Unisaw: 3 phase vs 220 single phase question

[Dave Bruce]

Hi Everyone, First post. I have an opportunity to get my hands on a 10 year old Delta Unisaw. The saw was purchased for industrial shop use but was never put into production. It essentially has been sitting for 10 years. Never been turned on. Brand "new" & spotless. It has a 3 phase motor & I do not have 3 phase power in my garage. But at $500.00 I'm trying to find a really good reason NOT to pass this up. Would I be better getting a 3 phase converter or buying a new 220 V motor ? Any recommendations ?
Thanks,
Dave B

[Rich Riddle]

Dave,

Many will tell you the Variable Frequency Drive is the way to go and simply keep the current motor. A 3 HP VFD won't prove excessively expensive like the larger models cost.

That said, I simply installed a Rotary Phase Converter in the garage. That way if I ever purchase another 3-phase machine, it gets plugged into the RPC output as well (but only running one machine at a time). I don't recommend a new motor, because it will require a new switch, etc.

Good luck and welcome to the creek.

[Mike Heidrick]

RPCs are nice if you get a good one that has balanced run caps and the work has been done to balance out the wild leg to be close to the voltage of teh power company supplied legs. Cheap RPCs are junk.

Does the unisaw have a LVC?

A VFD is great for one machine. Ton of features that really are not needed by a tablesaw but nice just the same. You will want a 2.2kw and I prefer Hitachi or GE/fuji or prob the minimum I would go is Teco FM50. Read hit or miss stories on the Hynang and other $140 Chinese ones on ebay. You will have a bit more wiring to do with a VFD and you will want wire the magnetic controls to the inputs of the VFD, and not use them to switch the motor side of the VFD output.

[Stephen Cherry]

How many HP? If it's 5, I would consider a static phase converter.

3 hp? Then the question might be if you are considering adding other three phase machines. If the answer is yes, then a rotary phase converter might be the best answer. If no, vfd (and Mikes run down on brands is right on the money) is the way to go, with the added benefit of controlled braking. You can even add an extra resistor for faster braking. (nothing like a sawstop in terms of speed though)

[Erik Manchester]

Dave, I run my 3 Phase Uni off of a Teco FM50 VFD and really recommend a VFD over an RPC unless you are looking to acquire more 3 phase tools. VFDs are quite cheap in comparison to the cost of phase converters and you can get used industrial VFDs for as cheap as a newer hobbiest grade (like the TECO which came with my Uni). The VFD offers the electronic braking and speed control that the phase converters don't. My Uni spools up to full speed in 4 seconds and stops in 2.5 which is neat to watch.

[Bradley Gray]

I have run my whole shop on a home made rotary converter for over 30 years. I set mine up with a pair of capacitors for push button start, but all you really need is an extra 220/440v 3 hp 3 phase (or larger) motor to run unloaded as an idler and a way to get it spinning. This can be done with a small single phase motor and a slip clutch, with starting capacitors as I do or, as an old machinist friend of mine used to do, spin the motor pulley with your foot before turning on 220v single phase to two of the idler's 3 leads. Once the idler is spinning and has power it will generate the 3rd leg of the 3 phase. There is an article in an old FWW magazine (c1980) that describes how to set up the capacitor start system.

[george newbury]

Really need more info.
In my case I lucked into 5,500 sq feet of shop with about 6 240V circuits and a 400 amp breaker box. I needed the whole shebang - Planer, bandsaw, jointer, tablesaw etc. All I had was 1 1950's Delta TS. I was trying to buy a planer when I found an auction with all of that plus for about the going price of a used planer. It's all 3 phase. Now I'm in the market for a 10HP RPC.

If there is the SLIGHTEST chance you will want another piece of 3 phase equipment a RPC is the way to go IMHO. For about $200 plus the cost of a 10HP motor you can get a CNC quality RPC.

[Graham Hutchinson]

A friend of mine just installed an RPC and idler motor. His main reason for going the RPC route was instant reverse. He uses a mill and instant reverse is pretty handy for threads and other things. The VFD units don't like the heat generated when you throw a 3 phase motor into reverse. He did mention that you only get about 2/3 of the horsepower out of the motor when you use an RPC. So if the saw has a 5hp 3 phase motor, you may only get 3hp out of it.

