Wasn't having any problems until......

[HoveringHMMWV]

My 1097A2 is a solid truck and really doesn't have any issues other than normal maintenance. All systems operate normally and it always starts quickly no matter the outside temp. No issues until I read some SS threads about Wait Light / Starting Difficulties. It's almost like my HMMWV knew what I had been doing. Yesterday evening I tried cranking but only got a quick flash of the wait light. It barely cranked while spitting white smoke for a short sec or two. Today I tested the glow plugs and found 4 of the 8 were bad. So a new set has been ordered and already shipped (Thanks to Black Dog Customs!).
My question..... Can glow plugs fail in multiples or has this been an incipient problem that I have been missing as the severity increased?
Thank you in advance,
- HoveringHMMWV

 

[NDT]

When one fails, the remaining 7 see higher voltage as the system is not dragged down as much, which causes them to glow hotter, which causes another to fail, rinse and repeat.

 

[Milcommoguy]

When one fails, the remaining 7 see higher voltage as the system is not dragged down as much, which causes them to glow hotter, which causes another to fail, rinse and repeat.

Little confused with this concept. Could you explain?

No need for a blow dryer, CAMO

little hair here LOL

 

[Action]

Little confused with this concept. Could you explain?

No need for a blow dryer, CAMO

little hair here LOL

Kind of like wheel studs. If one of the studs holding the wheel halves together breaks, the load on each remaining stud increases. Then another stud may fail, increasing the load on remaining studs even more.
air pressure in tire vs electricity to glow plugs

 

[Mogman]

The question should be does the EESS have a clue if the glow plugs are actually good or not, it just closes a relay the time dependent on the temp reported by the glow plug temp sending unit, I doubt it is smart enough to actually know if any glow plugs are good or not.

 

[Milcommoguy]

OK riddle me this. OK... I got the string of 8 patio light. 110 volt wired in a parallel circuit. Each bulb same voltage same wattage. One burns out... maybe two overtime. Did the other six get more voltage or brighter? I don't remember the others getting brighter and burn out like a string of Chinese fire crackers.

This is going to be V E R Y interesting, CAMO

 

[Coug]

OK riddle me this. OK... I got the string of 8 patio light. 110 volt wired in a parallel circuit. Each bulb same voltage same wattage. One burns out... maybe two overtime. Did the other six get more voltage or brighter? I don't remembe the others getting brighter and burn out like a string of Chinese fire crackers.

This is going to be V E R Y interesting, CAMO

I was kind of thinking the same thing.
Only reason I could see for a glow plug to get more power when others fail is if there is a restriction/resistance in the wiring between the batteries and the glow plugs, in which case as the overall load decreases from failed plugs, that power is available for use by the others.

To go back to their air analogy, it would be more like trying to run multiple tools off of a single air line. If the line is properly sized, all tools will see the same amount of pressure. If the line is undersized, then as one tool stops, the amount of air volume flowing can now be distributed to the remaining ones.
However, at no point will the amount of air volume or pressure available exceed the supply amount.

Glow plugs are a resistor, designed to heat up as power flows through. If the glow plug is rated for say 24 volts 10 amps (just as an example), then it doesn't matter how many amps are available at the battery, each individual plug will still draw at most 10 amps of power. The amount of voltage they see might change though, as a heavy load on the battery will drop the amount of voltage, and any resistance in the wiring will also cause it to drop, but in the end the glow plug is designed for 24V (nominal, meaning 24-30V operating voltage) and whatever the amps, so that's all it can use.

 

[NDT]

OK riddle me this. OK... I got the string of 8 patio light. 110 volt wired in a parallel circuit. Each bulb same voltage same wattage. One burns out... maybe two overtime. Did the other six get more voltage or brighter? I don't remembe the others getting brighter and burn out like a string of Chinese fire crackers.

This is going to be V E R Y interesting, CAMO

Ok you are quite correct that the glow plugs are wired in parallel. But in the case of the patio lights, the line voltage stays constant with the grid. In the HMMWV, the battery voltage dips significantly with the nearly 80 amp draw of all 8 plugs (the voltmeter dip we see). When you start losing plugs, the voltage dip is less significant. Make any sense?

