Advice on charging deep cycle from car...

[G-force]

How much your battery needs to be charged is of course going to depend on how much you use it. Most any small automotive battery charger should be able to be run off of the 1000i. My 5 amp Deltran pulls 1.5 amps or so...around 200 watts, an easy load for a 1000 watt genny. A simple 5,10, or 15 amp automatic charger from Sears or something similar would be fine with the 1000i General rule of thumb for deep cycle batteries is to charge at or below 20% of the batterys amp hour rating. If you got say a 75 amp hr rated battery, you should charge it at 15 amps or less. While there are many variables, most discharged batterys will charge in 6-10 hours with a 10 amp charger.

[brian_bp]

So what is the required "AC current output" --- measured in WATTS as all generators seem to be --- to run a "reasonable battery charger"?

Is there a formula to calculate such a thing, i.e., a generator that puts out 350 watts or 500 watts or 1,000 watts will power a battery charger that requires XXX power to function.

Watts = amps x volts, so as mentioned above if you know the 12V DC amps you need, the 120VAC amps would be one-tenth as much for the same power (watts). The only trick is that battery chargers are not perfectly efficient, so they'll take in more power from the AC supply than they provide to the battery.

In the end, you're unlikely to want more than, for instance, 24 A of charging current at 15 volts (make the math easy...) which is 360 watts. That would mean 3 amps at 120V (to again make 360 watts), or a bit more due to charger inefficiency. A generator rated for a continuous output of somewhat more than 360 watts will do, which is just about any of them.

No reason to buy a LARGER generator than necessary if the generator's SOLE function is simply to run a battery charger, RIGHT?

Right, except that as I mentioned a bigger generator will run more slowly, and therefore last longer, make less noise, probably burn less fuel, and just generally be less annoying... within reason. I still think a couple hundred horsepower worth of car engine is big for the job.

It might also be nice if the generator could occasionally be "borrowed" from the trailer for other purposes, so I would want one which would run most of my power tools (one at a time!). Even a 1000i would run things like drills, and is twice as powerful as really required for my battery charger; if I wanted to run my circular saw, I guess I would need the 2000i.

when I plug in my three-stage charger into a typical wall outlet in my garage, is the current the charger receiving "far higher" than needed?

No, the charger only gets as much current as it needs. It's like a faucet in your house: the plumbing is capable of delivering a high flow rate of water, but only gets as much as allowed through by the valve in the faucet.

For anyone who finds plumbing easier to understand than electricity (because you can see water...), water pressure is like voltage (volts), and flow rate of water (gallons per minute, or whatever) is like electrical current (amps).

[kayakrguy]

Folks,

Thanks for the good inputs and freshening of my grey cells!

I have one question for Steve about using the generator to charge the battery. Ok, I see why without a regulator I shouldn't charge from the 12v outlet. How about using the 120v line to my battery minder--that should work ok, right?

Also, I realize that I may want a generator even if I do charge from my car while on the road. Your discussions have made it very clear that charging the battery from the car while in camp is inefficient as hell and hard on the catalytic converter to boot....

I am much obliged...I hope others have benefited too!

Jim

[brian_bp]

How about using the 120v line to my battery minder--that should work ok, right?...

I think that's the ideal situation, for both the generator and the battery.

It would be really nice if the generator manufacturers put state-of-the-art chargers right inside their generator sets, for a more direct, more efficient, and much tidier package. Similarly, hybrid cars and trucks could have a real battery charger as an option, powered from the high-voltage system without needing an inverter to make 120VAC power. Maybe next year...

[xccelagator]

I rebuilt a pop-up and I can say that alot of camping people have done this.

I ran 10 gauge wires with a 50 amp quick-connector (available at NAPA) to the rear bumper of the tow vehicle connected to the battery The trailer do the same to the batteries on the TD WITH A FUSE! The tow vehicle has a dash switch, a 30 amp relay and a 30 amp fuse also. This way I control running it . I had in the pop-up igloo cooler connected via 12 volts and running down the road it helped "charge" and keep the igloo running. I did do a 2 week long trip and I have no on board charger or used a charger at the sites we went to. Alternators see voltage not how many batteries you have, plus if one is dead the system will equalize and then charge up to normal levels.

Tricks and tips to running this

1. Run the same type battery. In otherwords lead-acid and lead acid, not lead-acid to gel cell.

2. I did not run the circuit when idling, I only ran it when cruising down the road. The reason being that alternators do not put out much amperage idling, maybe 10 amps max!!! Plus when I started the tow vehicle I turned the system off.

All I can say this system worked when for me and I will run the same system for my new teardrop.

Dan

[Tombstonebilly]

Just get a one wire alt. and hook it to a bicyle on jacks and peddle charge it free