running 440v two speed saw on 220v single phase?

Hello everyone,

I bought a large saw that has a 5HP, two speed, three phase motor that runs on 440v only. I'd like to run the saw on single phase 220 and am unsure how best to go about it. Here are some constraints and (hopefully) helpful information:

1. The motor is special and can't be replaced easily.
2. The saw has a dual contactor setup similar to that used on reversible drill presses, etc. to engage the appropriate windings. Based on this, I believe that the motor has two separate sets of windings not the reconnectable wires like the smaller two speeds/two hp's motors commonly used on drill presses.
3. The saw is also equipped with a "shortstop" electronic brake which I'd like to keep but would remove if necessary.
4. This is a 16" table saw with a direct drive motor so the starting load isn't very high.
5. I don't want to rewind the motor.

I bought a three phase autotransformer with the intention of using it to run this saw. The autotransformer has taps for every imaginable voltage, including the ones I need. I did a quick and dirty connection with the autotransformer and my capacitor box to see if the thing would run at all and it wouldn't, it only hummed on "high" speed and wouldn't even engage on "low" speed. I regularly use the capacitor box to start 5HP 220v motors, so I don't think too little capacitance is the cause.

So my question to the community is, how do I make this thing run? What are my options? I prefer some sort of static solution, but I'm not against the idea of building a rotary phase converter if need be. I also have a 220V 10HP 3 phase VFD that runs conventional 5HP 220V motors without complaint from my single phase lines, but I believe that VFD's don't like transformers, and I am very reluctant to experiment with that expensive VFD.

btw, I'm sure that a valid answer would be that there are commercial units available that would solve this dilemma perfectly. But I'm sure those units would cost several times what I paid for the saw, and spending large amounts of money violates my code of ethics (as well as my bank book). I'd rather build something myself if at all possible.

All suggestions welcome and appreciated. Thank you in advance for your consideration.

Steve

All suggestions welcome and appreciated

Click to expand...

RPC and three phase dry type GP transformer used as a step up worked my 4 speed 440 only motor just fine. You need about 10 KVA transformer that is placarded 240/480.

John Oder

Steve,
I bought a large lathe that was 480 3 phase only and I have 230 3 phase via a rotary phase converter.

This is what I did... I took the motor to an electric motor repair/re-winder shop, and they were able to tap the motor with the extra leads to let it run on multiple voltages.

They only charged me $120.

I don't know if your motor can be rewired this way or not. They said that not all motors can be changed the way mine was.

What they did was heated the windings to melt the varnish, them taped the windings.

It just depends on how the motor was wound they told me.

If you have any other questions please ask.

Have a Merry Christmas

John

John O., I suspect that this is the approach I will end up using, involved though it may be. I like simple, one-box solutions, but they're not always available. Your input is helpful in that now I know that this approach will indeed work and is worth pursuing.

John McN., I'm afraid to go the route you did, because the motor is very compact with a lot of windings. I would be very loath to damage a good motor somehow, and I'm sure the cost to rewind the motor will be prohibitive. I also wonder about what the motor shop did. I assume they must have found the midpoint somehow of each winding, cut the winding, and brought the two new leads out so that the windings could be connected in parallel. An interesting approach, and one I would not have thought of, but also something that scares me, especially with this motor. Remember I have two things against me. One, the motor is small for its power, meaning very little room to work or add more leads. Second, a two speed three phase motor is a jungle of leads already, and going for dual voltage will double the number of leads. Yow! Your advice is helpful, though, in that it offers a solution I had not thought of, and encourages me to try to find others.

Thanks to both of you for your advice, and have a happy , safe and affordable holiday season!

If anyone else has any ideas about a static solution, using the transformer (with other components such as capacitors and relays, but no idler motor) to double my voltage and create the missing leg, I'm ready and willing to learn!

Steve

Static Converters

Steve,

The easiest and cheapest solution is the RPC that John O suggested.

If you want to go 480v static forget a standard cap start, cap run static. It probably won't work on a two speed motor. Also cap voltages will be over 800v (if you plan on building it yourself).

"Phase Perfect" is the best but would not meet your budget expectations.

Ronk makes an Add-a-Phase 240 to 480 autotransformer converter but I'm sure it would be very pricey.

You could make your own autotransformer converter 240 to 240 3ph and up the voltage with a 3ph transformer. Making one that would take 240 and output 480 3ph involves internal voltages of around 1000v, not a job for a tinkerer.
There is plently of info on autotransformer converters just use "autotransformer" in a search in this forum.

It would seem to me the solution that would meet as close as possible to your critera would be to get a used 10 hp VFD 480 v 3ph( Ebay $200-250). Down rate it to 5hp for single phase input and use a single phase autotransformer set up 240v to 480v for input into the vfd. If the vfd has phase loss protection be sure it can be bypassed.

Regards

Joe

Joe H.,

I have gotten some good ideas and good advice as a result of my question, but I think yours is the most valuable. "...involves internal voltages of around 1000v, not a job for a tinkerer." Until I read that, I didn't realize that I don't really have much of an appetite for messing with high power/high voltages. I'm OK with 240, and I have built plenty of static (capacitive) converters, but I'm simply not enthusiastic about building a 240/480 static converter.

I really liked your idea about the 480V VFD and single phase transformer, and even went so far as shopping around for one on everyone's least favorite online auction site. But then I realized that the VFD would not work properly with the post-VFD switching necessary for the two speeds, plus I would lose the electronic brake (but could presumably regain that functionality with the VFD and a resistor).

So for now, I will set up a 240V idler motor and transformer per John O.'s approach. I have everything I need, or nearly everything, on hand already so it's not a big leap.

