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Glow-plug coil inductance-could it matter? Babe_b10
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Glow-plug coil inductance-could it matter?

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Glow-plug coil inductance-could it matter? Empty Glow-plug coil inductance-could it matter?

Post  roddie on Tue Jan 08, 2019 8:06 pm

This is me being me.. Laughing and I may be wasting time.. but one of my duties (at work) is to wind inductor-coils for the "crossovers" which get installed in the speaker-cabinets that we manufacture. Depending on the design-frequency, a coil of copper-wire is wound (x-amount of turns) around a bobbin.. to be later soldered into a circuit on a PCB. Each wound-coil is checked with a multi-meter capable of taking inductance-readings which are in the mH (Millihenry) scale.

I won't pretend to understand it.. because I'm not an electrical engineer.. but was wondering if inductance (or inductance-measurements..) might be an indicator of glow-plug element-condition?

OTOH.... would taking "resistance-measurements" be an indicator?

It would certainly be advantageous to be able to test the condition of a glow-plug/head (beyond general continuity..) "if" a test could actually grade the condition of the coil-element on a given scale. Maybe a plugs' rated "temperature" could be determined.. if unknown?

Your thoughts? Huh...



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Post  Jason_WI on Tue Jan 08, 2019 8:53 pm

The number of windings is pretty low and the diameter being small it would be nano or pico Henry’s. To accurately measure this low inductance you need a very expensive LCR meter. Like $30k to $100k expensive. We have one at work that cost $32k. DMM inductance measurements are not very accurate. A small coil would need a megahertz test signal and usually 4 wire measurement to eliminate any parasitic inductance. These test leads or test heads can be several thousand dollars alone.

Inductors are usually made out of copper solid core magnet wire or woven litz wire that is varnish or polymer coated to keep the air gap between coils very tight. Any shorts between coils would affect the measurement.

At DC an inductor is basically a short.

An inductor is the most difficult component to accurately measure.
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Post  pkrankow on Tue Jan 08, 2019 8:58 pm

In a DC system inductance is moot. If it is present it will only slightly delay startup, in this case heating.

Phil
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Post  roddie on Tue Jan 08, 2019 9:30 pm

Very interesting! Thanks for your thoughts. I was going to bring some "known to be new" glow plugs to work to see if there was any variance in their inductance.. or their resistance. I don't really know how I would apply any differences noted.. but it would still be interesting if there were a wide-range of variance.
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Post  Cribbs74 on Tue Jan 08, 2019 10:56 pm

In this case resistance would be a better indicator on glowplug operability. And like Jason mentioned the inductance would be super low.

It’s a no go or go thing. If it tests good than you can run it and see if it stays lit. A glowhead is a simple device and pretty easy to troubleshoot if not working correctly.
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Post  GallopingGhostler on Tue Jan 08, 2019 11:00 pm

Wasn't it platinum or other rare earth metal (iridium, etc.) coating on the nichrome wire heating element responsible for catalytic glow ignition with methanol? I had plugs that checked out electrically OK, but somehow otherwise degraded. An E-Bay buy, a card full of old Swanson red hot standard long plugs worked beautifully out of their bubble pack. Then a week later, were duds, engine sputtered but wouldn't run. Pulled out a new one from the package, had good flights. Then next week, same deal.

Yet, I had an old Enya #30 standard long plug that came with a 1965 Enya .09-III TV, which worked week after week. Been a long time since those plugs were available.

Wouldn't you say there is more to the chemistry / electrical physics to the heating element, than inductance in the nano-Farad range or simple resistivity of the wire?
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Post  coxaddict on Wed Jan 09, 2019 3:37 am

Maybe someone could give us some history on the invention of the glow plug used for model airplane engines. I would be very interested.
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Post  ticomareado on Wed Jan 09, 2019 9:29 am

I believe a couple of things may be going on with glow plugs:

Some key people who knew how to manufacture good ones have departed this earth and there's some "skimming" going on in the precious metals departments of the remaining manufacturers.
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Post  Marleysky on Wed Jan 09, 2019 7:19 pm

coxaddict wrote:Maybe someone could give us some history on the invention of the glow plug used for model airplane engines. I would be very interested.

Here is the nickel tour:

Glow plugs in model engines differ from those in full-size diesel engines. Full-size engines only use the glow plug for starting. Model engines use a glow plug as an integral part of the ignition system because of the catalytic effect of the platinum wire, on the methanol-base fuel they are designed to run on.
Glowplug - Wikipedia
Wikipedia › wiki › Glowplug
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Post  ticomareado on Wed Jan 09, 2019 7:25 pm

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Post  ticomareado on Wed Jan 09, 2019 7:30 pm

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Post  Cribbs74 on Wed Jan 09, 2019 8:38 pm

ticomareado wrote:I believe a couple of things may be going on with glow plugs:

Some key people who knew how to manufacture good ones have departed this earth and there's some "skimming" going on in the precious metals departments of the remaining manufacturers.

