Need help measuring ignitor current draw

[manixFan]

Not sure where this thread belongs, but here goes: I would like to measure the current draw of various ignitors in a test environment. I’m ok with basic electrical circuits, but measuring current draw over short periods is new to me. I figure an oscilloscope would work, but most don’t seem to have high current limits, and I’d like something more portable. I found this Fluke:

https://www.fluke.com/en-us/product/electrical-testing/clamp-meters/fluke-375-fc
When connected to a phone, it looks like it offers pretty decent recording. But I can’t tell if it would capture the transients during firing an ignitor.

Any help or suggestions on equipment and methods would be greatly appreciated!

Thank you,


Tony

PS: budget is flexible, so open to all options that seem reasonable.

 

[cvanc]

Few options are reasonable ":^)

Turns out this is kinda hard to measure, consider reviewing prior art (there's lots) for how, exactly, folks skin this measurement cat.

 

[Art Upton]

E=IxR

If you measure the resistance of the ignitor, then a high speed digital storage scope should be able to measure the Voltage Across it and capture the Max I

I=E/R

 

[BEC]

Well....if 8 Hz sample rate is enough, there's a long-discontinued but still available for giveaway prices tool that was created for characterizing electric power systems for models that I've just been using to do exactly that.

You need an Emeter II and one of the data units, and some connectors as a minimum to do this. One source is https://rcdude.com/catalogsearch/result/?q=emeter

Data pulled from an Emeter II can be plotted. Here's an example done with MagicPlot. These are three firings of Estes Solar Starters through a Quest Phaser and powered by an Allmax 9V alkaline battery. This was done for an R&D that I just submitted to vNARCON.

 

[AllDigital]

I did this a few years ago in a very crude way to compare some ematches. I used a set of analog amp meters (0-1000ma and 0-2a and 0-5a) and an iPhone recording slo mo at 240fps. It was not very scientific, but it was enough to convince me that the "good brand" of eMatches all consistently fire with 500ma or less and the "orangies" often take more than one amp to fire and are very inconsistent.

 

[manixFan]

So far some great info, and I did find some other good threads. The devices @BEC mentioned seem promising, and I’ve also been able to find some relatively inexpensive digital oscilloscopes that would work as @Art Upton described.

I find it ironic that the first method I thought about – using analog meters, was also used by @AllDigital.

Thanks all for the suggestions, any others are still welcome.


Tony

 

[cls]

Best way is with a recording (DSO) oscilloscope. use a resistance shunt in line to get some V out of the I. Trigger the scope with the fire button.

G Wiz did something like this 20+ years ago, published screen shots etc.

 

[Art Upton]

So far some great info, and I did find some other good threads. The devices @BEC mentioned seem promising, and I’ve also been able to find some relatively inexpensive digital oscilloscopes that would work as @Art Upton described.

I find it ironic that the first method I thought about – using analog meters, was also used by @AllDigital.

Thanks all for the suggestions, any others are still welcome.


Tony

I'm thinking that Emeter II is the best bet. I am even thinking of buying one at $22 as then I don't have to worry about my 200mhz digital scope being outside my electronics bench.

 

[BEC]

If any of you go for the Emeter II, I'll be happy to help. There is also a HUGE thread on RC Groups about them.

The drawback is that the thing was created in 2008 or so, and has been out of production for at least ten years, and even the company the created them is not what it was. One of the original designers (in Australia!) was still accessible in 2020 when he tweaked the firmware for the Emeter II and the micro data unit for me a bit. I haven't tried to get in touch with Mark since then, but as I say, I can help some. The fellow that runs RCDude also is fairly knowledgeable about it.

 

[Adrian A]

Your Blue Raven will measure the current at 500 Hz in a ground test.

 

[MarsLander]

More resources for you?

