6.9 GP amp draw

[jauguston]

Hello again guys,

This is my first winter with my '86 E-350 chassis MH. The temps here are in the mid 20's at night and mid 30's during the day. My engine will start after 5 or 6 cycles of the GP timer but it doesn't sound too happy about it (-: The rig has 35,000 miles on it and I am curious if all the GP's are working or is that the way it is. I put my clamp-over meter on the red cable going from the battery to the GP solenoid and I get a reading of 11.5 amps. Is that the approximate correct current draw for eight GP's? If not what should it read for eight healthy GP's?

I know I could do the continuity check on each individual GP but in a E series that is not something that is really fun. If this reading is about right I can stop here, if not I will take my punishment and do the individual test.

Jim

 

[The Warden]

Actualy, I LOVED doing glow plug checks on my old E-350...pull the doghouse cover and the passenger's seat, sit down in the "comfort" of the cab, and check each one. Let me stay nice and dry when I did the glow plugs while it was raining outside. OTOH, my van was an N/A without factory air conditioning, so it was easier to get to the plugs than it probably is on your motorhome...

I asked a similar question a few months back (was trying to figure out what size wire to get for my plugs when I remake the wiring harness), and while I never got a definitive answer, I was told that it should be a LOT more than 11.5 amps. People were figuring on something in the range of 30 to 50 amps per plug. I think I'd be doing the individual test now if I were in your shoes...it's amazing how easily these trucks start with a happy glow plug system.

Also, what shape are your relay and controller in? As you've probably read already, the '84-'86 6.9l glow plug controller is infamous for failures (often burning out the glow plugs in the process), and many people have either switched to the 7.3l system (I plan to do this as soon as time allows) or simply put a pushbutton in place because they were sick of payig $80+ for a controller that doesn't work well. Are you hearing the relay click on and off?

Hope that helps a little bit...good luck!

 

[jauguston]

Thanks Warden,

I don't know who came up with 30 - 50 amps per GP but that is nonsense. The wire from the battery appears to be 10ga. 240 - 400 amps thru a 10 ga wire - I don't think so (-:

I believe the GP control system is working as designed. That system may have its weak points but for now I think it is fine.

Jim

 

[The Warden]

That's good to hear...I got about 2 years of good use out of my controller before it stuck on. Before it stuck on, it actually worked quite nicely.

Regarding the amp draw...the explanation they gave for the smaller wiring was that the circuit wasn't on long enough for the wire to get too hot. That said, I think the wires ARE a bit too small, which is why I'm custom-making a harness instead of just buying the stock 7.3l harness and saving myself the trouble. That said, I had the number wrong in the first post... I just double-checked, and it turns out the number was 12 amps per plug for a 6.9l system (and that number isn't necessarily set in concrete). Take a look at this and this thread...and if you get confused, don't worry...I did too; this is part of why my glow plug harness isn't wired yet. And, if it does make perfect sense to you, please let me know!!

 

[argve]

Jim,

Let's look at it this way... you have 8 resistors in parallel each resistor is 1~2 ohms cold each so by using the formula for resistance total you end up with 0.15Ω and you apply 12volts to the circuit to come up with 48~96amps... Do the math man do the math...

Now the resistors that are used in your application are "Positive Temp Coeffienct" devices meaning that as they start heating they will gain resistance (like any typical heater will) so that means when they are bone cold they are trying to pull the max amp draw but will dwindle off rather quickly. I know I tested a cold plug at 1.2Ω and tested the same plug when it was hot at 22Ω. I did this test on a bench with some pretty good test equipment so you can plug those numbers in the following formulas to prove or dissprove.

You will use ohms law which states I=V/R
then you will use the formula for reistance total in a parallel circuit which is

Rt = 1/[(1/R1)+(1/R2)+(1/R3)+(1/R4)+(1/R5)+(1/R6)+(1/R7)+(1/R8)] which basically says add up the inverse of the resistance.

