Hi guys,
I'm with Richard on the reasons for using separate banks.
I'd still encourage you to consider the advantages of charging the pack that is being used for propulsion. And the term "charging" is probably a misnomer in this mode of operation. Cos in reality the power from the charger is really going straight to the motor. So the practical effect is to reduce your current draw on the battery bank. I'm suggesting that if you ever have the genset on at the same time as the motor is running, you might as well have it connected to the pack that's being drained. Or even better, have the packs paralleled as well as having the charger on.
Even if the current draw is low, and the losses from Peukert's effect is small, there's still about a 10-15% loss of energy on charging the battery. That is, to have a 100 ah available you need to pump in about 110 to 115 ah.
As well there's other advantages that come with charging the loaded pack. Because the pack is being drained at a much lower current when the charger is connected, the pack voltage is higher. I'm guessing maybe 5-10% higher? And with higher voltage comes the advantage of lower amps being drawn from the pack to maintain the same wattage going to the motor. And so with lower amps, you're extending the range again. As well, with higher voltage comes lower operating temperatures of all the elements, and therefore lower losses there.
If you're like me you'll not be wanting to run the blessed genset for any longer than you can get away with. And charging the pack that is being used will increase your efficiency from 10 to 30%, and which means that you'll need to be running the charger for 10 - 30% less than if you charge the off duty pack. As well as less annoyance you also get savings from using less fuel, and shallower cycling of your batteries.
Cheers
Chris
--- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@...> wrote:
>
> Hi Guys,
> Chris' point is a good one. All batteries waste some power during charge and discharge, with wet-cells being the worst, AGMs better, and LiFePo best of the common types being discussed. IF your charger(s) can handle it, the best efficiency is to be had by charging the active propulsion bank while motoring.
>
> Lot's of ways to skin a cat though, and a lot depends on power settings. For low power use as Richard describes below, and especially with AGM as opposed to wet, the efficiency loss is pretty small.
>
> If you're running wet-cells and/or running at higher power levels the story changes. Then you'd want a fat battery bank (both strings paralleled in this case) and a bullet proof charger(s) that can be run continuously when you're motoring.
>
> Has anyone worked out the numbers to get an idea where that "crossover point" might be, and/or found any info on how much continuous current a typical 100AH AGM can handle routinely?
> Jim
>
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