2000 Brody Method:
a Hewlett-Packard 2Gs digitizing oscilloscope
https://studylib.net/doc/18141640/electrical-current-requirements-of-model-rocket-igniters
2009 Brohm Method:
https://www.rocketshoppe.com/info/Igniter_Continuity_Tests.pdf
2012 Lyngal Method:
https://www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf

 

[Reinhard]

For igniters, you want something that measures reasonably fast. E-matches fire on a time scale of milliseconds. Anything that looks like a multimeter is very unlikely to be able to resolve what's going there. Other igniter types (e.g. various "motor starters") may be slower, but with a slow measurement system you well never know for sure. The obvious choice for that is an oscilloscope. Affordable portable ones can be had these days. But there are also other options like various data recorders, digitizers or logic analyzers (only those with analog channels). You can also cook up something with a development board (e.g. Arduino).

For the current measurement, most of the time you need to convert your current into a voltage signal. For the off the shelf solution search for "oscilloscope current probe". Make sure it can handle DC currents. Avoid AC probes that are based on Rogowski coils or current transformers.
The classic low price option is a shunt resistor, as mentioned above.
Nowadays, I'd use a hall effect based current sensor. They have a couple advantages over a shunt (integrated amplifier, no trade-offs between current drop and resolution, can be mounted high side without worrying about reference voltage) but they need a simple power supply. The ACS712 seems to be a popular choice. Amazon is full of very affordable boards that can handle up to 30A.

Consider how many channels you want to measure. Besides current, it can be interesting to measure igniter voltage on a second channel too. Further channels can be combined with things like break wires or photo-diodes if you're interested to find out how long it takes from button pushed to pyrogen response.
Another simple trick would be to use a LED in parallel to the igniter and visually record the delay between LED and pyrogen with a camera (see the high-speed modes on modern phones).

Reinhard

 

[waltr]

Best way is with a recording (DSO) oscilloscope. use a resistance shunt in line to get some V out of the I. Trigger the scope with the fire button.

G Wiz did something like this 20+ years ago, published screen shots etc.

Yes, this is best way.
I would chose the value of the shunt to give about 1V per Amp which means a 1.0 Ohm resistor. Use one with a 1 Watt or more power rating.

 

[BEC]

More resources for you?

2000 Brody Method:
a Hewlett-Packard 2Gs digitizing oscilloscope
https://studylib.net/doc/18141640/electrical-current-requirements-of-model-rocket-igniters
2009 Brohm Method:
https://www.rocketshoppe.com/info/Igniter_Continuity_Tests.pdf
2012 Lyngal Method:
https://www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf

Thanks for that — especially that one by John Lyngdal (@Johnly). Tell me, how did you find that one? I just tried searching Apogee's site without turning it up. John's results bear directly on an R&D I'm presenting at NARCON in a couple of weeks. It's also nice to see that his really nice test rig and my less so test rig got similar results. Here's a pic that should be directly comparable to the plot I posted above.



Of course I was using a real battery to provide the power, and one that's barely up to the task at that, so the voltage and current fell as time went on. In my plot, the "first firing" burned out the igniter. It didn't in the other two.

 

[MarsLander]

Tell me, how did you find that one?

Do not read the next sentence and assume I'm being rodomontade. I am an extraordinary researcher. Being a Genealogist with the Son's of the American Revolution helps...and I stayed at a Holiday Inn Express last night for good measure.

I may not know what it all means, but I can usually find it...

 

[BEC]

Do not read the next sentence and assume I'm being rodomontade. I am an extraordinary researcher. Being a Genealogist with the Son's of the American Revolution helps...and I stayed at a Holiday Inn Express last night for good measure.

Had to look that one up.

I just want to be able to cite John's report properly in my presentation.

 

[rocket_troy]

For a compact solution, I have both a POKIT PRO and a standard keyring POKIT Meter that will log current draw in oscilloscope mode. At least I've used the POKIT Pro for that application.

TP

 

[MarsLander]

@BEC

Proper citation, APA 7th edition, English, Times New Roman 12:

Lyngdal, J. (2022, October 12). Igniter Performance and its Dependence on Firing Current: or. . .. . .Watts a Joule? Apogeerockets. Retrieved January 11, 2024, from https://www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf

Forum removes formatting. Second line should be indented and should look like this for proper APA formatting:



MLA 9th, same note on the formatting:

Lyngdal, John. “Igniter Performance and Its Dependence on Firing Current: Or……Watts a Joule?” Apogeerockets, 12 Oct. 2022, www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf. Accessed 11 Jan. 2024.

 

[tfish]

@Johnly
See above...

