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Old 01-14-2011, 08:45 PM   #1
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3 Phase to single phase conversion


Greetings. I am a welder/fabricator and a regular on the Miller welding site. I am in need of some electrical advice.I currently purchased a hydraulic ironworker (metal cutting and forming equipment.) It has a 3 phase 7.5 hp 1750 rpm motor that runs a hydraulic pump for a 60 ton hydraulic cylinder.I do not have 3 phase power but I can get the same motor in single phase.So my question is can a single phase electric motor with the same specifications work without loss of hydraulic power or should I go bigger? if so is the capicator start capicator run the best motor for this application? or should I get a 3 phase converter? My concern with a phase converter is that I will loose up to 10% of power

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Old 01-14-2011, 09:08 PM   #2
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3 Phase to single phase conversion


A single phase motor and 3 phase motor of the same size and rpms will produce the same results.
A single phase 7.5 hp motor pulls 46-47 amps, so you need to make sure your service will handle the extra load.

I looked at the table wrong last night.
The correct amps should be 40 amps@ 230 volts.

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Last edited by jbfan; 01-15-2011 at 11:55 AM. Reason: more info.
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Old 01-14-2011, 09:29 PM   #3
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3 Phase to single phase conversion


Ayuh,... Alota times it's cheaper to get a phase converter, 'n use it's original motor....
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Old 01-14-2011, 09:29 PM   #4
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3 Phase to single phase conversion


get a vfd
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Old 01-14-2011, 10:23 PM   #5
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3 Phase to single phase conversion


Vfd's are nice. Cost around $1000. New motor, around $800.
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Old 01-15-2011, 12:07 AM   #6
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3 Phase to single phase conversion


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Originally Posted by 3 legged dog View Post
Vfd's are nice. Cost around $1000. New motor, around $800.
Here's a suitable VFD for $799:
http://www.driveswarehouse.com/Drive...FD/PC1-75.html

I would solve this problem with a VFD rather than replacing the motor or using a rotary phase converter. The VFD replaces the electromechanical motor starter/contactor that would otherwise be needed, and is very easy to interface with other controls. Variable speed can be really useful in many applications.
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Old 01-15-2011, 01:06 AM   #7
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3 Phase to single phase conversion


If you want to keep that 7.5 CV { HP } three phase motor then you will need the VSD unit at least 15 CV rated due the single phase input set up.

So be aware with this due most VSD on med to larger units they will derated it.

The other option you can use is rotary phase converter { this will be next best appaction for this useage due you have hydrallic pump the staic unit will not really handle the surge very well. }

As Jbfan mention how much current it will draw on single phase verison so expect that and make sure if you have subpanel in there make sure it is large engouh to handle the motor load.

Merci.
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Old 01-15-2011, 02:34 AM   #8
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3 Phase to single phase conversion


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If you want to keep that 7.5 CV { HP } three phase motor then you will need the VSD unit at least 15 CV rated due the single phase input set up.

So be aware with this due most VSD on med to larger units they will derated it.
This is certainly true if the VFD is intended for 3-phase input but being used with single phase. The VFD I linked to is specifically a single-phase input device, so it does not need to be derated.
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Old 01-15-2011, 05:52 AM   #9
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3 Phase to single phase conversion


Thanks for your answers. I have plenty of 220/240 power. My shop is equiped with 400 amp service and all my 220/240 outlets are rated for 50 amps. Either way single or 3 phase I am still gonna replace the motor being it is 30 years old. I am doing a total rebuild on it including all new wiring, hydraulics, blades etc. So single phase conversion would be more cost efficient.
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Old 01-16-2011, 10:24 AM   #10
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3 Phase to single phase conversion


Go to www.automationdirect.com or www.wegelectric.com. for VFD pricing.
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Old 01-16-2011, 12:07 PM   #11
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3 Phase to single phase conversion


i think a vfd would be cheaper than changing to a single phase motor as a vfd will take a single phase input and output three phase
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Old 01-16-2011, 06:08 PM   #12
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3 Phase to single phase conversion


A 7.5 hp single phase motor is cheaper than a VFD.Think I will put a 10 hp single phase motor on it, they run in the $800.00 range. I am rewiring the whole thing anyways.
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Old 01-17-2011, 06:53 AM   #13
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3 Phase to single phase conversion


800 bones? you can get vfds cheaper
http://www.vfds.com/cart/index.php?m...ff8fda916abf96
for an example
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Old 01-17-2011, 09:41 AM   #14
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3 Phase to single phase conversion


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800 bones? you can get vfds cheaper
http://www.vfds.com/cart/index.php?m...ff8fda916abf96
for an example

Why does the input and output on this say the same thing? I also feel that adding one of these converters will not hold up long being it has a lot more electronics to go out, not the ideal conditions in a un-climate controlled welding shop. I can get a new 10 hp single phase motor for $700.00 the existing 3 phase motor is 30 years old so I might as well replace it anyways.
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Old 01-17-2011, 11:14 AM   #15
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3 Phase to single phase conversion


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Originally Posted by fabricator View Post
Why does the input and output on this say the same thing?
That VFD is intended for 3-phase input and output (most VFDs are). It is also 460V, not 208-240. It will not work for your application.

You can use a 3-phase input VFD with a single-phase source, but you need to over-size it by about 50%.

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