Glow plug indicator or gauge?

[Black dawg]

have any of you guys measured the voltage that the glow plugs produce while the engine is running?

 

[LCAM-01XA]

Wait, what? Glowplugs produce voltage? How does that work?

 

[Black dawg]

Wait, what? Glowplugs produce voltage? How does that work?

did you try it yet?

 

[LCAM-01XA]

You want me to measure voltage at any plug with the engine running and fully warmed-up? Dude, it's cold, dark, and windy out there, whereas in here I have heat, light, and a rather entertaining girlie - please do me a favor and save me the aggravation of dealing with this darn truck again (for the next time a glowplug connector breaks on me I will break out the shotgun) and share what you found out on yours lol

 

[Black dawg]

it has been awhile since I measured, Ill try to later this week.

 

[jim x 3]

Jim, how big are those diodes anyways? I can just see 8 fat monsters lined up in packs of four on each side of the intake, lol. You are right tho, more failure points in a pretty simple and reliable system, not really what we're going after...

LCAM, they look to be 1/2" in diameter. Regards,

 

[LCAM-01XA]

Black Dawg, no rush man, whenever you fee like it. I most certainly do not have the motivation for dealing with this mess yet again, several days in a row last week was more than plenty for me for one year.

Jim, 1/2" ain't bad at all. There is still the matter of adding another component to fail, and while I like aircraft-like instrumental panels as much as the next guy adding a monitoring circuit for those diodes will make the whole thing into one giant mess! I still may do the plugs monitor LEDs tho, those would be cool to have

 

[u2slow]

U2: Well, maybe I'm not understanding what you, LCAM, and 93CC have in mind, but I don't see how a separate set of 8 powered LEDs connected each to a GP would tell you anything other than at least 1 GP is not open. Remember the GPs are wired in parallel, so if even 1 GP has a path to ground, all 8 LEDs would light. (To prevent this you would need 8 diodes in series with the GPs, and these would need to be huge diodes capable of carrying the entire current for its GP).

Doh! Yeah, of course

I have heard of Hall-effect (DC) current sensors... dunno if anything is applicable to what we need.

I installed something like this back when I worked wiring high-rise condos. It sensed current flow in the laundry-dryer circuit and turned on a booster fan in the dryer duct. It was basically a donut with a pair of leads that hooked up to a relay. One of the dryer's hot legs got run through the donut. I imagine this is cheaper/easier with AC that DC, but my electronics background isn't the strongest.

 

[franklin2]

You can't add diodes, ammeters or anything inline with the original glowplug power circuit, this will affect the current flow of the original circuit and if you are running the original glowplug controller, it won't like that. A diode has .7v forward voltage drop.

Ammeters also introduce a small resistance in the circuit. Say your ammeter has a resistance of .1 ohms. .1 ohms X 40 amps = a 4v drop in that circuit. Only 8v left for the glowplug, and we all know the system barely holds 8 or 9 v when you are heating the plugs.

If you know your truck, you know when you have burnt out glowplugs.

Oh by the way, that comment about reading voltage FROM the glowplugs. There was a huge thread on another board about this. The glowplugs act like thermocouples when they are not heating. If your plugs are all the same, you can read the voltage from each plug, and it will tell you the relative temperature of each cylinder as the engine is running, which you can use to diagnose if all the cylinders are contributing their fair share of power.

 

[jim x 3]

Franklin:

You are correct:

Yes, diodes would drop voltage to the GPs.

Yes, a shunt would affect voltage as well. 0.1 ohm would be WAY to big. The GPs only get about 8 V anyway, given the GPC's shunt and wire size in the harness (GPC to GPs).
U2 has a good idea about using a toroid for voltage sensing. I had thought about that as well.

Yes, you need to know your machine. Then you don't need any of this stuff.

Not sure about GPs as thermocouples. Where would the cold junction be? They do have a PTC, so you can read resistance as an analog for cylinder temp, but they are still all connected in parallel - so we have the same measurement problem.

Regards,

 

[LCAM-01XA]

You can't add diodes, ammeters or anything inline with the original glowplug power circuit, this will affect the current flow of the original circuit and if you are running the original glowplug controller, it won't like that. A diode has .7v forward voltage drop.

But, if you no longer run the factory controller, and use a full-manual switch instead, you can run diodes just fine, and if you're losing voltage across them then you can bypass the resistor strip as well and feed the plugs directly off the big relay. You are correct tho, the factory controller is a finicky SOB, and about any changes done to the glowplugs power circuit will mess it up pretty bad.

 

[Brad S.]

I want to bring this thread back because I want to pose a little different angle, but with the same result.

Originally I wanted to make a indicator with 8 LED lights, each represents a cylinder, when the GP system is energized.

Now how about a "gauge" that has 8 LED's that light up when a person pushes a button or flips a switch. Kinda like testing all 8 GP's all at once.
Doing this before turning the key on and energizing the GP system???
Making this a permanent fixture so a person can check the GP's once a week or so????

 

[laserjock]

This is interesting. I read the whole thread. I'll chew on it and see if I can come up with anything simple. I can see the it's 20 below with windchill at 40 below and I don't want to be an hour trying to figure out which glow plug is bad scenario.

 

[laserjock]

After thinking about it and drawing a few pictures, this is a harder problem than I originally thought. I'm not even 100% sure that the power diodes in line would be good enough to isolate the GP's well enough for the LED to not find ground somewhere else. Maybe I'm wrong there but I have done control circuits just like that were I sensed ground through a diode in reverse to be able to isolate systems. Anyway, that aside, the fundamental problem is to test the GP's individually, you have to isolate them one way or another. You can do it electronically or manually. If you were really interested (and believe me I am in no way saying this is a great idea, why don't we all do this), what you could do is swap the big GP relay for 8 small ones (one for each GP). I went and dug up OLDBULL8's thread on GP draw.

http://www.oilburners.net/forums/showthread.php?67107-GP-Testing-2&highlight=testing+glow+plugs

He says 192 Amps in the system at start up dropping to about 126 after a few seconds. If you divide that out, and give yourself a little head space that's about 25 amps per GP. That's pretty manageable especially considering that the GP's are only one for a minute or two total in short bursts. That's essentially a headlight relay. Essentially instead of switching the big relay, the controller would switch all 8 relays at the same time. The controller shouldn't care how many small relays it's switching and it shouldn't upset the controller's ability to regulate the GP's.

Now you could do your 8 LED test light and have them be isolated.

One side benefit of this would be if the relay stuck and melted down the glow plugs, it would only be one plug not all 8.

Thoughts?

 

[OLDBULL8]

Eight (8) relays still only power the GP's, it won't tell you if the GP element is burned out, shorted or heating. The voltage to the GP's is ~12.5 VDC and drops to ~8.5 VDC as the GP's heat. If I could figure out a way to monitor if they are heating I would get weathy in a short. Cost of doing so would be quite high for a unit to do so. If I could stick a thermister in each hole? I figure if it could be done some electronic genius would have done it.