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Glow Plug Igniter with CONSTANT CURRENT --Oz-- Babe_b10
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Post  --Oz-- on Fri Oct 25, 2019 2:17 am

I read the other Glow Plug Igniter thread(s) and with my experience, I don't see a elegant/or correct/and simple solution to the problem igniting a glow plug CONSISTENTLY with multiple conditions the average pilot faces during starting of the glow motor.

A quick briefing nomenclature:
C.V.=Constant Voltage
C.C.=Constant Current

Using a completely unregulated battery at 1.5V output is crazy IMO (like a caveman in 18th century). Yes, it works when "everything" is in order (as a minimum, the current flow enough to light the mixture, but the plug maybe failed (open/short) or flooded or no fuel). A glow plug is simply a nichrome wire that heats up relative to it's current flow, and not to its voltage, this is why a C.C. circuit is more important than a unregulated voltage used by majority of the nitro pilots.

To glow the plug: battery/connector/wires/connector/plug will give various results. Why, because the low 1.5 volts output and sorta high current (couple amps) will give random voltage drops at each component in the path (different Ωs for each) and ultimately give a different current to the plug. Remember, current (not voltage) = heat.

So instead of using old school (1960's) unregulated battery voltage with varying glow plug output, (sure, a new plug, new battery, and good connector will work great). But when everything is used, you have multiple voltage drops (battery output, leads IR drops, connector IR drops), leading to random (to possible low) currents (and wattage) in the plug and starting issues.

My thinking is use a simple CV/CC dc-dc adapter with adjustable voltage and adjustable current. So simply set the voltage to say 2.0V and leave it and then limit the current to what the plug needs (E.G: 1.0 to 2.0A), if there is multiple voltage drops (battery/wire/plug-connector), they are all bypassed and the plug receives the correct current and motor starts easily.

I just need to do some simple testing, then tweak the electronics to make a decent adjustable current range (not to high or low adjustment range). I have several dc-dc cv/cc adapters that I can use to test with.

What's the highest/lowest current pilots have seen for their plug current? tia

With a integration of a V/A meter (couple bucks) and (tuned) pot (dialed in so the range is current appropriate for the plug(s) that's is used, for a high and low current range), the current could be easily dialed for each users needs, win/win, thoughts?  

https://www.banggood.com/DC-DC-CC-CV-Buck-Converter-Board-Step-Down-Power-Supply-Module-7-32V-to-0_8-28V-12A-p-1245047.html?rmmds=myaccout-bottom-alsolike__1&cur_warehouse=CN
No you dont need 12A, but that is adjustable. I am expecting around 1~3A, so something higher will work.
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EDIT: 11-6-2019  With my little testing, CC "only" is not the best way, a combination of CV/CC should work well.
---------------------------------------------------------------------------------------------------------------------------------------
11-20-2019
Testing summary of different modes:

CC Only Pros: (in other words, the glow plug is constantly in CC mode)
1. Removes all IR Losses (voltage loss across resistance causing lower plug temp), at battery connectors, wire losses and, clip on connector losses, this is its number one benefit.
2. Short circuit protection, if the clip on plug connector (or anywhere else) shorts accidently, the CC handles this issue without any issue (burning wires, arcing, melting, etc).
3. Can use any power source voltage (within dc-dc specs).

CC Only Cons:
1. CC does work well until the glow plug is flooded, it will take longer to clear if using only using CC control. Because the now colder plug has less resistance and therefore less voltage drop, even though the current stays the same, this totals up in lower power in the plug to clear the flooded plug. It still will clear the plug, but takes more time. My original thought was lasers and led's, the output is about current driven, but I was wrong with the PTC properties of the glow plug.

CV Pros:
1. A big step up over unregulated battery voltage setup, battery voltage does not matter in CV setup as output voltage is regulated, only IR drops can give inconsistencies.
Unlike a unregulated battery voltage that changes with its SOC (state of charge level), the output voltage will stay constant, this is significantly better than unregulated battery voltage. If you have good good setup (power supply connections, wire condition and clip on connector), this works well, maybe not as good in all conditions as the 10X the cost RCATS system provides.
There is a window the plug will run at (say for example 1.3V to 1.4V), but if you set the CV voltage to the higher side of this window, this clears the plug faster in a flood condition.
2. Can use any power source voltage (within dc-dc specs).

