Inverter help

Ok, I am new to the forum and have spent the last few days looking at all the topics on inverters, I have picked up some valuable tips but still not sure if my planned approach is correct.

I have a Fobco bench drill that is 3 phase 370 watt 400 volt @ Hz50 which I want to run as 1 phase 230 volt.

My simplified explanation is as follows, first change the motor to Delta, I have taken the 3 wires off terminal N and checked for a circuit (continuity) between A, B and C and the wires from N being Brown, Black and White, so I presume I connect the Brown, Black and White to the A, B and C terminals where there is continuity and that will set the motor in Delta mode 240 volt 3 phase.

Then purchase this **LINK**

can I then just run a cable to the inverter input from a 3 pin domestic plug and the 3 phase out to the motor terminals A, B and C.

another thing I am not sure of and that is, do I need to set the inverter to Hz 50 to keep the speed the same and will the switch on the side of the drill still work for forward and reverse.

Thanks for any guidance/help, David

It’s always good practice to get the next size up vfd to the power of your motor

yes you can connect up the vfd to a 3 core flex to a 3 pin plug but best to put it through a switch (nvr) as there could be voltage present ion the plug pins when its unplugged

the vfd connects directly to the motor (with nothing switchwise in between) using 4 core wire

then you use new switch gear start/stop speed(potentiometer) forward reverse switch emergency stop to control the VFD

you can set the frequency range between 25 hz and 100 hz and leave the belt on the second pulleys and have all the speeds you want at the turn of a knob

Is there a wiring diagram showing the wiring for delta/star on the inside of the terminal cover?

Why?

The product to which he links is made by WEG, designed for industrial use. It will supply the size of motor listed in its specifcations.

You might have a point if he was considering buying a generic Chinese VFD, but that is not so here.

It is possible to misinterpret your description above, so you might have to be more clear in the way you describe the connections.

In particular, you need to list clearly the relationship between the six wires.

I _think_ you are saying: red (A) and brown are connected; yellow (B) and black are connected; blue (C) and white are connected. However, my (or anyone else's) thinking is a particularly bad way to proceed. Certainty and clarity is required.

If this is the case, and you connect brown to terminal A (red), as you appear to be saying above, you are just connecting the two ends of the same coil together. No harm will come by doing so, but the motor will not work.

You have the delta triangle on the data plate. Each side of the triangle is one of the three coils. Each vertex of the triangle can be labelled sequentially A, B, C. So the 'start' of the first coil goes to 'A'. The 'end' of the first coil goes to 'B'. The start of the second coil goes to 'B'. The end of the second coil goes to 'C'. The start of the third coil goes to 'C'. The end of the third coil goes to 'A'. One each of the incoming phases goes to A, B, C.

Here's the wiring diagram from my brook crompton motor cover:

Your Plan will work, but there are some issues.

1/ The motor must be connected directly to the output of the VFD (inverter) wihout any switches, fuses etc.
2/ You need to provide an enclosure for the VFD.
3/ You need to provide Stop, Start and FWD/REV switches / controls. It may be possible to repurpose the existing controls depending on what they are. For anything other than your own hobby use it should also have a emergency stop and isolator to comply with safety regulations. You can maim yourself but not employees or members of the public.
4/ You could leave the VFD set at 50HZ but that is wasting a significant capability. Adding a simple potentiometer will give you variable speed control. You could set the maximum frequency to 60Hz and get 20% higher speed in each range.
5/ You don't need a NVR, the VFD can be set up so it will not automatically start when power is applied.

I agree with DC31K, with a branded VFD there is no need to derate it or buy a larger VFD than the motor rating. It actually has some disadvantages.

Robert

Robert

the nvr is to protect anyone who unplugs the supply and then touch’s the pins of the plug

i have had shocks this way in the past from quality drives

theres a warning re this in most manuals

I fitted my Fobco drill with a three phase motor and VFD years ago.

My advice:

Leave the belt on it’s slowest speed and incorporate a speed pot in a new control unit.

Forget the existing fwd/reverse switch and, if you need reverse, include a suitable switch on the control panel.

Wire the input to the VFD via a fused spur/fcu so it can’t be unplugged.

A little handwritten sign that says 'wait 30s before unplugging' is considerably cheaper, has no moving parts that might fail mechanically nor electrical parts that will emit smoke.

You could also locate the socket at ceiling level so by the time you have moved all the junk and fetched a ladder, the capacitors will have discharged.

I’ve never seen a commercial machine that didn’t have a NVR on the single phase input to a vfd

if you connect the input wires direct to the drive the pins are going to be possibly live for 30 seconds or so when unplugged

we can all do what we want with electricity in our own workshops but you do have to think about others..

