.37kw vfd for a .75kw motor 3

[Risingtenpi]

Guys,

In my searches, I have not found any information regarding the underspec of a VFD. I already have some 0.75kw motors on small conveyors (from another job), and need to purchase some VFD's for them. However, I do not need their full rated power. In fact, they are for conveying tree nuts, and could probably be a 1/10 hp motor on each conveyor.

Will I have problems using .37kw drives on these .75kw motors? Will the drives current protect themselves? (obviously they will be running a load below their power capacity) For reference, I am looking at WEG 240V single phase to 3 ph drive. (CFW10 240V EASYDRIVE IP20)

Thanks in advance,

Michael

 

[Skogsgurra]

You have to be careful with the excitation current. It can easily be 60 % of rated current (cos(phi)=.8). That would mean that a .37 inverter will be overloaded even if the motor is idling. Reducing motor voltage could help.

Why doing this? Is there an economic advantage?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Risingtenpi]

Skogsgurra,

Thanks for the response. There is quite an economic advantage, as a supplier has some surplus .37's which are about 1/2 price of the .75's. Is there an easy way to determine what excitation current would be drawn by my motors?

As for reduced voltage, I am think this VFD will be operating in constant V/f mode - and so operating at say 25hz (for Australia) would be half voltage.

If this is correct, then I *should* be fine?

Michael

 

[Skogsgurra]

Just test it!

Buy one of the .37 inverters. Connect and test run. There is usually (always) a parameter that sets motor voltage at nominal frequency. Adjust that so that your magnetizing current (proportional to voltage, more or less) when idling at full speed doesn't overload the inverter.

Also. If the motor can be wye/delta connected and delta is for your voltage. Then the wye connection reduces magnetizing current. The motor gets weaker in both cases, but since the shaft load is low, it will probably work out well.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Risingtenpi]

Good point with the wye/delta.

What I have learned so far:
*For a motor that is 'idling', then magnetizing current should be my limiting factor.
*I can get around this by decreasing voltage at 'X' frequency, or connecting in wye (it is currently delta)

So, on this information, I will get the smaller units at substantial savings...

Thanks for the tips.

Michael

 

[itsmoked]

I only see about a $20 difference between a 1/4hp and a 1hp drive - no messing around.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Risingtenpi]

I am looking at around aud $166 for a .5hp and aud $249 for a 1 hp. I figure that on 3 drives, I can drink a lot of beer for a little messing around...

Just for curiosity, can you find better value? I might have to share that beer if so...

cheers

 

[Skogsgurra]

Where are you Rising? Keith and I need to have a few beers together... And if you do the paying, I think it is worth messing a bit.

Hmm.. Sorry, came to think about Keith's idea of not drinking beer.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

LoL.. I do like root beer tremendously.

Risingtenpi; Here's an example: (Note the 230V single to 3ph)

http://www.factorymation.com/s.nl/sc.2/category.13/.f

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

That's a great site, Keith. I have bookmarked it for reference.
LPS for you and friend Gunnar.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[controlsdude]

that factory autmation link looks like the allen bradley 160 vfd that were the same footprint. They were at that HP and that cheap and lasted forever and never had one fail in infancy when it was installed.

 

[itsmoked]

Bill that is indeed a great little site. If I have to do a control panel I go there and can get 90% of what I need at excellent prices. They try really hard to put the stuff needed there. It has doubled it's offerings in the last year. I love the industrial switches offered. They're very nice and about 1/9th the cost of Allen Bradely's.

Check the motor starter prices.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Risingtenpi]

I am on the Gold Coast, Australia...

Looks like I'm Buying!

I too like that site. Shipping is a bit expensive to Australia, but I am heading over that way in 2 weeks - I can wait that long to save US$150 for shipping!!!