sinking from sense terminals in 6632B

[jkrbasu]

Dear EEVbloggers-

I've got some HP 6632B 2 quadrant DC power supplies that I'm using to test some coin cell Li-Ion batteries.

I've noticed that when I connect the S+ and S- sense terminals to measure voltage across the battery, the supply begins sinking current (about 3 mA). I've left the supply power terminals + and - disconnected.

Does anyone have an explanation for this? I assumed that the "sense" terminals only measured voltage and didn't pass this much current.

Thanks!

[alm]

Just connecting a large battery to a bench power supply can easily kill some power supplies or worse (what happens if the power supply shorts the battery terminals?). Pretty sure HP recommends disabling the over voltage crowbar and possibly series protection diodes on the output when charging batteries. The specifications will specify a maximum voltage between force and sense terminals, something like 0.5 - 1 V. You are exceeding this limits. Do not expect the power supply to behave in specification.

My guess is that there are protection diodes or resistors between force and sense to limit the voltage when a sense connection becomes open. Your exceeding the maximum force-sense voltage will force current through those devices.