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Car Forum / Mercedes-Benz Cars / March 2005Relay has double contacts ???
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. tnx  Signature73 Hank WD5JFR > 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 [quoted text clipped - 10 lines] > heating and when it goes out in a few seconds it OK to hit the starter. > tnx Just a weird hunch, maybe the second set is bimetallic? Maybe it closes when it's very cold; the plugs have to glow longer, and this way the first set is a bit relieved from the extra (long) load. Jeroen > 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 [quoted text clipped - 10 lines] > heating and when it goes out in a few seconds it OK to hit the starter. > tnx are you sure the other arm isn't some kind of termomatic timer? are they connected together ? They are both part of the same armature and it doesn't look like either one is bimetallic, just heavy copper Signature73 Hank WD5JFR... > >> The glow plug relay on my diesel Mercedes, an 83 300SD has two sets of [quoted text clipped - 15 lines] > are you sure the other arm isn't some kind of termomatic timer? are they > connected together ? > They are both part of the same armature and it doesn't look like either one > is bimetallic, just heavy copper Hi... I think you'll find that the relay has two distinct pull in positions. The first "gentle" position providing a little heat required for normal starting; the second providing far far more during extreme cold weather starts. Take care. Ken No signs of contact wear on the open set... Signature73 Hank WD5JFR > >> They are both part of the same armature and it doesn't look like either [quoted text clipped - 12 lines] > > Ken > No signs of contact wear on the open set... Hi... Can't tell where you live - perhaps you don't have any of the 30 and 40 below winter weather? Reason for my suspicion is I've seen here (real cold) the ignition turned on; voltmeter drops to 9 and a half or 10 volts... sits there for 20 seconds, then jumps to about 11 volts for a while... Makes me pretty sure that there's two levels available. Ken Ken I live in Tulsa, Oklahoma and it doesn't get that cold here. Each glow plug has a resistance of less than an ohm and all are wired in parallel and I can see how the second set of contacts could close and if they did I don't think the current would increase by that much. The leads going to the glow plugs look like a little less than No. 12 wire. Someone else asked if the armature was bifurcated and if we have the same definition for the term it is bifurcated and stamped out of one piece. Signature73 Hank WD5JFR > >> No signs of contact wear on the open set... [quoted text clipped - 13 lines] > > Ken > They are both part of the same armature and it doesn't look like either one > is bimetallic, just heavy copper its very possible that maybe its there for ware. in other words, as the first one burns away the contacts, material gets removed, at some point the other side will start contacting. ------- i have also seen relays being used for Peek and hold effects. they normally energize a larger solenoid or something. what happens is when the contacts are closed, the swing load of the arms will cause the other contact to slam down, giving it a full contact to deliver full current for a short pulse. then it bounces back and uses the other side to simply hold it at a lower current state. but normally those arms are made from some form of clad. giving it a copper look on the out side but steel in the inside. > 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 [quoted text clipped - 3 lines] > spaced so they didn't close. Are there any experts out there that can tell > why they do this? ... No good reason. Are they bifurcated contacts? N I've posted 2 pix to: alt.binaries.schematics.electronic Signature73 Hank WD5JFR >> 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 [quoted text clipped - 9 lines] > > N |
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