I am willing to bet this is what’s happening, but I bet it’s always been happening. This is the world we live in.
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Post  coxaddict on Wed Jan 09, 2019 8:38 pm

Wow! Thanks for all the info! Very Happy Smile
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Post  pkrankow on Wed Jan 09, 2019 9:07 pm

Another $0.02

Patinum was used inside the combustion chamber of the engine the Wright Brothers built.  The points were platinum tipped and inside the combustion chamber.

http://www.wright-brothers.org/Information_Desk/Just_the_Facts/Engines_&_Props/1903_Engine.htm

A pretty unique engine in so many ways.
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Post  Cribbs74 on Wed Jan 09, 2019 10:40 pm

Amd they built it with a drill press and a lathe. No computers or difficult math. Over a workbench. Just a little bit of know how and a little bit of luck.

Huffman Prairie is located on Wright-Patterson AFB. 7yrs I drove by the by their site on the way to work. Only stopped and looked a couple times. Birthplace of aviation.
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Post  balogh on Thu Jan 10, 2019 1:18 am

In a thread here we discussed earlier that even if the glow head tests electrically good it may be subject to ageing and in addition, some deposits from stale fuel components may also diminish the glow.

I have a couple of overused COX heads that still test electrically good but hardly glow even if I turn the Hobbyco starter panel knob to max. The filaments in these heads typically show a grey-ish deposit sitting on them. I am not sure if it was the castor that some folks here said was to be blamed, or other, highly hygroscopic components of the fuel that tend to absorb humidity form air if left in an open bottle too long?
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Post  GallopingGhostler on Thu Jan 10, 2019 8:35 am

balogh wrote:I have a couple of overused COX heads that still test electrically good but hardly glow even if I turn the Hobbyco starter panel knob to max. The filaments in these heads typically show a grey-ish deposit sitting on them. I am not sure if it was the castor that some folks here said was to be blamed, or other, highly hygroscopic components of the fuel that tend to absorb humidity form air if left in an open bottle too long?

I've observed the same thing with my Cox glow heads after many engine runs. I never put a magnifying glass to it. If I did, might be closer to the truth. I gathered that the nichrome wire material after many heat cycles, was finally breaking down. It did not have the wholesome appearance of a new one, it looks very frail, fragile, easy to break. Sometimes the coil would shrink back towards the top post in the head.

I only used the long gone "bell battery", a very large round single cell 1.5V zinc carbon battery about 10 inches high and 3 inches in diameter.

Glow-plug coil inductance-could it matter? No6-1d10

Yet once they got to that state, they'd blow, the element would break, no longer have conductivity. Back then over 30 years ago, glow heads weren't that expensive, I'd just buy another to replace.

Perhaps it was a breakdown of the heating element from extreme thermal activity?
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Post  Ken Cook on Thu Jan 10, 2019 6:45 pm

George those cells were reintroduced a few years back. Now with updated technology the old EN6 cell is known as the EBR40 or HO6 cell. They're about $20.
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Post  GallopingGhostler on Thu Jan 10, 2019 7:55 pm

Ken Cook wrote:George those cells were reintroduced a few years back. Now with updated technology the old EN6 cell is known as the EBR40 or HO6 cell. They're about $20.
Ken, at that cost is a good reason why I wouldn't buy it. Back 30 - 50 years ago, they were readily available everywhere, would last me a good season or two. They had the same Rayovac styled battery at Hobby Shack in Fountain Valley back in the early 1980's. Nowadays even the rechargeable glow igniters with a charger are cheaper.

When I worked at Bekesey Lab at the University of Hawaii as a paid student worker in the mid 1970's, we'd pull the soldered in "D" sized Duracells from their ocean bottom seismometers and throw them away then solder in new. (Batteries would power these instruments, about a dozen and a half were soldered into a battery pack.

Since we were throwing them away, I asked the boss if I could salvage some, which he allowed me. I took the best of the throw aways and take them home. There, I made my own battery pack with about 8 cells soldered in parallel. That battery pack was my ignition source for my glow engines on my RC planes I flew while at the U.

A couple years ago I made my own glow ignition battery with a 4 D-cell battery case from Radio Shack that I modified for mounting cells in parallel. Used that set up a couple seasons, but the cheap plastic broke easily. Now I have a power panel.
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