Use of induction motors in the home workshop - updated Iss2

[9fingers]

I have now compiled the parts into a single document at issue 1 located here

http://homepage.ntlworld.com/bob.minchi ... Issue1.pdf

Mod edit: Latest version: http://homepage.ntlworld.com/bob.minchi ... Issue2.pdf

I have changed the title as I spotted just in time that Jim Cox has a book out with the original title I had chosen. It also is more accurate as I have concentrated on Induction Motors.


I will leave it up to the moderators to decide if it stays as a normal post, becomes a sticky or gets placed somewhere else.

I hope it will be useful.

Bob

 

[devonwoody]

Thanks for your time freely given and sure that others have the same thoughts.

 

[laird]

Great job, well done and thanks.

 

[Boz62]

Excellent. Thankyou.

Boz

 

[Steve Maskery]

Bob
Thank you very much, that is excellent.

I have a q.

If I understand it correctly, the inverters you talk about only change SP to 3P. The input and output voltages are the same. Does this mean that, in order to run 3P, I would need a transformer to up the V from 240 to 415, then an inverter to change from SP to 3P?

Cheers
Steve

 

[9fingers]

Bob
Thank you very much, that is excellent.

I have a q.

If I understand it correctly, the inverters you talk about only change SP to 3P. The input and output voltages are the same. Does this mean that, in order to run 3P, I would need a transformer to up the V from 240 to 415, then an inverter to change from SP to 3P?

Cheers
Steve

That is certainly one route Steve but the inverter needs to be rated at 1.5 to 2 x the rating of the motor to avoid overloading the input stages of the inverter.
There are also the 'new' breed of 'converting inverters' that some of the traders are selling.
The first thing is to check to see if you have a dual voltage motor. If you have then only an inverter is needed.
Have a look at the rating plate and to be sure, whip the top off the connection box and look for the 6 terminal block as shown in figure 6 and 7.

Bob

 

[Steve Maskery]

Right, so it's possible to have a motor rated for 415V, 3P, converted to run on 240V but still 3P, running on an inverter.

Am I keeping up here?

Cheers
Steve

 

[9fingers]

Yup spot on track Steve.

3p is a power transmission method and theoretically it can be at any voltage.

The UK leccy board deliver it at 415 volts but a domestic inverter run on 240v input will generate 3p at 240v

If at the same time you have a motor that will accept 240 3P then all is well.

Bob

 

[SemiSkilled]

Bob,

Excellent write up, could be a classic in the making

Thanks

Lee

 

[Steve Maskery]

What an educational week!

I've also learned that the colour of an eggshell depends on the breed of hen, but the colour of the yolk depends on what they've been fed.

In Yorkshire they use knitting needles that stick out of their belt.

Larch can be used as soon as it is cut, it doesn't need to be seasoned.

I'll soon know everything.

Thanks very much, Bob.

Cheers
Steve

 

[Tony Spear]

Yup spot on track Steve.

3p is a power transmission method and theoretically it can be at any voltage.

The UK leccy board deliver it at 415 volts but a domestic inverter run on 240v input will generate 3p at 240v

If at the same time you have a motor that will accept 240 3P then all is well.

Bob

But what about the power output? Surely if you've got a motor rated 1.5 kW at 415V, it's certainly not going to deliver that at 240V?

 

[9fingers]

Yup spot on track Steve.

3p is a power transmission method and theoretically it can be at any voltage.

The UK leccy board deliver it at 415 volts but a domestic inverter run on 240v input will generate 3p at 240v

If at the same time you have a motor that will accept 240 3P then all is well.

Bob

But what about the power output? Surely if you've got a motor rated 1.5 kW at 415V, it's certainly not going to deliver that at 240V?

Yes it will deliver the same output because it will draw more current per phase from 230 volt see the rating plate and related text on pages 7 & 8
But it MUST be a motor designed for dual voltage (star/ delta)

Which ever way the motor is wired (star or delta) and run from 415 in star or 240 in delta , each coil gets the same voltage of 240 volts and so the motor delivers the same power.

Bob

 

[dewi]

Bob - thanks a lot - most helpful

get yourself a drink next time your near a pub :lol:

 

[9fingers]

Bob - thanks a lot - most helpful

get yourself a drink next time your near a pub :lol:

Cheers Dewi - you are all heart! :lol: :lol:

Bob

 

[ibcallus]

Hi Bob,
thank you for the info it is very interesting and helpful,

Ibcallus

 

[Steve Maskery]

Bob, I know his is cheeky but here goes.

An obvious source of motors for the likes of us is a defunct washing machine or tumble dryer. They always look scary when I open them up, and I've recently taken one to the tip. I did think of trying to salvage the motor (it was the programmer, I think, that wasn't working and I've learned from experience that these things are rarely worth repairing unless you can do the job yourself).

So, say I was a complete novice at this lark but had a perfectly good WM motor at my disposal, what would I need to do to be able to use it in the workshop?

As I say, cheeky, as it is even more work for you, but you've done such an excellent job so far, it would be a shame to stop now, wouldn't it?

Cheers
Steve

 

[9fingers]

Bob, I know his is cheeky but here goes.

An obvious source of motors for the likes of us is a defunct washing machine or tumble dryer. They always look scary when I open them up, and I've recently taken one to the tip. I did think of trying to salvage the motor (it was the programmer, I think, that wasn't working and I've learned from experience that these things are rarely worth repairing unless you can do the job yourself).

So, say I was a complete novice at this lark but had a perfectly good WM motor at my disposal, what would I need to do to be able to use it in the workshop?

As I say, cheeky, as it is even more work for you, but you've done such an excellent job so far, it would be a shame to stop now, wouldn't it?

Cheers
Steve

Most washing machine motors a quite unsuitable for workshop applications
They run far too fast and must be used with the controller from the machine. The motors incorporate a tacho generator which supply a speed proportional signal to the controller. The controller is driven by signals from the programmer that need to be duplicated for the controller to behave properly.

The other big problem is that they are normally 'open frame' with live parts such as the brushes totally exposed which will be dangerous as well as letting sawdust get into the works.

Finally they are not continuously rated only needing to deliver full power during say 10 minutes of spinning with breaks in between.

Generally speaking the best place for them is the tip.

Sorry to dissappoint you

Regards

Bob

 

[Steve Maskery]

I'll read that as a No then, shall I?


Thanks anyway
S

 

[9fingers]

I'll read that as a No then, shall I?


Thanks anyway
S

Yup that is correct Steve

I could have just said "no" but prefer to give reasons to increase knowledge of the subject.

Bob

 

[Steve Maskery]