Glow Plugs Voltage

[Gedeon Spilett]

one of these cheap RC power panel will show you immediately how much amp your set up requires...
so confortable !

https://www.google.fr/search?q=rc+p...VM4YUKHW4mA70Q_AUoAnoECB8QBA&biw=1366&bih=642

 

[mattb.351]

Motorman1946, the answer is stick the voltage at 1.5V and the current will fall where it may. It's been answered. Round about 3 amps or so I believe the answer was. It's in the third post because you missed it. People digressed after that answer because tornitore45 didn't specify in the original post that he has had some experience with transformers and power supplies. People assumed that he, or maybe others reading the thread, didn't consider the output impedance of whatever it was he was going to drive it with. Turns out he did. Ok great, but I'm not going to be rapped over the knuckles by you for posting relevant information.

 

[XD351]

Ok i had a play with a #4 OS plug - brand new never been near an engine and one problem became immediately apparent and that is the internal shunt inside a digital multimeter and the leads is of a sufficiently high resistance it effects the current flow through the plug so it won’t glow using a rechargeable ignitor that has a voltage of 1.27v with no load .
I hooked it up without the meter and it glowed nicely so i decided to do it another way , I hooked it up to my adjustable power supply and set the voltage to 1.27v but no dice - it would get hot but not glow so i cranked up the voltage to 1.4v and it glowed the same as when it was hooked up to the ignitor .
I’m guessing that because the voltage is so low any increase in resistance will severely effect the current flow . Anyhow with it glowing nicely the meter on my power supply read 3.8amps ( it is as accurate as any of my meters ) and it just started to glow at 3amps .
I did try to measure the resistance but the best any of my 3 meters could do was 0.3ohm but a dedicated low ohms meter would be better .
So on a #4 OS plug ( 2s) 3.8 amps works , just got to adjust the voltage to compensate for the voltage drop in the cables and anything else in series with the plug like meter shunts etc .

 

[petertha]

And that's about what my old school panel used to read back in the day: 2-4 amps depending on many variables. New plug vs old plug vs flooded plug vs heat rating vs cranking vs running.... I'm not sure what the actual delivery voltage was because the panels worked off a 12V battery & stepped down the voltage to the plug output. Yes, leads (resistance) do make a difference.

The OP wants to know a NiCd voltage/current combination. Unfortunately NiCd have been off the market for many years for environmental reasons. For all practical purposes lets say we are talking NiMh which are similar nominal voltage rating per cell. All cells have a set of discharge curves representing voltage (suppression) at different current loads. So using this as a generic picture, at any state of charge depletion (X-axis) go up to the corresponding amp load curve & read off the voltage Y-axis. The higher the current load, the lower the voltage or higher the suppression, same thing. The smaller the maH cell capacity, the more the curves spread apart. The older the pack (higher IR, chemical degradation) the steeper the curves. So even if you had a voltage/current level to 3 significant figures, it really isn't a good basis to design anything off.

 

[XD351]

Used much shorter and thicker leads and got a decent glow at 1.27v @ 3amps .

I’m not sure why the OP asked about current measurements on a 1/2 discharged NiCad but I’m sure he has his reasons .

Now what would be a juicy bit of science is if someone could work out the effect of AC vs DC in respect the life span and performance of the filament and if there is indeed some difference - which i bout there would be .

Anyhow that’s my 2cents worth - it kept me entertained for a few minutes anyways !

 

[Motorman1946]

mattb.351 - I missed it because post 3 quoted wikipedia rather than saying yep, I measured it and this is what I got! Which is what the OP asked, and only what he asked. All the rest of the comments/posts drowned out the answer. It seemed obvious to me from the long OP intro that he knew what he was doing and was just seeking some additional info before he got there himself. Wikipedia isn't always correct.

Not to worry tell your Mum, it really doesn't make any difference! Not rapping anyone over the knuckles, just making an observation, don't be so sensitive. Have a nice day now.

 

[stragenmitsuko]

This is from a book about a diy closed loop glow plug controller .
It uses the plug itself as a sensor . The temperature of the plug is related to the ohms resistance . So this little thingy
drives the glow plug with a constant current , then switches off for a millisec and measures the ohms resistance
of the glowing ( or not glowing ) plug . Then adjusts the current to achieve a preset level , measures again etc .

This had the adavantage of a plug that would glow alway's thesame regardless of battery voltage and engine conditions like wet start , cold start , winter , summer ....
Once I had this working my glow plugs destroyed number decreased dramaticly from at least a plug each day I would run the engine to maybe a plug a month .

Downside was that the unit needed to be adjusted for each plug .
Even same brand same type of plugs would have a slightly different resistance when glowing orange / red


The graph and table show the values for a fox std long 2V plug .
It goes from cold to glowing bright orange/red .

