charging a car battery with computer power supply

hi all,
I want to make a car battery charger that can charge a 12v-110Amp battery
usually this is done using a transformer and some circuitry that can give 12 volt with 20-30 amp
but it cost a lot.

so my question here is
why not using the computer power supply which provide 12 volt with 30 amp and cost a lot less that using a transformer !?
is this possible or not and if not then why ?! it seems reasonable to me that both give the same volt and almost the same amp so they must do the same job
i.e charging the car battery !

does anyone have any clue

the problem is that the charging time is lengthened with low current models voltage is fine you can charge but time will be long

You'll need to boost the PSU voltage to about 14.4 V and provide a current limiting means.

Also the charging voltage should be higher than 13V.
Exact charging voltage should be obtained from manufacturer. Also specification mention time, duration.
However common 12V Lead-acid (car) battery charges give output between 13V and 14V.

I know that the charging time will be long but the common battery chargers provide 30 amp
and I bought a power supply that provide 33 amp at 12 volt
does this 33 amp are fully provided or it's a matter of commercial thing ?!
for a 33 amp power supply it will take a bout 5 to 6 hours to charge a 110 amp battery isn't that the case ?!
what should be modified in the power supply to change the output voltage to 13.4 volt ?!
and a bout the ampere what should be modified to provide current limiting means

the problem is that the current specified is not always delivered constantly by the chargers due to many factors

therefore the estimated charging time be higher to charge your battery

kobre98 said:

hi all,
I want to make a car battery charger that can charge a 12v-110Amp battery
usually this is done using a transformer and some circuitry that can give 12 volt with 20-30 amp
but it cost a lot.

so my question here is
why not using the computer power supply which provide 12 volt with 30 amp and cost a lot less that using a transformer !?
is this possible or not and if not then why ?! it seems reasonable to me that both give the same volt and almost the same amp so they must do the same job
i.e charging the car battery !

does anyone have any clue

Click to expand...

You say 12V 110Ah battery, for C/10 you need around 11A of current at 13,5 or 13,8V.

Its possible to do direct modification of PC PSU, but my personal opinion is that is better to get some decent trafo 18V 12A-15A and make safe charger. Charging process needs high current on longer period, circuit should be safe. For voltage regulation and current limiting you can use LM338K with applications for higher current ratings, or any similar IC for that purposes, even switchers.

Converting Computer Power Supplies (PSU) to stabilized 13.8 V DC 20 A
https://elektronikbasteln.pl7.de/converting-computer-power-supplies-to-stabilized-138-v-dc-20-a.html

+13.5V 14Amp cont. 20 A for 20 sec.
https://www.webx.dk/oz2cpu/radios/psu-pc1.htm

Or you can boost voltage from PC PSU like FvM suggest, that also can be one of solutions.

Your charger greatly affect to life of your battery; hence it is better to have a good charger.

Followings is about general specifications of those battery charging;
https://www.powerstream.com/SLA.htm


Following has circuits for chargers;
https://www.aaroncake.net/circuits/charger2.asp
https://www.circuitstoday.com/lead-acid-battery-charger

Also if you have a power regulator that can adjust voltage and current, it also can use as a charger.

thanks a lot guys for your help
now, what I need to know is if I adjust the voltage coming out of the power supply to 13.4 or 13.8 instead of 12
and connect it to the car battery.
is it going to charge it or not
and in a very simple manner plz explain to me why the power supply after modification to give 13.4 volt at 33 amp isn't considered a decent charger ?!!
if u have the required voltage and ampere what could go wrong and in what way it might affect the battery life ?!

kobre98 said:

thanks a lot guys for your help
now, what I need to know is if I adjust the voltage coming out of the power supply to 13.4 or 13.8 instead of 12
and connect it to the car battery.
is it going to charge it or not
and in a very simple manner plz explain to me why the power supply after modification to give 13.4 volt at 33 amp isn't considered a decent charger ?!!
if u have the required voltage and ampere what could go wrong and in what way it might affect the battery life ?!

Click to expand...

My friend nothing cant replace good transformer design. Switchers are good until they stop working because some part burned out. If you have adequate voltage and current you can charge your battery. I talking in context of reliability and longevity of design. Good chargers with transformers can be transmitted from generation to generation of users, but switcher will work until some fan stop because bad quality or dust. Please do not understand me wrong, I just want to save your time and money.

Look this project:

Charge Controller for 12V lead-acid or SLA batteries
**broken link removed**

You have source code and you can adjust currents or charger functionality according to your needs.








