Glow plug amp draw

Hello all, I have been driving my 93 n/A around, and it is a sweetheart! Starts really well after changing the glow plugs, one was at 400 ohms!

Question here, what does the glow plug system roughly draw? The original harness for the power side of it was gone from someone doing midnight shopping, so I ran a 2 gauge wire to the solenoid with an inline circuit breaker.. after changing the glow plugs, it has been popping it off and on.. I think I have an 80 amp one? I'll check in a little bit, as I am going to check to make sure it's not grounding out somewhere

What size breaker would be adequate for a good functioning glow plug system? Don't think it matters, but I also replaced the actual plug harness with one off a 6.0 as they fit.. I have them individually connected on the controller..

I have never measured it, but it is a simple circuit with 8 resistors in parrallel. Using Ohm's Law, the total amperage would be equal to (8)*12.5/2 or 50 amps, assuming 2 ohms at each glow plug, and 12.5 V at the battery. If the resistance is closer to 1 ohm per plug, than the amp draw increases to 100 amps. Every functional glow plug I have ever measured fell in between 1 and 2 ohms.

It has been awhile since I tested amp draw on these glow plugs, but what I remember was close to 30 amps initialy, quickly falling in the first few seconds, and eventually settling about 10 amps. Per plug.

Sounds about right to me Black dawg.

I think you guys are way low. I seem to remember someone on here long ago did some testing and all of them together was a good bit over 100 amps, closer to 150 amps. That would explain why his 80 amp breaker is tripping.

The last time i measured my truck, it draws between 180a and 200a. I have a factory controller and all new beru plugs, new wires, etc.

I ended up running a 4 gauge from the starter solenoid to a 200a breaker mounted on the fender.

I agree with Franklin - I originally tried a 180a circuit breaker but it kept nuisance tripping so I upped it to a 200 and haven’t had any problems since.

franklin2 said:

I think you guys are way low. I seem to remember someone on here long ago did some testing and all of them together was a good bit over 100 amps, closer to 150 amps. That would explain why his 80 amp breaker is tripping.

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I also seem to remember it being higher... more like ~15A per GP.

u2slow said:

I also seem to remember it being higher... more like ~15A per GP.

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I think this would be a good average, but depending on temp, I have seen around 30 amps initially, with amps falling quickly as plug gets hot.

Black dawg said:

I think this would be a good average, but depending on temp, I have seen around 30 amps initially, with amps falling quickly as plug gets hot.

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I think they missed your last sentence in your previous post which was "Per plug."

Cold glowplugs have a 0.25 ohm resistance, each plug draws over 50A-60A(battery voltage drop dependent) each, they drop quickly to about 30A in 3 or so seconds. So initial switch on your up around 400A draw, dropping to about half after several seconds. These plugs draw a lot more than people think they do.

Here’s a scope image I did years back when testing a set of plugs, yellow trace is voltage, blue is current

When I went through mine last fall when I measured the draw an individual plug would draw 27 to 30 amps for a couple seconds. The set of eight would draw close to 250 and quickly drop off. Seems like they would drop down to around 140 or so in around 15 seconds. This was measured with an inductive ammeter. I do not recall the exact battery voltage when they started out and that will make some difference.

Thanks for the input guys! I'll get a 200 amp breaker, seems like that's the consensus on what is adequate