how does car battery charging work?

[icecoolwas]

Ok, I have modded a computer powersupply which outputs 60Amps continious @ 12v (I modded it to 12.45v via the senseline) all the grounds/12v+ wires that come out of the supply are soldered together and I have used 8awg jump leads to connect it to my car battery when it was flat, yeah it charged the car battery, i jumped in the car and all eletrical was running off the psu including My HID Headlights (I tested this for a mere few seconds to see if all the connections were perfect), after about an hour I disconnected the psu and tried starting the car, didnt start but compared to where i started it was trying more, however my brother came home so we jump started the car, I only had it running for 10 minutes then switched off the engine and I was able to start it again but one thing had stunned me, how does the car battery charge so fast of the car alternator? my psu outputs like many times the amperage compared to an average car battery charger, but could it be the 12.45voltage? of course it wouldnt fully charge the battery but it would be enough to start and it should have done it quickly (i think).

thanks.

[trd1587]

Voltage regulator on Car's alternator usually 14.6v if not 13.6v You need More that 12v on laod.

BTW if you use you alternator to charge your batterie it will shorten your alternator life. IT WILL OVERHEAT. IT 'IS THERE TO MAINTAIN THE ACCUMULATOR UP TO CHARGE AND FEED THE ACCESSORIES IN THE CAR WHILE SPINNING FAST.

COMON ALTERNATORS ARE AVERAGE 55 AMP DEPENDING OF AMOUNT OF EQUIPEMENTS IN CAR.

P=VI

55 AMP * 13 Volts gives 715 watts , hey that' half a toaster.
If you can really toast a bread with your computer power supply than you made a great thing! Be carefull no to put 2 of them on the same braker or it will heat and turn to off!

Regards

Marc

[icecoolwas]

oh well, alternators do it quick and easy in the end, if it dies it dies lol.

I guess I'll just keep my PSU to power my car amplifier in house. love 520 watt rms of bass XD.

thanks for the answer.

I wonder if I could add a pot mod to my psu to change it to 13.8v..

[dangus]

My rule of thumb for lead-acid charging is voltage limit to 13.8 to 14.4 volts, and current limit at C/5 or less, where C is the capacity in ampere-hours. A flat battery will current-limit the charger initially and sit at around 12V, then gradually rise to 13.8 to 14.4 volts (depending on temperature), and draw little or no current when finished.

It usually doesn't take extreme current to revive a car battery enough to get the engine started. I've used 1A bench supplies more than once, and just an hour of charge was usually enough. There are 12V smart chargers made for Power Wheels ride-on toy cars that make decent car chargers. I scored a couple cheap at a thrift store. They're small and light enough to keep in the car or a tool chest drawer. They quick-charge at a few amps until the battery reaches about 12.9 volts, then drop to 1A until charging complete, followed by a pulsed trickle charge to keep the battery topped up.

15 V (or higher) laptop supplies with an appropriate series resistor might work.

[Speedskater]

Here is an article on charging deep-cycle marine batteries.

West Marine: West Advisor

[armandjones82]

I think using a car battery as a power supply to the computer can be very harmful because of it's different power surges and sources in order to really set it all up to the true value of energy needed. But if you have used it successfully, that would be great! Be cautious if ever!

[ben12345]

If your car is fairly modern (i'm assuming it is because you have HID lights) then the alternator is likely to have an output in excess of 100 amps. Even 150> amps is not uncommon these days with all of the electrical gizmos in the cars.

As mentioned previously, an alternator will actually produce this current at more than 12volts... normally between 13.6 and 14.4v. You need this potential difference to fully charge the battery, as a conventional 12v car battery will actually float at around 12.6v when fully charged and if in good condition.

Don't worry too much about overheating the alternator - they are much more robust these days and have internal cooling fans, and unless you short it out or let it run with no battery connected, then they are quite hard to damage. Normally alternators fail when the brushes or slip rings are worn out, or the rectifier/voltage regulator fails. You will shorten the lifespan of the battery though by charging it from flat with the high current of the alternator - much better to use an 'intelligent' battery charger in these situations.