CV Cons:
1. Any IR losses in connectors/wire will lower plug voltage and temp. This can be offset a lot with remote 4 wire sensing at the plug connector.

Unregulated V Pros:
1. Very low cost, when everything is good, it works, but clearing floods will take the longest.

Unregulated V Cons:
1. As battery voltage drops, so does plug temp and also clearing a flood is much more time.

CV/CC Pros:
1. Not having to take out a second mortgage to light your plug. Smile Can be assembled for under $12~$20 depending on the plug clip you buy, ($4 for two 18650 2600mAH cells, $4 dc-dc CV/CC buck converter, and plug clip with wires, add a $1 more for USB Li-Ion charger board, and a couple more bucks for a V/A meter if wanted), for me it was $4 as I have batteries and plug clips.
2. Short circuit protection.
3. Can use any power source voltage (within dc-dc specs).
Unlike a unregulated battery voltage that changes with its SOC (state of charge level), The output voltage will stay constant, this is significantly better than unregulated battery voltage. This can be offset a lot with remote 4 wire sensing at the plug connector.

CV/CC Cons:
1. Have to assemble (about 4 wires) and set the two pots for CV and CC settings (pretty easy), takes time (10 minutes), but time is free in hobby. Smile
2. Any IR losses in connectors/wire will lower plug voltage and temp. This can be offset a lot with remote 4 wire sensing at the plug connector.

CR: there is a few possible ways to implement this function, couple of them are:
1. Simplest is a 4 wire (remote sense) at the plug clip connector (either 4 contacts at the connector (best, true 4 wire) or at least 4 wire sense at the plug connector) and use CV (I can see the comments coming, lol).
2. Another way is a arduino nano processor ($2) with current sense resistor and PWM drive, with the analog input, you could sense the plugs voltage (yes, this is equal to its resistance) when the PWM drive current is in the off state (with small bleeder resistor). With this, you could add extra features like, automatic turn off, 5 second delay, slow ramp up (I think are not beneficial). I would head down this route if I wasn't busy with other projects.
3. PWM drive with voltage feedback and analog control, such as the famous 555 timer and a lot of analog tweaking might be fun.

I am sure this list is not complete but it's a good start (more testing needed at the limits). Probably could use a proof read or two. Very Happy

It was mentioned, "Pylon, Team Race, Speed, Combat competitors use RCATS".
It makes sense, in competition, racers are willing to way overpay to get an advantage, even if its very slight or even a placebo, EG: instead of a sport $60 esc, would pay $250 (only difference was the FET's and could not tell the difference on the track). In big races like nationals and worlds, I would guess they use a new plug every qualifying and race run, club races probably not so much. Paying 10X is probably not even thought about in competition at that level.

It would be nice to see the RCATS preformance side by side with a properly set up CV/CC setup, anyone in SoCal area? Smile
Even a 15 second video of it clearing a 1 drop flood (hot, then 1 drop, then watch it clear the flood and back to hot). This is the only advantage I see the RCATS should have an advantage over CV/CC setup (as I dont care about auto turn off or 5 second delay features).

PS: I would like to change the thread name, but seems this forum does not allow that.


Last edited by --Oz-- on Wed Nov 20, 2019 10:53 pm; edited 7 times in total (Reason for editing : Added picture/link to dc-dc, also edit so link works/add summary)
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Post  Sunbird on Fri Oct 25, 2019 3:00 am

I agree with OZ. When bench running any glow plug engines I use this 1 to 24 volt AC - DC power supply. Cheap and easy to use. I soldered plugs on the supply lead to clip various plug adapters for different glow heads. I can adjust the voltage to get a nice red glow every time with different plugs and heads of differing voltage requirements. Hot and cold plugs etc. Works well for me when running engines at home. I got sick of "D" cells not quite giving enough glow!

https://www.ebay.com.au/itm/153508454256
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Post  --Oz-- on Fri Oct 25, 2019 3:14 am

Thanks Sunbird!
With my solution, a simple 1s to to 7S battery ((3 to 32V) LiPo/Li_ion/NiMH/NiCD could be used).