 

[tornitore45]

THANK you Motorman for adding some sanity.
You understood my question exactly and perhaps my frustration with some of the answers. Googling was not much help in this case but by distilling some of the answers and links info I did reach a few conclusions.
1) Forget the rated voltage, it means nothing because
2) All the modern (1.5V rated) plugs work well on NiCd which nevers delivers 1.5V except OTV for 5 seconds after disconnected by the charger.
3) Plugs can stand 1.5V but will glow ultra-bright and I think this is a Maximum Rating not to be run for extended time.
4) Since NiCd work well, the plugs must be designed for what a NiCd delivers. Namely: 1.4V to 1.1V . NiCd can be discharge to 1V but probably that is too low for the plug.
5) The current is pretty variable due to the heat range and the fact that the battery does change during discharge. However this pose no problem, a well designed circuit controls the voltage and is capable to source whatever current one expects the mos power hungry plug demands. I guess 5A capability would suffice.

My application:
My engine does not fly.
I built it for fun, will run it until broken-in and then spend its life on a shelf.
Since I like to run it fast and as slow as it can, the ability to keep the plug ON, possibly at reduce voltage is built into the feed circuit Will see how that works.
I opted for AC because I did not want to deal with a battery, its charger and associated shelf life trickle charge issue.

Multi-Cylinder glow need an harness for practical reasons. The easiest way is to run all plugs in parallel as one but the currents add up fast.
If I were flying I would use a buck converter from a 12V battery.
The battery would be kept charged by the Car Battery (Cigarette Lighter if you still have it) a diode+R will prevent back-flush and limit the current to safe level. The battery will be topped off on the drive to the field.

 

[74Sprint]

Ok lets go by the original post and dissect it.

I am done machining my Edward 5 and started the construction of the display base.
The base includes the fuel and gas tanks, a drawer for all the special keys, extractor a whatnot that goes with the engine and the powering and monitor system for the 5 glow plugs.

Ok 5 glow plugs and monitoring each plug, lots of options here.

I plan to heat the plugs with AC. A 24VA transformer rewound with 5 secondaries for about 1.5V each.
I want to sense each plug because if one goes bad I have no indication other than possibly rough running of failure to start. I have to disconnect them all and use my ohm-meter to find the bad plug.

Normally when someone says they are going to use a 24VA transformer it is assumed they are going to use a transformer that is normally used for things like doorbells, 110/220 in, 24 volts 1 amp out for a rating of 24 watts or 24VA. Since glow plugs are normally rated at 1.5 volts (standard) and the current consumption is tied to the applied volts and the resistance of the platinum wire one just needs to ensure not too overheat the glow wire. He also stated that he is going to use AC not DC voltage to heat the plugs which is ok but, 1.5 volts AC is too low. One must include the PFC (power factor correction) to do this properly. He also wants to monitor each plug to see if it is open or closed or maybe even dieing. I have to assume it is for opens because a standard multimeter is not sensitive enough to show minor deviations in resistance. One must use something like a Kelvin (4-wire) resistance meter. In retrospect since the OP has years of experience making 500 transformers then he would know that the best setup for 1 primary and 5 secondaries would be to wind a toroidal transformer (better cooling and easier to wind) and not to use a doorbell transformer (assumption). Using a switching power supply would be the best but, it is also the most expensive. As for monitoring each plug, now that would/could be anything from cheap to expensive, he needs to elaborate more.

I could use only one secondary but it will be too too thick a wire to bend sharply on the bobbin and would require a 5 floating shunts on the plugs tips side.
With 5 secondaries all the shunt can be grounded and the secondaries are smaller gauges.


But all this is not the reason of this post, just background for the real question.

Ok your opinion but, one still needs to match the secondaries to the current draw of each plug, regardless if one ties the grounds together. Whats wrong with running 1 heavy gauge ground wire to the motor?

First a bit of history
those of us old enough will remember that Glow Plugs use to be 2V, back then the only battery available was Lead-Acid. A single cell charges at around 2.3V, as soon as disconnected from the charger they fall to 2V and stay there until discharged to 1.8V. End of story.
Then came those wonderful NiCd, the high discharge rate made it possible to use a small capacity cell that could be coupled to the plug connector and the plug igniter stick was born.
I suppose, but have no direct knowledge that the old 2V plug would work enough on a freshly charged NiCd cell.
Everybody called the NiCd cell a 1.5V cell and the 1.5 Glow plug was born.

