Battery Charger Tester

[adex44yrs]

I am trying to test a battery charger with a battery simulation. I have a source follower configuration circuit with op-amp for voltage differential. I Keep running into different problems. It seems as if my FETs are not sinking the current properly. Any suggestion or ideas?

 

[chuckey]

What does VSI 40 do? R5 (70 ohms) this will limit your current draw. VG1 what is the likely range of battery voltages?
Frank

 

[adex44yrs]

VG1 is the charger input, the charger will supply voltage in the range of 45-60v. VSI 40 is to supply initial voltage into the charger so that the charger will think it is a real battery. R4 and R5 ensure the the load between the FET is balance. At this time the charger comes and for few seconds and turns off and the repeat the cycle.