[Rich Riddle]

A friend of mine just installed an RPC and idler motor. His main reason for going the RPC route was instant reverse. He uses a mill and instant reverse is pretty handy for threads and other things. The VFD units don't like the heat generated when you throw a 3 phase motor into reverse. He did mention that you only get about 2/3 of the horsepower out of the motor when you use an RPC. So if the saw has a 5hp 3 phase motor, you may only get 3hp out of it.
VFD also need to be de-rated to 2/3, some even derate them to 1/2. Thus any way you go, you need to get a "higher hp" unit. An interesting read that is quite simplistic is here: http://www.ebay.com/gds/Three-Phase-Shop-Power-with-Variable-Frequency-Drives-/10000000123009697/g.html

[Stephen Cherry]

static phase converter is good for about 2/3 of the rated power, rotary converter should give about the rated power. If you use a vfd that is intended to have three phase supply with single phase, the drive needs to be double sized, for example, to run a 5 hp machine you can use a 10 hp drive intended for three phase, but supply it with single phase.

But, there are plenty of vfds that are intended to use single phase supply.

[jack forsberg]

i imagine you could probable buy 5 VFD brand new for the price of a 10 Hp RPC if your machines are under 5HP each. this does not even take into acount the cost of wiring in the systems around the shop.The thing with a RPC is it is really only balanced to one hp so as far as clean power goes its fairly dirty. Good thing about motors is there dumb. just a big magnet. the static converter just kick starts a 3 phase motor and single Phases it. This is like a bike you had as a kid with one pedal. It was hard to start but if you got it rolling you could keep it going with just the one peddle. If you realty want to see how dumb a 3 phase motor is hock two of the legs to single phase power of the same voltage and put a pull cord on the pulley to spin it up and then turn the power on. this is how the very first RPCs were made.

why you would use a RPC for a 3 HP machine is beyond me. Come on a VFD is so easy to wire a monkey could do it. of all the Converter the VFD gives the cleanest power even better than Phase perfect( really a VFD with out the varying the frequency) . there is no difference over line other than the square wave. and at $200 shipped to your door its a no brainer.

[Bradley Gray]

The reason to use a homemade RPC is purely economic. When I set up my system many years ago I paid $20 for a used 3 phase motor and spent about $25 on capacitors and switches and 33 years later it all still works.

[jack forsberg]

The reason to use a homemade RPC is purely economic. When I set up my system many years ago I paid $20 for a used 3 phase motor and spent about $25 on capacitors and switches and 33 years later it all still works.

33 year ago VFDs were not around. Don't get me wrong I have a RPC i use to run large HP machines in my shop that are 600 volts . I find for large High voltage machines there is still not a better way.

[george newbury]

i imagine you could probable buy 5 VFD brand new for the price of a 10 Hp RPC if your machines are under 5HP each. <snip>

I am currently going thru a similar decision process. As I mentioned I've presently five 3 phase machines, the largest with a 5HP motor. And I envision on possibly getting more. In my surfing research I've only found VFD's to run a 5HP motor priced around $500. The small ones cost about $200..
American rotary sells a 10HP RPC for about $800 and it should be able to run a total of 15HP and start a 5HP. Thus I could run several machines (Planer, DC, CNC) at the same time.

Do you have a source of $200 VFD's strong enough to start and run a 5HP motor?

[Don Jarvie]

While the VFDs and RPCs have some merit in your case it's easier to replace the motor with a single phase. The saw new which it sounds like would cost 2500.00 at least so even if you buy a new motor for 400.00 your still 1600.00 ahead of the game.

I bought a PM 66 used with a 3 phase motor and thought had about getting a RPC and found it was the same price to get a new motor.

[Cary Falk]

While the VFDs and RPCs have some merit in your case it's easier to replace the motor with a single phase. The saw new which it sounds like would cost 2500.00 at least so even if you buy a new motor for 400.00 your still 1600.00 ahead of the game.

I bought a PM 66 used with a 3 phase motor and thought had about getting a RPC and found it was the same price to get a new motor.

No way is the OP $1600 ahead. If it is 3hp spend <$200 on a VFD. If have to spend $500 on the saw and $400 on a motor you have spent too much. There are better options. This Uni does not have a riving knife.