Thanks again everyone and happy holidays!

Steve

Static Converter

Steve,

If you like the VFD idea, I wouldn't give up quite yet. Certainly the RPC will get you running quickly. I have a 5hp 16" direct drive table saw running on a homemade autotransformer converter. It's been running for 25 years without a hiccup. It's 3600 rpm 230v so the internal volts are 480v(my maximum). I have a number of these converters on my woodworking equipment but i haven't built one since reasonably priced VFD's have appeared.

I wouldn't think you would need to change the speed of a table saw while it was running at least using the 2 speeds that are available from the motor. If the motor was set on Hi you would have infinitly variable speed using the VFD. If you were worried about inadverently switching while running you could possibly figure a way to hook up the starter coil through the speed control so that trying to change speed while running would shut off the power automatically.

I use a VFD on a two speed 13" Clausing Colchester lathe without any problems and I'm still able to use the 2 speed options and original lathe controls.


Regards,

Joe

SA100,

the solution to your problem is straightforward. i have posted it here many times in the past and will do so now. I have been using this method for many years and have it on a two speed drill press and a 4 speed patternmakers lathe.

single phase 240 volt fused disconnect switch
240 to 480 single phase transformer (KVA approx equal to 1.5 times the motor horsepower)
3 phase in x 3 phase out 460 volt VFD which must be 2 times the motor horspower as you will only get about 50% of the rated output.
connect VFD directly to the high speed motor winding with no switches in between
use the vfd at 50% setting to get the slow speed equivalent.

this is much easier than a RPC and three phase transformers.

here is one machine I am running:

30 amp disconnect
3 kva transformer, 1 phase, 240 x 480 (actually a 480 x 240 connected backwards)
3 hp rated 3 phase in x 3 phase out VFD, 460 volts
1.5 hp 460 volt two speed motor on drill press
I suspect a 2 KVA transformer would work on the application also but I had the 3 KVA.

Only trick is to get a VFD that will run on single phase input. Most of the Asian VFD will work fine and a ABB will also work. I am using a Reliance SP500 which works great.

Joe H., I have not given up on the idea of using a VFD. It's just that the VFD is the second choice approach right now, seeing as I have a spare 10HP motor and an autotransformer lying around just waiting for me to hook them up. Given the additional factors involved (two speed motor/starter, electronic brake already installed and wired) the rotary converter seems to be the overall path of least resistance.

Toolnut, thanks for the ideas. This is basically how I envisioned using a VFD. Be careful, though. SOME ABB VFD's will accept single phase input, and others will not. You can tell from the model number. I forget which is the significant digit, and which is the one to have. This can be found on the ABB website. I have two small 240V ABB VFDs that have the lost leg diagnostic and will not work on single phase. It would be interesting to find out whether or not that diagnostic can be overriden. Looking into this project I found that Allen Bradley VFDs, or some of 'em, anyway, can be used on single phase with the usual 50% output derating. A-B's seem to be very nice VFD's. Always best to check the specific VFD before buying.

I have another crazy question I am mulling, as a mental exercise as much as anything. Here goes: Can an idler motor be used as an auto transformer as well as a phase generator?

Here's what I'm getting at: The motor must be connected wye, with the leads in series as for high voltage. Connections would be made as follows:
Leads 1,2,3 connected to the 480V motor circuit. (4,7) connected to L1. (5,8) connected to L2. (6,9) connect to the starting/balancing capacitor circuitry. Normally in a 480 volt connection, these connections would be made internally and not brought out. Now these leads comprise the 240V portion of the circuit.

My hunch is that this will not work, but I'm not sure why. I think the problem may be that current will be flowing backward through the outer (1-4, 2-5, 3-6) legs. Maybe those legs would have to be connected backwards to make this idiot scheme work. Eek!

I suppose I could experiment with this, using a small 1/2hp 480V drill press motor and a smaller 3ph. idler motor, but at the moment my curiosity is on a theoretical plane rather than an empirical one. Plus I really hate smoke.

Thank you all for your ideas.

Steve

Steve,

What model table saw is this? I have yet to see a table saw with multiple sets of leads that is single voltage. Is it an old saw that could have had the motor rewound at some point? If it has been rewound, there's a good chance the tag never got updated (especially if it's like my Oliver, the motor tag isn't on the motor).

If you have 6 leads, I would take it to a motor shop and ask them to test what voltage it is wound for.

Matt

Matt,

It's a Greenlee model 495. The motor is single voltage because it is two speed. I have no reason to assume that anything in this regard has been changed from the original factory build. The motor looks completely unmolested and the saw has a period correct (mid-50's) GE two speed magnetic control and matching two speed start/stop station. Don't challenge me on why the saw would have a two speed motor in the first place, because I would deflate rapidly. Suffice to say I am interested in answering that question through use.

Once it warms up a tad I will do some more investigating to find out if the motor is a true dual winding or if it is a consequent pole, and a few other connection related matters. For the moment, I'm stayin' warm and trying to learn a little more about these things.

Steve

Steve,
I am in the same boat. I just got an Oliver 88D, which has a 5hp 3ph 440v direct drive motor. I took the motor apart and brought the stator down to the local motor shop. They told me they might be able to convert it to 220v depending upon the configuration of the wirings. A few days later they told me that it couldn't be done, so now I am thinking I will have to find a transformer. I am running a 10 hp rpc, so I will be building off of that. It might be worth a shot bringing it to a motor shop and having them check out the windings. Labor costs were fairly minimal for them to check it out and rule out the possibility. Good luck,
Rob