 

[Coug]

Ok you are quite correct that the glow plugs are wired in parallel. But in the case of the patio lights, the line voltage stays constant with the grid. In the HMMWV, the battery voltage dips significantly with the nearly 80 amp draw of all 8 plugs (the voltmeter dip we see). When you start losing plugs, the voltage dip is less significant. Make any sense?

So you're saying the glow plugs aren't actually designed to see full battery voltage when operating?

 

[NDT]

So you're saying the glow plugs aren't actually designed to see full battery voltage when operating?

Not saying that. I am saying that they get weak after time and susceptible to failing, which is exasperated by increased voltage when 1 or more are burned out.

 

[TechnoWeenie]

Not saying that. I am saying that they get weak after time and susceptible to failing, which is exasperated by increased voltage when 1 or more are burned out.

Umm... yeah.. no....not exactly.

Each of those plugs is designed to individually run at full rated voltage, and are self limiting, current-wise.

Unlike the CUCV, which uses a resistor bank to drop voltage to multiple plugs, HMMWVs use 24V GPs

The only thing is, if ONE plug fails, others are usually not that far behind, and people will attribute random crap to why the other ones failed.

You're talking about 80A draw, across 2 6TL batteries, for a max of 30 seconds, and the voltage shouldn't dip so low that they design the glow plug system around those lower voltages. Such a design, would also cause failures if the vehicle is jumped through the slave port, as it's seeing a full 28V+ and not the 24V+ from batteries without an alternator running.

 

[Milcommoguy]

NOPE ... and yes. That's why I say... KNOW your Humv voltmeter characteristics... static, discharging, glowing, charging. YEP, said that. 100 X's

Battery voltage fluctuation are common in the HumV. Many variables apply, poor batteries, connections, ohmic losses in the wires, loads place on the system etc.

Observing the voltage swings "on the voltmeter" is a sign of the LARGE current demand on the supply (batteries) and the variables above by glow plugs.

HumV battery is not a constant voltage supply (pressure) So pulling 100 amps (flow) the voltage is going down.

As stated glow plugs are a resistor... a VERY low value. To generate the required HEAT in this near short circuit of a glow plug requires LARGE current flows (electrons = heat) Hence the voltage drop.

Next part is TIME. Time is the killer. And like a light bulb (a controlled short too) you get so many on & off's and poof. The 2 or 3 volt swing is not the surge that takes out the plugs.

The primary killer is initial in rush current and then ON TIME. At a time there were plugs that had a PTC or Positive Temperature Coefficient. The idea was to self-regulate the heat by increasing resistance the hotter it got saving itself. Haven't seen them lately. Bigger $$ too.

Another killer is the design that went into the HumV "Quick Start System" Some engineer figured let's use the same plug / same resistance from the 12 volt system of a CUCV... change the connection from a blade to a bullet, and hit it with 24 volts and TRY to manage the ON time. Now that's going to shock the electron to get hot real fast. This product line there is no 12/24 volt plug same resistance. The Ballast resistor dropped the 24 CUCV system to 12.

The Nartron does have a "shunt" to measure / feedback for controlled "glow". If you have follow my post or rants... not fond of any "box""

Want to have some fun ?? Go to a on-line calculator for parallel resistors circuits. Plug in your 8 glow plug ohmic values, then the voltage. Hit calculate. then convert to Watts or ? And that's why one's diesel truck won't diesel... LOL

Does this let the air out? OK look at it this way. Welding more Amps = more heat. Voltage, AH not so much.

Pencil and paper in hand, CAMO

 

[TechnoWeenie]

The plugs are self-limiting. They won't draw more than X amps.... The internal resistance is usually 1-2 Ohms with a nominal resistance of 1.6 Ohms, per TM 9-2320-387-24-1

Using Ohms law... and the rated voltage of the wellman plugs (which I believe is 22v, not 24v, but we'll run with 24v)...

1.6 Ohm @ 24V gives us a theoretical maximum current of 15A, and, that's not only a theoretical maximum, but also doesn't take into account the fact that the plugs draw less current as they heat up.

So, worse case scenario, 15*8=120A... So, you're pulling 120A on a battery bank that's rated for a little over 100Ah, meaning you're discharging at ~C/10. That's a lot, but not really, considering the battery capacity, and the fact that, as mentioned, the plugs will draw less current as they heat up.

