Re: [electricboats] Recommendation for 48 v inboard motor + generator.

The answer to your question is (of course), it depends.    What is the output capacity of your AC charging system?  The gas generators you are considering are 120VAC output?  (The 5,000 watt may have a 220VAC output?)  You will be delivering the power to the batteries or the motor through the battery charger that you would plug in to shore power.  That means you have a max power limit that is set by the charger output.  If your charger output is 1500 watts max that's your limit.  You can't get more through the charger.  So you can't use any generator capacity beyond what the charger can put through to the battteries/motor.  

You have  speed limit on generator of whatever the max output of the charger is.  If it's 1500 watts that's all you can deliver from the genset through the charger regardless of the genset output capacity.  For your boat (assuming a well matched prop) that going to be about 4 knots.  Probably a bit less but I don't know the details of the installation (reduction, prop specs).   You can go faster but you'll be drawing the additional required power from the batteries. 

You can increase the charger capacity but there is no point in having a generator that has capacity several times what you can actually use?  My charger (Thunderstruck EV TSM2500) puts out 1500 watts with 120VAC input.  If I had 220VAC it could put out 2500 watts.  So a 220 VAC generator of 2500 watts could in theory get me motoring at about 5kts.  These chargers can be paralleled and two of them would get me to 5000 watts and 6kts continuous with a 220VAC generator. 

But there are some other limits as you start to try to motor at higher speeds.  Mainly heat.  Can your motor run at that output level continuously?  That's why I went with the 12kW liquid cooled motor.  It can.  The 10kW?  Not sure what it's limits are but its quite a bit lower for continuous operation. 

My project (same boat) is still developing and I thought I would want about 10kW of generator capacity to get continuous motoring speeds of 6+ knots (need that to transit Detroit river in reasonable time) but after running the electric drive for a few seasons I think I would be fine with 5 or 6kW.

As to the generator, I would rather NOT have a gas powered generator on board.  Refueling underway from a gas can sounds like a sloppy process.  Gas fumes can accumulate in the bilge though that can be mitigated with careful handling.   I would consider a propane powered unit.  Same fume issues but swapping out a new propane tank seems a lot easier at sea than re-filling the gas tank on the generator.  A little less output on propane Vs gas but the handling advantages seem worth it to me.  And these generators are strictly for above deck use.  Same for the fuel storage. 


Dan Pfeiffer


More on limits here:
http://dan.pfeiffer.net/10m/electric_drive_limits.htm

More on gensets:
http://dan.pfeiffer.net/10m/diesel_genset.htm

On 2023-12-26 1:46 pm, Scott E Erdman via groups.io wrote:

Hey Folks - I apologize for not maybe having all the specifics needed for this but related to this thread and a somewhat more simple question:

I did buy the Pearson 10M that had been converted to 10 kW Thunderstruck with 2x24 x 2 48V bank w/ 196 AH. 
Presently there is no other way on the boat to recharge other than plugged in on a slip. 
Looking at everything, I figure that purchasing a gas generator is the best insurance on expanding range and dealing with extended draw conditions (currents, etc)
So my question is this - does it make a big difference whether the generator I get is 2,000 vs. 5000 W ? 
I am looking on Craigslist and I can find quite a few used 5,000 W generators for good prices - I expect space is a consideration as well. I guess my main question is what would I gain from getting a 5,000 W generator vs. the smaller, more portable and perhaps more quiet 2,000W ones?

Trying to take care of some of these purchases this winter -

Thanks,