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12v Battery charger

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Kaylan70

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I have found the attached circuit through elecfree.com It is a 12v Battery charger with auto cut off. I have built this circuit on Veroboard. Upon powering it up I noticed that when the power was switched off the circuit remained ON being powered by the battery. I have now removed D1 from the relay coil and placed it in direction of current flow to the out out but before the R8 and R9 battery sence divider. The circuit now does power down. The next thing is that while charging the does not cut the power to the relay, and likewise when the battery needs charging the circuit does not switch the relay on. At the junction of R1 and R2 I am reading 2.75v. Any help will be very welcome.
 

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  • auto-fast-battery-charger-by-lm311-for-car.jpg
    auto-fast-battery-charger-by-lm311-for-car.jpg
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I have found the attached circuit through elecfree.com It is a 12v Battery charger with auto cut off. I have built this circuit on Veroboard. Upon powering it up I noticed that when the power was switched off the circuit remained ON being powered by the battery. I have now removed D1 from the relay coil and placed it in direction of current flow to the out out but before the R8 and R9 battery sence divider. The circuit now does power down. The next thing is that while charging the does not cut the power to the relay, and likewise when the battery needs charging the circuit does not switch the relay on. At the junction of R1 and R2 I am reading 2.75v. Any help will be very welcome.

hi,
What type of 12V battery is it,, open wet acid, SLA, etc..?
 
That it doesn't cut in when it needs charging is that the diode you replaced is blocking the power to the relay so the relay can only be activated when it is switch on

It's most likely that some component leads do make contact in the vero board (happens me also a few times) that stops tha circuit from working as it should be

first I would re build the circuit and try it again (I asume you use new components and if not you Know 100% sure they are OK)

Robert-Jan
 
hi Robert-Jan,

I'm concerned he may be trying to charge a SLA.
 
hi Robert-Jan,

I'm concerned he may be trying to charge a SLA.

I hope not, as that can have an exploding effect on the battery (normaly there are pressure vent valves build in but they work only once and say good bey to your battery)

this circuit would be fine for a wet lead cell battery

the only form of curent control is a fuse :D:D:D

Robert-Jan
 
Hello and thanks for the replies. The battery to be charged at the moment is a 2x 12v 5Ah SLA connected to give me 12v @ 10Ah. I have also checked the continuity of the board and that is ok. All components were purchased new for this project. The idea behind this project is that I need to power a central heating pump via an inverter when the power is out.
 
Hi Kaylan

this circuit is not suitible for a SLA battery
there is no curent control (except for the fuse) if the charge current is to big the electrolite will boil and gasses will build up in the battery

as written before there are pressure relieve valves build in normaly but that's also the end of your battery life if these get activated

what are the heating pumps spects it might be that it's gona give you a hard time to get it running on an inverter

pumps in circulation systems start with a load so there start currents are normaly 8 times bigger than normal running currents (nly for a short time (les than a second))

but that's enough to trigger the protection of an inverter

Robert-Jan
 
Hello and thanks for the replies. The battery to be charged at the moment is a 2x 12v 5Ah SLA connected to give me 12v @ 10Ah. I have also checked the continuity of the board and that is ok. All components were purchased new for this project. The idea behind this project is that I need to power a central heating pump via an inverter when the power is out.

hi,
As R-J states the charger is NOT designed for SLA battery charging.

The transformer is 13Vrms, which when rectified is about 18Vdc, which is about 4V over the recommended charge voltage for a 12V SLA.

Dont build it.:)
 
Different battery charger...

Hi all,
On further looking on the "net" I have found this attached circuit. I think it has both voltage and auto charge current supply. I guess this one would give me the required 13.8v ish needed by the battery and a maximum of 1.5 amps for the charge current.
I have done some current reading on the pump concerned and there is no initial spike just a constant 0.3 A when powered by the mains volatge. The same readings were taken when connected to the two 12v batteries via the inverter, with the inverter adding 0.6 A. So the total should be 1A.
 

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Hi all,
On further looking on the "net" I have found this attached circuit. I think it has both voltage and auto charge current supply. I guess this one would give me the required 13.8v ish needed by the battery and a maximum of 1.5 amps for the charge current.
I have done some current reading on the pump concerned and there is no initial spike just a constant 0.3 A when powered by the mains volatge. The same readings were taken when connected to the two 12v batteries via the inverter, with the inverter adding 0.6 A. So the total should be 1A.

hi,
That charger looks better for your SLA.
Whats the voltage input to the LM317, you may need a heatsink.
 
Last edited:
I have done some current reading on the pump concerned and there is no initial spike just a constant 0.3 A when powered by the mains volatge. The same readings were taken when connected to the two 12v batteries via the inverter, with the inverter adding 0.6 A. So the total should be 1A.

Hi Kaylan

I don't know how you did the measuring but the spike is normaly a tenth of a second when starting up so only with a very fast meter with peak hold function you are able to detect the spike.

but as you tried it out now and it doesn't coase problems for the inverter your fine.

the shematic you have now is as eric pointed out OK for your SLA batterys.

sucsess

Robert-Jan
 
Thanks you all for your help with this project.
Now if I wanted to add a charge complete LED, where would it be wired?
 
Thanks you all for your help with this project.
Now if I wanted to add a charge complete LED, where would it be wired?
hi,
It would require much more than an LED.
The circuit is only a constant voltage charger with a current limiter, no end of charge detection
 
A comparator and zener diode could be used to turn on the LED when the battery voltage exceeds a predeturmined threshold.
 
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