NiCd/NiMh are rated at 1.2 volts, not 1.5, they safely charge at 1.5 volts. I used to use the old dry cell battery that was 1.5 volts. Glow plugs as far as I know since 1974 (when I got into glow engines) they have always been rated at 1.5 volts. I used the old dry cell battery that was 1.5 volts and that's where it came from. I use NiCds even now (personally and commercially), there are tons of them out there and they are still the best rechargeable batteries for cold climates, below freezing, and still safer than Lithium.

Really?

A NiCd cell is charged until it reaches 1.5V. When connected to the load it quickly drops to 1.4V
Depending on the discharge rate I/Capacity and temperature it can be discharged down to 1-1.1 V
During a slow discharge the cell voltage is averaging 1.35V on a brisk discharge we may say the average voltage is about 1.2V.

Mostly correct

Calling NiCd cell a 1.5V cell is just marketing talk, technically speaking convey zero information.

I don't know of any manufacturer that rates NiCd/NiMh at 1.5 volts, they are always rated at 1.2 volts.

Now to the question: Has any one ACTUALLY measured the voltage and current on a properly working, capable to start the engine, plug powered by a middle of the charge stick or single cell NiCd?

This makes no sense at all, because nobody uses glow plugs from the 60s and plugs are rated for different heat/watts and sometimes voltage. The compression and nitro content usually dictate the plug heat type. Besides this info is easily found on the internet. I suggest contacting the manufacturer of the glow plug you want to use and get their recommendations, same as I did with Fox.

All the other data is just guessing.

You got that right, I'd say most of it.

There are 2 websites that have tons of valuable information available:
https://www.rcgroups.com/
https://www.rcuniverse.com/

 

[Motorman1946]

The OP gave a lot of info before the question, that basically just said where he was coming from. Nothing more. It wasn't an invite for comment.

The solitary question at the end was what needed, and gave an invite to give, a comment, or answer, on and thats what most seemed not to have done. So yes, one could understand the frustration.

Just saying, before anyone gets all upset.

Like in an exam, you only get points if you answer the question! That's why in an exam they tell you to read the question before you answer, but it's the same everywhere.

Now lets all move on, tomitore45 has his answer, life's too short...................

 

[mattb.351]

Not to worry tell your Mum, it really doesn't make any difference! Not rapping anyone over the knuckles, just making an observation, don't be so sensitive. Have a nice day now.

Haha, and I'm the sensitive one.

Output impedance of the source matters and it was unclear from the original post as to what it would end up being. True, that's not what OP asked, but are we allowed to probe a little to find out what he's actually trying to achieve, or should we all just stick to answering the exact questions that people post? That is way too restrictive and would lead to a boring forum. The OP's whole topic is very interesting and by its very nature invites people to chime in. Other people have questions or ideas that they want to share. I can understand the frustration if posts go too far off topic but it seemed OK to me.

 

[petertha]

Unfortunately NiCd have been off the market for many years for environmental reasons. For all practical purposes lets say we are talking NiMh which are similar nominal voltage rating per cell....

Quoting myself. I stand corrected. NiCd's are indeed still commercially available. I was naively extrapolating regulatory changes proposed more than a decade ago. But adoption looks to be in & out of vogue, varies by country & degree. Probably one common agreement point is cell taxation LOL!

https://en.wikipedia.org/wiki/Nickel–cadmium_battery

Ni–Cd batteries contain between 6% (for industrial batteries) and 18% (for commercial batteries) cadmium, which is a toxic heavy metal and therefore requires special care during battery disposal. In the United States, part of the battery price is a fee for its proper disposal at the end of its service lifetime. Under the so-called "batteries directive" (2006/66/EC), the sale of consumer Ni–Cd batteries has now been banned within the European Union except for medical use; alarm systems; emergency lighting; and portable power tools. This last category has been banned effective 2016.[12] Under the same EU directive, used industrial Ni–Cd batteries must be collected by their producers in order to be recycled in dedicated facilities.​

Good luck with whatever you decide. Hope to see some more machining pictures. I'm going to be facing this same issue for my 5 cylinders soon.

 

[tornitore45]

Stramgemitsuko
Back when I was flying U control I had exactly the same idea, but never implemented it.
Close the loop overt the temperature. Like any hot filament the resistance is non linear.
Stop the current
Inject a small current just enough to measure the voltage. 0.5A on a o.5 ohm plug should give a measurable voltage of 0.25V
The loop should use that voltage as the sensing V
Limit the initial current to avoid blasting the plug at start up, because the loop is slow to respond.

 

[tornitore45]

74sprint wrote

Normally when someone says they are going to use a 24VA transformer it is assumed they are going to use a transformer that is normally used for things like doorbells, 110/220 in, 24 volts 1 amp out for a rating of 24 watts or 24VA.