While you may have used it for that purpose an NVR is not intended to protect against residual voltages. An isolator will perfom that function if required. Or as DC31k says a notice and wait.

While an isolator is a good idea, it does not have to be a switch. At least one standard, EN60204, allows a local plug and socket to be used. So using a IEC60320 inlet (e.g. C14 type as used on computers etc https://en.wikipedia.org/wiki/IEC_60320) on the enclosure containing the VFD is adequate. It also reduces the chance of touching the pins.

Robert.

If the VFD / machine is connected to a fixed outlet, i.e no plug & socket, the outlet MUST have a isolation switch. Ideally this should be able to be locked in the off position with a padlock.

Robert.

Edited By Robert Atkinson 2 on 20/05/2023 09:03:38

I fitted a VFD to my Fobco quite some years ago. I used a 2 kw Yaskawa VFD and configured it to output a max frequency of 100hz rather than the more normal 50hz. Although the motor is rated at 1425 rpm these motors come in a 2 pole variant that run at 2850 rpm so no problem operating at 100hz. The higher frequency gives a slightly increased speed range and so I rarely need to change belt setting for the type of work I do.

It would be interesting to fit a Brushless DC industrial sewing machine motor as these are rated at 500w (3/4HP) and have tremendous torque even at low speed.

CS

My understanding of ‘NVR’ is “no volts release” simply meaning that the drive will not restart, after a power interruption, without intended input from the operator. Electrocution risk is taken care of by other means and an NVR switch only safeguards against physical injury.

so how do I test which of the free wires, Brown, Black and White go to the correct terminals A, B and C for delta?

I do not have the original plate that covered the wires but looking online it seems most of the Brook Crompton 3 phase motor are wired the same as the picture shown by Pixel_Porpoise.

My point about a NVR switch in this application is to stop the real risk of electrocution if someone unplugged the 3 pin plug wired directly to a drive.and touched the pins within the discharge time.

all drives make note of this in the manuals..( i have been shocked too by this)

in my day job i repair many machines with drives and have NEVER seen a machine without a NVR device (meaning if the power supply is removed the main machine is isolated from the plug). fitted to prevent back flow to the plug

NVR in this application isn’t to do with the machine restarting if power is restored

bigger machines with 3 phase supplies wired into idolaters with conduit still have a contactor to disconnect the supply from the machine control circuits if the supply goes down

Presumably the shock hazard is from the Class X and Y capacitors used to filter RFI? If so, electrocution is unlikely, in the strict sense that the word means receiving a fatal shock.

Filter capacitors don't hold much charge, so although they can leave as much 350Vdc on the pins of a 13A plug after disconnection, there's not enough energy in them to kill a fit human.

Well worth protecting against though in the workplace, because they deliver a painful shock, causing folk to jerk into live wires, fall off ladders, and get entangled in moving machinery etc.

Last time I had a shock was tidying the cable after unplugging a laptop. I touched the plug pins, still here, expletive deleted...

Dave

David

Fundamentally the motor coils all have to be the same way round. If one is reversed relative to the other pair the motor doesn't run as smoothly or efficiently.

If you still have the coloured sleeves on them then follow the diagram posted earlier.

If you don't have the colours but haven't yet mixed up the wires follow the same sequence. Star point wires are all at one end of a motor coil and the free ends are the power input. So in delta connection carries one of the old power input connections and one ex star point connection from another coil.

If you have mixed the connectors up there is a way of measuring current through the coils to figure out if one is the wrong way round. Fortunately only one can be wrong relative to the other too so it's not silly difficult. I have it written down somewhere so can post if need be.

Clive

Edited By Clive Foster on 21/05/2023 14:18:43

PP has the correct wiring illustrated and you should use "mesh" which is the equivalent of Delta if you are running an inverter from domestic single phase mains. I always recommend checking out "The Inverter Drive Supermarket" and you will find that some of their inverters have a free "quick start guide" which is invaluble in all the wiring, external controls and programming. So helpful that even a dummy like me was able to wire remote speed, on off and emergency stop buttons. Having a proper box for the controls is recommended as the controls on the inverter are only intended for initial setting up, not continuous use. It is recommended that shielded wiring between the inverter and the motor and for the control wires is used to minimise interference from or to the system. I would go for the 0.5 Kw size inverter for your Fobco.

Welcome to the forum.

Edited By old mart on 21/05/2023 14:37:20

Edited By old mart on 21/05/2023 14:38:34

Edited By old mart on 21/05/2023 14:41:06