Relay has double contacts ?? why
 

"Henry Kolesnik" wrote in message
. com...
This message was previously posted on alt.auto.mercedes,
sci.electronics.components, sci.electronics.repair

The glow plug relay on my diesel Mercedes, an 83 300SD has two sets of
parallel contacts but only uses one because the other has a gap of about
0.035" when the first set closes. I thought this was due to improper
alignment and I bent the other arm so that both would make contact. The
other day I found another relay and noticed that it had one set of
contacts
spaced so they didn't close. Are there any experts out there that can
tell
why they do this? My guess is that the open set is a spare for when the
first set wears too much. But that doesn't make sense because two sets
working in parallel wouldn't wear as fast. Also would like to know if
anyone has reversed engineered the circuit as it has an IC and a couple
transistors. The circuit acts as monitor to make sure glow plug no. one
is
drawing current and then turns a dash light indicating that the plugs are
heating and when it goes out in a few seconds it OK to hit the starter.

FWIW, only one set looks like full current contacts. IMO, it may be a relay
used for other purposes and they don't want to run current through the light
duty points.

N

No other use than supplying power to the glow plugs, turning a dash lamp on
and off, that's it.

--

73
Hank WD5JFR
"NSM" wrote in message
news:5bsVd.35599$ab2.22727@edtnps89...

"Henry Kolesnik" wrote in message
. com...
This message was previously posted on alt.auto.mercedes,
sci.electronics.components, sci.electronics.repair

The glow plug relay on my diesel Mercedes, an 83 300SD has two sets of
parallel contacts but only uses one because the other has a gap of about
0.035" when the first set closes. I thought this was due to improper
alignment and I bent the other arm so that both would make contact. The
other day I found another relay and noticed that it had one set of
contacts
spaced so they didn't close. Are there any experts out there that can
tell
why they do this? My guess is that the open set is a spare for when the
first set wears too much. But that doesn't make sense because two sets
working in parallel wouldn't wear as fast. Also would like to know if
anyone has reversed engineered the circuit as it has an IC and a couple
transistors. The circuit acts as monitor to make sure glow plug no. one
is
drawing current and then turns a dash light indicating that the plugs are
heating and when it goes out in a few seconds it OK to hit the starter.

FWIW, only one set looks like full current contacts. IMO, it may be a
relay
used for other purposes and they don't want to run current through the
light
duty points.

N

There's no other purpose, dash lamp and glow plugs.

--

73
Hank WD5JFR
"NSM" wrote in message
news:5bsVd.35599$ab2.22727@edtnps89...

"Henry Kolesnik" wrote in message
. com...
This message was previously posted on alt.auto.mercedes,
sci.electronics.components, sci.electronics.repair

The glow plug relay on my diesel Mercedes, an 83 300SD has two sets of
parallel contacts but only uses one because the other has a gap of about
0.035" when the first set closes. I thought this was due to improper
alignment and I bent the other arm so that both would make contact. The
other day I found another relay and noticed that it had one set of
contacts
spaced so they didn't close. Are there any experts out there that can
tell
why they do this? My guess is that the open set is a spare for when the
first set wears too much. But that doesn't make sense because two sets
working in parallel wouldn't wear as fast. Also would like to know if
anyone has reversed engineered the circuit as it has an IC and a couple
transistors. The circuit acts as monitor to make sure glow plug no. one
is
drawing current and then turns a dash light indicating that the plugs are
heating and when it goes out in a few seconds it OK to hit the starter.

FWIW, only one set looks like full current contacts. IMO, it may be a
relay
used for other purposes and they don't want to run current through the
light
duty points.

N

"Henry Kolesnik" wrote in message
. com...
No other use than supplying power to the glow plugs, turning a dash lamp
on
and off, that's it.

This is my best guess.
N

Sometimes there are two ,where one set takes the first high current ,then
the other set assure there is a true connection.
"NSM" wrote in message
news:5bsVd.35599$ab2.22727@edtnps89...

"Henry Kolesnik" wrote in message
. com...
This message was previously posted on alt.auto.mercedes,
sci.electronics.components, sci.electronics.repair

The glow plug relay on my diesel Mercedes, an 83 300SD has two sets of
parallel contacts but only uses one because the other has a gap of about
0.035" when the first set closes. I thought this was due to improper
alignment and I bent the other arm so that both would make contact. The
other day I found another relay and noticed that it had one set of
contacts
spaced so they didn't close. Are there any experts out there that can
tell
why they do this? My guess is that the open set is a spare for when the
first set wears too much. But that doesn't make sense because two sets
working in parallel wouldn't wear as fast. Also would like to know if
anyone has reversed engineered the circuit as it has an IC and a couple
transistors. The circuit acts as monitor to make sure glow plug no. one
is
drawing current and then turns a dash light indicating that the plugs are
heating and when it goes out in a few seconds it OK to hit the starter.

FWIW, only one set looks like full current contacts. IMO, it may be a
relay
used for other purposes and they don't want to run current through the
light
duty points.

N

"Andy" wrote in message
...
Sometimes there are two ,where one set takes the first high current ,then
the other set assure there is a true connection.

The picture doesn't imply this. I suspect they don't want to run current
through the second pair.

N

On Sat, 05 Mar 2005 18:33:32 GMT, "NSM" wrote:


"Andy" wrote in message
...
Sometimes there are two ,where one set takes the first high current ,then
the other set assure there is a true connection.

The picture doesn't imply this. I suspect they don't want to run current
through the second pair.

N


Perhaps the second pair of contacts make a momentary connection during
the initial closure, then spring back?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Jim Thompson wrote:

On Sat, 05 Mar 2005 18:33:32 GMT, "NSM" wrote:


"Andy" wrote in message
...

Sometimes there are two ,where one set takes the first high current ,then
the other set assure there is a true connection.

The picture doesn't imply this. I suspect they don't want to run current
through the second pair.

N



Perhaps the second pair of contacts make a momentary connection during
the initial closure, then spring back?

...Jim Thompson
that is exactly what i suggested also.
i have seen that config before used as a peek and hold relay.