Electrical/ Electronics Experts .. Help!
Electrical/ Electronics Experts .. Help!
Author
Discussion

vixpy1

Original Poster:

42,699 posts

293 months

Monday 4th July 2005
quotequote all
I need to control the speed of a 7.5kw 14amp 3 phase 415V fan.

I'm presuming you can get a simple speed control box, but i can't seem to find one anywhere.

Is it possible, can anybody give me a few pointers?

parrot of doom

23,075 posts

263 months

Monday 4th July 2005
quotequote all
Take one of the phases off

vixpy1

Original Poster:

42,699 posts

293 months

Monday 4th July 2005
quotequote all
Yes, but i really need a bit more control than that!

Vitesse39

731 posts

277 months

Monday 4th July 2005
quotequote all

Take 2 of the phases off

stefd

290 posts

257 months

Monday 4th July 2005
quotequote all
For a 3 phase motor you're going to need a frequency converter (aka inverter).

Quite a few out there but they aren't cheap. Simple voltage type speed controllers only work on single phase motors (as far as I'm aware).

Jon C

3,214 posts

276 months

Monday 4th July 2005
quotequote all
stefd said:
For a 3 phase motor you're going to need a frequency converter (aka inverter).

Quite a few out there but they aren't cheap. Simple voltage type speed controllers only work on single phase motors (as far as I'm aware).


Its amazing what you can find on E bay these days.....

vixpy1

Original Poster:

42,699 posts

293 months

Monday 4th July 2005
quotequote all
Back to the top for the evening guys...

dilbert

7,741 posts

260 months

Monday 4th July 2005
quotequote all
The inverter is the proper solution, but I'd have thought that for something like a fan, rather than something with a dynamic load, you could get away with mechaniclly ganging three single phase thyristor circuits.

I'm thinking that you literally buy three dimmer circuits and arrange for the potentiometer roatary control to be physically linked.

Pigeon

18,535 posts

275 months

Monday 4th July 2005
quotequote all
I agree that it might be possible to get away with that, but off-the-shelf dimmers won't be able to handle the power - they generally go to 500W. Here we've got 2.5kW per phase and you can reckon on considerably more than that on startup. You'd have to uprate the triacs, and they would need heatsinks.

I suppose you might have more luck looking at dimmers for theatrical lighting where you can have some pretty beefy single units.

Or you could run it off a three-phase diesel generator which you convert from fixed to adjustable throttle...

pearl nicholas

11,871 posts

262 months

Monday 4th July 2005
quotequote all
try rs spares

>> Edited by pearl nicholas on Monday 4th July 22:36

>> Edited by pearl nicholas on Monday 4th July 22:37

>> Edited by pearl nicholas on Monday 4th July 22:38

alexkp

16,484 posts

273 months

Monday 4th July 2005
quotequote all
pearl nicholas said:
try rs spares

>> Edited by pearl nicholas on Monday 4th July 22:36

>> Edited by pearl nicholas on Monday 4th July 22:37

>> Edited by pearl nicholas on Monday 4th July 22:38


How on earth did you need to edit that three times?

mybrainhurts

90,809 posts

284 months

Monday 4th July 2005
quotequote all
vixpy1 said:
I need to control the speed of a 7.5kw 14amp 3 phase 415V fanny shaker.


....VROOM, VROOM

dilbert

7,741 posts

260 months

Monday 4th July 2005
quotequote all
Pigeon said:
I agree that it might be possible to get away with that, but off-the-shelf dimmers won't be able to handle the power - they generally go to 500W. Here we've got 2.5kW per phase and you can reckon on considerably more than that on startup. You'd have to uprate the triacs, and they would need heatsinks.

I suppose you might have more luck looking at dimmers for theatrical lighting where you can have some pretty beefy single units.

Or you could run it off a three-phase diesel generator which you convert from fixed to adjustable throttle...


Good point.

I re-read the original post. A ten horsepower fan is one heck of a fan. What's it for? Certainly make for a good hairdryer!

vixpy1

Original Poster:

42,699 posts

293 months

Monday 4th July 2005
quotequote all
dilbert said:



Good point.

I re-read the original post. A ten horsepower fan is one heck of a fan. What's it for? Certainly make for a good hairdryer!


Cooling the cars on the dyno... It is quite possibly the most awesome thing i've ever seen, I mean... I might have gone overkill with the specs of it a bit..

BliarOut

72,863 posts

268 months

Monday 4th July 2005
quotequote all
His rolling road I would hazard a guess

vixpy1

Original Poster:

42,699 posts

293 months

Monday 4th July 2005
quotequote all
BliarOut said:
His rolling road I would hazard a guess


Wow, good guess!

dilbert

7,741 posts

260 months

vixpy1

Original Poster:

42,699 posts

293 months

Monday 4th July 2005
quotequote all
They look horrifically expensive!

dilbert

7,741 posts

260 months

Monday 4th July 2005
quotequote all
Well they might be, but I didn't bother with a price comparison.

I think much of that high end industrial control and automation equipment is expensive. I guess what you are paying for is the ability to tighten the screw terminals down knowing that installation wasn't a nightmare and that it'll work like you expect it to.

If you're an equipment manufacturer, you'll design your own from descretes. That means that volumes are comparitively low, and prices are high.

I wouldn't be surprised if it's the sort of product that is still keeping the EU engineering industry afloat. I doubt it's the sort of thing that China is that interested in.

I think most people forget how expensive non consumer electronics actually is.

Now try the defence industry, if you want expensive equipment.

>> Edited by dilbert on Monday 4th July 23:44

Pigeon

18,535 posts

275 months

Monday 4th July 2005
quotequote all
Check out the third entry down on this page... looks big enough for the job: www.cse-distributors.co.uk/old-stock/complete.asp

I reckon that's cheap as these things go. You can pay more than that for a telly