Re: [electricboats] Time to re-power

On Mon, May 25, 2020 at 07:41 AM, Ric Sanders wrote:

I looked up the Elcon line. They want a 230 volt input. I’m trying to not have to rewire my existing generator to that voltage. 

Hi Ric,

To make sure that I’ve got this right, you’re looking for a charger that runs on 115VAC and outputs close to 100A of charging current for a 48V (nominal) DC battery bank.  Let’s do the math...

Charging voltages for a 48V battery run past 56V (above 58V for LiFePO4], but I’ll use 56V for now.  The charger manufacturers often use 66V as max output voltage for a “48V” charger.  100A x 56V is 5600W.  If we assume a 95% efficiency for the charger (most are not that efficient), then the charger needs an input of 6000W or more.  Assuming solid 115VAC input, you’ll need a circuit that supports a 52A load.  Since 115VAC circuits greater than 30A are pretty rare, I doubt that you’re going to find an off the shelf charger that meets your needs.  Most electrical engineers that need more than 3400W (30A@115VAC), go to 230VAC.

So given all that, you are probably stuck with two 50A 48v chargers, if you can find them, on independent 30A 115VAC circuits, if your generator will support them.  

Alternatively, all of the electric boats that I’m aware of that use high output generators to support their electric drives go with DC generators, rather than AC, e.g. the Lagoon/Solomon catamarans.  This eliminates the added components, wiring, and losses related to converting from DC to AC and back to DC and gives a more efficient serial hybrid mode like you have described.

Boats like mine are using their onboard chargers as emergency backups, using what is already there, to avoid installing specialized equipment to support a dedicated hybrid drive system.  And as I’ve stated before, I haven’t needed the serial hybrid capabilities in the 10 years since converting to electric.

Fair winds,
Eric

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