Why assume? I wrote a 24VA transformer REWOUND for 1.5V
Whether the original secondary was 24V, 37.25V or 0.12V makes no difference
24VA at 1.5V gives 16A
I need max 4x5 20A for 10 seconds, enough to start the engine.
I did not relish to wind a 120V primary so a 6 buck transformer was the answer.

I have to assume it is for opens

Again you assume too much, just read the post
If you really like to assume you can assume that "goes bad" means it opens since is the most probable failure mode of a tiny filament at around 900*C

I want to sense each plug because if one goes bad I have no indication other than possibly rough running of failure to start. I have to disconnect them all and use my ohm-meter to find the bad plug.

then he would know that the best setup for 1 primary and 5 secondaries would be to wind a toroidal transformer (better cooling and easier to wind)

I do not want the best, I want the most practical. If you have ever wound a 120V primary on a small thoroid without "the machine" you would know it is impractical.

It this point I stop because you have shown to have no reading comprehension and a lot of fluff pseudo knowledge that may impress a potential date at a party but no real engineering experience.

 

[tornitore45]

Mattb.351 wrote

Output impedance of the source matters and it was unclear from the original post as to what it would end up being. True, that's not what OP asked, but are we allowed to probe a little to find out what he's actually trying to achieve,

I did give some background information. I believe knowing what the idea behind a question helps.
I do not profess to always be clear but I try and anyway I welcome questions. I do not mind people adding stuff I already know, they are trying to be helpful. What I mind, I am not directing this comment to you, is people that have only foggy notions of electronics trying to correct a guy that was paid to design stuff that worked and sold, for 50 years.

 

[tornitore45]

For those that I may have offended.
Believe or not I have worked in electronic for 0ver 50 years and designed a variety of system. From what I got paid I think my knowledge was appreciated.
I hate to brag but is necessary.
I also have taught in formal class and mentored budding talent on the job.
I love to teach, but this is not the place. However teaching is impossible when the fellow that is suppose to learn THINKS he know better that the teacher.

To those that helped, you know who you are. THANK YOU this is the spirit of the board.

I got my answer, go ahead and comment but you wont hear from me on this subject.

 

[XD351]

I was hoping you would return with a future update showing the finished unit and maybe some pictures of the build - it may help someone in the future including myself .
I have seen first hand the effect of a dying glow plug and what it does to the performance of an engine . This has made me think how can you test for this without the suck it and see approach of running it in an engine ? Some experimentation is needed but I’m thinking along the lines of using radio frequency and measuring for frequency drift due to either resistance or impedence changes in the coil .
You would of course have to get a baseline for every plug when new and ATM I’m not sure any of this would really work - it is just an idea !

 

[tornitore45]

I said I wont add to this post mainly fro the temperature of responses (not the plug).
However I respond to XD351 sensible comment.

I do not usually take pictures in the shop. Oily hand, always trying to go to the next phase of the work. I will take pictures when is finished. Installed inside the display base that include the tanks, the pot to adjust the plugs, and the 5 LED showing the plugs have current.
The circuit does not distinguish between a degraded plug and a good one.

Post #27 goes a long way to answer your desire to sense a degraded plug.
The circuit proposed maintains a fixed temperature on a new plug once the hot resistance is determined in some way.
Accurate measure of hot resistance, engine running, has its own challenge but can be done in a home shop.
Let's say the plug has one shorted turn.
The resistance is lower
The circuit loop "thinks" the plug is cold and raise the current.
Most likely the remaining turns will melt, open plug easy to detect.
Let's say the plug is old, the filament has evaporated and thinned down.
I do not know that affect the engine. Feed by a constant voltage this plug will take less current but a thinner filament may still be hot enough with less current. Dunno.
The loop sees the higher resistance and "think" the plug is too hot, it reduces the current. If that plug was bad enough to bother a little it will be worst at reduced current.

The proposed circuit works well on a good plug and react to a bad plug by exacerbating the current change into a bad plug.
I think that monitoring the current gives some insight in what is going on.
All this is just an exercise to examine what may be going on, I do not know since the circuit was never built.

Building such a circuit in a home shop will present some challenges for a multi cylinders.
Each channel must have its own sensor and loop.
Multiple current sensor must be floating because all plugs already have a common point connected to a single DC source.

V meter and Amp meter should select the plug to monitor because no body wants to deal with multiple pairs of meter.

When you say "using RF" I suppose you mean to superimpose a small RF perturbation on the DC feed. Is a good idea to avoid dealing with floating shunts and DiffAmps, offsets and Low V signals. I would use different frequency for each channel to avoid interference.

 

[bobden72]

This whole thread has got out of hand and really BORING people trying to out do each other. Think I will unsubscribe for a while and let it all blow over children.

 

[Motorman1946]

Quite agree bobden72 - I think tomitore45 felt that way too which is why he said he was bailing out................... Some people eh?!