The linked article has been discussed before; when I blew a rather large raspberry about it. After some discussion I think we decided that what he's actually doing is reducing the base speed of a star connected motor running from a 240V output inverter in order to maximise the constant power part of the curve. So I'd now blow half a raspberry.

The speed of an induction motor is primarily determined by the applied frequency. Voltage doesn't come into it. For any given motor at a given frerquency the voltage will determine the phase currents which in turn determine the torque.

I suspect the described problem is to do with internal parameters and/or the wiring of the pot not giving the voltages expected.

On the VFD that I happen to have sitting on the bench the heatsink has screws in two corners and the case has two moulded earth symbols next to the screws. That implies that the semiconductors on the heatsink are electrically isolated from the heatsink and the heatsink can be earthed. That may not be the case for cheap VFDs. If there isn't a terminal somewhere explicitly marked as earth I'd immediately bury the unit in the earth and forget about it.

Andrew

Can you post photos of the insides? If there's a switch or jumper should be visible, but it may be tiny. I don't understand the 5V/10V thing at all. I've read worse manuals, maybe some clot just left a paragraph out when it went to the printers!

Dave

This should do the trick. A 6.8k ohm resistor between 24V and a 4.7k ohm potentiometer should put 9.8V onto the pot, close enough for government work.

Can't help thinking this shouldn't be necessary, but it should work until an AT4 expert explains!

I recommend going down to a 4k7 pot because it should avoid the current / voltage problem you mentioned.

Dave

Gents I have 2 of these VFDs commissioned on a Dah Lih mill. They run the Vertical, Horizontal and Power Feed motors. All motors are 380/400V 3ph. They are wired up to expect that range.

As noted this model VFD converts 220-240V 1PH in and spits out 380V/3PH.

The control pot I use is 10K. It is wired per the manuals instructions. I used Parameters P73 and P74 as noted by Bruce to adjust to get the response I wanted from the 10K pot.

I am happy to check and post the parameters I have set for all the key values if that is of interest and would be helpful.

I know when I did my install the level of info on this control as a bit like getting blood from a stone. So after lots of experimenting I solved most things and have it operating.

Cheers,

James.

On my AT4 version, after some head scratching, I found the earth was located on the outer left-most terminal of the of the left hand green block above the 220v power input on your picture above- it is marked PE in minute lettering obscured by the casing (WTF!….yeah I know! …. don't start.), but don't take my word for it, check to ensure there is connection to the cooling plate.

On my device, parameter 74 is 63500 and P75 is 4200 basically the span and offset values for the external control.

Originally I noted these values along with other obscure parameters prior to use of the device (and a bloody good job too) seeing they were different from the 'manual'. As a test I input the values quoted in the 'manual' that were about half the 'as supplied' values and had similar half F issues.

I then did a reset (bad mistake – don't ever be tempted to do one). The reset resulted in the same low values replaced in P74 and P75 (among a whole lot of other unwanted changes).

I suggest you check what P74 P75 contain. If the stored values appear to be about 31000 and 1100, you could try the higher values quoted above and see if that helps and experiment from there until you are getting the range of control that you want.

Above all take care, this thing is a pretty scary device to have floating around on the test bench.

Edited By Martin of Wick on 23/05/2020 23:14:06

Martin – did you determine what P67 does? It is marked as "Voltage coefficient" in the manual.

Andrew,

Some mistakes in my original post – I referred to P74 and P75, when I should have said P73 and P74.

Originally out of the box, P73 was set at 61440 and P74 was set at 4096.

And P75 was set at 4196 with P67 at 45000.

I don't know what P75 and P67 do but have recorded the fact that they appear to change the reported output current and voltage on the VFD display.

I checked and confirmed with a clamp on that changing P75 did also appear to change the output current very approximately inline with the observed variance in the VFD display. Couldn't check the voltage as I don't have a filtering voltmeter.

As you see, all supplied values differ from the info sheet. Clearly the thoughtful manufacturers have provided a generic info sheet and couldn't be a***d to amend it for different products.

When I did the unit reset, all values returned (approximately) to those on the info sheet, but the AT4 was definitely not working as it should. Normal function was only restored when I re-entered the 'as supplied' parameter values as above.

On set up, I only checked to see if there was a voltage from the PE terminal ( you can actually just see it marked in your photo) to the mains earth and there was no potential, but then I wasn't expecting any – maybe I should check again because all may not be well if there is a voltage present.

I didn't ever record the voltage across the VR as it didn't seem to be an issue at the time. Unfortunately, my unit is not on the bench at the moment pending works to the drill for which it was purchased for. I will see If I can cobble something up tonight and let you know.