Last edited by --Oz-- on Fri Oct 25, 2019 3:16 am; edited 1 time in total
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Post  Sunbird on Fri Oct 25, 2019 3:17 am

OZ, can you show us an example of a simple CV/CC dc-dc adapter? Thanks.
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Post  1/2A Nut on Fri Oct 25, 2019 4:31 am

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Post  Oldenginerod on Fri Oct 25, 2019 5:01 am

1/2A Nut wrote:Has anyone ever tried one of these?

Output Voltage: 1.5V
Amperage: 40,000 mAh
Chemistry: Carbon Zinc

https://www.ebay.com/itm/Exell-Battery-EBR40-Type-R40-1-5V-Battery-EN6-HO40-906AC-Ignitor-USA-SHIP/232939971992?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

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I've used similar. (Local variety).  Surprised that they are still carbon zinc.  While they work really well when fresh, I found the ones I used started to leak and swell within a few months.  I thought they'd have alkaline cells inside, but was still a single cell carbon job. All I use now is two D cell alkalines soldered together & taped up.  (Couple of bucks). Current ones have lasted me over a year.
If you really need to adjust current, then there's plenty of these power panels available out there.
Glow Plug Igniter with CONSTANT CURRENT --Oz-- Pl267110
Not too expensive, current control, usually with other features like fuel pump switch, starter connections and charger.  Unlike the one Sunbird mentioned, this works off a 12 volt supply for field use, not mains voltage.  Pretty much does all you need.
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Post  Surfer_kris on Fri Oct 25, 2019 6:02 am

What you ideally want to have is a glow driver with a resistance detection. The resistance of the glow wire increases with the temperature, so the best drivers are actually measuring the resistance and driving the plug up to a certain desired temperature. Then if the plug gets wet with fuel it doesn't matter, the driver will simply drive it harder up to the desired temperature.

There are schematics of this available on the web, no need to re-invent the wheel here... Shh
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Post  1/2A Nut on Fri Oct 25, 2019 6:45 am

Today I use these have a few of them on tap.
One with a clamp on type for the plug the other deep reach for larger engines.

Has a indicator light so you know if the plug is glowing / no guessing.
Adjustable for flat coils, standards and Nelson plugs. I do a visual on
the glow quality and make a hash mark for each type plug to dial in
as needed per plug type. Nice low weight option in lieu of a power panel.

https://www.ebay.com/itm/12V-Glow-Plug-Starter-Driver-Cable-RC-WillPower/192042480700?epid=1900357437&hash=item2cb69fb43cⓂmlxDCX-_PA964tYK9XZ86bA

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Post  Levent Suberk on Fri Oct 25, 2019 10:11 am

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Post  --Oz-- on Fri Oct 25, 2019 11:12 am

Sunbird wrote:OZ,  can you show us an example of a simple CV/CC dc-dc adapter?  Thanks.

I updated my 1st post with links and picture


The good thing about this is the voltage is constant, unlike a battery. But is does not compensate for IR losses in connection/wire. I am sure it works better than a battery too.

@ 1/2A Nut, is that version CV or CC?

Power panels are nice with adjustable current and ammeter for visual, but they are large and pricey (relativity).
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Post  Surfer_kris on Fri Oct 25, 2019 11:53 am

This is one of the best "drivers" that is handheld, corrects for temperature, and uses a Lipo for power: https://www.rcatsystems.com/rc.php

Glow Plug Igniter with CONSTANT CURRENT --Oz-- Ligd_c
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Post  --Oz-- on Fri Oct 25, 2019 3:59 pm

Wow, $154 shipped to my door (more than all my fuel planes and motors combined).  Very Happy   Thanks for posting that.

