I always thought there was supposed to be a noticeable difference in the resistance of a non-working glowplug as compared to a working glow plug. I ohmed out some bad and new one and got about 0.5-0.8 Ohms for all of them.

I thought good plugs were suppoesed to be 1.5 Ohms and bad ones would be less?

 

They generally read high or 0 if they're bad. .08-1.5 is normal for good working GP's.

Diesel Rod

 

All ohm meters are not created equal, especially on the low end of the ohm scale. Unless you have a meter known to be calibrated specifically for those lower measurements, at best, it's just a guess.

 

I use a test lamp for a go/no go test . I have tested with a ohm meter , Fluke , and gotten conflicting results . I test them all with a test lamp , if one fails , I replace them all .

 

I wanted to put a fuse in line with each GP that way when it went bad the fuse would pop before the harnesses melted. I was trying to determine what size fuse to use. Any thoughts?

 

You've got the right idea! I wish I had done glow plugs in this kind of weather instead of in the cold of winter.

 

Ohm's Law (hasn't changed since high school ) -- V=I*R. Going with the lowest resistance (thus highest current):
12V = I * 0.5ohm
12V / 0.5ohm = I.
I = 24 (amperes)
So I'd say a 30A fuse to be safe.

 

Keep in mind that it 30 amps per glow plug.

Richard

EDT: I would use a 25a fuse....

 

Thats what I was thinking. I bought some fuse blocks from summit racing and am making some brackets. I'm also converting to SD harnesses so between these two measures I shouldn't have any more problems.

 

New glow plugs should be about 1.5 ohms. Theoretically each bank is designed to draw 32 amps, or 8 amps per glow plug. Ohms law states R=E/I thus R=12/8 so R=1.5 ohms. If the glow plugs were truly 0.5 to 0.8 ohms then each glow plug would draw 24 amps and 15 amps respectively. Under those conditions it would not take long for connectors to overheat, melt and cause havoc on the GPR contacts.

 

First, I have never seen E used to represent voltage before.

Second, All I know is that every single UVCH and external pigtail connection is melted on my truck again. I measured the resistance on my old GP and got 0.5-0.8 Ohms on them. I ordered new ones from RR and they also read 0.5 Ohms. I only measured 2 of the new ones. My multimeter probebly isn't accurate at such a low level of resistance as stated above, but I would like to think it would register a difference atleast.

So would you use a 10 amp fuse then?
I know the wiring will add to the resistance, but could it add 1 Ohm?

 

Rule of thumb is double the expected current draw, so go 15 Amp. If it was me I would put an amp meter on one of the glow plugs and check total current draw before fusing. Another option would be to fuse the entire bank, maybe 50 amp but I would still put an amp meter on to check for sure.

 

I'll be honest I think you're going to all this trouble for nothing. When the glow plugs fail, they burn out and don't draw anything. Putting a fuse inline will only protect it from drawing too much, and that's not the way the GP's fail. More power to you (pun intended) if that's what you want to do, but the pins don't go bad IMO because the GP's need to be replaced. They fail because the connection is under-designed for the kinds of amperages that the GP's draw when they are working exactly like thy're supposed to be. You're addressing that issue bu putting in the SD VCG's and UVCWH's. That makes the fuses, in my opinion, a wasted effort.

Again, I'm not going to stop you if that's what you want to do, but I don't think it is going to help you much.

 

I'm starting to think the same thing now that I can't measure a difference in resistance. But I think I'm gonna do it anyway since I already bought the fuse blocks, and it really can't hurt anything. It might save some trouble down the road though.

 

Voltage has always been E. I was through electrician school 10 years ago and it was E....

R.I.E.P multiply as you move right, divide as you move left....


Fuses inline with the glow plugs is a BAD idea.... If you plan for 1.5 Ohms each thats 8 amps per plug. no 2 plugs are created equal and as they age there resistance drops. once there down to .8 Ohms the current draw is up to 15. If you put a 10 amp fuse in as soon as they age you will start blowing fuses and now you have NO glow plugs.....they don't start very good without glow plugs.

Diesel Rod