First CNC build - VFD wiring question

**Clive S** · 15-02-2015

Originally Posted by 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.

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

**IanParkin** · 15-02-2015

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** · 15-02-2015

Originally Posted by Clive S

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** · 15-02-2015

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!

**Bez** · 15-02-2015

Cheers for the replies guys :)

Looking through the manual it states its output current at 10A. Its not a fancy VFD just a huflugdung (Huanyeng) special bought from here http://www.cnc4you.co.uk/Spindle/Spi...h-Matching-VFD.

13A plug sounds like a winner to me but I will obviously be careful with other items running on the same ring until I can figure out its own ring for it to sit on.

So looking under the front panel I'm faced with this:

Motor wires are self explanatory so no need to go over those. Where I'm a bit confused is R S T ...... does it matter which one the live and neutral go to? Obviously the earth goes to "9"

I'm using a KK01 breakout board which has a relay output ..... am I correct in thinking this can be used to start and stop the spindle. If so which would be the correct blocks to wire it into from the basic mention in the manual DCM looks like it might be the one but rather than mess things up I'd appreciate any input for people who have run or are running a similar setup.

Thanks again.

**Neale** · 15-02-2015

Mains input is easy - just use two out of RST, and it doesn't matter which one is live and which is neutral.
Can't help off-hand with the spindle switching as I don't use it at the moment. One day I'll get round to proper spindle speed and on/off control, but I'm not there yet! For the time being, I just use the front panel controls.