Glow Plugs; series vs parallel

[mark82]

If I upgrade to pencil/parallel plugs the old (series) controller will or will not work?

Or it will function but timer will not?

Is the old controller plug compatable with the new style controller?

If I then install a new style controller will it function (correctly) with the new (parallel) plugs?

I have an early type car and it works fine. While the upgrade may have a minor advantage (shorter glow time) it wouldnt be an overall upgrade if I have to push additional glow button or the timer isnt functional.

79 240d

[jay_bob]

Yes the controller will still work with a parallel glow plug arrangement.

Just make sure you delete the "bed springs" between the plugs, these are resistor wires, and put regular wire between the plug terminals.

And be sure to delete the grounded wire at the end of the line!

You will end up with the "hot" wire coming from the controller hitting the terminal on the rearmost plug (either #4 or #5 depending on your engine), then you want to make jumpers to each plug in succession to the front of the engine.
Plug #1 at the front of the engine should only have one wire, the jumper from #2.

On your series plugs, you have stacked terminals (there is a spacer between the two connections on each plug). Now since you're making a parallel circuit, the two wires at #2 through the last plugs can (and should) touch each other on the terminal.

[Diseasel300]

Will the old style controller handle the amperage of the parallel glow plugs? I'd expect there to be a significantly higher amperage requirement with the parallel vs. the series setup.

Other than the shorter glow time, the biggest improvement with the parallel setup is that if you have a glow plug fail, it doesn't disable the entire glow system, only the cylinder that the plug failed in.

[mark82]

I tried to be pretty specific with my questions.

The issue is not can the plugs be upgraded, or how to do it. The issue is whether the early controller will work or work correctly with the new plugs and then if not, can the later controller be substituted and work correctly?

There is a reason I asked them; I have one parts seller that claims only the late model controller will work correctly with the late plugs (but not the early controller). Also, one parts seller implies that the old controller will not work with parallel plugs and he sells a silly push button work-around.

So my questions still stand...

[Diseasel300]

I'm not familiar with the series controller, but I'd strongly suspect the original controller would need to be upgraded or bypassed to convert to parallel plugs. A 4 cylinder setup will pull 50-60A when glowing. If the wiring or contacts in the existing controller are not designed for that kind of current, you're looking at blown fuses, melted wires, or possibly a fire!

If you're competent with wiring, you should be able to install the newer controller without much fuss, or adapt the existing controller to operate a relay of some variety to control power to the glow plugs. The preglow light would no longer be relevant if you adapt the existing controller since the glow cycle will be significantly shorter.

[mark82]

Originally Posted by Diseasel300

The preglow light would no longer be relevant if you adapt the existing controller since the glow cycle will be significantly shorter.

Which brings it back to my third question; if I install the newer controller, along with newer plugs, then will the glow light work correctly?

[Diseasel300]

If you wire in the newer controller, it should operate the light if you wire it in. The light is controlled from a pin on the controller.

[Diesel911]

Originally Posted by mark82

I tried to be pretty specific with my questions.

The issue is not can the plugs be upgraded, or how to do it. The issue is whether the early controller will work or work correctly with the new plugs and then if not, can the later controller be substituted and work correctly?

There is a reason I asked them; I have one parts seller that claims only the late model controller will work correctly with the late plugs (but not the early controller). Also, one parts seller implies that the old controller will not work with parallel plugs and he sells a silly push button work-around.

So my questions still stand...

If the old system had a fuses in it what is the amperage of that stock fuse?
If the system had no fuse then the controller will likely not work because I believe there is a reed switch inside of it which when getting hot cuts off the voltage.
Some systems had a 50 amp fuse instead of th 80 amp one.

1976 is the year the multiple members have had issues with.
1976 Glow Plug Update but no voltage to the glow Plugs when key is turned on
http://www.peachparts.com/shopforum/showthread.php?t=181503&highlight=pencil+plug+relay+ground+wire+115

Part of the issue is the older models might have different makes of Glow Plug Controllers. So it would be handy to know what company made the stock relay. You might look at your favorite parts sellers sites and see if they show more then one Glow Plug Relay for your year and model.

People have used the newer Glow Plug Relays like the one on my 300D and run a seperate wire from each Plug to the Relay. Mercedes at one time sold all of the electrical connector parts. Of course you have a wiring issue with the rest of the connection.

