# Vfd Innards ?



## miro (Jan 26, 2016)

I've looked at VDs and have a basic grasp from the block schematics that abound on the web. But I'm trying to get a bit deeper, in particular, , the DC voltage that is made by the rectifier.
Is it a low voltage eg 12V ) or a high voltage (eg 220V).
I suppose that I could try measuring it , but I'd like to get some better education before I unbutton the box - or preferably without unbuttoning the box.

M


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## JimDawson (Jan 26, 2016)

It's high voltage.  About 1.414 * the input voltage, or around 330 volts DC in the case of a 230 volt input.


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## mksj (Jan 26, 2016)

Nice blurb from Fluke, lots of info online. It is hard to just read the VFD voltages with a DVM and get anything meaningful and sometimes there can be grounding issues with non battery operated scopes.  Getting scopes and probes that can handle the high voltages also needs to also be factored in. The bus voltage can  go higher when the motor is stopping and you get regenerative voltage, on a 240VAC unit this can be around 38oV going to the braking resistor. 
http://www.goies.com/Fluke-VFD-output-app-note.pdf


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## ch2co (Jan 26, 2016)

There's a lot more to most VFD's then just the voltage, phase, and frequency control, theres a huge amount of electronics having do with logic. Ramp up and down speeds, braking, external control capabilities, both computer and physical, torque modifications etc. The innards of my little Hitachi look more like a computer that an inverter.

CHuck the grumpy old guy


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## miro (Jan 26, 2016)

ch2co said:


> There's a lot more to most VFD's then just the voltage, phase, and frequency control, theres a huge amount of electronics having do with logic. Ramp up and down speeds, braking, external control capabilities, both computer and physical, torque modifications etc. The innards of my little Hitachi look more like a computer that an inverter.
> 
> CHuck the grumpy old guy



Guys, that helps a lot - these are very useful devices and it sure makes me appreciate the people who designed them originally.
Thanks.
M


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## Joe in Oz (Jan 29, 2016)

If you want to learn more, have a look at the schematic of the power section of the Huanyang VFDs here:
http://www.machsupport.com/forum/index.php/topic,14182.msg119422.html#msg119422
In fact you can learn a lot about these VFDs in the entire thread. People have reverse engineered the communications section as well.
As already mentioned, the control sections of VFDs are the complex bit. The power section is relatively easy to understand and trouble shoot.


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