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can i charge a car battery with a simple home transformer

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i have a 12v car battery

can i charge it with a device
AC input
220v
0.2-0.5 A
60/50 hz

dc output
12 v
1.25A
and i would pore a distilled water .

its a transformer for my scanner
is it possible?
 
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ok,
can i split one AC current source into 6 ones
and connect these transformers to each split
output of each one:
A. 6v 1A
B. 19v 0.8A
C. 12v 1.25A
D. 12v 1.5A
E. 12v 0.5A
f. 12v 0.1A

can i some how connect the pairs of the output wires from each transformer to sum their amperes
to make one pair of wires wich carries 5 or more amp
??
 
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Thunderchild

New Member
wo wo wo, your not even making sense, just get the appropriate sized transformer, which is best found in the form of a prebuilt battery charger, unless you happen to come accross one out of an old unit
 

tcmtech

Banned
Most Helpful Member
Many of the small power packs with 12 volt ratings are transformer type. They may be rated at 12 volts but often have a 16 -20 volt open circuit outputs. They do make fair trickle/float chargers and maintainers but they cant cut it if trying to charge a low or dead car battery simply because they will burn up long before the battery ever gets any usable charge built up.

Like thunderchild said you need the right voltage and a bit more current available to charge car battery.

The right type of power packs may be able to do it but it could take a week and still the battery may never reach the fully charged level anyway.
 

Thunderchild

New Member
the problem with the power packs is they are not desinged for this purpose and so the only thing regulating the current is the internal resistance of the battery and power pack, might not be enough to stop your house buring down !
 

giftiger_wunsch

New Member
Just out of interest, is the "at least 5A" strictly necessary for some reason, or will it just ensure that the battery is charged to a reasonable level before the natural end of your life? :D

I was told before that 1/10 of the battery's capacity is usually a suitable current to trickle-charge at (though that may specifically apply to NiMH batteries, which is what I was using, I don't know), but that the current could be reduced, it'd just cause slower charging.

Is there a minimum current for charging a car battery? Other than the leakage current of the battery of course :D
 

bountyhunter

Well-Known Member
Just out of interest, is the "at least 5A" strictly necessary for some reason, or will it just ensure that the battery is charged to a reasonable level before the natural end of your life? :D

I was told before that 1/10 of the battery's capacity is usually a suitable current to trickle-charge at (though that may specifically apply to NiMH batteries, which is what I was using, I don't know), but that the current could be reduced, it'd just cause slower charging.

Is there a minimum current for charging a car battery? Other than the leakage current of the battery of course :D
Lead acid batteries are not set up for continuous current charging, although they will tolerate a low current... how low? Don't know, because their makers specify a charge VOLTAGE, not current. That's why you need a constant voltage (current limited) charger. In systems where you want fast recovery of battery charge (like a car) the typical set voltage for the charger is 14V. For float charge where you just want to maintain charge long term, use a lower voltage. I run about 13.2V on mine.
 

giftiger_wunsch

New Member
What about an upper current limit for charging? Should a resistor be used in series to prevent too much current with a car battery?
 

bountyhunter

Well-Known Member
What about an upper current limit for charging? Should a resistor be used in series to prevent too much current with a car battery?
Some kind of current limit is needed to make sure the battery doesn't get cooked while charging. I suppose s eries resistor is a brute force way, I usually build the current limiting in.
 

mneary

New Member
Car batteries are designed to be (quickly) recharged to a specific charge cutoff voltage, and then floated at a specific voltage. In your car, the charging current is in the neighborhood of 30 amperes (if the battery wants it).

Since car batteries aren't really designed for continuous charging, a trickle charger must be designed carefully. It's wise to have a current limit in float mode. The current limit would slow the electrolyte loss if the float voltage isn't exactly correct.
 

kinarfi

Well-Known Member
If you take a 16 volt source and limit the current with a resistor, your going to boil it dry, as the battery charges up the current goes down and the drop across the resistor goes away and voltage to battery goes up and the fluid bubbles away. and with a transformer your going to be dealing with the peak voltage, not rms.
 
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Thunderchild

New Member
Just out of interest, is the "at least 5A" strictly necessary for some reason, or will it just ensure that the battery is charged to a reasonable level before the natural end of your life? :D

you hit the nail on the head ! and thats just my opinion so don't quote me on your insurance when the house burnt down !
 

Thunderchild

New Member
what if i whould pore distilled water into the battery
to prevent it from drying

it already has water in it you will be continually topping it up
 

MrAl

Well-Known Member
Most Helpful Member
Hi,


Believe it or not, you can charge a car battery from a house voltage of
120vac or whatever, but you need a good diode and a current limiting
resistor. A 100 watt light bulb limits the current, and a 5 amp diode
should handle the current. You might need a couple light bulbs
in parallel to get higher and therefore faster charging.
The only drawback here is that if you apply it while it is still connected
in the car, the whole car body can become live with 120vac. Thus,
you have to be careful or else remove the battery from the car first.
You also can not leave it charging forever. You have to limit the time
you allow it to charge this way or it may overcharge.
It's also very inefficient to do it this way, but it does work.
 
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5 amp diode
??
diode is short circuit on positive voltage
and open circuit on negative voltage

so it doesnt matter what is the size of the current
just its direction
thats what ive been tought so far
 

tcmtech

Banned
Most Helpful Member
A few years ago I built a experimental battery regenerator for breaking down the built up sulfate in batteries that have been deeply discharged for to long.
I used a set of 100uF power factor capacitors and 25 amp bridge rectifier for the circuit. It puts out about 15 amps constant current and up to about 150 volts open circuit.
So far I have have been able to regenerate a number of batteries with it and with no ill effects as well.
I have left small car batteries sit and do constant current charging for several days with it and never cooked one or boiled it dry yet. Non have ever shown a measurable drop in electrolyte levels while having been force charge for that time and and that current. They get just slightly warm to the touch though. If one cell is bad that one will usually show up as being higher or lower temperature wise in reference to the others. Shorted cell = low temp open plates = higher temp. Then that battery is junk any way.

Given a low constant current charge it takes a very long time to boil a battery out likely many months to several years.

But still I wouldn't recommend trying to recharge a near dead battery off of a wall power pack unless its designed for it or has been properly modified to handle it.
 
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