XPost: sci.electronics.design, sci.electronics.misc
From: dhky@shaw.ca
On 14/07/2014 11:11 PM, upsidedown@downunder.com wrote:
> On Mon, 14 Jul 2014 09:00:10 -0700, DaveC wrote:
>
>> I need to provide jog function on a machine (run the motor for a few seconds
>> under load) without use of VFD**. It was done on this small printing press
>> with a 3 HP, 3-phase motor but the customer has no multiphase power so Iım
>> changing to a 220 ³single phase² 5 HP motor.
>
> The classical trick running an existing three phase motor from a
> single phase supply is to connect capacitors between the three motor
> terminals and then connect the single phase source between two of the
> terminals.
Yes, you could do this-I'm not sure, without further analysis, that
there will not be a considerable hit on the effective motor rating.
The phase converter,even without capacitors will work. The limiting
current is dependent on the larger machine-and is not a hit on the
capacity of the smaller load machine.
However, in this case of a jog function- If a single phase capacitor
start single phase motor has the same starting torque as the 3 phase
motor (and with the right capacitor- this may well be done) a single
phase motor may well fit the needs-electrically-but likely not
mechanically with respect to mounting.
>
> Of course, the voltage is now lower, so less power is available.
> Perhaps a autotransformer could be used to beef up the voltage. Having
> intermediate taps in the autotransformer could be used to alter
> starter or tongue performance.
--
Don Kelly
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