Minimum starting voltage of a 240V motor 3

[Elredeye]

What is the minimum starting Voltage for a 240V rated motor on a compressor? I have 215V line voltage and I thought of using a 24V buck/boost transformer to boost the voltage 24 volts.

 

[magoo2]

By NEMA standard MG-1, a motor is suitable for operating at +/- 10% from its nameplate rating.

If it is rated 240 V, then 216 V is the minimum.

If it is rated 230 V, then 207 V is the minimum. The reason I mention this is because 230 V motors are normally applied on 240 V systems.

Also, your 215 V supply sounds like a 208 V system. You can expect the tolerance of +/- 5% on supply voltage. All in all, the addition of a buck/boost transformer is a good idea.

All of these comments relate to North American practice.

 

[itsmoked]

Use the boost transformer.. Most definitely. Your 215V could easily drop below 215 at different times.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

When sizing the transformer, only the secondary winding has to carry the motor full load current.
24V x Motor FLA will give you the KVA required for single phase boosting.
The primary of the transformer is probably 240V. That will give you a voltage of 215V + (24 x 215/240) = 236.5V
This reduced voltage doesn't affect the calculation of the required KVA given above.

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

 

[Elredeye]

Thank You all for your comments, I do have a 208 system and it does drop below 215V at times, And I will use this formula to size and purchase the transformer for a 9A motor. Any ideas where I could find a cheap one, possibly used?

 

[itsmoked]

Ebay?

A lot of towns of moderate size have at least one store that sells used electrical equipment. Where are you? California?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

9 Amps x 24 Volts = 216VA.
Use a 250 VA as a minimum. A transformer will generally wistand the motor starting current, but you may consider going oversized to 500 VA. If this was my installation I would base the choice on price, availability and budget. If the budget would stand it I would go for the 500 VA, but if the 500 VA was not available I would use a 250 VA.
We typically installed our buck/boost transformers permanently wired to the motors and adjusted the OL settings accordingly. As for physical location, we had transformers adjecent to the motors, at the control consoles, and at the MCC.

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

 

[Elredeye]

I'm in the Los Angeles area (Whittier), I came up with 250VA as appropriate also, My choice would also be a 500VA however I'm doing it for a really good friend, business is slow for him and I promised to help him.

 

[itsmoked]

Heck, new! Under a hundred bucks.

http://www.factorymation.com/s.nl/sc.2/category.85874/.f

Keith Cress
kcress -

http://www.flaminsystems.com