What is the resistance of the wavy shunt on the GPR controllers?

[Burnt]

I don't have a GPR controller that has the wavy shunt resistor, so I can't measure myself.

But I'm curious, and while searching for more information about this era of GP relay/controller, I read a comment that said the folks at OilBurners.net know more about the glow plugs and controller of the IDI than any other forum on the net.

So I joined, and am asking.

Prior to asking, I did do a search, but after an hour or so, became bleary eyed because the goal of most of the threads found was oriented toward folks getting their glow plugs to work so their trucks would start.

That's not my goal.

My goal is just to know how much resistance this wavy metal shunt presents between the top of the relay post where it receives power once the relay latches, to the bottom of the wavy thing where it terminates at the black phenolic base of the relay, delivering power to the glow plugs.

How much resistance between the top and the bottom?

Is the metal ribbon made of a material that changes resistance as it heats up?

If it changes resistance, is that how power is limited to the glow plugs, as the glow plugs heat up?

Is there a voltage drop from the top of the wavy shunt to the bottom of the wavy shunt, such that voltage measured at the top is 12 v, but voltage measured at the bottom is 10 v, where the wavy shunt has heated up once the relay latches, and voltage is lost to the resistor's open air dissipation of heat?

I noticed the shape of the wavy shunt resistor is very similar to some old school battery load testers, that had a wavy nichrome resistor to simulate a load to test the batteries. The glow plug controller resistor looks like a miniaturized version of the nichrome resistor of a battery load tester.

Thank you in advance for any testing you can do, or have already done, to give me an idea of what to expect if I added this shunt in series with the output of a regular glow plug relay, and attached my glow plug leads to the bottom of this wavy resistor. Would the voltage delivered to the glow plugs drop, by virtue of the resistance of the shunt? How much of a voltage drop might I expect?

Thanks again.

PS...

One relatively recent post I found, written by @aggiediesel01, encapsulates the limited education I have received on Oilburners about this relay and shunt so far. I'll quote it below, just so you know that I've read it for reference sake, but still do not quite know how much voltage drop or resistance this shunt presents.

You are correct, it's not right; you should have as much voltage coming out at that point as going into the solenoid on the heavy wires. The bendy metal connection is called a Shunt. It is used by the controller to measure the current being delivered to the glowplugs. The resistance/length is very specific and the length is very specific and from those known values a fairly accurate current can be calculated for the controller to use. Unfortunately this information isn't able to be viewed outside of the controller unless one were to connect a calibrated (to the shunt value) ammeter to the top and bottom of the shunt just like the controller uses. Now to your question: The voltage at the bottom of the shunt should be identical to the voltage coming into the system as it's under load. If you can measure 12V at the incoming wire (heavy dual yellow) then you should be able to measure 12V at the output terminal where the two brown wires are. HOWEVER; several parts of the overall system can and do affect how much voltage you will measure at the incoming terminal:

1. The condition of the voltage supply (batteries). When the glowplugs are energized in the system they are a large load and the battery voltage will drop depending on how good the batteries are, good batteries are able to deliver more current to the load resulting in less of a voltage drop. Bad batteries could measure 12V+ with no load, and when a load is applied can squat below 9V.

2 Condition of the multiple connections between the battery and the glowplug controller. Dirty/corroded/overheated terminals/connections add resistance to power flow path and increase the voltage drop to the GP system. The more corrosion and overheated connections are between the battery and the GP controller the lower the voltage to start with at the GP Controller. This leads to problems at and after the GP controller. If you know/remember V=IR (ohm's law) and resistance of your R (load, i.e. glowplugs) stays the same and V starts dropping (b/c of bad connections upstream) then I (current) has to go up to keep the equation balanced. B/C the current goes up, as V drops, you see increased heating and damage of wiring feeding the controller and downstream of the controller (this is why the nuts on top of your solenoid are rusty, they've been over heated and cooked off the cad plating leading to corrosion and more overheating).

