First CNC build - VFD wiring question

[Bez]

Hi All,

Fingers crossed I have put this thread in the right place - apologies if not..

I recently stumbled across this forum, not sure how I missed it up until now but that's another story lol

Anyway to cut to the chase I started building my first CNC towards the end of last year, as is normally the way things set me back and other projects took all my time up. On the proside I how have it 95% wired up and motion control is working a treat. All I'm left with is the VFD.

Now I'm sure this is a pretty basic/stupid question but here goes:

Am I correct in thinking the VFD (2.2kw) can be powered directly from the plug socket (via an isolator)? Or does it have to be wired via a separate power source?

I just don't want to plug it in and blow it up within seconds,

Many thanks in advance.

Bez

[Neale]

There was a discussion about this a little while ago. Simple answer is to stick a 13A plug on it and plug it in the nearest socket - no problem.

[EddyCurrent]

According to the manual my 2.2kW inverter can take up to 21 amps on the input but that allows for overcurrent. I have the max amps set to 17.6 A.
It's only because we don't run them flat out that a plug works.

[Clive S]

According to the manual my 2.2kW inverter can take up to 21 amps on the input but that allows for overcurrent. I have the max amps set to 17.6 A.
It's only because we don't run them flat out that a plug works.

Eddy You can plug a 3kw dryer into a 13A socket or washing machine. So I think 2.2Kw is no problem ..Clive

[IanParkin]

Clive a dryer is mainly a resistive load rather than a reactive load as an inverter is...so its not quite as simple as that

[EddyCurrent]

Eddy You can plug a 3kw dryer into a 13A socket or washing machine. So I think 2.2Kw is no problem ..Clive

I only said the manual states it can take 21 amps input, I can't argue with what the manual says.
You need to multiply three phase amps by sqrt 3 to get single phase amps.
2.2 kW 3 phase motor amps = 9.5 A, single phase input amps 9.5 * 1.73 = 16.45 A

[Neale]

I think that Eddy has already pointed out that the inverter manual takes into account over-current. Not sure what that inverter is rated at, but I use a 5KW inverter on my lathe which is rated at something like a few seconds at 100% overload and 30 sec at 50% overload. I think that this is probably to allow for motor run-up initial surge, although I'm not driving it that hard. However, let's say max load for a normal Chinese VFD/spindle combination is a nominal 2.2KW, and allowing for conversion inefficiency, that's going to draw maybe 2.5KW from the supply. That's about 10A. Short-term permitted overload is about twice that, which neatly comes out to about 20A - which is where we started!

In real life, though, I would suggest that there are two possible times when the inverter is likely to trip the supply fuse/breaker. One is when you first switch it on. These devices typically rectify the incoming single-phase supply to give a DC supply internally which then drives the 3-phase output generator. There will be a small surge at that time which can give problems. Sometimes the problem is due to funny phase relationships between input current and voltage which can trip RCDs. However, my limited experience with my 2.2KW inverter is that this never happens (although it is a problem for the big inverter I use). Second time it might trip is when the load comes on, i.e. motor startup. However, the inverter is generally set to soft-start the motor - ramp up speed over a few seconds - and that keeps the peak load down. Anyway, you will be spinning up a motor when it is not cutting, so that reduces the load as well.

Upshot of all this in practical terms - it works fine for typical router purposes off a standard 13A socket!