RE: was : Testing a relay? Now FI light problem fixed!

I am going to assume you are not testing the voltage at the light with the
relay attached.
The 1.5v you are getting from the ground side of the license light is a bad
ground connection. There is resistsnce between the wire at the socket
(where you are testing it) and the ground. If this is the green wire (and
it should be if it is a ground wire), either trace it though the harness to
the common ground point, or just splice into it and run a new ground wire.
You can also verify it is a bad ground by pulling the bulb out and checking
the resistance from the contact in the base of the socket to ground. Ensure
the key is off first (or better yet disconnect the battery or harness from
power). You should have 0 ohms to ground. You should also see the bulb get
brighter once you fix the ground connection.

Why not just take the ground wire from the relay and put it straight to
ground? There are lots of points you can run a wire to on the subframe.
Best location is right to the main ground connection or better yet, right to
the battery.

>From your description you must have a switch on the power wire (what you
called primary side) as well somewhere. Where are you getting power from
for that?

doug


-----Original Message-----
From: vfr-bounces@xxxxxx.wisc.edu [mailto:vfr-bounces@xxxxxx.wisc.edu] On Behalf Of
Bob Chappuis
Sent: January 25, 2006 11:18 PM
To: Grant Gathagan
Cc: vfr@xxxxxx.wisc.edu
Subject: was : Testing a relay? Now FI light problem fixed!

Hi Grant
Thanks for the reply. You assumed correct. My initial test was with the
realy still hooked up but I have retested as you decribe. Ithink the relay
is OK. The problem was in the ground wire for the license bulb which I was
using as ground for the relay control circuit (proper terminolgy for what
I previously referred to as "primary") This wire is hot and I am pretty
sure it sould not be. By hot I mean if you put the positive probe of a
voltmeter on it and the negative probe to ground you get a reading of 1.5
volts. If you test the other wire from the license bulb you get battery
voltage. I am using this wire to enrgize the relay control circuit.

I bought a new relay (just in case) and rewired it using a new wire to
the main ground point on the right side frame. Now everything is working
fine. No FI light and my heated grips are heating up.

The question now is why does the licence bulb ground show positive
voltage? It is possible the relay may have damaged something upstream of the
tailight circuit. On a website about relays that another lister put me on to
(Thanks, I'd give due credit but your message is not available at my
current loc and I can't recall your name) it said that the coil in a relay
generates a reverse voltage that may be up to 200 volts when the relay is
powered down, collapsing the magnetic field generated by the coil. It goes
on to say this can cause premature failure of switch contact points in an
unfused circuit. Everything seems to be working but only time will tell.
I should have time to put everything back together by Saturday and give it a
good test ride.


Cheers,
Bob


_______________________________________________
Vfr mailing list
Vfr@xxxxxx.wisc.edu
For subscription and delivery options:
https://lists.cs.wisc.edu/mailman/listinfo/vfr

Yeah, what he said.

1.5v isn't a huge amount, if you're only dealing with stuff like bulbs, but it can cause problems with electronics, and that's not a good thing.
The total voltage seen by any device using that ground point is now dropped to 10.5 volts.
Bulbs will not glow as bright, and many electronic devices won't see that as being enough voltage to operate.

(Now, because I'm bored...)

As to the 200v reverse voltage: That'll never happen in your circumstances.
While the theory and presence of reverse voltage are correct, you'd have to have a LOT more than 12v powering a relay to get that kind of reverse voltage.
Furthermore, reverse voltage is momentary at best.

This is kind of like the problem of electrical contacts being eroded over time due to the arcing that occurs across the contacts just before the connection actually closes.

People argue against turning off lights, computers, etc, due to the degradation that the on-off process produces on electrical components.
There's also the arguement that the current surge which occurs due to the arcing wastes as much electricity as you save when you are anal about turning off lights.

It DOES happen, but with your average house circuit or computer component, it is at such a miniscule level that only extensive, long-term testing can measure its effect on equipment.

Same with the reverse voltage in your average 12v circuit; not a big enough problem for anyone but engineers to care about.