As I recall, there is a heavy wire coming from battery + to the starter solenoid, then a heavy two wires (on one ring terminal) headed to the engine harness connector ('87-'91)('92-'94 have a heavy red wire going directly to the GP Controller), then through the engine harness connector on to the GP Controller. All those connections need to be super clean and tight and protected with anti corrosion grease or spray to minimize issues at and beyond the controller. I would also suggest that for '91 and older trucks that the engine harness connector be bypassed like the newer trucks. If you haven't had the connector melt yet, it's coming your way after all these years; head it off sooner than having to rebuild the connector and deal with damage to other circuits in the connector.

3. Resistance through the GP solenoid at the controller. Ideally there is no resistance through the solenoid but over time and use and overheating (due to above) the resistance of the connections through the solenoid goes up. Eventually the solenoid only passes almost nothing and has failed. This is likely your condition but the overheating and failure is likely a result of bad connections upstream. Since you are measuring .5V at the output of the terminal, you need to compare that to the voltage of the input terminal. If it's more than .2-.5V difference I would suspect that the solenoid is on it's way out. I believe the solenoid can be replaced separate from the controller if you think the controller is still good.



I can't really see what the black wire is connected to but if you can take a resistance reading from that point back to the neg terminal of the battery you should see less than a half an ohm. If you see that or more, then you need to check the ground cables/connections from your block to the chassis and batteries to ensure that the return path can handle the current of the GP system as well.

 

[franklin2]

I have never measured it, but it's very very low. You might not be able to measure it very well with a regular meter.

The idea is to generate a voltage that is relative to the current flowing to the glowplugs. But you do not want the resistance very high, since it does cause a voltage drop to the glowplugs.

So they have a circuit board inside the controller with some electronics that can measure the very small voltage drop generated by the very low resistance of the strip, and that is enough for them to monitor the current going to the plugs.

Someone has done some testing before, and measured around 30 amps flowing through one glowplug when hooked to 12v directly. 30 x 8 would be approx 240 amps being drawn by all 8 glowplugs.

Let's take a wild guess, and say the metal strip is .1 ohms resistance.

voltage=current x resistance

240 amps x .1 ohms = 24v. That is way too much voltage drop of course.

Let's take another guess. Let's say the electronics in the controller need 0 to .5v to work properly

240amps x ? resistance = .5v

.5 divided by 240 =.002 ohms resistance.

I don't know what the exact resistance is, but you can see it's very very low. No reason to even include this strip unless you are using the original controller.

 

[Burnt]

I'm looking for some means to reduce voltage to the glow plugs... but not all the time.

It isn't necessary to reduce the voltage when the glow plugs are pre-heating the cylinders prior to the engine starting.

However, it is necessary to reduce the voltage to the glow plugs once the engine has started, and the alternator kicks the voltage up to 14v.

The PCM commands the glow plugs to remain on after the engine starts for up to two minutes if the oil temperature is below 131° F.

It is during this 2 minute time period that the glow plugs are exposed to more voltage generated by the alternator than the glow plugs are exposed to from the batteries alone.

The glow plugs were designed to run on 9v - 11.5v from the batteries, but once the engine starts, are exposed to 13v - 14.2v from the alternator.

I was looking at that IDI relay with the wavy shunt resistor as a way of limiting the voltage sent to the glow plugs when the engine is running.

Rather than just shut the glow plugs off once the engine starts, I wanted to retain whatever emissions control function they serve by being on for the period of time the PCM commands them to be on. I'm just trying to mitigate the effects of what I changed (the alternator... to a larger one.)

I was hoping that the wavy shunt was made from an alloy that had a large temperature coefficient, where the resistance would increase (reducing voltage sent to the glow plugs) when the wavy shunt heated up from increased voltage (from the alternator once the engine starts) and longer run times (during the up to 120 seconds the PCM keeps glow plugs on after engine already started). The goal is to prevent glow plug failure.

 

[The_Josh_Bear]

I'm looking for some means to reduce voltage to the glow plugs... but not all the time.

It isn't necessary to reduce the voltage when the glow plugs are pre-heating the cylinders prior to the engine starting.

However, it is necessary to reduce the voltage to the glow plugs once the engine has started, and the alternator kicks the voltage up to 14v.

