charging a car battery with computer power supply

So once again, if you measure 13.8 V across the battery with only mA current into the battery, either the battey is fully charged or it's at the end of it's lifetime.

Dude I have doubt can we charge with Pc power supply or not??The only requirement is just voltage ? or some thing else? my power supply is AT and 250watt 12v@10amp.

casamiro said:

Dude I have doubt can we charge with Pc power supply or not??The only requirement is just voltage ? or some thing else? my power supply is AT and 250watt 12v@10amp.

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Like FvM say, if you measure 13,8V on battery terminals and charging current is in mA range (500mA and less), then your charging process is over. Also battery can be defective or old and can show the same voltage, but exploatation shows low capacity.

You can charge lead acid with ATX psu if psu gives at least 13,5-13,8V voltage. also psu need to be capable to supply some current.

How battery voltage approaching 13,8V voltage level charging current will decresing.

I suggest reading tutorials about lead acid batteries before like this projects.

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I dont know how you modify your atx psu, but you can see this article:
http://danyk.cz/at_atx_en.html

Thank you so much yes the battery is poor now I test i can vary the voltage from 12 to 24+ :wink: but another problem is that when i connect this with 100ah batter at 10v initially it charge at 10 amp but with in a 2 minutes the amperage drop to 2A..it gradually decrease...how is it possible that such a large batter is charge with in minutes? by the way battery is not old.can you tell me plz what the reason?

boost the PSU voltage to about 14.4 V and provide a current limiting means.

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I have tried this method - it was got quite well. And more simply and reliable than remaking internals ATX PSU.

casamiro said:

Thank you so much yes the battery is poor now I test i can vary the voltage from 12 to 24+ :wink: but another problem is that when i connect this with 100ah batter at 10v initially it charge at 10 amp but with in a 2 minutes the amperage drop to 2A..it gradually decrease...how is it possible that such a large batter is charge with in minutes? by the way battery is not old.can you tell me plz what the reason?

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No, that current decreasing to 2A is because you have poor charger (atx psu) which cant handle that load. When lead acid is discharged below half capacity or complete, then battery knows to drain lots of current, for 100Ah this is over 10A for sure. Lead acid requires voltage and current controlled charger. Maybe you have another bad battery.



Lead Acid is completely full if voltage on terminals show 12,72V-12,73V for new battery and measuring is done 24h of resting after finished charging process.

Voltage for charging cycle can be 14,2V-14,4V after battery reach that level charging is stoped or switched to float charge voltage.

Float charge voltage is 13,5V-13,8V depending from ambiental temperature.

When battery reach 13,5V-13,8V-14,2V-14,4V and when you disconect charger from battery voltage should not drop rappidly. Voltage will go down and should stay on 12,72-12,73V after 24h.

For longer life of battery maximum charging current should not be over C/10.

Possible for modern lead&acid batteries with calcium additive may need charger with < 16V output voltage.

"Charging overview:
===============================
Battery type:
VARTA SILVER (BLUE) dynamic
===============================
Key charging values:
Ideal for 100%-charge: 2x l20 recharging 5h l20
Ubatt.=16,5
===============================
Currents:
0,1xK20 (=2xl20) to 5xl20
==============================="

Ca/Ca with silver on lead plates also go up to 14,4V over that is not smart. This lead acid are maded for cars and trucks to prolong lead plates life, avoiding microcracking and cracking with silver. Charging system in every car is up to 14,4V over that I dont think that we can find car with that alternator, except in brand new cars 2012-2013. Ca/Ca with silver can be used in older cars even maded from 70-80'.

Exposing battery to higher voltage on longer time you cause sulphatisation process to start, and you will decrease battery life and capacity.

But always is good to check manufacturer datasheets and recommendations.

Best starter lead acid for now from Bosch is S5, and can be used in standard lead acid range of charging.





:wink:

casamiro said:

I measured the out put it actually gives 13,8V irrespective to load,similarly when it was at 12v there is only a negligible change when load is connect.I as in battery case it does not charge it seem like a open circuit.

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Hi casamiro,
When you connect the load if The battery voltage is immedeately reaching 13.8v from 12v and there is current flow of only milliamps Then I think your battery is not good.

Thank you to you guys i have successfully modify it,I just loaded the 12v rail with 50 ohm 10watt resistor and done,now it perfectly charging and its voltage is adjusted from 7 to 28 voltage.I modify another psu which i got from old P3 pc it is branded Dell power supply of 10watt and can only delivery 12v/4 amp after modify I can able to get 10-25v@ of 10+ ampere and really cool.The only problem I faced is that forget to replace the capacitor so that when i increase the value I heard 3 big burst but yet power supply work perfectly.I just remove all these capacitors and that's all folks .:wink:

casamiro said:

Thank you to you guys i have successfully modify it,I just loaded the 12v rail with 50 ohm 10watt resistor and done,now it perfectly charging and its voltage is adjusted from 7 to 28 voltage.I modify another psu which i got from old P3 pc it is branded Dell power supply of 10watt and can only delivery 12v/4 amp after modify I can able to get 10-25v@ of 10+ ampere and really cool.The only problem I faced is that forget to replace the capacitor so that when i increase the value I heard 3 big burst but yet power supply work perfectly.I just remove all these capacitors and that's all folks .:wink:

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can you tell me how can you modify PSU adjusted to 28V, I need charging two accu in series thanks in advance