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# SCR SUPERCAPACITOR OSCILLATOR

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#### Danwvw

##### Active Member
Looking for a simple Low impedance 6 VDC SCR Oscillator Supercapacitor circuit Design that blinks a (High Side 32 Ohm when lit lamp) on and off every 2 seconds or so? The Low Side will drive about 1 ohm DC resistance but Inductive load (6 volt generator) 0-7 volts output that will be excited by the pulse and start charging if it's turning fast enough.
Given:
6.3 Volt 1000 A Optima AGM Battery,
4.5 volt .4F Supercapacitor,
32 ohm lamp,
2 Amp 500 Volt SCR,
3.9 Volt 5 Watt Zeners,
.5V diodes etc...
0-7 Volt Automotive Generator Neg. Ground.

This is what I am thinking but can it be made to pulse repeatedly until the generator starts charging?
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If there is any current through a thyristor, it will simply not turn off.

That's why they are normally only used in AC powered devices, where a zero-current point is predictable.

Yes thanks, they latch on, And that is part of the design I need help with, SCR's are on hand. However I would be open to a SCS, But really what I was hoping to find was a Super Cap Oscillator circuit design of some type, it wouldn't need to look like the Idea above at all,. Just have a way to discharge the Super Cap into the 1 ohm load every 2 or 3 or 5 seconds till the load is gone. . .

I've spent the last hour or so trying to come up with some simple circuit to do that, but nothing so far...

If you dump a capacitor charge across the thyristor you can turn it off, particularly if you have a resistance like a lamp in series with the rail.
Old lancer boss fork lifts used something like that to control the motors.

What with backwards polarity? It would then need another RC circuit and probably not a Super Cap that would kick another SCR in to dump the charge across the first SCR?

Not necessarily reverse polarity although that might work.
I cant remember the exact circuit of the traction controllers but yes I'm pretty sure a smaller thyristor switched a cap across the larger thyristor and turned it off.
The cap and associated circuit needs to provide enough energy for long enough to turn off said thyristor.
Y ou can get gate turn off thyristors, might be worth looking at those, though they are probably rare.

What with backwards polarity? It would then need another RC circuit and probably not a Super Cap that would kick another SCR in to dump the charge across the first SCR?

I suggest you google scr dc power control, essentially it's like an SCR bistable, with the capacitor between the two SCR's - you only need one large SCR though, as that's the only one carrying the load current.

So it only takes 10 micro F to drop the SCR out?
Is there a way to keep them oscillating?

So it only takes 10 micro F to drop the SCR out?
Is there a way to keep them oscillating?
Maybe. All you really know is that in the circuit linked in post #8 it is probably enough. (maybe, see next)

But, I have a concern about that circuit. C1, R2 and SCR-2 provide a mechanism for turning off SCR-1. But what turns off SCR2? Once triggered, R2 will continue to supply more than the 0.2mA of current that SCR-2 needs to stay latched on.

As such, it will work once. But you'll have to find another way to turn off SCR-2 before the reset circuit can re-arm.

The energy in the cap must be enough to reduce the current through the ecr for long enough so it turns off.
The amount depends on the load, the scr and the parasitic's in the circuit.

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