On Sat, 5 Aug 2006, RJ Kanary wrote:
Because high resistance in a circuit , coupled with a
high
impedance sand based meter will 'tell' you that voltage is
there........but
not enough current flow to do any work. Not until a load is
present will you
see what's really up.
Ah, I see what you're getting at. That doesn't seem to be the case
here
though - I found that I am getting voltage coming off of wire 41 at
card 1
when moving the switch to reverse, but no voltage at the relay
itself.
Still need to find where it's disappearing between there, but in the
mean
time, I discovered something else. I decided to test the resistance
of the
coil on the relay (the powered connections), and it's zero. Checked
two
identical new relays (these are the $4.50 or so 3PDT 36VDC relays
from the
Surplus Electronics place someone else mentioned here), and across
the
coil they measure a bit over 1 kiliohm. So, either the relay was bad
before I put it in, or there was a failure in the coil when after
putting
it in. Having a short there likely caused something else to fail, by
getting too much current through the relay, and may be why I'm not
seeing
any voltage at the relay anymore. So, I'll backtrack between the
relay and
wire 41s connection to card 1, to find the problem connection.
The bigger question though now is whether the relay was bad
before
putting it in (should have tested it - damn), or if it failed after
putting it in. And if the latter, why.
I'm not familiar with the internals of relays - I know they
work
based on a solenoid switch, but I'm not sure if it matters with
relays
which way the current flows through the solenoid (I know you'll get
a B
field in opposite directions depending on the current flow, but
since I'm
not sure how exactly it operates the switch, I don't know if that
matters). So, if I had wired the power connections up backwards,
could
that have fried the relay? I wouldn't think so, but.... (I did check
and
see that it has the powered connections labelled A and B, as did the
old
relay, and I connected the new one the same way as the old one, so I
wouldn't think this should be an issue though.....).
Now to find what got fried by having a short across the relay....
Mike
If you are working on more delicate things, such as
computers, a
high impedance tool is a must.
Draw too much current from a circuit, the minimal trouble
you'll
have is a low reading that is in error, since the meter is sinking
more power
that the device can source. The maximum grief you can have is
letting the
smoke out of some very important pieces. <VBF>
Don't get me wrong. A Fluke 87® sits right next to my Simpson
260® on
the tool cart. Both have their strengths and weaknesses. The trick
is
learning how to use this knowledge to best arm you for the battle
at hand.
And yes, the voltages that you are observing should be within
5 or 10%
of what system voltage is.
Here's hoping that the odor of Ersin® Multicore solder is NOT
filling
your nostrils this afternoon. :)
----- Original Message ----- From: "Michael S Briggs"
<msbriggs alberti unh edu>
To: "RJ Kanary" <rjkanary nauticom net>
Cc: <elec-trak cosmos phy tufts edu>
Sent: Saturday, August 05, 2006 10:56 AM
Subject: Re: (ET) new relay in - now no reverse
RJ,
On Fri, 4 Aug 2006, RJ Kanary wrote:
Prove out all the voltages that SHOULD be present with an
ANALOG
VOM.High impedance sand based DMMs will lie to you especially at
these
voltages.
I don't see why a DMM should be inaccurate on voltage. Don't you
*want* a
voltmeter to have high (very very high) impedance? Otherwise when
you
connect it in parallel with some circuit element, the combined
parallel
resistance of the voltmeter and the element you're measuring
voltage across
can drop some, so the voltage you would read wouldn't be the
voltage it
normally sees. So, I don't see why you would want a lower
impedance on your
meter.
Verify that voltage AND current is available at Pad 8 {Wire
41} of
Card 1 when Reverse is selected. If this proves out move to Pad
9, {Wire
Alrighty. I'm assuming it should have the full 36V (or 38V, or
whatever the
pack is putting out) at those points.
38}. If voltage and current is present here, now you can suspect
a wiring
error at the other relay terminals.If voltage and current is NOT
present
here, you are about to embark on one of the finer adventures of
owning and
repairing an AA model E-15, repairing Card 1. :(
D'oh. I'll check it in an hour or two - need to finish making
some
biodiesel for our cars and furnace first. Given that I thought I
heard a
"pop" noise when I first put it in reverse after putting in the
new relay,
I'm unfortunately thinking it's not going to be a simple wiring
issue. :(
But, if it's just a case of a blown resistor or cap on card 1,
that
shouldn't be too bad - I've done a fair amount of electronics
work in the
past. Well, it shouldn't be bad if it's obvious which element
blew. :)
Chasing down a bad circuit element can be a pain in the tuckus.
Thanks,
Mike
----- Original Message ----- From: "Michael S Briggs"
<msbriggs alberti unh edu>
To: <elec-trak cosmos phy tufts edu>
Sent: Friday, August 04, 2006 9:35 PM
Subject: (ET) new relay in - now no reverse
So I finally had time to put in a new relay in place of the
blown
forward/reverse relay. Forward works fine now - even took it
out for a
spin around the neighborhood. When I then went to back it into
the
garage,
I discovered that when I try to go in reverse, it goes forward.
D'oh!
My first thought was that I had hooked up the
forward/reverse
relay wrong. I checked, and nope, it's fine. The problem is
that the
relay
isn't firing when I move the switch to the reverse-neutral
side. I hear
the reverse microswitch click, but the relay doesn't move.
Checked the
power connections on the relay, and it doesn't seem to be
getting any
power when I move the speed lever to reverse.
Now, I suppose I could have just knocked something loose while
fiddling with everything in there, but I'm wondering if there
could be
some greater problem going on that I'm overlooking (considering
all the
failures that I've had - while mowing last week, it stopped
running - the
control fuse had blown, and took out the fuse block in the
process.
Put in an inline fuseholder in place of the fuse block, with a
fresh
fuse,
and found that I couldn't go forward due to a blown
forward/reverse
relay.
Put in a new relay, and now the relay isn't getting voltage to
fire. It
seems like each time I fix one thing, something else breaks).
After putting in the new relay, the first time I moved the
speed
control lever to reverse, I thought I heard the sound of
something
blowing
- wasn't sure though if it was just the reverse microswitch
clicking, or
if something did in fact blow. It looks like control of the
reverse relay
goes through card#1 somewhere (still need to look over the
schematics to
figure out which "port(s)" on card 1, so I can see if something
is just
loose, or if something did in fact blow). I should be able to
troubleshoot
it ok, but what I'm concerned about is if there might be some
greater
problem underlying these little annoying problems. There have
just been
too many failures one after another for it to just be a
coincidence, I
think.
Actually - if I had wired the power connections to the reverse
relay backwards, what would that do? From looking at the relay,
I assume
it just uses a current through a solenoid to control a switch.
If the
current goes the wrong way, the B field would point in the
opposite
direction - but since I'm not sure exactly how it controls the
switch,
I'm
not sure if that would be a problem or not, or if it could blow
something.
So, any tips anyone can offer (again) would be appreciated.
Thanks,
Mike
--
--------------------------------------------------------------
Michael S. Briggs
UNH Physics Department
(603) 862-2828
---------------------------------------------------------------
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