Interesting device, I watched the video, what was a little strange was I did not see the current go up when he placed it in the fuel, maybe the ammeter is slow responding, or maybe the resolution is low, not sure.

When a nichrome wire heats up, the ohms also goes up, so when cooling the plug I would think the current would rise.

The 5 second delay was added for some engines (YS 4 stroke), you want to start spinning the motor before the plug lights, or it could backfire.

The ramp up feature I am not sure its really necessary. I would like to see a scope capture with a current probe on the rcats and what I will build (CV/CC). Here is my reasoning. With a standard voltage style (battery or regulated voltage), the glow plug is close to a short (0Ω) when cold, so the start peak current is very high for a short time till the plug starts glowing. With CV/CC this will not happen, it will limit the the current to the setpoint and slightly take longer to start glowing (effectively a slower ramp up time) and maybe slightly easier on the plug. Thoughts?

I will put mine on the scope and compare to CV, should be interesting to see the differences.
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Post  --Oz-- on Fri Oct 25, 2019 4:55 pm

1/2A Nut wrote:Has anyone ever tried one of these?

Output Voltage: 1.5V
Amperage: 40,000 mAh
Chemistry: Carbon Zinc

https://www.ebay.com/itm/Exell-Battery-EBR40-Type-R40-1-5V-Battery-EN6-HO40-906AC-Ignitor-USA-SHIP/232939971992?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
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Never seen that one before.
That battery has only twice the capacity of a Duracell/Energizer D-cell alkaline battery, so 2 D-cells equal that big old battery.

I used to buy surplus 22.5V photo flash batteries (they look very similar to a AA cell in size), I would put 8 in series and add a mercury tilt switch, then wrap it all up in tape, but add aluminum tape in two sections with a gap between them. When a friend (victim) came over, I asked him what is that, it was a lump of batteries until they tilt it enough for the mercury to make contact, providing a friendly (lol) 180V shock! Very Happy Of course we called everybody over to "check" it out, I was 13yo back then (1977).
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Post  Surfer_kris on Sat Oct 26, 2019 1:37 am

--Oz-- wrote:Wow, $154 shipped to my door (more than all my fuel planes and motors combined).  Very Happy

Really, do you only have one? lol!
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Post  fredvon4 on Sat Oct 26, 2019 8:44 am

And a 12vdc driven power panel, and several clip on glow drivers

Lithium Glow Driver

In a hurry to fly on that sunny day? Did you forget to charge your ni-starter? No problem. This unique device allows you unprecedented starting reliability and will outlast any ni-cad! It will even automatically adjust the current to keep your foul plug glowing for trouble free starts.

• 5200 mAh battery capacity for long battery life (over 1 year with normal use)
• Adjusts current automatically to keep the plug lit
• “Soft Start” slowly delivers current to prolong plug life
• User-selectable startup delay feature (~5 seconds)
• Built in charging system
• Auto shut-off
• Easy to read LED bar graph
• Modular plug clip for easy customization
• Internationally rated power supply (100-240V, 50/60Hz)
• Optional protective glove

https://www.rcatsystems.com/rc.php

IMO best clip on is Sonic Tronic

This NI-STARTER® has a 1.5" barrel and is supplied with an UL Approved 110V AC Charger. The Battery is a NiMH 3800ma cell. It locks onto the glow plug. Just push down, rotate, and it's locked for hands free operation.
It has a durable, shock resistant, dual faced amp meter to show the condition of your glow plug. When attached to your glow plug the meter will indicate plug condition, good or failed. This aids in determining the cause of many starting problems. The meter does not indicate the NI-STARTER charge condition.
All versions of the NI-STARTER® carry a 180 day warranty against defects in workmanship or the materials used. We further have an original ownership policy for the NI-STARTER® beyond the warranty, contact us directly for the details.

http://www.sonictronics.com/xcart/product.php?productid=16440&cat=0&page=1

One school of thought on seemingly expensive tools.....Buy once kry once

My, at the time, $123 RCATS - is now 7 years old. ...from 1965 until 2012 I am certain I spent more on various glow drivers and batteries

