What is the current draw of the glow plugs?

[MarcusOReallyus]

Okay, I searched. What do I mean?

I mean I have spent the last 6 hours searching this site and others for a definitive answer to the current draw of the glow plugs in a 6.2.

I found the ACDelco site very interesting. There's exactly ONE page about glow plugs, and the text on that page is about spark plugs. No specifications, just some general marketing hoo-ha about spark plugs. Nice. Search their parts catalog and you get a picture of an AC60g (seems to be their only one), plus a link to a listing of vehicles that might use the thing. That's it. Oh, you should probably know that there are 666 possible applications for it, so avoid that devil plug! You have been warned.



I have read countless threads here and on diesel forums, and have gotten conflicting figures. One person said he had measured the current in a civi 6.2, and gave 15 amps per plug, or 120 amps total. Our own Mistaken1 says 80 amps total (lost the link, sorry.) Several online parts stores list them as being 200 watt plugs, but the nominal voltage they list varies from 10.4 to 12, giving anywhere between 16.7 and 19.2 amps, or 116.7 and 153.8 total system current.

Parts stores give more info than the manufacturer. That's pathetic.

[sigh]

The reason I want to know is that I'm finally getting around to doing the resister bypass, and I am considering going straight to the battery instead of to the 12v junction box. I know, I know, that works just fine for a billion people so I'm over complicating it.

But I'm still probably going to do that. I don't like the idea of pulling all that juice through the existing fusible link... (I know, I know, it's fine. It works. I still don't like it.)

So, running that line over to the batteries requires fusing (or a circuit breaker), and inquiring minds want to know how to size it.

I suppose I could just assume a safe 200 amps and be done with it, but this is bugging me.


So, does anyone have anything definitive?

 

[peapvp]

The MEP 002A/003A uses 24 Volt Glow Plugs which have a cold state resistance of 5 Ohm +/- 0.25 Ohm tolerance. At 24 V they draw 4.8 Amps then they tapper off when the Glow Plug gets hot.

Peter

 

[MarcusOReallyus]

Well, that's interesting, but this is in the CUCV forum, and I'm pretty sure the MEPs don't use a 6.2 liter engine, so I'm not sure I can use the info you've posted.

 

[peapvp]

See if you can find the resistance for your glow plug - then just use Ohm Law to calculate your cold current. That's the highest current the Glow Plug will draw - similar to a light bulb

 

[MarcusOReallyus]

I could do that if I pulled the glow plug out. And that would only tell me what that particular GP was drawing. And if it's bad, I'll have bad figures.

I was hoping to find some accurate specs. I've seen various measurements posted for the resistance, so I'm still left with varying current draw.

 

[peapvp]

Do the glow plugs you use have a NSN? If yes I hen I may be able to find the specs.

 

[MarcusOReallyus]

I'm looking for the specs on AC60Gs, from Delco. That's what most folks on here recommend, and I'm switching to them.

The TM would probably have an NSN on the stock Wellmans, but that's not what I want.

Hmmm. That would probably be close enough, though. The ACs will have to draw a similar value.

Let me see if I can find that NSN in the TM....

 

[Hasdrubal]

I understood the load to be 80 amps. The ST85 GP relay that many use is rated for continuous 85 Amps.

 

[doghead]

Maybe Antennaclimber will post on this, since he manufactures the controller cards.

There is a big difference between constant duty rating and intermittent duty rating.

The load also changes as they heat. So, the load actually changes as they operate.

We all know from the TM that to test a cold GP, it should read 1-3 ohms.

Maybe someone with a DC amp clamp and a CUCV will measure their truck.

There is no need to supply the GP relay with a wire that can handle 200 amps. The next problem that comes with that is protection(fusing).

If you simply jumper wire to the 12v stud, all this is done already(and well proven to work just fine).

