Need help deciding how to convert to 3 phase

dodgediesel2 · Jan 23, 2021

My wife surprised me with an old DoAll C8a bandsaw for our anniversary. It has a 2 motors, one 2hp, the other 1/2hp. Little did she know that it is 3 phase, which I don’t have in my shop at home. She bought it from a guy saying it ran a few years ago when it got unplugged and put in storage.

More on the saw later, when I get it wired up to see if it runs.

I have 60 amps (single phase) running to the shop from my 200 amp service at the house.

I’m leaning towards a rotary converter instead of a VFD. The bandsaw is not a variable speed saw and my neighbor, who is an electrician and will help me wire everything up, is more familiar with RPCs then VFDs.

I’m not 100% set on the RPC, just going off of what my neighbor recommends. Any reason why I should go with the VFD instead of the RPC?

If I do go with the RPC, I was thinking a 5hp one should be fine for this saw.

Also, I’m hoping to acquire more machining equipment later on in the future (lathe and mill). Just searching and waiting for a good deal to pop up.

Would I be better going with a larger hp RPC initially, such as a 10 or 20hp, if I want to power more equipment later on?

Or should I just swap out the 2 motors on the saw to equivalent rpms and more hp?

All seems a little overwhelming on which route to go. Sorry for the long post.

Any help much appreciated.

JST · Jan 23, 2021

With 2 motors, the RPC is the better way, in most cases.

Phil in Montana · Jan 24, 2021

With only a 2hp and a 1/2hp motors just get 2 vfd,s easy to wire and cheap... no need for a rpc. Also your saw will now be viri speed... whats not to like? and it will cost less than a rpc...Phil

rons · Jan 24, 2021

dodgediesel2 said:
My wife surprised me with an old DoAll C8a bandsaw for our anniversary. It has a 2 motors, one 2hp, the other 1/2hp. Little did she know that it is 3 phase, which I don’t have in my shop at home. She bought it from a guy saying it ran a few years ago when it got unplugged and put in storage.

More on the saw later, when I get it wired up to see if it runs.

I have 60 amps (single phase) running to the shop from my 200 amp service at the house.

I’m leaning towards a rotary converter instead of a VFD. The bandsaw is not a variable speed saw and my neighbor, who is an electrician and will help me wire everything up, is more familiar with RPCs then VFDs.

I’m not 100% set on the RPC, just going off of what my neighbor recommends. Any reason why I should go with the VFD instead of the RPC?

If I do go with the RPC, I was thinking a 5hp one should be fine for this saw.

Also, I’m hoping to acquire more machining equipment later on in the future (lathe and mill). Just searching and waiting for a good deal to pop up.

Would I be better going with a larger hp RPC initially, such as a 10 or 20hp, if I want to power more equipment later on?

Or should I just swap out the 2 motors on the saw to equivalent rpms and more hp?

All seems a little overwhelming on which route to go. Sorry for the long post.

Any help much appreciated.

You can start with 5Hp. A used one would not cost more than $100. Later one if you needed a 10hp RPC for just one big sized equipment then connect another 5hp motor
in parallel with your existing 5Hp motor. But in reality, one 5hp motor will probably be all you need.

It's better to rig up something temporary to see if it fits your needs. Then when the trial period is over, make it clean and sanitary.

steve-l · Jan 24, 2021

I'm converted now after living in Europe for awhile. Single phase power in a workshop is truly primitive. I am spoiled. There is no comparison between single and 3 phase power. RPCs and VFDs are band-aids. Another common misconception is that VFDs are a legitimate substitute to gears. They are not. Gears multiply torque, VFDs do not. I understand you have to do what you have to do, but the only right answer is direct 3 phase power in the whole house and shop.

neilho · Jan 24, 2021

Split opinions here, obviously. Color me firmly in the RPC camp, but it also seems to me if your buddy likes RPC's, he's more likely to want to work on the system when it needs it.

dodgediesel2 · Jan 24, 2021

I actually called power company to get a ballpark price of running 3 phase. $12k to $15k is what they said over the phone. Out of the question.

dodgediesel2 · Jan 24, 2021

rons said:
You can start with 5Hp. A used one would not cost more than $100.

I’ve looked all over the web and can’t seem to find one for less than $500 range. Am I looking in the right place? eBay and marketplace

Strostkovy · Jan 24, 2021

dodgediesel2 said:
I’ve looked all over the web and can’t seem to find one for less than $500 range. Am I looking in the right place? eBay and marketplace

3 Phase Motors Base Mount | AC 3 Phase Motors | Electric Motors | www.surpluscenter.com

Surplus center has all sorts of motors, and ones with special shafts meant to fit pumps or whatever are worth a lot less because fewer people can use them. They work fine for an idler.

I recommend capacitor start and no balancing capacitors if you go with 5hp (which I would). Potential relays work great but can be a bit tricky to wire for the uninitiated, or you can just use a "push to start" sort of button. (Off-on-momentary, like starting a car)

Just a Sparky · Jan 24, 2021

Check Facebook Marketplace and Craigslist for old motors. Be patient and you can find really big ones for dirt cheap. I've seen 20-30 horses go for around $100-200. There was a particular 100 horse that someone wanted gone for $100.

For instance: Buy and Sell in San Antonio, Texas | Facebook Marketplace

neilho · Jan 25, 2021

Another potential source is the local electric motor shop, if there is one local to you. Local is good - I'm sure there are plenty of folks here that have some in the back shed, but freight is expensive.

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