The PCM commands the glow plugs to remain on after the engine starts for up to two minutes if the oil temperature is below 131° F.

It is during this 2 minute time period that the glow plugs are exposed to more voltage generated by the alternator than the glow plugs are exposed to from the batteries alone.

The glow plugs were designed to run on 9v - 11.5v from the batteries, but once the engine starts, are exposed to 13v - 14.2v from the alternator.

I was looking at that IDI relay with the wavy shunt resistor as a way of limiting the voltage sent to the glow plugs when the engine is running.

Rather than just shut the glow plugs off once the engine starts, I wanted to retain whatever emissions control function they serve by being on for the period of time the PCM commands them to be on. I'm just trying to mitigate the effects of what I changed (the alternator... to a larger one.)

I was hoping that the wavy shunt was made from an alloy that had a large temperature coefficient, where the resistance would increase (reducing voltage sent to the glow plugs) when the wavy shunt heated up from increased voltage (from the alternator once the engine starts) and longer run times (during the up to 120 seconds the PCM keeps glow plugs on after engine already started). The goal is to prevent glow plug failure.

You may have a point about the engine running voltage increase, but the GPC(whats a PCM?) doesn't run them full-on after startup-- it cycles them on and off for a bit.
Also standing voltage is 12.8v in any vehicle. Not 9-11.5v. Now when the GPs are active they draw down to about 10v but that's because they draw over 200 amps. So if your alt is pushing 14v, then when active the GPs would pull around 11.5v.
If all you want to do is keep your glow plugs in good shape then buy Motorcraft/Beru. End of story.
I've had the same set of glowplugs for 10 years, they work good. I have a manual glowplug button and in the winter will hold them on for 20+seconds, when the temps are in the single digits.
And by the by the afterglow does very little for emissions. You can replicate it by cycling them manually if you want, I do that in cold weather a bit because it does help even out the idle.
I've played with Beru's a bit on the bench and couldn't burn one out on purpose hooked up to a battery. I tested like 5 of them individually up to 1 minute 30 seconds. I went for broke and left one on for 5 mins, it was fine.

Are you having issues with your GPs burning up?

 

[aggiediesel01]

I don't have a GPR controller that has the wavy shunt resistor, so I can't measure myself.

But I'm curious, and while searching for more information about this era of GP relay/controller, I read a comment that said the folks at OilBurners.net know more about the glow plugs and controller of the IDI than any other forum on the net.

So I joined, and am asking.

Prior to asking, I did do a search, but after an hour or so, became bleary eyed because the goal of most of the threads found was oriented toward folks getting their glow plugs to work so their trucks would start.

That's not my goal.

My goal is just to know how much resistance this wavy metal shunt presents between the top of the relay post where it receives power once the relay latches, to the bottom of the wavy thing where it terminates at the black phenolic base of the relay, delivering power to the glow plugs.

How much resistance between the top and the bottom?

Is the metal ribbon made of a material that changes resistance as it heats up?

If it changes resistance, is that how power is limited to the glow plugs, as the glow plugs heat up?

Is there a voltage drop from the top of the wavy shunt to the bottom of the wavy shunt, such that voltage measured at the top is 12 v, but voltage measured at the bottom is 10 v, where the wavy shunt has heated up once the relay latches, and voltage is lost to the resistor's open air dissipation of heat?

I noticed the shape of the wavy shunt resistor is very similar to some old school battery load testers, that had a wavy nichrome resistor to simulate a load to test the batteries. The glow plug controller resistor looks like a miniaturized version of the nichrome resistor of a battery load tester.

Thank you in advance for any testing you can do, or have already done, to give me an idea of what to expect if I added this shunt in series with the output of a regular glow plug relay, and attached my glow plug leads to the bottom of this wavy resistor. Would the voltage delivered to the glow plugs drop, by virtue of the resistance of the shunt? How much of a voltage drop might I expect?

Thanks again.

PS...

One relatively recent post I found, written by @aggiediesel01, encapsulates the limited education I have received on Oilburners about this relay and shunt so far. I'll quote it below, just so you know that I've read it for reference sake, but still do not quite know how much voltage drop or resistance this shunt presents.

