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phase inverters pros and cons

1/30/15       
john Member

I am looking at a 16 inch radial arm saw that is 3 phase I need an inverter don't know anything about them any help appreicated

1/30/15       #2: phase inverters pros and cons ...
John Costin

If you are trying to run a 3-phase machine from a single phase power source you are looking for a 'phase converter'. Inverters produce AC power from DC power.

Everything you need to know about phase converters should be available on the internet or at your local library.

Best of luck,

John Costin
Veneer Services Unlimited
vsu@gwi.net
207-985-7221
Custom Veneered Products for the Woodworking Industry

1/30/15       #3: phase inverters pros and cons ...
EC Aumiller Member

The easiest way to do it is with a VFD... it can take single phase 220vac input and put out three phase 220vac... there are many available.. Go to bing or ebay and search for VFD.. just get one that will handle the HP of your saw...

On 3-phase, be sure your saw is turning in the correct direction BEFORE putting a blade on it... if it is turning in the wrong direction, simply swap any two of the hot wires to correct the rotation of motor...

You should be able to get one for less than $200...

You can also use a "Rotary Phase Converter" which is a motor/generator to develop three phase but is more expensive..

Also you can buy a "Static Phase Converter" but it will reduce the HP of your saw by 1/3.. ie, a 3HP saw will only develop 2HP...

The best was I have found is with a properly sized VFD..

1/30/15       #4: phase inverters pros and cons ...
rich c.

I'd be surprised that you could get a VFD for that saw for less than $200. I guess we don't know the motor size, but a 16" radial arm probably is at least 3 hp, probably 5. You might be able to get a Chinese VFD for that money, but I sure wouldn't trust those.
EC Aumiller, where do you buy your VFDs?
Maybe I'm missing out! I need a 5hp VFD for a custom wood lathe I am building.

1/30/15       #5: phase inverters pros and cons ...
EC Aumiller Member

eBay mostly... quick search shows item 221668300083 is a used Toshiba, good brand... from 100% seller.. no affiliation, etc

A used working unit will probably last a long time as failures are within a short time frame of manufacture usually..

There are also new units (from China) in the $200 range...
In reality, most VFD's are from China (sadly)..

Sold a 16" Dewalt RAS several years ago with a Chinese VFD and still working...

Only problem with VFD is you need to turn saw off/on via the VFD and keep motor wired to the VFD direct... however this also provides electronic braking to the saw also...

1/31/15       #7: phase inverters pros and cons ...
rich c.

I looked that one up "eBay mostly... quick search shows item 221668300083 is a used Toshiba, good brand... from 100% seller.. no affiliation, etc" and it's a 3 phase in. I need single phase in. I'm just nervous about getting support or early hour failure on the Chinese VFD and likely difficult customer service. Sounds like your experience is positive, I've just read a lot of the opposite on metal working forums.

2/1/15       #8: phase inverters pros and cons ...
EC Aumiller Member

ALL VFDs are 3 phase in, 3 phase out.. but they work with single phase also.. you have 3 input power lines.. pick any two and apply 220vac and you will get 3 phase out... they take the input, rectify it (change it to DC), then generate 3 phase AC output... study the different forums to learn how they work..
The folks who have trouble 99% of the time make one of two major errors..
First, they try to power them up without a load on them and it often ruins them.. they need a load constantly to limit voltages within the VFD..
Second, they overload them, they try to run a 5HP motor on a 1-2HP VFD.. the motor will run fine but as soon as you put a mechanical load on the motor (i.e. cutting a board), it tries to produce more HP and the VFD senses the overload and shuts down with an error..

2/1/15       #9: phase inverters pros and cons ...
rich c.

One more question EC. Do you oversize the VFD if running on single phase in? I've seen folks talk about at least 50% over rating. Like at least a 7.5 hp rated VFD for my 5 hp motor. Do you agree with that? Thanks for helping out!

2/1/15       #10: phase inverters pros and cons ...
EC Aumiller Member

It is a good idea especially if you will be using the full HP... The current on the input lines is greater on single phase so yes..

However, on the saw I had, it never came close to operating at the full HP as I used it to cut boards, etc to length and had a 5HP VFD on a 5HP motor and never had a problem..

But to be safe, Yes, put in a 50% greater vfd than motor...

If using it for a saw, then make sure it is set to run for full speed all the time..

If using it on a lathe, it is great to change the speed as needed.. put one on my old Powermatic lathe and it is so much nicer to be able to turn a knob instead of changing belts... same thing for drill press's

Also, on any equipment I always use the remote on/off function of the vfd so I can mount a switch on or very near the equipment in use for safety reasons..

2/2/15       #11: phase inverters pros and cons ...
john Member

what is a vfd

2/2/15       #12: phase inverters pros and cons ...
EC Aumiller Member

Please see this link...
http://en.wikipedia.org/wiki/Variable-frequency_drive

They are also a convenient method to go from single phase power to 3 phase power..


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