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Author Topic: Mixed battery charging - electric outboards  (Read 1331 times)
Paulh_Boats
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« on: May 03, 2012, 01:36:19 PM »

I've had a Numax XV24MF 85Ah leisure battery for a couple of years and I'm pleased with it. I use it on my boat to drive an electric outboard (12V). It's had just a few cycles but I'm impressed with its very low self discharge. So with a trip down the Thames planned for June I want to upgrade to a 24V system.

I have bought a 24V e-bike controller which because of its switched mode design will boost the motor current (because of the motor inductance) i.e. 10amps on the battery side might produce 20A on the motor side at part throttle. A friend who has built a few e-bikes has confirmed this. So the net result is running the 12V outboard from 24V batteries with reduced battery current and associated benefits.

A key benefit is bypassing the resistors in series with the outboard motor that provide 5 speeds - only top speed has a direct connection to the motor. This is a classic problem with the cheaper electric outboards and people have reported at least 20% extra range by using an efficient PWM controller at speed 5, hence the e-bike controller.

I'd prefer to buy a Numax XV32MF 100Ah battery to maximise range, rather than another 85Ah. They will be charged in series by a 24V solar controller and a beefy 24V 20A mains charger for a "splash and dash" charge, either at fixed charging points along the river or with a portable genny.

So despite the battery imbalance I think if I recharge both when the 85Ah battery voltage is low both batteries will be ok - being the same model type they will have similar chemistry for example.

Any opinions on charging the 85Ah and 100Ah in series?

cheers
Paul
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