So yes you will have sky high amp draw when you first turn the system on but within a second or less the amp draw will be down. Then you have to figure in the thing that only so much current can be crammed through a given size of wire so it will limit your total current draw. I doubt you will find a clamp on amp meter that can react fast enough to see the higher amp draw. I have a Fluke 336 which is one of the higher end ones and trust me it's not that quick even my 87III is not that quick with the add on clamp meter leads... I use my 87III to watch for voltage spikes at work when we have Frequency drives that are tripping out for no apparent reason but it's not that quick for amperage.

The key to making the glow plug system work on these IDI's is GOOD CLEAN CONNECTIONS I can't stress that enough.

Best bet is to check each and every plug for resistance. I know it's a pain but it's the only way to be sure. No you don't have to yank the plug to test it - just remove the connection from the plug then with your meter lead firmly clamped to ground somewhere (I always liked to wedge it in my neg bat post on my truck) then touch the terminal end of the glow plug it's self with the other lead. If the plug showed somewhere in the ball park of 1~2Ω I called it good and moved on. One or two bad glow plugs will cause hard starting so this is why it's a must to check each one.

 

[argve]

Or you can do the math this way....


Each plug sees 12volts and is 1~2Ω so with ohms law we come up with 12amps - correct? I=V/R

So then apply Kirchoff's current law which states that all current flowing in node has to flow out of the node. Which means that we have 8 resistors so we can take 12+12+12+12+12+12+12+12=96amps... or cut to the chase with 8*12=96

I'm not bashing ya - I'm just showing you that yes the system is trying to pull that many amps.

 

[160k87F250]

I was installing an ammeter, and somehow ran the glow plug system through it by mistake. When I turned the key on, the meter pegged -60amps, and it was not enough juice to properly heat the glow plugs. So 96 amps or so seems correct.
John

 

[jauguston]

Hello Again,

Dummy reporting in again!!

Seems I am decimal point challenged (-:

I went back and did my test again - 115 amps DUH.

Checked a few individually - 15-16 amps.

I think they are fine.

Jim

 

[Agnem]

Travis, you're sure not as stupid as you look!

 

[argve]

thanks...


hey wait a cotton picking minute

 

[DieselDon]

Ford indicated that the normal GP drew was about 16 amps cold ( 1 ohm or less ). As they heat up, the resistance increases, so the amperage drops to around 7 to 8 amps per GP or around 70 to 75 amps for the total GP system.

Temperature change is always a problem when trying to compute the current draw in a component when you base it on cold resistance.

One other tidbit. Ford changed the solid state GP relay resistor bar to increase GP max temperature. They installed a 3/8" hole in both ends close to the end of the resistor bar. This increased GP max temp by about 200 degrees, up to about 1800 F.

 

[The Warden]

Ford indicated that the normal GP drew was about 16 amps cold ( 1 ohm or less ). As they heat up, the resistance increases, so the amperage drops to around 7 to 8 amps per GP or around 70 to 75 amps for the total GP system.

Welcome aboard, Don!!
Are those resistance numbers for the spade-connector plugs or the bullet-connector plugs? Or are they the same?

Someone (can't remember if it was in this thread or in a different one) claimed that the two plugs have different resistance values...

Actually, if you have a few minutes, if you'd be willing to take a look at the two threads I linked to earlier in this thread and if you have any input, I would GREATLY appreciate it. I'd love to get my GP system wired up before Christmas, if time allows...

Thank you in advance!!

 

[jauguston]

I just noticed in the Chilton manual there is a GP schematic for the solid state 6.9 controller and it is noted on the power wire from the battery "127 amps". FWIW.

Jim

 

[DieselDon]

Spade type and bullet type GPs had same resistance. It varied a little from GP to GP but usually were 1 ohm or less cold.

Either go to a slow blow fuse or fusible link. I know, initially, the GP circuit draws more than 150 amps, but it is for a very short period of time. This may blow a normal fuse. Looking through a Ford EVTM, I ran across something it identifies as a "Fusible Link Cartridge". Looks sort of like a mega fuse, but works like a fisible link ( slow blow ). This might be the answer to you circuit protection needs.