I was concerned the non user serviceable battery would eventually crap out Since I do not fly any more. Tech at RCATS told me recharge ever 6 to 12 month the bat should be good more than a decade....Ideal is constant use.  But If the RCATS stops holding a charge, mail to them and replacement new  bat installed for not many bucks....no quote cuz all I remember it was relatively inexpensive

                in fact many companies like this just ship a new unit and later do a batch battery replacement on the bench day

many many racing, speed, and combat control line guys use the RCATS....My first exposure was Bladder Graber 2011
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Post  --Oz-- on Sat Oct 26, 2019 3:16 pm

@ fredvon4
Thanks for that post.

Regarding the rcats battery, its simply a 1S2P (1 series-2 parallel configuration) 18650 (18mm diam x 65mm long) 2600mAh cells Li-Ion cells. Couple bucks each cell on ebay if needed. There is quite a few fake capacity rates cells on ebay, nothing is ever going to be higher than 3500mAH/cell, anything above that rating is bs. If I need these types of cells, I get HP 12 cells notebook battery for ~$20 shipped, ~$1.70/cell, most times they are ~2800mah cells. Yes, you have to take it apart, I use these 18650 cells in a lot of projects.

Like this https://www.ebay.com/itm/Notebook-Spare-Battery-Charger-fr-HP-Compaq-593553-001-MU06-MU09-593554-001-CQ62/322111477606?hash=item4aff571766ⓂmKLoC-6gbNEaP3Iii4sglUA

Last night I was reading a little more on different driver types and the pros and cons of each style. I think I will add voltage probe across the glow plug (in addition to the current probe) for better feedback, more info is better to see what's going on (and a dmm connected right at the plug for no voltage drop reading). The drivers that claim they sense temp, are only able to see either the voltage drop of the plug (but this also includes, the wire/connector/plug clip voltage drops) and/or are looking at current change. Will be interesting to analyze what data comes out.
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Post  66 Malibu on Sat Oct 26, 2019 5:45 pm

1/2A Nut wrote:Has anyone ever tried one of these?

Output Voltage: 1.5V
Amperage: 40,000 mAh
Chemistry: Carbon Zinc

https://www.ebay.com/itm/Exell-Battery-EBR40-Type-R40-1-5V-Battery-EN6-HO40-906AC-Ignitor-USA-SHIP/232939971992?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

Glow Plug Igniter with CONSTANT CURRENT --Oz-- S-l16031

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Wow !!! what a monumental ripoff the hobbyists of the world selling the old 6 inch ignitor battery system that died off in 1992 !!!
By far the most expensive part of the whole battery is the label and the next most expensive parts are the brass terminal screws or brass fahnestock clips if you prefer. We are talking pennies here. My nearly 30 years with Eveready/Energizer tells me that given ChiCom labor costs, the TPC&D ( total plant cost and distribution handling cost) the battery goes out the factory door at no more than .30 cents USD. Add another .20 or .30 cents to land FOB at Long Beach and there you have it !!!!
Oh yea, someone mentioned using old batteries for joking with friends ..Be Careful... some batteries even CZ retain residual amperage for years. I can see someone picking up an old 497 510V. photo battery at a flea market/antique shop and be lit up like a Christmas tree from 340 CZ cells in series !!!
FWIW Steve
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Post  fredvon4 on Sun Oct 27, 2019 9:11 am

Steve glad you posted, I knew we had a member with direct experience in batteries, but could not remember who

Oz, remember the glow plug is a variable resistor

VDC is PUSHED* by available source

Current is Pulled by the circuit up to the max source and connections can supply

As an experiment hobby interest...drive on (a pun)

BUT truth is for 80% ----a 1,2,3~infinity 1.5VDC primary Cells in Parallel is the absolute easiest system---- to Pre Heat a catalyst Glow Plug....only thing More cells bring to the table, is more amp hours of supply...current is limited by the internal resistance of the highest resistance cell

Pylon, Team Race, Speed, Combat competitors want / desired, needed a glow heat system to rapidly detect a blown plug. Additionally as long as that circuit was used why not also detect flooded and add HEAT but NOT also blow plugs.  

