parallel and serial, as for wiring, is the parallel connector setup, correct? If that is a lower gauge, or has a connector-to-wire or connector-contact-to-contact issue causing higher resistance, then you would get voltage drop across that which you don't get otherwise. You could see that drop in the wattmeter display (if it is visible on the handlebars), during the highest current draws (hills or startups from a stop). If there's no significant drop across that cable (from the back of the battery-side connector to the back of the controller-side connector, to include contact-voltage-drops), then there's no significant losses in it either.
Another test that can be done is to leave the parallel cable in place for the non-parallel test, but connected to only one pack, and the controller (or rather, wattmeter, then controller). If this is done on each pack, then if it is a problem with the cable, you should see a difference with one or both packs this way, just like in parallel. If the problem is at either of the battery-end connectors, or the separate battery-end wires, the difference should be proportional to (the capacity difference between parallel and non) or the same as when in parallel. If the problem is in the common connection point or wiring, then the difference will be the same regardless of which non-paralleled pack is under test.
As far as "balancing flow" goes, I'm not sure what you mean. If both batteries are essentially equally capable, and the wiring is the same, then all the flow goes from both batteries to the controller. There should be no flow from one battery to the other, unless one is lower voltage (which won't happen if they are about equally capable, as both will drop in voltage by the same amount for the same load).
A possible issue: I don't see anywhere that you've said this is the case, but if the balancing leads are connected between the packs, then perhaps that is creating a problem, if some of the groups of each pack are imbalanced in capability (not static voltage) different from the same groups in the other pack. That could cause current flow between them under load, thru the balance wires, which are typically very small , and could waste some power as heat in those wires and the interconnects.
I'm too tired to think of anything else right now, but i"ll post back if I do.