Easiest would be to keep your original Relay (if it works) and run the positive wire that would normally go to the Glow Plugs to a Ford type Starter Solenoid (On Fords they are usually on the Fender Well or Fire Wall). You activate you relay which in tern activates the Starter Solenoid (that does not pull much amperage) and the Solenoid closes and connects the Glow Plugs to the Battery Voltage.
Note I did that on my Volvo Diesel.

In you case you would need to run the positive wire to activate the Starter Solenoid to one of the small terminals on the Starter Solenoid which in my case I used the S termina.

Because I used a seperate switch I had to run wire from the + side of the Starter Solenoid to the Switch and another wire from the switch back to the S termina.

[Diesel911]

Also the updated plugs have the voltage in series (but they could be in parallel with no damage to the plugs.) but the grounds are in parallel. I think that makes it a series-parallel circuit.

In the past there was more complete glow plug update kits that came with a Bosch or Hueco realy.

[Diseasel300]

A misunderstanding of series vs. parallel here.

Pencil glow plugs are a parallel circuit. All of the power ends are "common" from the relay and all of the ground ends are "common" with the block. The series plugs have the power from one plug series through the next, and the next, and the next, until the circuit is finally grounded to the block.

[Diesel911]

Originally Posted by Diseasel300

A misunderstanding of series vs. parallel here.

Pencil glow plugs are a parallel circuit. All of the power ends are "common" from the relay and all of the ground ends are "common" with the block. The series plugs have the power from one plug series through the next, and the next, and the next, until the circuit is finally grounded to the block.

I understand what I wrote. On mine the Glow Plugs are wired in parallel up to the Relay but I don't know how they are wired inside of the relay.

It is clear that on the updated glow plugs the + voltage is a series circuit and the grounds are parallel circuits.

[NZScott]

FWIW, I have a 1978 300D which had series loop plugs, and now has pencil parallel ones. Best thing you can ever do...

Re: the stock loop style controller, yes it will work the glow plugs, but it will not turn them off until you start cranking- the light stays on indefinitely - something people not familiar with your car will need mentioning of the fact. I just count to 10 or whatever. Looking at going the push button way myself eventually.

[Diseasel300]

Originally Posted by Diesel911

I understand what I wrote. On mine the Glow Plugs are wired in parallel up to the Relay but I don't know how they are wired inside of the relay.

It is clear that on the updated glow plugs the + voltage is a series circuit and the grounds are parallel circuits.

The individual wires to each glow plug are to make life easier for the harness maker. Inside the glow plug relay, they are all common with each other, electrically identical to simply taking all 4/5/6 wires and tying them together with a wire nut. It is a parallel circuit, the only thing "series" about it is the relay switching B+.

[barry12345]

The time constant for the length of time activated. May be different than the parallel plugs require. Probably longer. Actually I know it is longer. So you have to mentally decide when you have had enough glow plug time. Or just wait until a much longer cycle than they require has occurred.

There is a differance in current draw I believe as well. The parallel plugs use a higher amperage fuse I think. My 77 300d will remain with the loop plugs as they do well enough in reasonable temperatures.

If the car was to be used in the winter I would change them. Actually when having loop plugs if one fails they all cease working. So a small kit to deal with this event should be in the trunk. While with the parallel system if one plug goes south the others remain in service.

Most important to remember is never test loop plugs with twelve volts. They are rated at something like 1.3 volts. They may or may not stand the abuse. So the only reason I see to upgrade the controller is to get a normal cycle time for the newer type.. Plus the controller may have a little heavier set of contacts. Although this is not known. Each type would have been designed either the same contact wise or not. Designed for more current than expected as an life expected issue.

The original controller does not sense what it is servicing. So the long cycle will persist if used. The only change it might experience is a greater current flow through the heavy duty contacts when using the parallel plugs.

Series plugs will also be far less tolerant of any additional resistance In their circuit. Many if those systems may have been upgraded because of age and cycling. Thermal cycling especially may have oxidized some of the connections in their circuits.

[Screwdriva]

Jumping in here. Just acquired a 76 240D and this upgrade is #1 on my list. I planned to purchase the following kit from Kent Bergsma's website called "early-123-240d-4-cylinder-diesel-fast-pencil-glow-plug-conversion-kit"

They sell another kit with a relay but I don't want a non-OE push button on my vehicle. Has anyone seen an installation guide for this modification? I'm concerned that I may fry something.