Spot the connection

Steve,

2 wire= binary logic IE. Stop is wired with NC switch feeding start & direction NO switches (often of the momentary variety but not exclusively which is why you can use your existing rotary switch). If stop is NOT pressed then start or reverse will result in a signal at the inverter. As long as inputs are latching then things are fine for basic operation. If you want more control you need more wires - I don't know why it is called "2 wire" but it might be due to the logic of the basic switch arrangement being along the lines of binary? Or it could just be a generic name the electricians I know have come to use.....

You will find that the different makes have different ideas but they will all do the same basic operation, it will just be a case of working out how!

Having a workshop running exclusively on inverters I can strongly advocate the use of load reactors (output filters/chokes) on the motor side and line filters on the mains side - I was amazed how effective they are at killing the electrical noise and high voltages. I concluded that messing with winding conversion warranted giving the motor all the help I could in continuing to work and these help a lot.

Mark

I had meant to add that your motor was very much like the small motor I did in that the star point was wired using tails, the other two I did had just the windings joined without tails, the 3/4 hp was on the outside of the windings and the hard one was buried under all the field winding connections which is why it was a pig to do!

If you take the covers off and can see three tails all going the same place they are a good candidate for the star point, I checked mine when I had split the star point out for equal resistance in case I had it wrong but they are going to be quite low resistance so you need a decent meter for the job.

Mark

Mark

2 wire control is used if you have latching switches so your start switch is n/o and wired in series with a n/c stop switch only if the switch latches on will the inverter start and carry on running

and i dont think this system is a no volt release system as if your start switch is on and the stop switch is out then the inverter will start on power up

Most inverters allow you to make the inputs latching or not.

if you want to use normal switches (unlatching) you need 3 wire control

Ian

Ian,

Yes, you are correct about the power on problem with latching switches, not a hope of HSE passing that one off! Industrial practice is quite a bit different to our workshop requirements but we should all be working safe all the same.

Getting the wiring correct for latching inputs can sometimes be a bit confusing but I don't think any of the modern inverters lack this function, not even the cheap imported types.

The idea that you can run inverters 2 or 3 wire is a bit of a confusion at best, you really need a few more than that in reality. Most of the time the minimum you need is 7. This comprises a digital common, the start stop logic and the three wires for speed control - the analogue input often uses a different ground to the digital common - all of which I suspect you know already... but it might help others just getting their hands on inverter drives for the first time.

When Steve gets his inverter he can probably get a fair bit of help here setting it up if he is finding it a bit daunting - some of the parameters can be a bit confusing at the first attempt.

Mark

PS. I mention 7 wires as it is very irritating to get home with all your new toys only to discover that the six core you got for the job is a wire short for the job in hand.....

Edited By Mark C on 05/10/2015 21:38:53

Judging from what you've written in the above posts I think you're right, I will need some help with the wiring.

I've just checked the coils and I get 3.2 ohms for each of the coils.

That sounds to be ball park to me. More important is that they are all the same.

Mark

What make of inverter?

If you go for an IMO one, see here for some ideas on wiring up.

Neil

Neil,

I use all sorts including the cheap import ones. Probably my favorite is the small GS1 offered by Lamonde Automation, they are a good price, very compact and reliable.

Mark

Lamonde Automotion are also a good source of push button switches if you are making up your own control boxes.

My question was aimed at Steve!

Neil

Yes, I knew that - I was just adding a spurious comment in case Bill or anyone else was interested! Perhaps I could have worded it better?

Mark

I now have 6 wires appearing out of the connection box, all the new wiring connected, sleeved and tied in. The connection box itself has three terminal posts, and I have labelled the three original wires 1, 2 and 3. The other ends of each of the coils are labelled 1B, 2B and 3B respectively, and these are the ends which were originally connected together to form the star point.

Presumably I can now connect the wires up to the three terminal posts as follows: 1 and 3B together, 3 and 2B together and 2 and 1B together, my thinking being that if one or two of the coils are reversed there won't be 120º between the phases.

As to the inverter Neil, I have yet to buy one. I keep looking on eBay and see models by Huanyuang at around £100, compared to around the £250 mark for a known name like Hitachi or Mitsubishi. I have no idea which to go for.

