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Toggle switch for small aircraft charging system in case of failure

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richard.cs:
@Floobydust, the schematic you just posted is simplified (missing the SCR gate drive) but shows the SCRs as shunt regulators. With the SCRs off you just have a rectifier bridge. With them on one SCR and one bottom diode will conduct at any time, shorting the stator. The top diodes prevent any current flowing backwards from the battery into the short under this condition. The SCRs are not in series with the output so are not acting as switchable rectifiers.

The 3phase version in the second post is similar only with the SCRs inverted so it's the top diodes that conduct when shunting the winding.

Knowing the specified open circuit voltage is useful, not only in itself but the shear fact they specify it means that it is measurable without damaging the stator insulation. Transients from opening disconnecting the battery whilst running could still be many kV and trash the insulation though.

The other common constant-current dynamo is the bog standard 3W pedal bike dymano. It's roughly a 0.5A current source which is how it (usually) avoids blowing tungsten lamps at high speeds. Modern ones with rare earth magnets are better, giving higher open-circuit volts per rpm so both lighting at lower speeds and being closer to constant current (because Voc>>Vload).

richard.cs:
@ITman496, the simplest measurement is short circuit current (without rectifier or regulator), measure it at idle and then even if it's not a shuntable type you shouldn't break anything with a brief test. A shuntable one will have Isc perhaps 1.1*Inominal, whereas for a low impedance one it might be 5-10*Inominal and may well stall the engine. Don't remove it under power unless you have a TVS fitted because you'll get a huge voltage spike - stop the engine instead to stop the test (actually I'm not sure I'd switch a short *in* with the engine running and no TVs either because switch bounce will make spikes).

If you don't fancy that then measure the resistance and inductance of the winding (one of the cheap component testers will do), and then measure the frequency and open circuit voltage at tickover. You can then calculate how it behaves at any speed or even put it into SPICE. I have done this to fully (well, mostly) model one when designing regulators. That then allows you to see what the current will be shorted or with any given load (resistor, battery, etc.), at any rpm, which it kind of cool.

ITman496:
This is a picture of the unit that I found online.



I will take those measurements when I can!  And good point about the test. I'm not gonna do it until I have the TVS diodes in place anyway.

I've never done a spice model before but I'd certainly love to try.  When I get those measurements I'll do my best!

floobydust:
The Tymphanium is series, and old Kawasaki is shunt-type. I find there are many types of dynamo regulators, series and shunt, SCR or MOSFET i.e. https://www.shindengen.com/products/electro/motorcycle/reg
The series-type is only two diodes, not four. I just can't get over the waste in a shunt reg or why use more parts.

ITman496:

--- Quote from: floobydust on April 17, 2020, 11:22:51 pm ---The Tymphanium is series, and old Kawasaki is shunt-type. I find there are many types of dynamo regulators, series and shunt, SCR or MOSFET i.e. https://www.shindengen.com/products/electro/motorcycle/reg
The series-type is only two diodes, not four. I just can't get over the waste in a shunt reg or why use more parts.

--- End quote ---

That page was extremely helpful to explain how my system works.  Thank you!

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