My apologies... it seems that I swapped image02 and image03 in my explanationIs Image 02 what you are referring to as the 'third image' ?
Both scope channels are set to "x100". 100 times what?
Does the machine include a SMPS generating the high voltage from 12V, or is the 120V mains-derived ?
OMG! this is beautiful... I'll start studying it right away!I think the thing in question is where the circuit ground is.
Here is one with the basics like your pictures.
I suspect your right. The inductance probably changes as the plunger pulls in and things like that.@ronv, I'm beginning to think that the best approach to solving this problem would be to build the last circuit you've proposed, tweak it, and see how it behaves.
The coil's inductance was measured using a different waveform and frequency than the one being used to operate it, so its inductance could be different from 1.1 mH (although I wouldn't know by how much). And that could mean that the simulations are off the mark. We need real interactions to to infer a realistic scenario.
Not to brag, but I'm excellent at microcode . Regarding electronics, that's the area in which I need no help. So no, generating the 28 kHz pulses and the rest of the switching involved doesn't scare me one bit. I'm an expert on the 8051 architecture, and don't feel attracted to the raspberry or arduino fads. This is because I write all of my code in assembly, and design all of the digital circuits in my projects myself... But I'm rather weak when it comes to analog stuff. I just hope I can eventually return you the favor somehow, you've helped quite a bit already.I suspect your right. The inductance probably changes as the plunger pulls in and things like that.
Are you good at microcode? I'm not but I have a few ideas for the PWM of the high current pulse. It seems like maybe they are trying to control the timing very close. Is that the case? What does it dispensed, Is the amount set by time energized? Does the setting on this machine need to match others?
I think it's a great idea... though I have little familiarity with op-amps and/or comparators (I suspect they'll be involved for the current sense somehow) I trust I'll have your guidance for designing things properly.Alright! ... I give you my idea anyway.
So you're saying I should build a simple supply with its primary being fed from 120VAC, and focus my efforts on the driver circuit, instead of making things too complicated at first?I think it might be easier to just build a little AC supply with a budget regulator. Something like this:
With a transformer like this.
http://www.hammondmfg.com/186_187.htm
Thanks for your input, and yes, I think I'll build ronv's suggested power supply instead.I agree with Ron re the 120V supply. Since the machine uses 220VAC mains, a step-down transformer plus rectifier bridge would be simpler than a SMPS.
One difficulty with implementing a design with high-side switching of the 120V to the coil is the P-FET gate drive arrangement. I realise Ron's sim is just an outline, but note that M1 wouldn't really appreciate a Vgs of 120V .
You also need to look at power handling and efficiency in a practical circuit. For example, R1 is dissipating an average 35W (cf the coil's 9W) ! Can that be reduced by a PWM system?
The inductance was measured without the plunger installed. Only the coil was tested, and not the entire assembly, since the lab equipment used for this purpose did not allow it.The good news it the duty cycle is very low for the high voltage circuit - only 0.5 ms out of 20 ms. So average power is not very high.
I've been trying to figure out why they use such a high voltage and the only thought so far is that the inductance of the coil goes way up as the plunger goes into the coil. Did you measure the inductance with the plunger in and out of the coil?? Could it be 10 times higher? Might be...
Thanks... I'll be waiting for your response, since I'll be ordering all the parts from Digikey as soon as the circuit is complete. Although I do have lots of other components available, I'd like to keep improvisation on this project at a minimum, at least on the beginning phase.Aha, I think that solves the mystery.
At some point we will need to know what the current waveform looks like as the solenoid actuate, but it looks like you have that capability.
I have some honey dos, but back later.
Let me see if I can't come up with the rest of the circuit.
Thanks Alec_t, your opinion is thoroughly appreciated. What about M2, is it ok being driven as it is?An opto-isolated driver similar to one in the link (albeit for DC not AC) looks ok for M1.
Inductance will certainly increase when the pintle (plunger) is present and will change with its position. Another variable, difficult to model with any accuracy, is the (relatively minor, I believe) coil current change due to the emf generated when the pintle accelerates and decelerates.