Re: (ET) Charger problems.

[Chad Bush <bushman165s aol com>]

Chris,

Sounds like you have the short 20uf capacitor in your charger. I would 
suggest buying more than one when you order parts.

Also, instead of checking the diodes through voltage, you only need to 
test them with continuity (resistance) in BOTH directions, meaning one 
direction should be a direct short and the other should be a complete 
open circuit. That's a perfect check. The diodes will not test bad only 
under a load. You can't check the capacitor without an LCR meter, one 
that has a capacitance function on it.

Where is this charger molex connector you were talking about? You 
should be checking the charger output voltage at the batteries or at 
the charger itself between the heat sink plate and the ground lug on 
the secondary side of the transformer. I always check the output of the 
charger on a DC and an AC voltage setting on my meter. You should be 
getting at least 42 VDC when it's working correctly and maybe 2 to 10 
VAC at most. Anything other than that, I would check the breaker and 
disconnect. If those are good, change the cap AND diodes.

Hope you get it fixed.

Chad


-----Original Message-----
From: Christopher Zach <cz alembic crystel com>
To: Elec-Trak <elec-trak cosmos phy tufts edu>
Sent: Fri, Jul 6, 2012 8:54 pm
Subject: (ET) Charger problems.


Hm, this is interesting. First I used my diode tester to check the
voltage drop across the diodes. Then I remembered that since they are
connected at both ends (by the plate and the transformer windings) that
I would have to de-solder one of them.

De-soldered and checked. Both showed infinite resistance in one
direction, one showed .4 volt drop and the other showed a .38 volt drop.

Not too bad. Then I re-connected and did another voltage test. With the
charger connected I get 36 volts at the charger molex connector to the
battery pack. So the fuses and breakers are ok.

I then checked voltage differential between the diodes and the board.
Both sides read 35 volts, so the diodes are dropping voltage.

Then I checked the transformer with the capacitor out of circuit. Read
30 volts. Odd again.

I then disconnected the capacitor and put the diode tester across it to
charge it. It held a 1.5 volt charge.

So hm. Might be the capacitor, without it the transformer hums quietly.
Then again maybe the diodes are bad under load, which would be odd but
not impossible.

Thoughts? Wish I had a spare cap. And does cap size give any clue as to
capacity? This one is short and squat.

Chris

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