Electronics > Beginners

RC glow plug driver and voltmeter: constructive criticism needed

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Rerouter:
My thoughs for dumb analog would be

1x Op amp - Howland current source (He provides the measurement current
1x Op amp - Oscialltor (He switches between measure and heat)
2x Op amp - Sample and hold (He holds the measurement result, and gets reset by the oscialltor)
1x op amp - Comparitor (If your below your desired voltage, turn on the heater for the heating cycle)

So how you arrange it is up to you, but for the howland current source, its very easy to make them for above ground, you can probably leave him running if the current is small, the plug heat will be based on its resistance,

So now the meat of it, the oscialltor disables the comparitor (probably via summing with one of its inputs) for the measuring phase, and updates the sample and hold,
Then for the heating phase the sample is fed to the comparitor

This would be a loose PWM, mainly because based on thermal mass, I'm going to guess the response time is multiple seconds, not fractions of a second,
Equally there is no reason the duty cycle has to be 50/50,

I will say this way is fairly idiot proof, if the wiring fails open, it thinks its over temp and never heats, and if its shorted, well its not heating the plug.

oldway:
As far as I remember, a french member of this forum have developped a project on this forum to solve the same problem.
You should use the search fonction to find it.  :-+

fmzambon:

--- Quote from: cleaningOut on April 23, 2018, 08:15:27 am ---You could just use an electric motor.

--- End quote ---

Where's the fun then  ;)

In addition, you can't beat the sound of a multicylinder four stroke engine  8)

fmzambon:
Thank you max_torque and Rerouter, these are very good ideas.

I had thought about sensing the plug resistance, but dismissed it as too complex without an MCU (as I said I'd rather do it "the old way"). I'll definitely investigate the options suggested to add temperature sensing. I'd probably have to incorporate some kind of adjustment anyway because different makes and types of glow plugs seem to have drastically different resistance values, so I can't just hardwire a current value and call it a day.

oldway, as for the project of the french member, is it this one https://www.eevblog.com/forum/projects/improving-glow-plug-drive-design-for-rc-plane-radial-engine/ ?
I guess it's a modeller's trait to start with a text-wall first post  ;D

oldway:
Yes, it is....
What do you think about it ?

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