Battery Charging Engine v. Generator

P

Pete in NY

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C Dory Year
2004
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25 Cruiser
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CD025072E404
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Miss Pam
Question for the experts: Is it more economoical gasoline usage to use a generator and battery charger combo or just run the main engine to charge batteries? If underway, battery charging is a function of the alternator obviously. How about at anchor? Generator or run the main engine?
 
Pete-

That's a pretty good question, because of the relative sizes of the engines to their alternators. Let's check out the crystal ball predictions:

crystal_ball_MED.jpg


You might think that the larger engine with it's larger alternator might charge faster and therefore be as efficent as a smaller engine running a smaller generator taking longer, etc.

However, the smaller generator package is designed to be as absolutely efficient as possible, and connecting it through a smart charger of close to the generator's most efficient output level has to be the most efficient package possible. The charger should be or approach 90% efficiency in converting the 120 VAC into 12 VDC to charge the batteries.

The larger engine is proportionately larger than the alternator it turns as compared to the generator package above, as the engine is designed for output levels of torque and energy to drive the boat, and the alternator is only an addditional and necessary subsystem to the motor package. This of course, means that much of the energy developed by the main motor is wasted, even at idle or fast idle charging speeds.

One could do a day or two of calculations to work this all out as an engineering study, but I think the handwriting is on the wall!

That's my story and I'm stickin' to it!!!


Joe.
 
Agree with Joe.
A lot depends on what charger you have--unfortunately the factory chargers are too small for the house bannk, so many have added a larger charger. The Honda generators sip fuel at eco throttle, vs a obligatory use of the main engines--and the alternator output requires the engine spin up to a certain RPM--but do not put out full 44 amps (or what ever) at idle. A gallon of gas will go much further with the generator--let alone the hours on the main engine.
 
Bob makes a good point bout the size of the charger that I alluded to above.

I use a Honda EU 1000i charger to drive a Vector 40 amp charger to charge 4 group 27 batteries used for trolling, or while recharging that same battery capacity used at anchor.

The 40 amp charger puts out 480 watts of power (12 v x 40 amps), and also consumes power to run itself, thus consuming something in the neighborhood of 600-650 watts when operating at full charge.

This is a good match for the generator, which is rated at 1000 watts intermittentently, and about 750 watts continuous. It's an efficient match.

The charger is an automotive type, not marine specific, but is located up in the v-berth well away from gasoline fumes.

Joe.
 
Sorry, Folks - Post Deleted By Author
 
dogon dory":127489pp said:
OK, Joe. Time to cut back on the caffiene again???
Click to expand...

So look who's also up at 3 am and typin' away on the site, huh?

Admittedly, the language in the post was a bit convoluted and unnecessarily difficult, strained, and "hyper extended", etc., etc..............

I guess the lion doesn't sleep tonight, huh?

1995-07-31.gif


Joe.
 
Sorry, Folks - Post Deleted By Author
 
I agree with Joe (but in much fewer words :lol: ) My Outback inverter has an 80 amp charge rate. My 2000w. Honda generator will bring the 550AH house bank from 12v to full charge in about a half hour and a tea cup worth of fuel.

It's a no brainer deciding which to use. The Honda 2000i generator sitting on the engine bracket is quiet and safe. I made up a very heavy 12' adapter cable to hook directly to the shore power inlet.
 
I agree that the genset is the way to go for battery charging. The Honda 1000 and 2000 both have 12V 8Amp charging line, but have to run at full throttle (no Eco) for that small 8 amps. Like Joe and Pat, I just run the Honda at Eco thru the shorepower inlet so the charger does the charging.

I had to use the Honda's 8amp on a riding mower in the shed this weekend and it charged up the mower batter in about 10 minutes.

John
 
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