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Thing I got on eBay...
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GadgetBoy:
So, I picked up a thing on eBay, claims it's a "4000W 220V SCR Motor Speed Controller Module Voltage Regulator Dimmer". I was hoping I could use it to reduce mains voltage to something I could rectify and feed to a power supply. Not trusting some random piece of Chinese electronics, I started doing some research, and it seems it doesn't actually regulate the voltage, it just nips parts of the waveform off - basically changing the duty cycle.

Is there a way I could still use this to get 50v out, or should I look for a transformer? Is there a non transformer way I can turn mains (120V) into 50V without a transformer/switching power supply?

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ogden:

--- Quote from: GadgetBoy on September 06, 2018, 12:00:52 am ---Is there a non transformer way I can turn mains (120V) into 50V without a transformer/switching power supply?

--- End quote ---

Motor coupled to generator :)
JS:
capacitive divider?

Resistive divider! Nah, not efficent, just a drop out resistor!

Ha... 4kW @220V, so you need 18A, 3.9Ω resistor of barely 1260W, then you just connect your load (a bridge rectifier in between). Put a zener, so if the load is unconnected you still get 50V, that's a 900W zener, buy one in the drugstore!

Now, seriously, what kind of what are you trying to power up... SCRs are like triacs for DC, or more precisely, to convert from DC to AC but with the kind of waveform triacs do. Power supplies are either linear (with transformer) or switching.

You could use something like what you described to make what I think you want, in any case you could need some kind of storage (cap) if you actually need DC with any reasonable ripple. Now you can trigger the SCR at the point, about 3/8 wave after the zero crossing so the output has ~50V peak and you charge that cap for your load to use. Is that what you expect?

JS

Edit: one thing you might not notice, a half wave rectifier DC is 0.45 times the input voltage, so with a 36A diode you can have your 50V DC you want, it will be a half wave rectified signal, then if you want to get a steady DC and not just some average of a crappy thing, just a cap will make the voltage way too high, so you will need some inductance as well.
GadgetBoy:

--- Quote from: JS on September 06, 2018, 12:37:30 am ---capacitive divider?

Resistive divider! Nah, not efficent, just a drop out resistor!

Ha... 4kW @220V, so you need 18A, 3.9Ω resistor of barely 1260W, then you just connect your load (a bridge rectifier in between). Put a zener, so if the load is unconnected you still get 50V, that's a 900W zener, buy one in the drugstore!

Now, seriously, what kind of what are you trying to power up... SCRs are like triacs for DC, or more precisely, to convert from DC to AC but with the kind of waveform triacs do. Power supplies are either linear (with transformer) or switching.

You could use something like what you described to make what I think you want, in any case you could need some kind of storage (cap) if you actually need DC with any reasonable ripple. Now you can trigger the SCR at the point, about 3/8 wave after the zero crossing so the output has ~50V peak and you charge that cap for your load to use. Is that what you expect?

JS

Edit: one thing you might not notice, a half wave rectifier DC is 0.45 times the input voltage, so with a 36A diode you can have your 50V DC you want, it will be a half wave rectified signal, then if you want to get a steady DC and not just some average of a crappy thing, just a cap will make the voltage way too high, so you will need some inductance as well.

--- End quote ---
I'm trying to get 50v DC for this thing - https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F401368742041 just with materials I have on hand

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GadgetBoy:

--- Quote from: blueskull on September 06, 2018, 01:10:52 am ---
--- Quote from: GadgetBoy on September 06, 2018, 12:00:52 am ---Is there a way I could still use this to get 50v out, or should I look for a transformer? Is there a non transformer way I can turn mains (120V) into 50V without a transformer/switching power supply?

--- End quote ---

Yes, but that would probably illegal, or at least illegal in near future. Those SCR choppers inject a heck lot of noise to the grid. Considering high frequency MOSFET chopper technology is so mature and cheap these days, SCR choppers should have been abolished.

--- End quote ---
So basically, I should stay far, far away from it. It didn't look safe to use

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