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Bucking to match V/Hz

Bucking to match V/Hz

Bucking to match V/Hz

(OP)
Can you guys help me be sure I'm thinking this through correctly?

I have a 208-230v singlephase 60Hz motor running on a 240v 50Hz supply, and want to get it down to 190v. I am not able to touch the motor, add a VFD, or get different power. I may however, be able to add a transformer near the source.

I was thinking of wiring a 750VA (240/480P 24/48S) (acme T181066)autotransformer in to get 192v, 2995VA, 15.6a.

Using the formula

TOTAL OUTPUT VOLTS X SECONDARY CURRENT (RATING)= VA (192v X 15.6a = 2995VA)

This would be the total available power to my load as I understand it.

The 2HP motor FLA @ 208-230v 60Hz is 11A (only one # for both V on data sheet). I was at the site last week and found it pulling 12a at 240v, peaking around 20a when starting. If I reduce the voltage 20% to meet the V/Hz ratio, I assume the current would rise 20%, which would mean it will go from 12a to 14.4a.

If this is ok, the only hiccup I've got is that the ACME transformer is not CE marked. If you could recommend a European transformer company (as opposed to a random google search)that might have a similar model, it would help.

On another subject, I found the starting cap on the motor was rated 125v. (which blew and was successfully replaced with a 300v cap) This motor is a dual winding 115/230v and I thought the cap should be rated at least 250v if not higher, and asked the motor manufacturer and he said that 125v was correct for that motor, and that only when using a VFD would the cap v rating be 2x or so.

Your input is invaluable. Thanks in advance.




RE: Bucking to match V/Hz

The motor current will be running through the 48 Volt winding only.
You need 48 volts times 11 Amps = 528 VA for the transformer.
The Volts per Hertz ratio also applies to the transformer.
The transformer that you have selected is a 60 Hz transformer.
Some folk see a subtle difference between a buck connection and an autotransformer connection when dropping voltages.
You need the autotransformer connection.
The 48 Volt winding is wired in series with the 240 Volt winding. The voltage rating is now 288 Volts at 60 Hz.
That rating drops to 240 Volts at 50 Hz.
240V/288V = 83% The 240 Volt winding will develop 83% of 240 Volts or 200 Volts. This should be OK for the motor.
Current: The 48 Volt winding will carry 11 Amps for the motor and 2.2 Amps to excite the 240 Volt winding for a total of 13.2 Amps.
13.2 Amps x 48 Volts = 633 VA.
If the motor is overheating due to magnetic saturation this should cure the problem. If you get out of the saturation zone, the current will drop.
If the motor is overheating due to overloading you must either lower the load or find a larger motor.
What is your load? The motor will be turning 5/6 slower.
You may need to increase the capacity of the starting capacitor for best starting torque.

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

RE: Bucking to match V/Hz

(OP)
Thanks Bill,
The load is a hydraulic pump. According the ACME, their transformers 1kVA and under are 50/60Hz, even though the data sheets say only 60Hz.
I am having horrible luck finding a CE marked transformer. Any suggestions?

RE: Bucking to match V/Hz

Loads of UK-based transformer manufacturers could supply what you're looking for. I say UK rather than European because there won't be a language barrier (well, not as much of one. winky smile ) but there are plenty European options if you fancy trying out your language skills.

Are you looking for a component-level bare transformer, or a finished product in a metal case ready to connect up?

RE: Bucking to match V/Hz

Is this for export?
Acme transformers are U.L. rated for the US and Canada and many are also CSA rated for Canada.

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

RE: Bucking to match V/Hz

Something like this perhaps? http://www.airlinktransformers.com/industrial_tran... That one is just from a quick look on Google, but Airlink have been around for quite a while. Price is better than I expected although I imagine the shipping costs will be steep.

RE: Bucking to match V/Hz

(OP)
Thanks for the replies...If this gets implemented, I'll post an update....thanks again!

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