Doug Scott wrote:
I am going to assume you are not testing the voltage at the light with the
relay attached.
The 1.5v you are getting from the ground side of the license light is a bad
ground connection. There is resistsnce between the wire at the socket
(where you are testing it) and the ground. If this is the green wire (and
it should be if it is a ground wire), either trace it though the harness to
the common ground point, or just splice into it and run a new ground wire.
You can also verify it is a bad ground by pulling the bulb out and checking
the resistance from the contact in the base of the socket to ground. Ensure
the key is off first (or better yet disconnect the battery or harness from
power). You should have 0 ohms to ground. You should also see the bulb get
brighter once you fix the ground connection.

Why not just take the ground wire from the relay and put it straight to
ground? There are lots of points you can run a wire to on the subframe.
Best location is right to the main ground connection or better yet, right to
the battery.

>From your description you must have a switch on the power wire (what you
called primary side) as well somewhere. Where are you getting power from
for that?

doug


-----Original Message-----
From: vfr-bounces@xxxxxx.wisc.edu [mailto:vfr-bounces@xxxxxx.wisc.edu] On Behalf Of
Bob Chappuis
Sent: January 25, 2006 11:18 PM
To: Grant Gathagan
Cc: vfr@xxxxxx.wisc.edu
Subject: was : Testing a relay? Now FI light problem fixed!

Hi Grant
Thanks for the reply. You assumed correct. My initial test was with the
realy still hooked up but I have retested as you decribe. Ithink the relay
is OK. The problem was in the ground wire for the license bulb which I was
using as ground for the relay control circuit (proper terminolgy for what
I previously referred to as "primary") This wire is hot and I am pretty
sure it sould not be. By hot I mean if you put the positive probe of a
voltmeter on it and the negative probe to ground you get a reading of 1.5
volts. If you test the other wire from the license bulb you get battery
voltage. I am using this wire to enrgize the relay control circuit.

I bought a new relay (just in case) and rewired it using a new wire to
the main ground point on the right side frame. Now everything is working
fine. No FI light and my heated grips are heating up.

The question now is why does the licence bulb ground show positive
voltage? It is possible the relay may have damaged something upstream of the
tailight circuit. On a website about relays that another lister put me on to
(Thanks, I'd give due credit but your message is not available at my
current loc and I can't recall your name) it said that the coil in a relay
generates a reverse voltage that may be up to 200 volts when the relay is
powered down, collapsing the magnetic field generated by the coil. It goes
on to say this can cause premature failure of switch contact points in an
unfused circuit. Everything seems to be working but only time will tell.
I should have time to put everything back together by Saturday and give it a
good test ride.


Cheers,
Bob





---------------------------------
Yahoo! Autos. Looking for a sweet ride? Get pricing, reviews, & more on new and used cars.
_______________________________________________
Vfr mailing list
Vfr@xxxxxx.wisc.edu
For subscription and delivery options:
https://lists.cs.wisc.edu/mailman/listinfo/vfr

Grant Gathagan wrote:
> It DOES happen, but with your average house circuit or computer
> component, it is at such a miniscule level that only extensive,
> long-term testing can measure its effect on equipment.

It's not so much the size of the supply ("house circuit") that affects
the size of the voltage spike, but rather the size of the inductor
in the circuit. In this case, it's a tiny relay coil which stores
very little energy.

However, even on a household circuit, a large inductor with very large
stored energy can cause a significant energy surge. To be specific,
large induction motors, like those on large stationary power tools, can
generate significant voltage spikes as the inductor tries to dissipate
the energy stored in the coils of the spinning motor (which has just
become a generator). This is why they have rather expensive switches
on them that physically force the contacts far apart to minize arcing.



--
*********************************
Chris Merrill
cmerrill@xxxxxx.rr.com
*********************************
_______________________________________________
Vfr mailing list
Vfr@xxxxxx.wisc.edu
For subscription and delivery options:
https://lists.cs.wisc.edu/mailman/listinfo/vfr