Second project is :

A Charger For Deep-Cycle 12V Batteries (project is not for deep cycle bat, they just call project like that. You can adjust currents in charging phases, by project default goes up to 16A)
http://www.siliconchip.com.au/cms/A_103191/article.html

You have source code and you can adjust currents or charger functionality according to your needs.

You understand that I cant post whole project in forum.



Simple and cheaper solution :

Battery charger using LM338K (TO-3 case) limited to current up to 5A
You can set 13,5V 13,8V float voltage depends from temperature, current is internaly limited in LM338K. Capacitor 4700uF not needed, replace him with 220uF-330uF.



Example for current up to 10A you can see here :
**broken link removed**

You can even make small smarter improvements of this charger with selecting resistors by manualy or by some controller or uC and by this select output voltage for charging.




or you can see this project :

AVR450: Battery Charger for SLA, NiCd, NiMH and Li-Ion Batteries
http://www.atmel.com/Images/doc1659.pdf


There are tons of project and designs, I cant post lots of them because rules and copyright, but you keyboard stand up between you and Internet and Google search field....


My advice specially for battery chargers for safety:
When you make battery chargers for LA batteries make sure that they are safe, and can be left alone unattended long time, that chargers have full control of start and stop also like voltage and current. Parts should be adequate dimensioned for job, and always use good parts. PCB should be protected together with parts on it with protective coating to avoid humidity, acid and others things to destroy PCB, tracks and parts on it. Use metal case for charger with temperature protection, also fuse and varistor are good.



:wink:

DineshSL said:

Your charger greatly affect to life of your battery; hence it is better to have a good charger.

Followings is about general specifications of those battery charging;
https://www.powerstream.com/SLA.htm


Following has circuits for chargers;
https://www.aaroncake.net/circuits/charger2.asp
https://www.circuitstoday.com/lead-acid-battery-charger

Also if you have a power regulator that can adjust voltage and current, it also can use as a charger.

Click to expand...

Suggested chargers do not meet requirements of thread poster.

For battery 110Ah for C/10 is 10A of current. This chargers cant give that current. If we look LM317 datasheet all is clear.

kobre98 said:

thanks a lot guys for your help
now, what I need to know is if I adjust the voltage coming out of the power supply to 13.4 or 13.8 instead of 12
and connect it to the car battery.
is it going to charge it or not
and in a very simple manner plz explain to me why the power supply after modification to give 13.4 volt at 33 amp isn't considered a decent charger ?!!
if u have the required voltage and ampere what could go wrong and in what way it might affect the battery life ?!

Click to expand...

If you modify the output from 12V to 13.8V, it'll charge the battery.

The PSU label may state that it can provide 33A at 12V, but it may not be the case. Which power supply did you buy? Is it a non-brand one?

If you charge the battery at 13.8V and the power supply can handle between 12A to 15A current, not much should go wrong. Only charging time will be long. But that should be good for the battery.

Hope this helps.
Tahmid.

hi
may anyone post simple circuit to change 12v to 13.8v or high volt like dc\dc converter (using diode and coil....).

rassoft said:

hi
may anyone post simple circuit to change 12v to 13.8v or high volt like dc\dc converter (using diode and coil....).

Click to expand...

There is no simple DC/DC StepUp conversion specially at higher currents. If you want to buy DC/DC converter from shop, you will see that price is not so low. Simpler is to make charger from beginning, buy decent transformer....

Higher current chargers/PSU is last thing what you want to leave unattended and in bad shape bad maded with scotch tape and with unknown bad modifications. My suggestion is to made this on right and clean way. If you dont know what you doing better is to stop.

:wink:

Well i modify the computer power supply and now it gives 13.8-14.2 volt but the problem is till there!it is not charging the battery just only few milliampere! plz help any idea!

casamiro said:

Well i modify the computer power supply and now it gives 13.8-14.2 volt but the problem is till there!it is not charging the battery just only few milliampere! plz help any idea!

Click to expand...

Hi please check the battery terminal voltage if you are connecting fully charged battery it may not take more current. If you are connecting discharged battery and it is not taking the current it may be limiting the current check that.

thanks

Either the battery is full or done in.

darla1 said:

If you are connecting discharged battery and it is not taking the current it may be limiting the current check that.

thanks

Click to expand...

what do you mean by that "it may limiting the current?" and battery is not fully charge it's voltage is about 11.34v.I tried to charge by connecting series bulb but nothing happened similarly I also connect dummy load across +5v and Gnd it just slightly increase the current .12mA to 15mA.:sad:

I guess, your previous post isn't correct respectively misleading. You said

Well i modify the computer power supply and now it gives 13.8-14.2 volt

Click to expand...

But apparently, the power supply does not give13.8V when a load is connected.

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.