Car battery charging voltage

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darwenn
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Car battery charging voltage




by darwenn » 21/08/09, 22:18

Hello, for recharging a car battery, by wind turbine or solar panel (or even with a home charger), what is the no-load voltage of the source ?. I have read that it should never exceed 14,2 volts (commercial charger for car battery etc.), but I see 12v wind turbines which output 21 volts when empty, I also have a solar charger which vacuum delivers 22 volts and a car alternator which when empty delivers 18 volts, and all this intended for charging a 12 volt car battery. So when I read that the voltage that must be sent to a car battery to recharge it must be "slightly" higher than what it will charge, I no longer understand. What stabilized voltage should I not exceed no load to send to a car battery ?. Thank you for your insight, I won't want to ruin my batteries. Me, it seems to me that it should not exceed 14,2v but I am in the dark.

I specify that anyway I use a regulator at the source output, but it is for me to determine precisely how much I must calibrate the no-load output voltage of my regulator.
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Alain G
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by Alain G » 21/08/09, 23:26

Good evening Darwenn!

For a 12 volt car battery it is 14,5 volts, most car alternators are set to this voltage, now it can vary with the battery used, sometimes a small charger to keep the battery active doesn't go up more high than 12.5 volts, too low in voltage and you will take too long to charge because the amperage will not be high enough.

A 180 amps deep cycle battery can easily accept 30 amps and can rise at the end of the charge to 16 volts, except that you must not leave this voltage too long or it will wear out.
:D
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by darwenn » 22/08/09, 07:51

Thank you very much for these clarifications Alain.
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by chatelot16 » 22/08/09, 08:06

of course the generator's no-load voltage must be greater than the useful voltage: but this no-load voltage must not exist as long as there is a regulator working

regulating at 14.5V is good for a car which must charge its battery very quickly to be always full even if you drive little

14,5v is a bit too much for a permanent charge

you can choose between 13.8v and 14,2 depending on the battery

a tired battery requires a higher voltage to be fully charged

a low charge voltage is better so as not to overuse the battery, but from time to time an equalization charge is required: constant current charging even if the voltage rises higher than the usual regulation
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by darwenn » 22/08/09, 11:55

Ok thank you Chatelot.
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by Christophe » 22/08/09, 12:31

I confirm the 14.5V (max) and for the discharge do not go below 10.5V to extend the life of the batteries.

10.5 V is the "trip" limit for 12 V DC -> 230V AC inverters and 14.5 is the overvoltage limit for solar regulators.

If you want to optimize your batteries, ask about optimizer style battery chargers "optimate charger" (it's a brand)
Last edited by Christophe the 22 / 08 / 09, 12: 47, 1 edited once.
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by chatelot16 » 22/08/09, 12:47

10.5V is too low for discharge

a battery left at 10.5V at the end of discharge will quickly die if it is not recharged immediately

an inverter which accepts 10.5V does so to accept a certain voltage drop due to current

to check that the battery is not dangerously drained, the current must often be interrupted to measure the no-load voltage: it is necessary to stop at 12V

I have in project where each element of 2V can be put out of service in turn without interrupting the circuit: it just lowers the total voltage of 2v: it does not matter if the inverter is planned for

This will allow you to measure the no-load voltage of all the elements during the discharge and to know exactly when to stop

It will also allow to put more element than it would take to make the nominal voltage but not to put them all in circuit: when the weakest elements reach the end of their discharge AC puts others into service: This will allow the correct use of age element therefore of different capacity
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by Christophe » 22/08/09, 12:49

Accuracy: 10.5 V is charging.
And 10.5 V on load (up to several hundred watts) = 12V see 12.5V off-load ... (depending on the load ...)

I don't think this is bullshit because all UPS manufacturers use this protection value a priori.
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by chatelot16 » 22/08/09, 12:52

in the case of a car battery where we cannot access each element I prefer to put 2battery and run alternately on one and the other: stop as soon as the voltage of a battery does not rise to 12v when it is disconnected
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by Christophe » 22/08/09, 12:57

Ben I regularly use 2 inverters (1 solar pump of 400W and 1 solar bike charger).

In both cases when it is 2 V "plugged in" (= current flowing) it goes back to 10.5V "unplugged".
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