How much resistance between the top and the bottom?
You will need a micro-ohm meter to measure this small of a resistance.

Is the metal ribbon made of a material that changes resistance as it heats up?
All materials change resistance as heat is applied or removed but the goal of this component is to affect the system current as little as possible while producing an accurate micro-volt difference between the top and bottom post. This micro-volt difference generates a very small milli-amp current that can be easily measured at the circuit board in the base of the glowplug controller. That translates into the total amount of current being drawn by the load (glowplugs). This value is used by the glowplug controller so that it can perform it's "on time" functions based on how much current is being drawn by the system.

If it changes resistance, is that how power is limited to the glow plugs, as the glow plugs heat up?
It should not change resistance or limit power to the GPs.

Most of the testing done on this site revolves around life and stability of the glowplugs themselves. There is a lot of useful information in what other members here have done but I have yet to come across much effort/research on here or anywhere to understand how and why the glowplug controller behaves the way it does. The GPC on these trucks is nearly an open loop system that expects all components to be functional in-order to deliver the programmed/engineered amount of heat to each cylinder for efficient start up. There are two inputs to the system when it is functioning, current drawn by the system and the temperature of the engine from a dedicated sensor. The current drawn may not even factor into the calculations, it may simply be used to prevent overload of the system. Which might explain why as glowplugs fail the system cycles on and off faster and faster. Again, I'm not aware of much research done on how the system works.

The controller is a common failure point in the overall GP system and most are satisfied with either replacing it with manual control of the solenoid or replacing the controller with a new one.

Adding the shunt from this GP system will not accomplish what you are asking to do. You would be better off attaching additional glowplugs or a custom resistor of a calculated size in parallel to your existing system that is energized via solenoid after the primary cycle of your existing glowplugs. This would in effect share the available current amongst more loads thereby reducing the current on each load (GP). This might cause it's own issues with the GP control system in your truck by setting codes or otherwise. I'm not sure what truck you're working with but in my '97 powerstroke and all subsequent 7.3 engines the PCM uses a similar measurement arrangement to verify that the GPs are in good order and Ford had to issue PCM updates for these functions as flagrant error codes started popping up when the system was functioning correctly.

In the next couple posts, I'll post some pages from an IH manual that has a better diagnostic section for the controller than Ford published.

 

[aggiediesel01]

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[aggiediesel01]

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[aggiediesel01]

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[aggiediesel01]

It is during this 2 minute time period that the glow plugs are exposed to more voltage generated by the alternator than the glow plugs are exposed to from the batteries alone.

The glow plugs were designed to run on 9v - 11.5v from the batteries, but once the engine starts, are exposed to 13v - 14.2v from the alternator.

Use Ohms law to double check this. I think more power (watts) are produced by increasing the voltage but I don't believe the current drawn by the plug will go up since the resistance remains the same or approximately so once the plug is heated up. Of course the resistance will be changing with the heating of the plugs but once again the controller is measuring this and should compensate the "on time" so in actuality the plug might be cycled more but the same amount of power (watts) should be delivered to the plugs and they will draw the same amount of current.

 

[Burnt]

Wow... I'm so glad I joined OILburners.net.

Just imagine being stranded out in the middle of a desert, where you can't even see the horizon cause the air is wiggling so vigorously from the heat rising off of the parched dry hot sand. It's so dry, that there is no sweat left in your body to perspire. You're so thirsty, the pus from the body of a fire ant would do nicely... but up ahead in the distance, way past that shimmering light, you think you see a sign that says "Quench your thirst here". Believing it to be a mirage, what else is there to lose? So you crawl on your hands and knees until you reach...

A freakin 7-11 that still open 24 hours a day that is stocked full of water, soda, slushees, icees, and they even have a liquor license along with 4 full length full width commercial refrigerators serving every imaginable beer ever brewed... ice cold. And best of all, it's all free. And the staff speak English. And are friendly. And they have chairs you can sit on and they'll drink with you!

That's what finding OILburners.net is like for me today.

