No "glow" Glow Plugs

[JohnS]

Re: No \"glow\" Glow Plugs

Greg,

I have seen the 0.7ohm figure listed before, but I don't think that is a good glow plug. Anything less than an ohm will draw more amps than volts supplied. (I=E/R) that would be 17 amps per plug!

So, I pulled my stock of spare glow plugs (12). I took resistance readings from the block threads to the terminal threads, and made sure I had a good "bite" with the probes. On 11 of the 12, I read a little more than 2 ohms. One did read 0.77 ohms. All measured at room temp. Given the odds, I'd say this 0.77 is a "bad" glowplug. Also, 2 ohms make more sense for the current, ie 6 amps per plug.

Colder temps should decrease the resistance slightly, and increase the amount of initial current. As they heat-up, the resistance should increase, decreasing the current draw.

I think that I have this right. I even checked to make sure I remembered ohms law correctly! /forums/images/graemlins/blush.gif

PS: 0.7 ohm at the buss bar is correct, for three 2 ohm resistors in parrellel.

 

[greg_g]

Re: No \"glow\" Glow Plugs

I stand corrected John. I'm comm-elex by (ancient) training, and reflexively (mis)applied the Ohm's power variant. Unfortunately edit time has elapsed, making it impossible for me to correct the misleading number in the earlier post.

Strangely enough, the warm/clean plugs I bench-tested at 0.7 ohms worked fine when put back into the engine. Makes one wonder about the accuracy of the ammeter, and the value of the system fuse. Since the numbers "seemed" to compute, the meter didn't peg, and the fuse didn't blow - I had no reason to actually confirm the amperage draw with my multimeter.

//greg//

 

[JohnS]

Re: No \"glow\" Glow Plugs

I have never measured the ones in the tractor. They have worked from day 1, and the tractor ammeter is only good for very gross measurements. So as long as they are not all open or causing a fuse to blow, probably wouldn't notice. If a couple where gone, might notice hard starting.

If all three of your glow plugs were 0.7 ohms, I can't explain why your wires didn't melt /forums/images/graemlins/confused.gif but, if you had only one at 0.7 and the others were 2 ohms, thats about 20 amps, and probably not blow a fuse.

Anyway, this little ohms thing, shouldn't detract from the rest of the excellent debug help you provided.

Just a note for others: many low-cost multimeters will not read low ohm loads, like this, accuratly. I have seen some so bad, that you can watch the reading climb, as the meter battery is discharging. /forums/images/graemlins/blush.gif You also need to zero out, or subtract lead resistance.

 

[ToolManRick]

Re: No \"glow\" Glow Plugs

Man, lots of good input. Thanks guys.

Okay, pulled 2 of the 3 plugs for a visual and independent OHM check. Open or infiinity on all three plugs. Now that I think of it... when I was researching the purchase of my Jinma I recall reading the 30 amp, 12 ga. wire for the glow plugs in other threads. And I recall testing my "H" position when going through the initial inspection of my new Jinma. The ammeter registered around 15 amps. That reading didn't set off any alarms, but I'll bet to say that all three plugs never worked. Personally I like the turn-to-left start option. Why fire the glow plugs if not necessary? Just have to remember to set the switch to "run" for lights and recharging the battery.

On this next point I have to plead ignorance. I've never seen a diesel glow plug other than a little 2 cycle airplane engine type. It had a small glow wire. Does a Jinma glow plug have a glow wire? For the life of me I can't imagine what glows on the plugs I looked at. There did appear to be a small spot weld where a wire could have been attached, but no wire. Maybe something else glows?

At this time the switch is functioning correctly. However, I've decided that a small yellow indicator light connected into the glow plug circuit is a good idea and I'll add that tonight.

In the event that Northern Tool ignores me (I called them Friday and got the old answering machine) and they haven't called back... any suggestions on where I can purchase 3 glow plugs? Hopefuly they stand by the warranty and send me replacements.

 

[bluechip]

Re: No \"glow\" Glow Plugs

If you need the glow plugs we have them. I sent you a PM with price.

 

[JohnS]

Re: No \"glow\" Glow Plugs

The tip below the sealing washer is what does the job.

If all 3 are open, you should not get any current draw with the key in plug position, but since you did have current draw at one time, they worked initialy, or at least one did. With all 3 open, and with little or no use, like you described, I suspect that they were getting energized, while the tractor was running. Follow Gregs recommendations, but if you find nothing now, changinging to the Ford switch might be the best bet.

 

[ToolManRick]

Re: No \"glow\" Glow Plugs

I thinks I'll add an indicator light (very low wattage) on that circuit for easy monitoring just in case, as you mentioned, that the circuit is getting energized in the "run" position. I'll keep ya'll posted on results. Just thankful the weather has been warm and I store it indoors. Still, this winter I suspect I may need the glow plugs when the old temperature drops.

 

[Soundguy]

Re: No \"glow\" Glow Plugs

</font><font color="blue" class="small">( The glowplugs are connected in parrellel and when any glow plug burns out, the current is reduced and the voltage increases. The higher the voltage, the quicker the remaining glow plugs will burn out. In my V8 situation, once the 2nd or 3rd plug burns out, the remaining plugs are getting the full 12 volts and will burn out after a couple starts.
)</font>

Sounds iffy.. I'd like to see a schematic showing what you explain. If the glow plugs -are- parallel hookups, then there is no change of voltage or current on any of the plugs when anothe rone opens. The only way their could be is if the battery could not source the current for the combined load, and as the plugs burned out ( open ) then more current was available.. etc. Otherwise.. electrical devices in parallel each have access to the max power they can draw, without regaurd to other loads in the circuit. This assumes the wire feeding the glow plugs can handle the current of all attached devices at full load.

Soundguy

 

[Soundguy]

Re: No \"glow\" Glow Plugs

</font><font color="blue" class="small">( And the glow plugs are connected in series-parallel. I know that sounds contradictory, but consider that Yangdong typically gangs the glowplugs with a bussbar (jumper wire on the deuce). That means that all glow plugs are getting a nominal 12v when applied, but that the failure of one glow plug will not block the voltage to the rest. )</font>

What you've described is just plain -Parallel- electrical conection. It doesn't matter that the power bus bar physically daisy chains from one plug to the next in a series fashion. That is still just providing for common power hookup for individual circuites.. etc.. each plug is a seperate circuit.. just sharing the power bus..

On an electrical schematic.. each plug references bat positive, and common ground.

The rest of what you say would be correct.. any plug opening doe not effect the other plugs, as they each have their own connection at the buss bar. The only thing that would cause a problem, would be a short at a plug, which may melt one of those daisy chained buss bars, isolating one or more plugs that would otherwise work, if they had power.

I know it is a tad nit picky.. but for the electrical novices that have just taken basic ac and dc electronics.. the use of series and parallel in the above fashion may confuse some.

Soundguy

 

[ToolManRick]

Re: No \"glow\" Glow Plugs

All is well in Jinma Land.

NorTrac just called and is UPSing me 3 new ones. Said they have them in stock and they'll go out today. I'm still going to put that indicator light on the circuit and probably go down to my local tractor supply and get the Ford switch just in case. Thanks to all of you!