I ( even as a well trained aircraft and HAM radio electrical dude) still do not fully understand why 1.5 VDC is good but 2.0 VC will snuff a plug. While anything from .05 Amps to 7 Amps just varies the "GLOW"

* unless you accept the "holes" theory
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Post  --Oz-- on Mon Oct 28, 2019 6:25 pm

fredvon4 wrote:Oz, remember the glow plug is a variable resistor
Yes, completely non-linear.

...current is limited by the internal resistance of the highest resistance cell
Sorry, not really, when you parallel cells, the total IR (internal resistance) of the total pack lowers. Like putting a watch battery in parallel with a RC LiPo, the very low IR of the LiPo will do all the work. My little 1300mAH LiPo cells pump 120A in my quad.

I ( even as a well trained aircraft and HAM radio electrical dude) still do not fully understand why 1.5 VDC is good but 2.0 VC will snuff a plug. While anything from .05 Amps to 7 Amps just varies the "GLOW"
Many variables, but generally, when a plug is cold its very low Ohms, almost a short (guessing ~300mΩ), when you first connect the power, their is a inrush of current (mostly limited my the battery IR, wire and connector resistance), then a short while later the plug gets hot and its resistance goes way up, this limits its current. Generally a plug is taking 2A at 1.5V, then the plug is now 750mΩ (simple ohm's law). This is the same reason why the old incandescent light bulbs fail when you turn them on, if your unlucky, you switch them on the instant the voltage is maximum (~170V in USA, 120V is the rms value). Smart switches turn on at the zero crossing (0V) and make the bulb last way longer. Was to busy at work to test yet (had to Watch MotoGP at lunch today  Very Happy )
[/quote]
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Post  PV Pilot on Tue Nov 05, 2019 9:06 pm

Have used the heck out of my Rcats liion driver.  Bought 2 when they first were released.  One was a standard model and I paid a bit more for the adjustable voltage mod that Rcats did at that time.  Basically they added a pot thru the blue plastic case on the backside to tweak it up a bit.  Have used it to start big 91 Nova Marine engines on 60-70% as well as Cox stuff on 25%.  Nova offroad and onroad of various sizes and power outputs for many years now.  Good units.  Made a cox cable for the glow head stuff.  A dumb short vid I did on it years ago down below.  Almost as used as my Hobbico Super Hot Shot headlock style of about same age (5000mah NiMh D cell),,which I also added a wired adapter for Clip-on heads. Cheers Folks!

https://www.youtube.com/watch?v=0tP73WuHSOA
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Post  --Oz-- on Wed Nov 06, 2019 10:26 am

@ PV Pilot
Thanks for the post and video. I know it's deceiving (camera metering the overall seen and adjusting its brightness), the video shows them plugs pretty hot.

What amps it the driver driving?
Could you do a couple quick tests, test the output voltage without a plug connected:
1. on the stock driver,
2. on your modified driver the minimum and maximum voltage setting?
TIA


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Post  --Oz-- on Wed Nov 06, 2019 11:13 am

I did some quick testing and the stock wire on the cox glow plug connector.

The results were all over the place (inconsistent current and wattage to the plug), mostly the plug connector to plug mating was the most inconsistent connection. After I cleaned up the plug connector I started to get somewhat consistent results, but not as consistent as I wanted. BTW, I was using a 4 wire approach to measure the exact voltage getting to the plug, this made it easy to spot the inconsistent wire/connection to the plug.

The stock cox plug wire is tiny 22 AWG wire (0.022" diam and 15Ω per 1000"). But the wire was old, hard, nitro soaked so I replaced it with what I had laying around 17 AWG (0.044" diam and 5Ω per 1000') and made it a little longer,  instantly I got much better consistent results (after the plug connector clean up).

I was using a $1300 bench power supply (CV/CC 20v 10A capability), so the source was not a factor in my first round of testing.

