Inverter

Can you run say a 1hp motor through a 1.5hp inverter or even a 2hp inverter does it damage either one of these motor or inverter, hope this makes sense.

Al.

Yes, shouldn't be a problem....In fact I'm running my Chester Eagle 30 mill with a 1.1kw (1.5hp) motor and using a 1.5kw vfd bought from Ebay

No problem, though it's wise to programme the motor's characteristics jnto the inverter. Most important is the max current to prevent motor overload. The advice used to be that the inverter should be one size smaller than the motor, but I think that advice is now obsolete.  Ps it probably depends on the make of inverter. They're not all the same, but probably not different enough to matter greatly. Get the best you can afford.

Edited By jonathan heppel on 15/11/2013 22:13:25

Seen a 1hp inverter for sale at a good price but I would have preferred to fit a 1.5 hp motor that's the problem, my have to go for the smaller 1hp motor after all.

Thanks Al.

I have one Teco 2HP Inverter which has for years been powering various different machines all with different size motors ranging from 1/3 hp to 2 hp with no problems at all.

Swapping machines/motors is done by using a 3 phase socket and plug system.

Paul

Still no problem. The reason for the manufacturer's advice to use a motor one size bigger had to do with the spiky nature of the output. By all means use the 1.5 Kw motor.

Just checking Jonathon do you mean it's OK to run a 1.5hp motor with a 1hp inverter it's just you put 1.5KW motor.

Al.

Paul, what you're doing is fine as long as there isn't an overload any time. A DOL starter has thermal protection. Your small motors don't, and fuses aren't recommended for the drive's sake. You may well be fine for ever, but it is a potentially dangerous set up.

Alan, yes sure. As I said earlier, it used to be the manufacturer's recommendation, and is still good practice, particularly with budget drives and older non-vfd rated motors.

Whats dangerous about it then?

Your 2hp vfd thinks the1/3 hp motor is 2hp. If for example the rotor locked, the vfd would try to produce the current for a 2 hp motor, and fry it. Overloads or fuses between them could prevent it, but then you run the risk of blowing up the vfd- they really don't like having the load disconnected while running.

It's not hugely dangerous, but a drives pro wouldn't do it.

How strange... the recommendation to use such a setup came from Dave the chap that owns Drives Direct probably one of the biggest retailers of VFD's in the UK.

The newer vfd's or inverters , have the ability to "assess", for want of a better word, the motor its connected to the first time it is connected and powered up. I bought a Yaskawa vfd to run a 5hp colchester lathe and it did this for me. The electronics are getting really sopfisticated now and can do things only dreamt of a decade ago.

I still agree with what jonathan says though, match the vfd to the motor, if for no other reason than to save money, the bigger the inverter the bigger the bill. Why pay for engineering you are not going to use ?

If you don't tell the inverter that it's actually got a smaller motor connected and it tries to generate full torque or boost torque, it's going to put some serious amps into the machine that it wasn't designed for. This is likely to saturate the machine and certainly won't result in the required performance. And the various operating and protection schemes for the motor and inverter won't be set up correctly.

Modern inverters do some wonderful things as noted but they need to know some key information about the motor. This often requires little more than entering the motor plate ratings but it's worth taking the time to do so and isn't usually difficult.

So you don't have to choose matching motor and inverter but you should "match" them by correctly setting the inverter up. Obviously there's no harm running a large motor with a small inverter (the max limits are hard coded) but you simply won't be able to develop the rated torque and power due to the current limitation.

Merry

I would have thought that 1.5KW unit to be a minimum for a 1 hp motor and i'm currently setting up a 3/4hp motor to run from a 3.3kw inverter .
Overkill I know but the price difference between units is so small I thought I would get something that would cover anything i'm likely to need and so far no problems .

Other than motor voltage and frequency I have not noticed anything in the programming for maximum current but I would have to double check this , I did have an issue when first connecting this unit for its first run though - wired it up , double checked everything then hit the start - nothing but noise !
Went over everything again and could find no issues with wiring etc but was curious about the noise and it seemed like a frequency issue so I went to the manual and went through the settings for anything that had anything to do with frequency and checked for factory settings , it seems as though some of these units (hyoungyang ) are set up for the small high speed spindle motors and not a 50 hz induction motor ,easy fix is to change to 50hz max output and 10hz start then go from there .

I also had some fun setting up the emergency stop /fwd jog/rev jog as these use 3 of the 4 input terminals as one was labelled incorrectly but I eventually sorted this and marked it down in the manual..
The potentiometer they recommended (10K ohm) seemed to do nothing for the last half of its travel so I ended up having a play with this also and found a 1M ohm unit seemed to spread it a little and gave better slow speed control but it is still a little bunched up at the top end but I can live with it .

The manual clearly states not to place contactors between the VFD and motor nor a power cut out between the power supply and the VFD , from this I would say that opening contactors on the motor side of the VFD will kill the MOSFETS as they don't like to be disconnected while operating and the gate of a MOSFET is only a very thin layer of metal oxide , a voltage spike will find the least resistance and the gate will be it . Cutting the power to the VFD by turning it's power off while running isn't going to help but there should be protection diodes to kill any back emf but not worth the risk and there is an emergency stop feature in the programming if you look for it .

Other than that i'm very pleased with the unit .

Ian

Ian, I suspect that the pots you used are log types intended to be used as volume controls. A VFD should use a linear type.

Hi John ,

I thought of that but the pot is marked LIN and a check with a meter would suggest this is correct .

The pot on the VFD is the same , it only works in the first half of its travel so I am starting to think it may be an internal issue or something to do with the reference voltage that is set up for the pot .

I am thinking about trying a logarithmic pot at 10k as it may counteract the effects i'm getting from a linear pot at the same value ?

The reference voltage is 10v but there is also an output for 5v so I may also try this tomorrow although I suspect I will not achieve full rpm with this but ...

Ian

Ian (Slo...)

My first thought was that a log pot had inadvertently been used. As its not then something else is clearly amiss. Is the fact you mentioned wrongly labelled terminals a clue?

I have not heard of the manufacturer you mentioned, nor of a VFD that did not work out of the box (after making a few simple checks or changes).

What is the documentation like? does it give proper wiring diagrams and input output details of each connection? I would assume the pot is wired across a reference supply and the wiper feeds an analogue input terminal. It sounds (just possibly) that the pot is wired incorrectly.

Ian P

There really isn't a need to over specify a quality inverter. The manufacturers know what they're doing.