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3 phase inverter with SCR

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MosherIV:

--- Quote ---Naturaly commutated, do you mean using AC supply voltage where do you can expect zero cossing for sure?
--- End quote ---
Yes.
SCRs can be turned on by the control gate but not turned off.
The way to turn off SCRs is for the supply voltage to reach 0V, zero switching as you refer to. Hence they are mainly used to control AC circuits.

Your suggested circuit may work with transistor or mosfets BUT you will not be able to get negative part of AC waveform.

Zero999:

--- Quote from: miso156 on February 07, 2020, 12:03:14 am ---
--- Quote from: Zero999 on February 06, 2020, 11:22:57 pm ---Sorry this is a bad idea. SCRs are not ideal at such a low voltage, because they have a high voltage drop, compared to MOSFETs and a car alternator will give a rubbish efficiency anyway. A good old brushed motor will give a higher efficiency than this and is much easier to control.

--- End quote ---

I know.  When I look at KTxxx thyristors they say 1.4V, but BJT like BD911 are also high 1-2V and when hfe is 20 the base current is  also not neglibigle from losses point of view.

The car alternator is only temporary solution, next i will buy some motor with higher voltage rating.

Thx anyway.

--- End quote ---
Apart from the fact that the BD911 is far too small to drive an alternator, BJTs are also unsuitable for this application, hence why I mentioned MOSFETs, which have much lower on losses.

A quick flick through the RS-Components catalogue gives the IRFS7430, which has a maximum on resistance of 0.75mΩ, so hardly any voltage loss even at hundreds of Amps.
https://docs.rs-online.com/cba3/0900766b813c79c2.pdf

What voltage are you eventually going to be running the motor at? If it's over 600V, then you can consider IGBTs, which have similar on losses to SCRs, but are much easier to switch off.

Circlotron:
This is the kind of project that separates the men from the boys!
The fact that the car alternator is being used as a synchronous motor means that if the motor has sufficient rotor excitation it will present a leading power factor to the inverter.  That means extra commutation components are not needed. The SCRs will commutate naturally. I have never built one like this. My experience was with DC choppers some 35 years ago.

https://www.google.com.au/search?source=hp&ei=60w9XouhJrfFz7sPjou82AQ&q=scr+inverter+synchronous+motor&oq=scr+inverter+synchronouis+motor&gs_l=psy-ab.3.0.33i22i10i29i30.950.11839..13552...0.0..0.247.5682.0j26j5....2..0....1..gws-wiz.......0i131j0j0i22i30j0i333j33i160j33i21.WnFEcZpJnx8

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