[Mike Heidrick]

For about $200 plus the cost of a 10HP motor you can get a CNC quality RPC.

Where is a 10hp CNC quality RPC $200 minus the ideler?

[george newbury]

Where is a 10hp CNC quality RPC $200 minus the ideler?
PhaseCraft on ebay.
Several people here recommended him.

My "problem" is trying to do it on the cheap. I just missed a CL 10hp motor for $50 and have not found another turning up.

After a while I'll probably have to go for a $200 rebuilt.

[jack forsberg]

http://www.ebay.com/itm/NEW-TOP-QUALITY-220V-4KW-5HP-VARIABLE-FREQUENCY-DRIVE-INVERTER-VFD-/261236961617?pt=LH_DefaultDomain_0&hash=item3cd2efb151


understand that run 15 hp of motors off a 10 RPC is not the same a run them to to full HP rating. This rating is with machine idling. a 10 hp RPC will only give 30 amps 3 phase if feed single 1.75 times the amps


I am currently going thru a similar decision process. As I mentioned I've presently five 3 phase machines, the largest with a 5HP motor. And I envision on possibly getting more. In my surfing research I've only found VFD's to run a 5HP motor priced around $500. The small ones cost about $200..
American rotary sells a 10HP RPC for about $800 and it should be able to run a total of 15HP and start a 5HP. Thus I could run several machines (Planer, DC, CNC) at the same time.

Do you have a source of $200 VFD's strong enough to start and run a 5HP motor?

[Don Jarvie]

No way is the OP $1600 ahead. If it is 3hp spend <$200 on a VFD. If have to spend $500 on the saw and $400 on a motor you have spent too much. There are better options. This Uni does not have a riving knife.

I have respectfully disagree. A 10 yr old Unisaw in new condition for 900.00 is a deal. You can get an aftermarket riving knife if Delta didnt have one.

[jack forsberg]

I have respectfully disagree. A 10 yr old Unisaw in new condition for 900.00 is a deal. You can get an aftermarket riving knife if Delta didnt have one.

sorry buddy but an old uni is a dime a dozen and i can find one for less than $100 in 3 phase any day of the week. don't matter if its 10 years old or not there all the same saw. not like they improved anything on the design over the years but the HP and that's the motor were talking about.

[george newbury]

http://www.ebay.com/itm/NEW-TOP-QUALITY-220V-4KW-5HP-VARIABLE-FREQUENCY-DRIVE-INVERTER-VFD-/261236961617?pt=LH_DefaultDomain_0&hash=item3cd2efb151


understand that run 15 hp of motors off a 10 RPC is not the same a run them to to full HP rating. This rating is with machine idling. a 10 hp RPC will only give 30 amps 3 phase if feed single 1.75 times the amps

Well since I'm going to be a one man hobby shop my main concern is running the biggest and a good DC.

[jack forsberg]

Well since I'm going to be a one man hobby shop my main concern is running the biggest and a good DC.
The problem with what they told you about the starts 5 run 15 hp is that it is true. The real answer is how it works is as a machine come on line with the RPC it in turn gives up power to the system and become a RPC too. how much power does each motor give in the system you ask? On a 10 HP RPC 30 amps 3 phase Max is the limit well it all depends on how hard the other motors are working. Lets say you have your table saw running there and your not working it its just idling. Its a 3 hp saw lets say and has a full load apm rated motor of 7 amps and at idle is burning 2 amps. it will give the system 5 amps for other motors up to the FLA of the 10 HP idler. Now if you go use the saw it will only give what you are not using the remaining apms of its FLA rating. A DC on the other hand is a working motor and will not feed the system much if any amps. it will only draw amps from the system because the motor is working. A vfd is a much better chose for the Dust collector than a RPC IMO. It has been proven that speed control on DC motors save money and improves the CFM as well.

there the other half the story.

[David Kumm]

If you like to buy used, bite the bullet and go RPC ( and vfd for anything needing speed control and for the dust collector ). You will find the good stuff is almost always three phase and a bargain. I bought two Whitney saws for about what you are paying for the Uni. Dave276619

Sorry, couldn't get the second saw to upload.276620