(ET) Found the problem with the charger

[The CZ Unit <cz alembic crystel com>]

So this morning I bench tested the charger. Without any connections to 
anything the transformer put out 70 volts AC on the secondary windings. 
35 volts per side.

The high voltage lines to the cap read about 210 volts AC.

Then I cleaned off the contacts on the cap with the grunder brush and 
hooked it up. 90 volts AC on the secondary (45.5/44.5) and 290 volts at 
the capacitor. So the cap does boost the current.

Then I hooked up the rectifiers and checked voltage output. 44 volts DC, 
no problem.

Then I hooked up a motor as a test load. Didn't run. 0 volts at the motor.

Then I heard a *snap* from the charger and the motor stated. Then 
stopped. Then started. Oh great. Checked motor, 43 volts, no problem.

Stopped the charger, started up. Nothing. No voltage at motor. Checked 
the diodes, 45 volts at the diodes.

Oh.........................................................

I checked the diodes at the transformer common and the heat sink. Hooked 
an aligator clip from the heat sink to the motor. Motor started right up 
no problem.

The issue was that the positive connection from the bottom of the heat 
sink to the molex plug (+) had gone high resistance. Due to corrosion 
and so forth.

Took off the diodes, took off the diode assembly, ground away all the 
crud at the spot where the lug comes off, cleaned up the lug (tinned 
copper), put it all together again.

Everything works. Puts out a nice solid 20a at 40 volts tapering off as 
you pass 41. By the way under load the voltage (AC) across the capacitor 
drops, my guess is that is the current control. Neat.

Anyway, that's the problem. I just ran it for an hour to charge the 20ah 
lithium pack, the whole heat sink gets *very warm* under load, I'm 
guessing it's the older inefficient diodes. But still, it does work 
properly.

I'll put it back in the tractor later and start testing the Lithium pack 
next weekend.

C