 

[peapvp]

I see - 200W @ 10.5 V
= 19 Amp per glow plug

with a battery voltage of 12.5 Volt that would give you 16 Amps per plug
with a battery voltage of 13.25 Volt that would give you 15 Amps per plug

multiply the amps for the battery voltage you got by the number of plugs your engine uses - that will give you the total current during pre heat of the engine.

 

[antennaclimber]

100 amps. I measured it.

 

[MarcusOReallyus]

Found it!

Thanks to peapvp mentioning the NSN, I started thinking about the original spec'd Wellmans. Did a search, and found a nice chart:

http://www.dieselrxproducts.com/glow-plugs.php

Yes, Wellman is now Diesel Rx. The Wellman site said so.


So, on this chart we see the Wellman current draw vs. time, and an unnamed competitor.

Since most glow plugs are going to be in the same ballpark, I think it's safe to assume the values here as representative of the market. It's probably an AC60G anyway.


The competitor starts at a whopping 26 amps! Times 8 that's 208 amps!

After 5 seconds, it's down to about 22 amps. That's still 176 amps. Wow.


Even after 15 seconds it's still 13 amps, or 104 total. It takes a full 40 seconds to finally settle down to a steady-state 11 amps.


Do you folks find this believable? Or is that chart actually in milliseconds? Maybe a mislabeling mistake?

What do you think?

 

[MarcusOReallyus]

100 amps. I measured it.

We cross posted.

So, we can assume that the Wellman chart is.... less than completely accurate.

Unless it's really in milliseconds, not seconds. Then it's in the right ballpark with your measurement.



Climber, what were the conditions when you measured it? Temp? Measurement point, etc.? Multiple measurements?

Not that I'm doubting, I'm just curious.

 

[peapvp]

Well, it appears that the ac60g is a constant wattage plug and the other with the chart a constant temperature plug -then we would compare apples with bananas

 

[antennaclimber]

I used an ammeter on one of the orange wires that feeds 4 of the glow plugs a the GP relay.

The engine was not started and was "cold". I observed the meter deflect to the far right of the meter between 45 and 50 amps. So 100 amps is a safe number.
I posted a picture of the actual current draw on here but I can not find it.

The glow plugs were all AC60G.

The picture must be on my work computer.

 

[MarcusOReallyus]

Yes, I agree with your point, but still, if they are to interchange in the same system, they must have comparable current draws. It wouldn't work out very well to have it otherwise.


I think 'Climber's number is good enough for my purposes, but I'm still wondering about those numbers on the Wellman/Diesel Rx chart. I'm strongly leaning toward it being a mislabel, and the time should be in milliseconds, not seconds. An inrush current lasting essentially 20 seconds seems a bit much!

 

[MarcusOReallyus]

I used an ammeter on one of the orange wires that feeds 4 of the glow plugs a the GP relay.

The engine was not started and was "cold". I observed the meter deflect to the far right of the meter between 45 and 50 amps. So 100 amps is a safe number.
I posted a picture of the actual current draw on here but I can not find it.

The glow plugs were all AC60G.

The picture must be on my work computer.

Excellent! Thanks!

What do you think about the Wellman chart? Milliseconds? If so, the inrush wouldn't show on an ammeter, and the steady state agrees with your number.

It's either got to be that, or they are, uh, fudging maybe?

 

[peapvp]

The Wellman's reach their peak temperature in 15 seconds and that's when the plug reaches its highest resistance - the current chart confirms this - so it's seconds for the current. The ac60g is a different type of glow plug the temperature increase does not change the resistance / current over time - the 45 to Amps 50 sound reasonable for the ac plug

 

[MarcusOReallyus]

So, yet another reason to avoid the Wellmans! All other considerations aside, if one plug puts a 200 amp load on my batteries, and another draws half that, I'd have to have a very compelling reason to choose the higher amp draw to get the same job done.

 

[peapvp]

The ac60g are what we call 1 minute plugs vs the Wellman are 15 sec plugs or fast start plugs