Three Phase Converter Question

[GaryBDavis]

I need to get a 3-phase converter for a 16" metal chop saw. The only experience I have with phase converters is the static type I have on my mill.

I know there are static and rotary converters, but don't know for sure which one I should get.

The chop saw has a 5HP motor that runs at 1720RPM. I've heard that static converts aren't good for "freewheeling" loads, high starting current and frequent starts. I'm not sure if the chop saw would fall into that category or not.

If you guys know of a good on-line source to buy them from and what brand to get/stay away from, please let me know.

Thanks.

 

[ZJ_HR]

You can use variable speed drive for that purpose. It will vary frequency from 0 to desired freq, and will run your saw as you want. Just two questions:
-network voltage (single phase)
-saw motor nominal voltage (phase to phase)
These values need to be similar for VSD, as it is not a transformer.
-saw motor nominal current

I'm familiar with Telemecanique (Europe) or SQUARE D (America) speed drives.

 

[RedRocker]

I run my Mill on a three phase motor that I rope start. Cheap and easy way to do it. A three phase will run on single phase power, it just won't start. All you have to do is get it spinning and shoot the juice to it, it will generate a third leg for your other machine.

 

[SPIKER]

Hey:

A rotary converter is basically a 3 phase motor which has a speed switch and some inductors or caps in the line side which slows the phase shift for a few seconds once it gets up to speed they are usual;ly switched out. to run the 5 hp grinder you will need a 7.5 hp converter or better yet a 10hp unit. there is a good amount of power loss when running it this way. they are also not cheap... they can be built by home users with kits and provide you're own 3hase motor then. often for a 1 or 2 units it is better to but a freq drive as mentioned above they can be had for a few hundred bucks NEW and e-bay stuff even cheaper. you have to watch the input voltage and phase requirements, in you're case 240 single phase input and then output of 240 volts-3phase.

at one time I had some links to parts, one place is http://www.surpluscenter.com
(I think I typed that right?) that you could buy or build the rotary setups.

MarkM

 

[AntrimMan]

I have walked away from some opportunities cause they had 3 phase motors and IMHO they wern't worth the cash for a converter or new single phase motor. Would have been nice to have but too beat for the needed investment.
Do you have any way of posting a schematic of this motor approach you mention? How is the phase supply motor sized vs the tool motor? I have 220V single phase in the garage, how would the other phases affect the rest of the supply?

Thanks,
Martin

 

[Farwell]

There is a guy on Ebay that has all of the information on the phase conversion and he sells it for a few bucks. It is cheaper if you download it. The information is very clear and easy to understand with all of the information you would need.
Farwell

 

[DougM]

Would it be possible to run a older 3 phase welder with a converter ????

and if so how large would one need ??

DougM

 

[Charlie_in_TX]

I believe most 3 phase welders can be run single phase. It will have a little more DC ripple and it will need to be derated to 2/3s nameplate (you would be using 2 sets of diodes instead of 3). So if it was rated for 400 amps you would derate to 270 amps.

 

[Farwell]

I do not know much about 3 phase equipment. I have been reading up on 3 phase thinking that at some point I will be buying a Bridgeport mill. A lot of metal working equipment is wired for 3 phase and can be bought at a lower price because a lot of hobby machinists are afraid of 3 phase. I never thought about a 3 phase welder set up. I will have to keep an eye on this thread to see if your question is answered.
Farwell

 

[Larstan]

The answer is yes you can run a 3 phase welder on a converter. The problem is that a welder is actually putting out a lot of amperage, not just turning a spindle to do some work. I have a 300 amp hobart tig 3 phase welder, transformer type. I have done extensive research on making this thing work on single phase. I talked to a rep at Temco and he told me that to run the welder at 200 amps the converter would cost around 5K thats $5000.00. You have to almost double the capacity of the converter for the output that you want and welders are a completely different animal than a motor. Here is a link to a conversion chart Temco phase conversion It might be cost effective on a really small welder or if you have a business and moved to a new area with no 3 phase but for even a medium sized welder to get full use you would spend more than the cost of a brand new single phase welder.

 

[Farwell]

You answered any question that I might of had about a 3 phase welder. If I see one for sale cheap, don't buy it.
Thanks
Farwell

 

[v8dave]

A cheap, quick and dirty 3 phase converter can be made from a 3 phase motor.

Cheap: Get another 220V 3 phase motor.

Quick: Hook the 220v single phase mains across two of the three motor terminals. Hook the three phase "output" across all three motor terminals, yes this means two of the three terminals will have two wires on them.