The voltage drop across the wire will determine the voltage at the plugs. Likewise, the AC60G commonly used to replace the welleman plugs in the CUCV are 10.5V plugs, even though they're commonly called 12V plugs, which is calculated with the wiring to include voltage drop. I believe the welleman are likewise rated at a lower voltage, but I don't have a data sheet so I can't say for sure, which is why I gave the theoretical max as 24V... But, as an example, lowering the voltage to 20V drops to 12.5A/plug max = 100A total.


Voltage too high = burn out
On too long = burn out
Excess cycling = burn out

 

[Milcommoguy]

Very GOOD write up's on the plug thing. In the CAMO lab I have done a bit of testing (20 years) as to my failed plugs CUCV's to HumV's.

TechnoWeenie Nailed it with this:
Voltage too high = burn out
On too long = burn out
Excess cycling = burn out

Not a lot of control over voltage. It's doesn't take long should a box fail. Every time they are energized "stressed"

Here's a video couple years back of a normal plug going to its death. https://www.steelsoldiers.com/threads/glow-plug-the-movie.186536/

For now... I'am putting a cork in it. Bigger fish to fry, CAMO

 

[M1123 Greg]

My 1097A2 is a solid truck and really doesn't have any issues other than normal maintenance. All systems operate normally and it always starts quickly no matter the outside temp. No issues until I read some SS threads about Wait Light / Starting Difficulties. It's almost like my HMMWV knew what I had been doing. Yesterday evening I tried cranking but only got a quick flash of the wait light. It barely cranked while spitting white smoke for a short sec or two. Today I tested the glow plugs and found 4 of the 8 were bad. So a new set has been ordered and already shipped (Thanks to Black Dog Customs!).
My question..... Can glow plugs fail in multiples or has this been an incipient problem that I have been missing as the severity increased?
Thank you in advance,
- HoveringHMMWV

I think the boys got a little off topic, definitely some great information there but the short answer to your question is yes. I smoked all 8 at once. Someone mentioned below that TIME is one of the big factors. If they stay on too long, poof! They are gone. I don’t think anyone can say for certain when your plugs started going or how many at a time. It’s a wear item and they probably dropped off one by one without you knowing, until the last one went. Then no start. IMO your humvee caught you reading about this and decided to show you what for, lol. Slap the new ones in and move on

 

[HoveringHMMWV]

I

I think the boys got a little off topic, definitely some great information there but the short answer to your question is yes. I smoked all 8 at once. Someone mentioned below that TIME is one of the big factors. If they stay on too long, poof! They are gone. I don’t think anyone can say for certain when your plugs started going or how many at a time. It’s a wear item and they probably dropped off one by one without you knowing, until the last one went. Then no start. IMO your humvee caught you reading about this and decided to show you what for, lol. Slap the new ones in and move on

While doing some reading on the problem, I came across a similar thread.

Electrical issues.... Voltage gauge in yellow and not green

So had my humvee for a few years now. Nothing ever gone wrong with it. Except for the smart box burning out the glow plugs recently. Bought an eess s3 box, and noticed that my old temp sensor was perma fried. So that prolly explained that. Anyways, I haven't been able to drive the truck for a...

www.steelsoldiers.com

In it, RWH stated in post #12, "For the boxes to work correctly they need the glow plugs in the circuit, not necessarily all of them, “like 4”." I'm surmising that 3 of my 8 had failed at some point. And when the 4th failed, the Wait light must have quit functioning correctly via the PCB. The system is functioning correctly now after swapping out all 8 glow plugs.
- HoveringHMMWV

 

[M1123 Greg]

I

While doing some reading on the problem, I came across a similar thread.

Electrical issues.... Voltage gauge in yellow and not green

So had my humvee for a few years now. Nothing ever gone wrong with it. Except for the smart box burning out the glow plugs recently. Bought an eess s3 box, and noticed that my old temp sensor was perma fried. So that prolly explained that. Anyways, I haven't been able to drive the truck for a...

www.steelsoldiers.com

In it, RWH stated in post #12, "For the boxes to work correctly they need the glow plugs in the circuit, not necessarily all of them, “like 4”." I'm surmising that 3 of my 8 had failed at some point. And when the 4th failed, the Wait light must have quit functioning correctly via the PCB. The system is functioning correctly now after swapping out all 8 glow plugs.
- HoveringHMMWV

Good to hear