Tony

 

[MarsLander]

I just tried searching Apogee's site without turning it up.

Try this search term in google:

site:apogeerockets.com igniter watts

First result. That doesn't get you proper citation, but will help you find it.

 

[BEC]

Great, thanks.

 

[manixFan]

I normally do a pretty decent search before asking questions, but I clearly missed some good sources this time. Thanks to everyone who replied, lots of good info here.


Tony

 

[rocket_troy]

Best way is with a recording (DSO) oscilloscope. use a resistance shunt in line to get some V out of the I. Trigger the scope with the fire button.

I agree. I'd be very surprised if you can use the igniter's resistance as a reference coz that's obviously going to change in the process.

TP

 

[cls]

I agree. I'd be very surprised if you can use the igniter's resistance as a reference coz that's obviously going to change in the process.

TP

That's a good point. In fact, tests show that the ignitor plasma conducts really well, like zero ohms. So for milliseconds, that's why serial ignitors work. The fireworks guys laugh at us parallel wired rocketeers.

 

[Johnly]

I'm glad to see that an experiment I did decades ago is still relevant.
I'm one of many that miss the Q2G2 igniters.

John

 

[Art Upton]

I'm one of many that miss the Q2G2 igniters.

John

I still have a few, I wonder if they still will work.

 

[MarsLander]

I'm glad to see that an experiment I did decades ago is still relevant.
I'm one of many that miss the Q2G2 igniters.

This confirms my concern about the date citation of the work, and confirms the work was in 2012. (the document properties were ambiguous about the dates).

Proper citations, APA 7th:

Lyngdal, J. (2012, October 22). Igniter Performance and its Dependence on Firing Current: or. . .. . .Watts a Joule? apogeerockets. Retrieved January 11, 2024, from https://www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf

MLA 9th:

Lyngdal, John. “Igniter Performance and Its Dependence on Firing Current: Or……Watts a Joule?” apogeerockets, 22 Oct. 2012, www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf. Accessed 11 Jan. 2024.

 

[Rocketjunkie]

I still have a few, I wonder if they still will work.

Mine do I bought 4 24 packs each time Quest had a sale. Still have about 200. Q2G2s are about as sensitive as ematches. However, I had an ATFE license and bought a case of 2400 ematches. Now, ATFE legal ematches and BP motor starters are available.

When I needed to test all fire and no fire currents on igniters, I used the following:
7805 5V voltage regulator, an assortment of 10W power resistors, 12V battery, a couple of switches, wire, and some clips.
Connect the + side of the battery through a switch to the 7805 input. Connect the output to one end of a resistor. Connect the other end to the ground pin of the regulator and a clip. Connect another wire from battery - to the other clip. Output current is 5/R amps. Change resistors as needed. You can use a potentiometer instead of a resistor but ones big enough are expensive. Start with a high resistance, and measure the current. Gradually increase the current (reduce resistance) until it smoulders. Measure current. Use 1/2 this value and use about 1/2 this value as the no fire current.

 

[BEC]

I still have a few, I wonder if they still will work.

I hope so. I have quite a few, which are reserved for clusters or drag racing only.

I'm glad to see that an experiment I did decades ago is still relevant.
I'm one of many that miss the Q2G2 igniters.

John

Yes you have lots of company there. Gary keeps telling us they couldn't buy them without buying the motors, too. *sigh*

This confirms my concern about the date citation of the work, and confirms the work was in 2012. (the document properties were ambiguous about the dates).

Proper citations, APA 7th:

Lyngdal, J. (2012, October 22). Igniter Performance and its Dependence on Firing Current: or. . .. . .Watts a Joule? apogeerockets. Retrieved January 11, 2024, from https://www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf

MLA 9th:

Lyngdal, John. “Igniter Performance and Its Dependence on Firing Current: Or……Watts a Joule?” apogeerockets, 22 Oct. 2012, www.apogeerockets.com/education/downloads/Q2G2_Igniter_Report.pdf. Accessed 11 Jan. 2024.

Thank you sir! Either of those will suit my relatively informal needs.

 

[MarsLander]

Thank you sir! Either of those will suit my relatively informal needs.

Happy to overdeliver...