Replies

1. 
   roc | Oct 30, 2011 03:58pm | #1

   Hmmmmm

   I have never heard of that one.

   I usually find from all these fudgit three phase to single phase discussions that it is usually best, in the long run , to just get a 220 single phase Baldor motor suited to the load requrements of your table saw.

   PS: are you positive you don't have three phase outside that can be brought to your building ?

1. 
   tsk | Nov 01, 2011 11:48am | #3

   Hi Roc, Thanks for your comments.

   I got the idea of using a “starting capacitor” from a retired, H.S. wood shop teacher. He has one on a heavy duty sander in his home shop that formerly ran on three phase power in a commercial shop. His “s.c.” runs on a spring switch, that goes back to its “off” (resting) position once he releases it. To start up his machine he simultaneously flips both switches (i.e., normal on/off swithch, and “s.c.” switch).

    I have residential power and have always had the understanding that three phase power is not available to residential customers (If it was, why would people want to convert them to single  phase use?)  Since you raised the question though, I should call the power company to be sure, but I am not optimistic this is an option for me.

   Another person had looked into the possibility of just replacing the saw’s existing motor, as  you suggested, with one that runs on single phase. He estimated the cost of the new motor to be around $600—too expensive for me.

1. 
   roc | Nov 02, 2011 12:42am | #6

   Heck you could be next to a farm for all I know . . .

   or your shop is in a building near a commercial area.  Where I work the three phase goes down an alley where there are way more houses than commercial buildings.

   http://amfone.net/Amforum/index.php?action=printpage;topic=19215.0

   See the link and page down to :

    >If you have poles & wires feeding your place, you may be in luck.  There need to be three wires up on the high tension side,<

   Anyway an interesting exchange in the link.

   When the one guy says "oil caps" on the motor I think he means oil filled capacitors.  That is kind of what you were thinking.  They say it can be noisier and less torque obviously.

2. 
   bones | Oct 30, 2011 09:00pm | #2

   don't do it.

   If you want to go the 3 phase route which I think is great, go on and get a phase converter.  There are two main types (not going to talk digital)  VFD's and Rotary phase converters.   VFD's allow you to do basically what you want to do it gives it 3 phase to get her running and thats it.  A rotary phase converter uses single phase and another motor referred to as an idler motor to generate true three phase power.   VFD's are relatively inexpensive but again your are not running 3 phase.   A VFD is for a single machine, while a RFD is for all your equipment.   You can find a lot of great 3 phase tools used for a song.  Don't go on something you hear about on the internet.  You want to spend a grand on a saw and potential screw it up to save a hundred bucks.   A three phase motor was designed to run on 3 phase power.   Don't short it.    I an reccomend american rotary great products and they stand by what they sell. 

1. 
   tsk | Nov 01, 2011 12:14pm | #4

   Some more questions

   Hi bones,

   Initially, I looked into a means of converting the saw so it could run on three phase from my single phase power source. I think it was a VFD that I looked at. (Currently, I am away from home for about a week and my notes on this are not with me.), but the cost was prohibitive. It was around $900, as I recall! I remember reading that there were some means of converting (I believe it was the rotary, but not sure) that should be avoided because the results were too unreliable. So, from my research I tried not to skimp and rather go with the most reputable brand. Don’t recall what it was. I have it written in my notes back home.

   You say one can buy three phase equipment for “a song”. Would you expect a table saw such as I described to be discounted even lower than $1000 that I mentioned?

   What does “RFD” stand for?

   I don’t know your background, bones. If the “starting capacitor” method that I suggested  was a viable option, do you believe you would have heard about it before me presenting it?

   Thanks for your input

2. 
   tsk | Nov 01, 2011 02:07pm | #5

   Tsk's response to bone's comments

   Hi bones,

   Initially, I looked into a means of converting the saw so it could run on three phase from my single phase power source. I think it was a VFD that I looked at. (Currently, I am away from home for about a week and my notes on this are not with me.), but the cost was prohibitive. It was around $900, as I recall! I remember reading that there were some means of converting (I believe it was the rotary, but not sure) that should be avoided because the results were too unreliable. So, from my research I tried not to skimp and rather go with the most reputable brand. Don’t recall what it was. I have it written in my notes back home.

   You say one can buy three phase equipment for “a song”. Would you expect a table saw such as I described to be discounted even lower than $1000 that I mentioned?

   What does “RFD” stand for?

   I don’t know your background, bones. If the “starting capacitor” method that I suggested  was a viable option, do you believe you would have heard about it before me presenting it?

   Thanks for your input.

3. 
   oldwindowguy | Nov 02, 2011 09:25pm | #7

   Capacitors, in general, produce phase shifts in alternating current circuits by storing power briefly and releasing it out of phase to the supplied power.  Starter capacitors are designed to do this for a short period of time only.  They power a starter circuit in single phase capacitor start motors BRIEFLY until the motor comes up to speed and then a relay switch turns them off.  They explode if run too long as they are not sturdy enough mechanically to withstand the internal force created by the  electromagnetic energy  they store.

   Very small three phase motors can be powered off single phase power by oil filled capacitors, which are sturdier.  It is not ideal.

   Your 7 1/2 hp motor is far too large to do this.

   A dynamic three phase convertor is essentially a three phase motor which is got up to speed (with a starter capacitor circuit) and then run on single phase power without a mechanical load on it.  So long as it is free to spin without mechanical load, its internal windings will generate an electromotive back force which can drive another three phase motor.  Oil filled capacitors may be added to the circuit to equalize the voltages it generates.

   There's lots more to a table saw than the motor that has been hung on it.  If you plan on doing heavy, rough work, a light saw with a big motor makes sense.  It won't do the precision work that could be expected of a heavy saw more sensibly matched to that much power.