Thank you for all the details... I haven't even downloaded the pictures yet, but I'm about to, but wanted to pay my respects first and give you thanks, because I really appreciate your help.

Before I run off to study those materials, I wanted to let you know that I'm currently working with a "regular" or "normal" relay for the glow plugs, not a controller. I was considering retrofitting a controller... to get more control over the voltage reaching the glow plugs... without the diagnostics feeding back to the PCM, which isn't calibrated for it.

A poster above asked "What is a PCM", and the answer to that is Powertrain Control Module.

My application is a 2000 7.3L, federal calibration, no GPCM (ie, no solid state Glow Plug Control Module).

The issue is that I "upgraded" the charging system, which now produces twice as many amps at idle, so the system voltage increases to 14.2 very rapidly after start, instead of languishing at 12v until the glow plugs are commanded off. So there is an up to 2 minute period of time when the glow plugs are seeing more voltage than they were designed to deal with, once the engine is started. Therefore, without turning off the glow plugs, I'm trying to reduce the voltage that the glow plugs see, down to what they used to see before I upgraded the charging system.

Now, I'm going to download and study all those photos.

 

[IDIBRONCO]

I was going to suggest going to a manual control instead of trying to reinvent the wheel until I saw that you're working on a Powerstroke. This is for IDIs. Now a lot of us right here have both, or even just a PSD. There's nothing really wrong with you posting this here, but you may want to also try the Powerstroke subforum. I'm not trying to be a jerk, but I believe that there's been a little bit of confusion.

 

[Burnt]

You may have a point about the engine running voltage increase, but the GPC(whats a PCM?) doesn't run them full-on after startup-- it cycles them on and off for a bit.

That aspect of short cycling the glow plugs, as a protective measure to prevent burnout from over voltage, is one of the aspects that attracted my interest in retrofitting a Glow Plug Controller in lieu of the regular relay that is currently installed. I've since learned that folks have a lot of trouble with the GPC, and often ditch it in favor of a regular GPR, which is essentially the opposite of what I was contemplating doing. But I'm not going to ignore all that experience.

So then I thought to just borrow one aspect of the controller, the resistor (as I understood it prior to posting), and allow the resistor to be the limiter of higher voltage. Looks like that was a fantasy. At least with the GPC wavy thing. Maybe I can find another device that has a calibrated temperature coefficient that can handle over 2,000 watts peak... which also sounds like a fantasy.

But I'm not going to give up so easily. The solution is just an education away, so I'm going after the education, and hopefully, a solution will then present itself.

Also standing voltage is 12.8v in any vehicle. Not 9-11.5v.

Ha... I thought I had good batteries, but you have GREAT batteries. At rest, my older batteries dwindle down to 12.65v. I haven't measured my newer batteries at rest, but I'm a bit envious if your batteries are holding 12.8. Regardless, the "standing voltage" I was referring to was under the load of the glow plugs, when powered by batteries alone, prior to engine start. That's when I read 10V to 10.5V. While I'm waiting to start.

Now when the GPs are active they draw down to about 10v but that's because they draw over 200 amps.

Yes... we're on the same page!

So if your alt is pushing 14v, then when active the GPs would pull around 11.5v.

Maybe, maybe not. Beru doesn't seem to think so. Because... by the time I start the engine, and the alternator kicks up the system voltage to 14.2 v, the glow plugs have already been heating for a while. They were heating for all the time I patiently waited for the WTS light to extinguish, and, they were heating during all the time I kept waiting after the WTS went out (because the WTS light has no correlation to glow plug on time... the glow plugs remain energized after the WTS light turns off) and, the glow plugs are STILL on after the engine starts.

Once the engine starts, the glow plugs are not only being heated from electric power internally, they are also being heated from combustion externally. This is why I don't think that the glow plugs are consuming 200 amps after the engine is started, and this is also why I think the glow plugs are being exposed to an over voltage condition with my high amp alternator, that is able to meet the recharging current demand of the batteries, and still maintain the system voltage up to the limits of the regulator.

