Okay, I have some more information. I removed the wires from the diodes and measured the voltage according to the manual. With one transformer lead removed from the capacitor, I got 70 v ac across the leads that go to the diodes, 35v from each lead to test point S3. With the transformer lead reattached to the capacitor, I got 90v ac and 45v ac. All normal according to the manual. I also measured the voltage from S1 (+) to S3 (-) and got 21 volts dc.
I next soldered the wires back to the diodes and measured resistance from each diode to the heat plate, and the reversed the probes and measured again. I got 0.42 in one direction and .OF (infinity, I think) in the other direction for both diodes. According to the manual that came with my meter, the diodes are fine.
I also measured the voltage on the batteries:
B5 to B6: 12.66v
B5 to B4: 18.98v
B5 to B3: 25.32v
B5 to B2: 31.66v
B5 to B1: 31.66v
The charge on the tractor is lower than it ever has been since I've owned it. It still moves, but very slowly.
Paul
----- Original Message -----
From: "Jim Coate" <jbc_lists_NO_REPLY coate org>
To: "Elec-trak tufts" <elec-trak cosmos phy tufts edu>
Sent: Monday, May 11, 2009 11:49:21 AM GMT -05:00 US/Canada Eastern
Subject: Re: (ET) charger problem
I'd also want to know what the voltages are doing, as the amount of
humming is rather subjective.
You mention the resistance from the diodes to the heat sink plate is
zero... this should only be true in one direction. And to really test
them, you need to disconnect the diodes from the transformer wires.
I do have heat sink plates available, but... it is just a piece of
metal, so it doesn't really go bad. It's job is to hold the diodes and
dissipate the heat from them. The main reason for replacing the plate is
that trying to press new diodes into a used plate generally doesn't work
well - the aluminum is already stretched so the new diodes don't seat
tightly and have a shortened life. (ie once it gets onto my web site,
expect to see it as a complete unit: heat sink with diodes already mounted).
To answer one of Tim's Q's: The capacitor came from me (my store), so it
is 4 uF, which is the most common size. Some chargers use a 20 uF with a
different transformer, but the size difference is significant so should
be obvious if trying to replace with the wrong thing.
--
Jim Coate
*The Electric Tractor Store*
http://www.ElectricTractorStore.com
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paul mitchell2007 comcast net wrote:
> Sorry, it's an E12, and yes, it should be S3, not S2. I understand that
> wire 30 has to be connected, but the loud humming noise seems unusually
> loud. When I first got the tractor, one of the diodes was blown and
> when I tried to charge, the charger made this same loud noise. So,
> there's the normal noise (a sort of soft hum) of the charger when it's
> not connected to the battery pack, and then there' this very loud noise
> (more of a loud buzz) when the charger is connected to the battery
> pack. It never used to be this loud.
>
> Some background. I mowed the lawn for the first time a couple of weeks
> ago, and I think I was mowing in the wrong gear, since the power use
> guage was often in the red. Things seemed a bit hot when I plugged
> in the charger. When I left the garage, the charger was humming as
> usual. A few hours later when I returned to the garage, I found it had
> tripped the house breaker. When I reset the breaker and started the
> charger again, I got this loud buzz instead of the soft hum. When I
> removed the charger, I found that the capacitor top had bulged upward,
> rather than being flat. I suspected that was now trash, and replaced it
> with a brand new one. When I hooked it all back up again and tried to
> charge, the charger continued to make this loud buzzing noise instead of
> the soft hum it usually makes.
>
>
>
> ----- Original Message -----
> From: "RJ Kanary" <rjkanary nauticom net>
>
> I'm confused.{ But then it IS Monday morning, and I've had
> but one cup of coffee.} What flavor of ET are we working on? The first
> charger diagram I pulled up (since I'm just guessing. <G>) shows an S1
> and an S3 but no S2.
>
> Wire 30 goes to CB-2.It HAS to be there, or the charger's
> output is not directed to the battery pack. The loud humming noise you
> hear when it's connected could well be the sound of the charger doing
> exactly what it's supposed to be doing. Charging. :)
>
> What conditions existed previously to start this investigation?
>
> Fetching that much needed second cup of Joe........
>
> RJ
>
>
> paul mitchell2007 comcast net wrote:
>
> My charger hums quietly when plugged in and the #30 wire from the
> circuit breaker is not attached to S2 on the charger, but when
> attached to S2, makes a very loud humming noise. The capacitor is
> brand new and I a local alternator shop that rebuilt all my tractor
> motors told me that the diodes are fine (they recently replaced
> them). The resistance from each diode to the heat plate measures
> zero. Any ideas? Do I need a new heat plate? If so, where do I
> get one?
>
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