Battery charger input question

[AKDoug]

I have been carrying a Honda 2000W generator, running it occasionally to top up my batteries when on the hook for extended periods of time. I haven't needed it for the past couple of years, so I loaned it out, but hate to not have some backup available given the remote areas I operate in.

So the question is, running a 20A charger, how many watts of generated power are required? There is a guy selling a Honda 800 for $200, and I am wanting to be sure that's enough power to max out my battery charging system. The 2000 charges my system on low idle, so I am thinking it doesn't require much power. I am not finding input wattage consumption on the data sheets for any of the chargers.

Having the ability to power up my systems and get home if I lose my single 100A alternator is something I am reluctant to give up...

 

[gsholz]

Are you talking 20A AC or 20A DC? If DC, you'll need only about 240-300W AC generator.

If you want to supply a 20 amp AC current you'll need about a 2400 VA generator. Which means probably a 3000 Watt generator given the lousy power factor most chargers have. This would put about 200 amps into a 12V battery bank.

 

[jimdavi]

Watts = current * Volts
2,300= 20* 115

My simple guess at peak load.

 

[AKDoug]

I was sure it was a simple formula to calculate, just didn't remember the formula Thank you!

 

[DavidM]

Hold it. 20A is almost certainly the DC output of the charger. The charger probably is putting out about 14 V at that rate or 14*20= 280 watts. But chargers are very inefficient, so multiply the foregoing by 1.5 and you will be close. 1.5*280= 420 watts AC input to the charger.

So the 800 watt Honda should be able to handle that load and in Eco mode.

David

 

[LaBomba]

Hold it. 20A is almost certainly the DC output of the charger. The charger probably is putting out about 14 V at that rate or 14*20= 280 watts. But chargers are very inefficient, so multiply the foregoing by 1.5 and you will be close. 1.5*280= 420 watts AC input to the charger.

So the 800 watt Honda should be able to handle that load and in Eco mode.

David

I agree with David . 20 amp battery charger will run fine on an 800 w generator

 

[AKDoug]

That makes more sense, since the 2000 always ran in ECO mode when only the charger was turned on. It was the conversion from AC to DC amperage that had me stumped as to the conversion. Thank you all!

 

[High Wire]

Agree that a 800W gen will power a 20A DC charger easily. Less than 5 amp draw on the genny. BUT don't you want enough to also run a frig while charging?

 

[AKDoug]

I run the refrigerator DC only, have 420 AH house bank, and being in Alaska the temperatures are cool enough almost always that the fridge doesn't run much to stay cold. If I just run the generator while I am off kayaking and hiking the batteries stay "more" up between cruises.

It's as much to be sure if I lose my alternator I can use my systems to navigate back to port as for any other reason. If I have to go back without my refrigerator, I can live with that.