The reason why I think that the current consumption of the glow plugs is reduced is because the Beru glow plugs that I have are built with two coils inside each glow plug... a heating coil, which has a constant resistance, and a regulating coil, which has a variable resistance. The coils are connected in series, with the regulating coil getting the juice first, and passing it on to the heating coil. The hotter the glow plug gets, the more resistance the regulating coil presents, because it is made with some type of metal that has a very large thermal coefficient that changes resistance with temperature.

In fact, I kind of wish I knew exactly what that material was, and how to buy it calibrated to the load I want to limit. But that's me, living in a fantasy world, wishing I could find stuff like this next to the cereal aisle at the grocery store. But alas, not so easy.

Anyway, if heat, both from within and without, changes the resistance of the regulating coil inside the glow plug, then the current draw will be reduced. Unfortunately, Beru says that despite this regulating coil, if the glow plugs are hit with too much voltage, they'll blow... meaning that the regulating coil will separate from the heating coil inside, and I'll know this when I measure an open in the glow plug. And I did. Wide open. Dead glow plug.

If all you want to do is keep your glow plugs in good shape then buy Motorcraft/Beru. End of story.

Once again... we are on the same page!

I've had the same set of glowplugs for 10 years, they work good.

I've had my original set for 20 years, but I live in a climate where the glow plugs are not challenged. I presented a challenge when I upgraded the charging system, and I paid for it by having to buy a new set of glow plugs, which arguably was time to do anyway, after 20 years. But still, knowing what I know from both Ford and Beru, I want to address the over voltage after engine start up... and was looking at previous schemes that were used to limit glow plug exposure to over voltage, yet still enable glow plug heating.

From the photos aggie shared, I learned that the GPC rapidly cycles the glow plugs to control the input power. It looks like you have a manual scheme going on...

I have a manual glowplug button and in the winter will hold them on for 20+seconds, when the temps are in the single digits.

I'm trying to make the solution workable for a non mechanically minded person (wife) to be able to still drive the truck. She can watch a WTS light, but telling her she has to hold this and count to that but not if the temp is this or that... she'll nod her head sweetly and say OK, but... I'd rather the solution just work silently on it's own.

I've played with Beru's a bit on the bench and couldn't burn one out on purpose hooked up to a battery. I tested like 5 of them individually up to 1 minute 30 seconds. I went for broke and left one on for 5 mins, it was fine. Are you having issues with your GPs burning up?

No dramatic explosions or tip burn offs or anything like that... just the open and the distortion/dimpling of the heating rod.[/QUOTE][/QUOTE]

 

[Burnt]

I was going to suggest going to a manual control instead of trying to reinvent the wheel until I saw that you're working on a Powerstroke. This is for IDIs. Now a lot of us right here have both, or even just a PSD. There's nothing really wrong with you posting this here, but you may want to also try the Powerstroke subforum. I'm not trying to be a jerk, but I believe that there's been a little bit of confusion.

I'm not at all confused. I'm in the exact right place. It is the IDI's who have the controller I was interested in. The Powerstrokers know nothing about it.

 

[franklin2]

If you did use one of our old controllers on your newer truck, and your newer truck used the same glowplugs our old trucks use, I think it would self compensate for the the higher voltage. The "brain" in the controller is controlling the current to the glowplugs by cycling them. It doesn't just cycle them after the engine starts, it cycles them when they heat up enough.

The controller monitors the current flowing through the strip. As the glowplugs heat up, their resistance increases so the current starts dropping. When it drops to a point, the brain starts cutting the relay on and off. If you have a higher voltage, this means the glowplugs will heat faster, and it will automatically cut the glow time.

The controller works great, but it has one problem you have to keep on top of; Burnt out glowplugs and poor wiring connections. Both will cause the controller to short cycle the plugs. This is something you can deal with once you know how the controller works, but for newbies it's very confusing when their glowplugs short cycle and the engine won't start.

 

[IDIBRONCO]

I'm not at all confused. I'm in the exact right place. It is the IDI's who have the controller I was interested in. The Powerstrokers know nothing about it.

I was meaning on the part of others. I was confused when you started talking about a PCM.