Re: (ET) new relay in - now no reverse

[David C Robie <mycroftxx1 juno com>]

AHA !   assuming you had your meter set to the proper range.   A shorted
coil sure would pull enough current to do that little zap you heard
somewhere.  Possibly took out a PC trace (which most all of em on that
board act like fuses) or a board contact.

Dave
Weymouth MA

On Sat, 5 Aug 2006 12:44:40 -0400 (EDT) Michael S Briggs
<msbriggs alberti unh edu> writes:
> 
> 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
> >>>> ---------------------------------------------------------------
> >>>> 
> >>>> _______________________________________________
> >>>> Elec-trak mailing list
> >>>> Elec-trak cosmos phy tufts edu
> >>>> https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
> >>>> 
> >>> 
> >> 
> >