I did look at the resistance (of course calculated as you cant measure it when load current it running through it) of the plug when hot and cold. I was very surprised the resistance did not double, this is a good clue to what's going on when a plug floods. With my little amount of testing a quick summary.

Good source (battery/etc), good wire, good connector contact and good plug you can get good results for under 10 bucks with bone stock equipment. If any start to have an issue the preformance drops.

The voltage at the plug really makes a difference is glow plug output, so any IR drops along the way hurts its preformance (look at the table and wattage numbers). I did not go above 2.0A in my quick testing as the plug really was glowing in the lab (in bright daylight it probably will look different).

With my little testing, CC "only" is not the best way, a combination of CV/CC should work well.
A pair of 18650 2.6AH cells ($4),
A good (not stock cox) wire/plug connector (guessing $10)
Add a usb li-Ion charge board for $1,
And a dc-dc CV/CC adapter ($5) will work as good as the rcats for a total of ~$20.
it would not have the 5 second on time delay or the auto-turn of functions (neither I need), but it would save me about $130 over the gold standard.
For $3 more I could add a digital voltage/amps gauge, this would show the output voltage and current (making it easy to adjust the dc-dc's output) and showing you the status of the connected plug.

More testing to come.
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Post  kevbo on Wed Nov 06, 2019 12:16 pm

A couple of points: Glowplug elements are made of platinum, not nichrome. Nichrome has very little resistance change as it heats, and thus does not present a large current surge when you push the bread down in the toaster.

Platinum catalyses methanol/oxygen combustion, and that is why it used. Palladium is an alternative. Either metal has a large resistance change as it heats. As a result, temperature is fairly constant when driven with a low impedance constant voltage source. A cold filament draws more current, and thus more power, a hot element draws less power. Dry cells have fairly high impedance, and get worse with age, so are not ideal. Paralleling a number of them reduces the impedance proportionally. Nicads have very low internal impedance, so perform well even if the voltage is a tad low. Some plugs (norvel) are specifically designed to work well at 1.2V nicad voltage.

Driving a heater with this strongly positive resistance/temperature characteristic is a mistake. An overheating element will be supplied with ever-increasing voltage, and will burn out in short order. Conversely, power will be reduced to a cold/flooded element.

Bridge type drivers that maintain a constant resistance of the plug element are an ideal solution. Because the temperature change is minimal, they can respond very quickly to changing conditions.
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Post  fredvon4 on Wed Nov 06, 2019 1:36 pm

kevbo....no argument BUT....very few plug makers use pure Platinum, Palladium,(nobel elements)  or a mix. Most plate a carrier wire, usually nichrome ( for strength, and reduce cost of the expensive nobel elements). Better plugs like OS, Enya, Merlin, or Nelson are plated thicker than the lower cost Turnigy or other economy versions

I sure wish the Merlin family would get back to production and distribution but two years now...it is doubtful
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Post  --Oz-- on Wed Nov 06, 2019 11:25 pm

kevbo wrote:A cold filament draws more current, and thus more power, a hot element draws less power.
Sorry, not if you look at my graph, just look at the wattage column. I will do some more testing on this.

Driving a heater with this strongly positive resistance/temperature characteristic is a mistake.
Please clarify, did you mean with CV/CC or? CV/CC can't be any worse than just a battery (unless misadjusted) that a lot of pilots use, so why is this a mistake?

 An overheating element will be supplied with ever-increasing voltage, and will burn out in short order.
I am confused, the glow plug is PTC (positive temp coefficient), not NTC. PTC will increase resistance with heat (see my graph), so with a constant voltage, the plug will self regulate, in other words, it will not run-away and burn (unless voltage is set too high). You seem to say the opposite or please clarify?

Conversely, power will be reduced to a cold/flooded element.
This is true, lower resistance, but also lower voltage, total power is lower.

Bridge type drivers that maintain a constant resistance of the plug element are an ideal solution. Because the temperature change is minimal, they can respond very quickly to changing conditions.
Thanks for the info, I will look into this more after some quick CV testing/graphs to understand plugs better.

What are the best glow plug connectors for 0.049 and regular plugs?
Thanks for the post.
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