Steve,

Sounds good to me!

At 3 HP you are going to be spending a bit more than the normal 1HP drives cost. I have a 4kW Huanyang from ebay. The cost for anything else was well over 300 quid for one this size new. I would be happy to buy another with the reservation that you will probably "need" rather than "want" a drive reactor as I mentioned. I get mine from Lamonde as they are the only place I have found that sell the correct spec reactor for the application (voltage and power) at a sensible price. the only down side to these inverters is the size which - they are bigger than comparable "named" drives. If you are sticking it on the wall up in the air that should make little difference.

They are also easy to set up if you get some help - Along with others who have been down this route, I would be happy to assist with the parameters that you need to change for a lathe/mill installation.

Mark

Nice looking Yaskawa V1000 2.2-3.0kW drive for about £200 inc vat and delivery?

Never heard of a load reactor before - is it to iron out the peaks or to provide some sort of suppression?

Also I've seen some people mention that I might need a vfd with a higher rating than the motor size. Is this true?

Thanks for the Lamonde link, which may come in handy in a week or two.

Muzzers prices are better than I could manage - wish I had found that outfit a while back (I have spent quite a bit of money on drives for my products).

You only need a drive rated for your application, you can always use one with a higher power output and use it de-rated should you choose.

Drive reactor (choke) produces an output that is closer to the mains than the HF output from the inverter. You need to look at the output with an oscilloscope to see and appreciate the difference - it is a drastic improvement over the unfiltered output. If you get interference up the line onto the ring main, you will also want a filter on the input side but they are much cheaper.

Mark

What matters to a motor is the current in the windings which ultimately is what generates the torque. If you are going to look at the motor with a scope it's more instructive to use a current transformer to observe the phase current than to look at the PWM voltage. The motor inductance filters out the high frequencies so that the current is highly sinusoidal - often more sinusoidal than when the motor is connected directly on line. The mains waveform is often fairly distorted.

The main benefit of a filter choke on the output of the inverter is to reduce the interference due to the voltage transitions resulting from the PWM waveform. The voltage transitions on a single phase input VFD are typically of the order of 340V in a few hundreds of nanoseconds. This can generate significant recirculating currents in the motor wiring. After the filter choke (where fitted), the voltage edges are almost eliminated - at a cost obviously. Keeping the wiring short and using shielded cables can help too.

Murray

Murray, I don't know about the AC theory involved particularly but I can speak from practical experience that once I fitted a choke all my problems with analogue signals went away and looking at the screen, it went from a mass of traces all over the screen to a nice tight steady voltage trace with a few volts of ripple. I did notice that the signal (once smoothed through the choke) showed a distorted form from a sinusoidal trace - it seemed to be pulled down on the falling side of the trace, equal on all three phases? Is this what you meant when you say the motor can distort the line voltages?

Mark

No, what I meant was that the waveform generated by VFDs is generally very sinusoidal, as it's digitally generated. In contrast, when you look at the mains voltage, it's often distorted, particularly at the crest, due to the non-linear loads connected to it. A lot of equipment only takes power from the crest of the waveform, leading to a flat top there. Doesn't affect the motor power really. You'd have to post a picture of what you meant to understand better what you mean.

The output filter significantly reduces all the switching frequency edges, so it's not surprising you have got much cleaner analogue voltages. If you imagine being one of the analogue inputs and trying to figure out what the "real" signal is amongst all the noise, you can understand why filtering the noise at source is the best fix. Engineers often think they can simply filter out noise on the inputs with low pass filters and / or software filtering (averaging etc) but it generally doesn't work like that.

My background is power electronics, so designing with this mixture of noisy power and quiet analogue signals is what it is all about for me. Bottom line is that each installation will be different and must be commissioned carefully to ensure it works as intended.

Sounds as if you've got a good, solid setup on your systems. Hopefully this will avoid strange unintended behaviour later on!

Murray

After reading the above regarding interference, I wonder if one of those input filters as fitted to washing machine would be of help. After all they are readily available and appear to be well made. I have fixed several front loaders for the family and have never seen a faulty one. Just a though.John