Question on a static 3ph converter???

JD Seller

Well-known Member
I am looking at getting a static 3 phase converter. Mainly using it to run a lathe or milling machine.

I have found a good deal on a PHASE-A-MATIC PAM-1200HD converter.

The question I have is why do they list a minimum and maximum HP for the motors??? The 1200 HD is rated a 8-12 HP converter. The maximum is easy to understand but the minimum is not. I would think you would not harm it using a larger converter even if it is on a smaller motor. An example would be a 4 HP one.

I have used a rotary converter but not a static one.

I may still go to a rotary converter as I might buy a 3 phase plasma cutter. I have been told it you are using some thing that has a transformer load you need to sue a rotary not a static converter.
 
(quoted from post at 00:03:06 10/22/14) I am looking at getting a static 3 phase converter. Mainly using it to run a lathe or milling machine.

I have found a good deal on a PHASE-A-MATIC PAM-1200HD converter.

The question I have is why do they list a minimum and maximum HP for the motors??? The 1200 HD is rated a 8-12 HP converter. The maximum is easy to understand but the minimum is not. I would think you would not harm it using a larger converter even if it is on a smaller motor. An example would be a 4 HP one.

I have used a rotary converter but not a static one.

I may still go to a rotary converter as I might buy a 3 phase plasma cutter. I have been told it you are using some thing that has a transformer load you need to sue a rotary not a static converter.

It comes down to what is "good enough". Not that long ago the choices in order of preference was utility three phase, a single phase motor driving a three phase alternator. A rotary converter then lastly and justly so, the lowly static converter.
There is some reduction in the motor's rated power with the rotary but don't expect much more than single phase rating on a three phase motor . Which is the inverse square root of 3 or 57.7%
For all a VFD costs these days. The true three phase power . Variable speed. Soft start, reversing and torque limiting if desired. It's becoming more and more difficult to justify a static or rotary.

As for the plasma cutter or welder. Look inside first at the specs. Many a welder etc connected to a 480 or 600 volt service is only using two of the live lines, not three lines. Just like the old Lincon welder. 480 and 600 is used because it's available in industry and allows smaller power conductor sizing.
 
What is a VFD converter??? I know little about three phase. I understand how a rotary converter works but do not understand how a static or VFD actually work.
 
A VFD rectifies the incoming AC to DC and then generates a three phase sign wave at the appropriate frequency to control the motor speed. It also has the ability to adjust the amperage at each frequency to compensate for torque loss.

It will always generate 3 phase, even when fed with single phase. You need enough watts to keep the DC bus charged, thus the requirement to oversize the drive when feeding with single phase.

I think that single phase VFD's are coming out that handle the starting issue that precluded their use.
 
The reason there is a HP rating on the static is because of the capacitors used to "jump start" the third leg need to be different sizes depending on the size of the motor. My experiance with them is is if you cant get exactly the one you need that you are better off to be a bit over sized than even a little bit undersized. One staic will start several motors as long as you only start one at a time and the largest one first. How well a static will preform on the machine depends on how much overkill was designed into the drive, most of the time it is a LOT on a machine tool. There is still good situations for both static and rotary converters same as there are situations where a VFD is the only way to go. There is so much to read about it on the net if you search. One thing that has come to light with VFD drives is they are very hard on older motors, something about voltage spikes? If you have to replace or rewind your motor any cost advantage to VFD is lost and then some. Also be sure to carefully size the VFD, a cheap "3HP" VFD from Ebay will NOT run a 3HP 3 phase motor from single phase power.
 
(quoted from post at 00:03:06 10/22/14) I am looking at getting a static 3 phase converter. Mainly using it to run a lathe or milling machine.

I have found a good deal on a PHASE-A-MATIC PAM-1200HD converter.

The question I have is why do they list a minimum and maximum HP for the motors??? The 1200 HD is rated a 8-12 HP converter. The maximum is easy to understand but the minimum is not. I would think you would not harm it using a larger converter even if it is on a smaller motor. An example would be a 4 HP one.

I have used a rotary converter but not a static one.

I may still go to a rotary converter as I might buy a 3 phase plasma cutter. I have been told it you are using some thing that has a transformer load you need to sue a rotary not a static converter.
utch(OH) answered your question in his first sentence. Those static converters simple switch a capacitor into the 3rd leg of the motor for 2-3 seconds to start it, pretty much like a capacitor-start single phase motor,,,,,,,,,,,,so, the cap needs to be somewhat matched to the size of the motor that it is starting. To me, calling the things a static phase converter is a real stretch.
 
When is the power company going to realize they need to give every home 3 phase where the guy needs a Bridgeport for his darn hobby.Heck we will even change the single phase panels out , just give us the lines coming in .
 
A static converter is basically a set of relays and start capacitors.

The start caps shift the phase enough that the 3 phase motor will start and after that it produces about 2/3 its rated power.

Brad
 
The utility company has to run 3 times as many conductors, that is not cheap to do, so not gonna happen.
 
50 years ago, my dad made static converters with relays, which we called motor contactors, start capacitors, which we used a 1 second timer to disconnect them and run capacitors, which were used all the time.

There wasn't a one size fits all. We adjusted the run capacitors to get the best balance on the running current.

Dad had a rule of thumb, so many MFD's per hp for the run and about 4-5 times the MFD's for start.

Brad, what did you finally end up using for your bandsaw? If I recall it had some weird voltage. You were thinking of using a transformer to increase the voltage. Did you go with a static, rotor, or electronic converter?
 

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