Dirty: The motor will not self start! You need to somehow start the motor turning in the direction stamped on the motor. Here is how to start the motor turning Building a Three Phase Converter. I knew of a guy who just mounted the motor low and just kicked a pulley on the shaft to get the converter motor running. I'd recommend against that, especially since a push button capacitor start is so easy do as described in the link.

CAUTION, bolt the motor down. If you don't when it does start to spin up, it will roll and wrap up the wires creating an electrical hazard. It will also roll when the end use motor is loaded down.

You don't use the motor to run anything, it just makes the three phase power. It's the basis of a "rotary 3 phase converter."

This approach is only good for up to several HP motors. You aren't going to be able to run a 10 HP 3 phase motor off this scheme on normal house wiring. The link points out, use a HP of converter motor for each HP of end use motor.

Your mileage may vary, use this approach with caution. If you are not comfortable with electricity do attempt this. As a cross check to make sure converter motor size is big enough, check the converter (motor) temperature to make sure you don't burn the place down.

 

[AntrimMan]

v8dave Oooohhhh Deeeee, that page is exactly what I was looking for. Thank you very much. Now, in between drunken stupors, I can sit down and rationalize the machine tool requirements.

Farwell Do not despair, not all Bridgeports are 3 phase so you can still have hope. Mine is 220v single phase, it's an oldie but does everything I need. There may be optional motor voltages / phase available as spare parts. Just keep your eyes open for one that suits you. Maybe you can have 3 phase run to your garage. I failed after having a wee-wee contest with the building inspector. He wouldn't allow a separate service entrance to the garage and also forbid 3 phase into the residence. Patience paid off and a 220v model materialized.
Another thing to watch out for is voltage requirements. Most of the 3 phase tools I look at need 477v so a boost transformer is also needed, and so the final the cost continues to rise.
If you get real serious and do your home work you will find what you want / need, out there some where.

All the best,
Martin

 

[Jim57]

I purchased a three phase air compressor to add to my paint shop. I am not sure if it can be converted or not. I will go out and take some pictures of it and post them. Maybe someone here can tell me if I wasted my money. I surely would like to get it operational.


Jim

 

[Farwell]

I have considered having a 3 phase drop added to different places I have lived but always come back to the expense. I have reached the conclusion that it would be much cheaper to purchase a new single phase motor or if I was really serious, go the phase converter route. I priced a 3 phase drop in my California residence and the cost was approximately $2000 just for the hook-up and there was a minimum monthly cost. I can buy several single phase motors or several converters for that price.
Farwell

 

[Farwell]

Dave,
Thanks for the link and information.
I have always wanted to build a phase converter, if for no other reason than I have a few 3 phase motors that are just gathering dust and I am a build it my self nut. I may never use the phase converter but it will sit on a shelf along with all of the other projects and everytime I see it I will remember having built one.
Farwell

 

[Farwell]

Jim,
The cost and size of larger horse power single phase motors have dropped considerably over the past several years. If the compressor itself is in good condition and will pump the amount and pressure of air you need, I would go the new motor route. Do not know if a phase converter will take heavy start load required on an air compressor. Maybe someone else can answer the load start issue.
Farwell

 

[ns_in_tex]

Jim, Years ago I took an old 3 phase, 4 ton air conditioner compressor & used it as an air compressor on single phase. It was junk, so I didn't have anything to lose.

I got several run capacitors (2 or maybe 4) & hooked them up in parallel to one leg of my single phase supply, then connected the other side of them to the 3rd leg of the compressor. I did not have a unloader valve on this setup, so it had to start under pressure. Sometimes it would fail to start, so I took a couple of start capacitors, hooked them up parallel along with the first start relay I took out of the junk box, and it never looked back.

It ran that way for several years. My main problem was keeping oil in the compressor, since this type tends to pump the oil out.

If you are considering buying a new motor and could get access to somebodys junk pile on capacitors & relays, I would certainly try this first.

 

[Taylortractornut]

My old highschool shop teacher had a setup like that several years ago then when iI went through his class he had started a shop. We got to build his converter. somehow he later wired his machines all over to extend the usage of some others that went past his original HP ratings. Youd see 2 mills in a line with gaurds over the quills running and he's be at on in on a blanchard grinder or cutoff saw while some one else was running the big lathe. I think the 2 idling mills were being used as a slave motor. I also working in a shop that had one and they used an old tiller frame witth the motor still on it to start the slave motor.

 

[MadReferee]

Here is a link to the Practical Machinist discussion forums. They have a forum specifically for phase converters and VFD's. Take a look. There are over 8000 posts and you will find many interesting discussions.

Practical Machinist Discussion Forums