Glow plug troubleshooting

[Quebecguy]

All the glow plug diagrams I have seen have the glow plugs connected in parallel. So the formula for connecting resister in parallel is 1/r1+ 1/r2+1/r3

My Kioti manual says the glow plugs in the Kioti are .43 ohm each. I suspect others would be near the same.

Hi again James,
So you are saying if the current is 20 amperes and the glow plugs are connected in parallel then each glowplug would measure 5 ohms?
.6 = 1/5 + 1/5 + 1/5

 

[Quebecguy]

Hi,
I have to agree with James on all counts. Never seen glow plugs wired in series. If they were to be wired in series, they would have to be isolated from ground, and then if any one failed none would work. Wired in parallel a failure doesn't kill all them. It make it harder to trouble shoot though. If you can remove the jumper from all of them, you don't have to remove them from the engine to test them. Remove the jumper, and check each to ground. They are like light bulbs, if open then bad, shorted is good. Most meters don't show the half ohm and once again, OPEN IS BAD, SHORTED IS GOOD! You don't need to replace all when one fails, especially if you can find an open one with out too much difficultly.
Donnie

Hi Donnie,
Your words almost make me think that you don't believe glowplugs could be wired in series. I can't show you these tractors but I will try and attach a couple of wiring diagrams from an I&T Shop Service manual.

View attachment 452065View attachment 452066

 

[k0ua]

Hi again James,
So you are saying if the current is 20 amperes and the glow plugs are connected in parallel then each glowplug would measure 5 ohms?
.6 = 1/5 + 1/5 + 1/5

I was saying the maximum current is about 20 amperes for EACH glow plug. x3 for a 3 cylinder diesel, or x4 for a 4 cylinder. That is why the total glow plug current is 60 to 80 amps initially. They do draw somewhat less after a couple of seconds as they heat up, but it is a "ship load" of current to suck out of a cold battery. Each glow plug statically measures less than 1/2 an ohm when cold on my Kioti. I assume others are similar.

 

[k0ua]

Hi Donnie,
Your words almost make me think that you don't believe glowplugs could be wired in series. I can't show you these tractors but I will try and attach a couple of wiring diagrams from an I&T Shop Service manual.

View attachment 452065View attachment 452066

Well sure enough, now we have seen two glow plugs in series. with that left diagram.. I can't make much out of that right hand schematic. That is about the most PiXX Poor version of a schematic I have seen lately. The guy that drew that one, has never worked with electrical schematics much.

So yes I guess you CAN have glow plugs in series.. Why in the heck you would want to do that is beyond me. It is not a good way of doing things for many reason.s

 

[Quebecguy]

I was saying the maximum current is about 20 amperes for EACH glow plug. x3 for a 3 cylinder diesel, or x4 for a 4 cylinder. That is why the total glow plug current is 60 to 80 amps initially. They do draw somewhat less after a couple of seconds as they heat up, but it is a "ship load" of current to suck out of a cold battery. Each glow plug statically measures less than 1/2 an ohm when cold on my Kioti. I assume others are similar.

Hi again James,
Thank you for your prompt reply. Let me see if I understand you correctly: with 3 glowplugs connected in parallel each passing roughly 20 amperes the total current is about 60 amperes. So using Ohm's Law:
12 V = 60 I (1/R + 1/R + 1/R)
or .2 = 1/R + 1/R + 1/R
or .2 = 3/R
or .2R = 3
or R = 15 ohms.
This is much more than your Kioti. What am I missing now?

 

[k0ua]

Hi again James,
Thank you for your prompt reply. Let me see if I understand you correctly: with 3 glowplugs connected in parallel each passing roughly 20 amperes the total current is about 60 amperes. So using Ohm's Law:
12 V = 60 I (1/R + 1/R + 1/R)
or .2 = 1/R + 1/R + 1/R
or .2 = 3/R
or .2R = 3
or R = 15 ohms.
This is much more than your Kioti. What am I missing now?

What is missing is I didn't state the resistors in parallel formula correctly. MY BAD. it is 1/Rtotal= 1/R1+1/R2+1/R3.

So E=IR
Therefore 12=60 (Rtotal) This 60 amp current load is the total current load for all 3 of our glow plugs

12/60 =Rtotal (dividing thru both sides by 60)

.2ohms = Resistance of the total of the 3 glow plugs in Parallel.

So if the total resistance is .2 ohms then each of the 3 glow plugs would be .6 ohms So it would appear that My Kioti with the cold resistance of somewhere around .5 ohms probably draws a bit more than the 60 amps upon initial application of power Keep in mind as the glow plugs heat up the resistance changes.

Also keep in mind it takes one heck of a sophisticated ohm meter to read .4 or .5 or .6 ohms. Not something your average guy is gonna have. They will look pretty much as a dead short.

 

[oberscrounge]

Oberscrounge ,here, I have the other two glow plugs out , Both read infinity-- "Open Circuit", second two are "Isolated" from the plug casing, not like the first one where all surfaces were "Common", -- one has a hole melted in the tip, with a deposit, I believe from the inside , welded at the hole --- see pics , no wonder this thing is "Hard "starting" !!! No fuses, Just the 20A breaker , I will replace it seeing as it is 27 Yrs old already (1988 machine)

 

[oberscrounge]

Can someone tell me why my pics are not posting ? I went thru the browse computer for pics several times, also I cannot find a "Help" tab anywhere on this site to look it up ?? @@@------@@@

 

[k0ua]

Can someone tell me why my pics are not posting ? I went thru the browse computer for pics several times, also I cannot find a "Help" tab anywhere on this site to look it up ?? @@@------@@@

After you browsed and found the filename of the picture did you hit the upload button?

 

[Quebecguy]

What is missing is I didn't state the resistors in parallel formula correctly. MY BAD. it is 1/Rtotal= 1/R1+1/R2+1/R3.

So E=IR
Therefore 12=60 (Rtotal) This 60 amp current load is the total current load for all 3 of our glow plugs

12/60 =Rtotal (dividing thru both sides by 60)

.2ohms = Resistance of the total of the 3 glow plugs in Parallel.

So if the total resistance is .2 ohms then each of the 3 glow plugs would be .6 ohms So it would appear that My Kioti with the cold resistance of somewhere around .5 ohms probably draws a bit more than the 60 amps upon initial application of power Keep in mind as the glow plugs heat up the resistance changes.

Also keep in mind it takes one heck of a sophisticated ohm meter to read .4 or .5 or .6 ohms. Not something your average guy is gonna have. They will look pretty much as a dead short.

Hi again James,
Thanks for another prompt reply. I think you have the calculation right this time. I'm surprised by some of your comments. The ohmmeter I have was the cheapest available when I bought it almost forty years ago and it is fairly easy to see the difference between a half ohm resistance and a short. As for glowplugs connected in series: there were probably some good reasons for doing it that way but I'm getting off topic with that. I would guess there were many tractors wired that way - those two schematics were the first two I looked at and I stopped looking after finding those. At any rate, it seems that oberscrounge has found his problem which is the main thing.