quasi
Stainless
- Joined
- Dec 18, 2003
- Location
- Calgary, Alberta, Canada
will a VFD that is not specifically rated for single phase input/three phase output function properly with single phase input.?
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Unless the manual specifically says that it IS rated for single-phase input, it should not be used with single-phase input.will a VFD that is not specifically rated for single phase input/three phase output function properly with single phase input.?
That's why they print manuals
For other input voltages, derating information, etc, please contact the factory
Nothing in a VFD is going to measure phase-to-ground. It will look at essentially phase angle differences between the 3 phases. So with 1 phase, no matter what you do, two of them will not have any difference.Question: can you fool phase loss detection by connecting one of the single-phase legs to two VFD input terminals, instead of just one? I imagine this might work if the phase loss detector looks at voltage phase to ground, rather than phase to phase.
A lot of drive designs use a DC-DC power supply and tap off for control power from the DC bus, which means it doesn't matter at all which line terminals you connect to. I'm not sure why they don't all do it that way, but they don't.
Because you're adding an entire additional inverter and drive system for a simple function that could be accomplished with a small transformer.I'm not sure why they don't all do it that way, but they don't.
Because you're adding an entire additional inverter and drive system for a simple function that could be accomplished with a small transformer.
The AC source for the control system is not variable frequency, so the inverter drive would need to be independent of the drive signal for the VFD main outputs.
Regulating the HV DC bus down to 24 volts or so for the control system, given a drain of a couple of amps, would increase the power dissipation within the VFD by a huge amount.
Probably best to avoid the concept entirely and put in a little transformer and a standard switching supply.
- Leigh
That's not sufficient for safe operation.And, I know I have power so long as there is DC, even if I am given DC on a common bus.
That's not sufficient for safe operation.
Modern controllers, i.e. those using any type of "intelligent" control system, be it CPU-based or similar, require time to initialize before they are operational.
Simply applying power to the control system at the same time you apply power to the output stages leaves a time interval during which there is no active control of the output. In fact you would have output stage power applied BEFORE power was available to the control system due to capacitor charge delays.
It also prevents the control system from doing a proper power-up self test to determine whether it and associated systems are functioning correctly before applying power to the output stages.
In other words...
Extremely bad product design from a safety standpoint.
- Leigh
That's an interesting concept... Power-on testing with power off.2) Power on testing is easily performed whether or not the main power is applied..... it depends on what you decide to test.....
That's an interesting concept... Power-on testing with power off.
Given your earlier statement that ALL power had to come from the main DC bus, there's no other interpretation possible.
I guess the laws of physics don't apply to VFDs.
And BTW, I don't dispute the claim that your solution was common practice. I just said it was bad design.
- Leigh
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