Single Phase cap start cap run with VFD 2

[mitsi]

I have an application with two single phase cap start/ cap run motors.The control gear is shot and the customer wants to up grade using single Phase vfd,s. Has anyone done this before? Regards

 

[jraef]

You can't do it, or at least shouldn't. The PWM output of the VFD will eventually damage the caps, the charging current of the caps will eventually damage the transistors in the VFD. It's just a race to see which one lets out the magic smoke the fastest. If you read carefully in the details of ALL of the 1 phase VFD literature, it clearly states that they are to be used on PSC or shaded pole motors only.

 

[mitsi]

Hi jraef, thanks for the advise. I gather that the caps would have to come out of circuit and as the pumps are submersible it is not a supprise they are in the cabinet and not on the motor as usally seen. The windings are the main intrest, IE: 2 or 3 sets?. I will have to bell out to confirm, as if they are 3 sets it may be okay to connect to the VFD or if 2 sets ( start and run ) I may have to use capacitors. What do you advise ?

Best Regards

 

[LionelHutz]

Stick with a full-voltage starter or use a soft-starter. Using a VFD with those motors is not an option.

 

[jraef]

Yes, if the motor was designed as a cap start single phase, you cannot take out the caps.

But some submersibles from European or Asian suppliers are actually 3 phase motors and their N. American sales divisions give you a static phase-adder panel with them for derated 1 phase operation. Check the pump manufacturer on that one, but be aware that if you now use them as 3 phase motors with a VFD, the HP may be higher than you thought it was, meaning a larger VFD than what the 1 phase nameplate may indicate.

 

[mitsi]

Thanks Guys

 

[Skogsgurra]

It may not be known to many. And I do not think that they are available in the US. But there are VFDs with a pure sine output that can be used in applications where VFDs have been considered impossible.

(Yes, I have been involved in that company, if you ask. But I left the board four or five years ago, so I think that it is OK to tell you about them now).

Go to

http://www.nfodrives.se/

and click the English flag. These inverters are the only ones that are allowed onboard stealth vessels, because they have lalmost no emission and the acoustic noise from the motors is nil.

Gunnar Englund

http://www.gke.org

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