How to charge a 12V battery from a gas generator?

[Speo]

A friend of mine bought a gas generator (a cheap 950W one) with a 220V(he is in Europe) and a 12V receptacle.

-Is it possible to charge a 12V car battery directly from the 12V receptacle? From what I know, the voltage should be at least 13.5V to charge a 12V battery.

-If yes, how does it work then?

-If it is not possible, what is ihe 12V good for then? Just for direct usage of 12V?

-Another way of charging is to use a 220V battery charger hooked to the 220V receptacle, but that means extra expenses for the carger.

Thanks,

Speo

[ghurd]

My friend has a cheap 1100W that sounds about the same.

A very low battery will stall the motor if direct connected to the 12V receptacle.

He uses a cheap AC battery charger to bring the battery voltage up a little, then charges from the 12V receptacle. The charging amps are then lower, freeing up power so the 120VAC receptacles can be used for other things while the battery is charging, like charging other batteries.

A very low ohm, high power resistor in the line may work.  Or extra long wires to the battery.

A 220V 100W light bulb in line (in series between the 2 positives) may work, then remove the bulb and connect them directly after the battery voltage has risen.

The 12V receptacle probably makes around 14V, maybe a little more.

The '12V' receptacle is probably designed to simulate the voltage of running car alternator, which is also charging the car's battery.

I would not worry about overcharge, it would take a very long time.

In North America the center is positive. The outer ring is negative.

It would be connected to the battery the same way. Pos to pos, neg to neg.

A car battery needing charged is probably below 11.5V. The 12V recptacle will try to bring the battery to 14V instantly, and it takes so much power the motor stalls.

Resistance in the charging cables slows the amps so the motor can keep going and the battery keeps charging.

When the battery first reaches 13.5V it is still not full charged. It is more "surface charged". After disconnecting the charger the battery voltage will fall fast, without use.

To full charge the battery will take a long time at low amps, and a lot of gas. Not very efficient or cost effective ($ gasoline).

The high amps at the begining of charge is bad for the battery, but the lightbulb will help.

For a battery being used in a car it should be fine for sometimes use.

G-

[hiker]

i bought a used honda gen from a pawn shop a while back--only like 750 watts..

it had two 110 outlets and one 12v out..worked okay  as a small gen..

when i hooked up a batt. to the 12v output somthing blew in the gen ,and now it puts out 220 on the 110 outlet side-24v on the 12v output...and yes the batt. was hooked up plus to plus and neg to neg..    any ideas what happened... must have blown out the voltage reg is what im thinkin--dam thing is so compact its a hassle to take apart......good week end project..

[finnsawyer]

The internal transformer/alternator that supplies the volts probably was center tapped and you may have burned out the wire to the center tap.  Seems like that would have carried twice the output current.  It seems like the answer here is to add an external regulator to the twelve volt supply to limit the maximum current that can flow to the battery.

[Speo]

Thanks for the answer ghurd.

Yow were saying: "A very low battery will stall the motor if direct connected to the 12V receptacle."

That's strange. The generator is rated 950W. Doesn't that mean 950W @ 12V and 950W @ 12V, but at different amps? There is no way the battery will drain anything close to that.

Thanks,

Speo

[Speo]

I wanted to say : 950W @ 12V and 950W @ 220V, but at different amps.

[ghurd]

I know what you mean.  But it stalls just the same.  

If it is done fast maybe 3 times, then the fuses blow. Maybe it has breakers instead of fuses, I can't remember.

Maybe it is related to poor efficiency at high amp 12V.

Maybe it is related to being very cheap.

G-