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Topic Title: 3 phase motor help
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Created On: 13 August 2014 11:06 PM
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 13 August 2014 11:06 PM
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Avatar for hifly.
hifly

Posts: 726
Joined: 06 November 2005

I have an unplated 3 phase motor which i would like to use for my apple scratter.

it is wired in star configuration, i have read that some smaller motors are star config only so that's how i am planning to leave it, unless anyone has any tips on working out if it's delta compatible without burning it out in the process.

on no load running it pulls 0.99A per phase.

can someone advise me what overload rating i should install in the DOL

Cheers
Vince

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Vince

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 13 August 2014 11:13 PM
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peteTLM

Posts: 3231
Joined: 31 March 2005

http://www.tlc-direct.co.uk/Ma...ers/Mem/DOL_Starters/

For such a tiny motor, why complicate matters with star/delta?

Id leave a bit of leaway with the protection unless you have another figure for the on load demand

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 14 August 2014 07:28 AM
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Jaymack

Posts: 4785
Joined: 07 April 2004

Originally posted by: hifly
I have an unplated 3 phase motor which i would like to use for my apple scratter.

Is that their new i-phone?

it is wired in star configuration, i have read that some smaller motors are star config only so that's how i am planning to leave it, unless anyone has any tips on working out if it's delta compatible without burning it out in the process.

If it starts then meets the running load requirement, without an excess temperature on the casing, say a maximum of 80°C at an ambient of 20°C, then I would leave it on the star connection. The temperature can be measured and monitored by taping a thermometer/thermometers, to the top of the casing. Connection in delta will give 3 times more torque, but with an increase in current and motor temperature. The current on no load is not very meaningful, since the power factor is low, but an estimate of 0.3 P.F. would suggest a "kW rating" on no load of 0.17. A full load rating could be estimated as 2kW on Star, with a rating of 6kW on delta assuming that the connections can be changed. The determining factor is the outside temperature rise at ambient; you could estimate this based upon an insulation class of E, say 80°C on the casing as mentioned.

Assuming the motor meets the load requirement without an excessive temperature on the casing, a thermal overload setting of say 10% above the measured current could be made.

Note: For a 3 phase motor - P(Watts) = 1.73 × V (Line Volts) × I (Line amps) × P.F. × Efficiency.

For insulation classes. see: -

http://en.wikipedia.org/wiki/Insulation_system
 14 August 2014 07:37 AM
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zeeper

Posts: 1427
Joined: 11 July 2008

If you have a star connected motor it could be dual voltage(400V-star,230-Delta). I see alot of motors like that here.

unloaded motor current is no good for selecting O/L rating.
 14 August 2014 08:35 AM
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paulskyrme

Posts: 863
Joined: 12 February 2003

Check the motor frame height, length & shaft sizes with other manufacturers units, that will give you an idea of the motor size, thus rating, thus approximate typical FLC for a similar motor.
Not the most scientific method, but, probably the best you can do given the circumstances.
 14 August 2014 11:01 AM
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Avatar for hifly.
hifly

Posts: 726
Joined: 06 November 2005

thanks for your thoughts i will have a measure up and see what i come up with

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Vince

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