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+--- Thread: why are the GPs on separate wires? (/showthread.php?tid=7667)
why are the GPs on separate wires? - bricktron - 03-17-2017
i have an '85 GP relay with 5 outputs and 5 wires leading to the 5 glow plugs.
why aren't the GPs just wired in parallel on one big rail? would something bad happen if i replaced those 5 wires with one big one?
RE: why are the GPs on separate wires? - DiseaselWeasel - 03-17-2017
Depending on which plug fails, all following fail too... With separate wires you have only one failing and starting is still fairly easy. Up until ~'80 (IIRC), plugs were actually wired in series...
RE: why are the GPs on separate wires? - Alec300SD - 03-17-2017
Old syle loop glowplugs were wired in series, but there is too much of a voltage drop when wired in series.
The connector wires would get very hot, and IIRC when one glowplug failed none would work.
With the 5 individual connections, you still get adedquate glow (most of the time), even with one glowplug burnt out.
RE: why are the GPs on separate wires? - NZScott - 03-18-2017
There is no reason not to wire the plugs off one connection, MB made individual wires to detect if a GP had burnt out with a clever GP relay.
Series plugs have nothing to do with an '85 car and should've stopped production 30 years ago....
RE: why are the GPs on separate wires? - bricktron - 04-09-2017
series is just a bad idea all around. in parallel, like NZScott said, one advantage is in independent treatment of the power lines. i'm not sure if plugs ever ever fail closed but a breaker for each would let one line go out and leave the rest working. if failing open is the only problem then the one failed plug will fall out on its own accord, unlike the series circuit.
what are the more common failure modes of GPs in fact?
RE: why are the GPs on separate wires? - Fishman - 04-09-2017
In the GP relay they are all connected an fed by one relay. So replacing them with 1 wire would be fine.
RE: why are the GPs on separate wires? - bricktron - 04-09-2017
series is just a bad idea all around. in parallel, like NZScott said, one advantage is in independent treatment of the power lines. i'm not sure if plugs ever ever fail closed but a breaker for each would let one line go out and leave the rest working. if failing open is the only problem then the one failed plug will fall out on its own accord, unlike the series circuit.
what are the more common failure modes of GPs in fact?
RE: why are the GPs on separate wires? - AlanMcR - 04-10-2017
You will need to figure out some way to balance the current to the individual GPs. That will be a challenge if you wire to one, then from there to the next one. Series solves that problem, but then a single burned out GP kills the entire string. Parallel with individual wires gets close to equal distribution, even if the wires are not exactly the same length.
RE: why are the GPs on separate wires? - NZScott - 04-11-2017
Forget series!!! Dead technology. Just put the main wire to the rear cylinder and 'daisy chain' to the rest, /thread
RE: why are the GPs on separate wires? - Fishman - 04-11-2017
Series is not even an optiion, since they only get a 6th of the voltage. Like NZScott says, just chain them together.
RE: why are the GPs on separate wires? - barrote - 04-11-2017
That black box has a lot more to it than it looks at first glance!!! Grab a multmetter and check voltages amps and Hz... u'll be amazed to what u'll find.
Anyway heating the gp works better with a paralel system.
RE: why are the GPs on separate wires? - Fishman - 04-11-2017
I opened the black box. All the wires are connected to 1 relay. So they all are parallel. The rest is for glow time etc.
RE: why are the GPs on separate wires? - baldur - 04-11-2017
The reason they're separate is because the glow relay monitors the current to each plug for diagnostics. A handy side effect of that is you can unplug the glow harness and measure each glow plug at the harness connector without having to remove the inlet manifold.