Small VFD

[najrao]

I need to run a small (<150W) three-phase motor at higher adjustable speed than the 1400 rpm @50Hz. As luck would have it, I have found a pcb seemingly ideal for this. I do not know what it was meant for originally.

Other than the mains input and motor connections, there is only just a four pin socket (header), with markings as in pic.The external circuitry to be connected is entirely isolated by the two opto's, needing only logic level (5V). One opto has its LED input at the header pins, and is wired to the pin marked '5V' through a resistor, with the cathode left open at the third pin. The other opto is assembled with its LED input on the live micro controller side, and just the transistor output at the remaining two pins of the header. The markings are 'RPM' and 'FB' respectively. I would have thought FB is for feedback, and cannot be the output of an opto.

I have removed the heatsink to see markings on the power chip, there are none. The microcontroller is also undecodable. The IGBT bridge should be several amps at least. The power input is wired for 230V single phase.

Connecting a dc 5V supply ANYWAYS does not enable operation.

What is wrong?

[Bratster]

The RPM input is active low, but will need some sort of pwm or something along those lines to make the controller happy most likely.

The feedback output is also active low, but needs a pull-up resistor to 5v.

I'm going to guess that board may have come from a washing machine.
EDIT: nevermind, looked up the part number and it looks like it's from a refrigerator. Weird.

Here is an article where someone salvaged the motor and controller from a washing machine and made it work. It's a different board and manufacturer, however there is some overlap.

https://hackaday.io/project/28630-variable-speed-washer-motor-and-controller-reuse

Be safe.

Sent from my Nexus 6 using Tapatalk

[Theobald]

But too reach high efficiency, I guess you can find VFD in refrigerator also.
Big 400V caps, dissipator, rectifier, it really looks like a 3-phase VFD or brushless driver.
Theo

[najrao]

Thank you, Bratster. I had come to the same conclusion, refrigerator.
I have several af and rf signal generators, but none offers duty cycle adjust. Have to make up a 555 circuit, with isolated 5V Vcc for it. Or is there anything even simpler? Closing the loop is far away yet.
Hackaday was helpful, but how did he guess low duty cycles will do it? Remarkable.
Need time to get back and report if pwm and duty will set it up.