I need to design a constant current Lead acid battery dis charger.
Specifications of the 12V Lead Acid Battery discharger
discharge current rating 0-8A
We need to get the constant current from the battery through out the discharge period.
I want to know about a suitable circuit diagram and parts for this design.
Can anybody help me.....

 

Will be pretty large and take some power transistors. You will be dissipating about 100W in the transistors during battery discharge so you will need a big heatsink and a fan.

I would use N channel mosfets as a current sink in the negative return lead from the battery. You can parallel FETs to spread the power out.

 

Have you got any schematic of where you are starting from?? I have seen several of them, the most successful used a PIC. The basic set up is to measure the current with the PIC and PWM a output to control your load current.

 

Here's a fancy one. If you like it, fine. If not, start removing options.

 

Will be pretty large and take some power transistors. You will be dissipating about 100W in the transistors during battery discharge so you will need a big heatsink and a fan.

I would use N channel mosfets as a current sink in the negative return lead from the battery. You can parallel FETs to spread the power out.

I agree with all that except for putting the transistors in the negative lead.
The current sink has to be in parallel with the battery.

 

Here is one:
http://hackaday.com/2012/05/15/constant-current-dummy-load/

 

I agree with all that except for putting the transistors in the negative lead.
The current sink has to be in parallel with the battery.

Yes, shouldn't post at 1AM. It has to be connected across the battery terminals.

The one shown in the circuit in the previous post above by #12 has the right idea.

 

I need to design a battery test bench to perform capacity test for starting type lead acid batteries.
Full charged lead acid battery 12.6V and do the constant current discharge until 10.5±0.05v
According to the battery capacity discharging constant current should be able to change and these data should be able to take to computer. Timer should be included and also the voltage cutoff to stop the discharge at 10.5±0.05V. This should be automated one.
I was thinking about to do this using a switching dc load which keep the constant current through out the test when the battery voltage change. If somebody can give me a suitable switching load design to perform this it may be very helpful. Thanx
Adding something more about the project have to be done. The discharging constant current may vary from 1A to 8A. So this design must be suitable to discharge any constant current ranges from 1A to 8A.Can any body help me with this ............