The Forestry Forum

General Forestry => Timber Framing/Log construction => Topic started by: flyingparks on September 09, 2021, 07:36:43 PM

Title: Phase Convertor for Mafell Bandsaw
Post by: flyingparks on September 09, 2021, 07:36:43 PM
Hey all. Does anyone here have experience with running a three phase tool off single phase power? I'm looking at phase converters. Seems too easy. I'm getting a used Mafell portable bandsaw but it's three phase. I don't have that at my house. Does anyone have any experience with this? Thanks
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: btulloh on September 09, 2021, 08:16:24 PM
What hp motor is on the bandsaw?  VFDs for motors less than 3hp are inexpensive and will give you 3ph from your single phase. Rotary phase converters are a standard option and you can even make your own from a 3ph motor and some motor start caps. Not difficult or unusual to turn single phase into three phase for a specific tool.

3hp vfd (https://www.amazon.com/Single-Phase-Variable-Frequency-Inverter-Controller/dp/B07L8XZFYG)
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: YellowHammer on September 10, 2021, 06:52:47 AM
Yes, we would need to know the horsepower requirements.  

I have and use a phase converter every day.  Yes they work, and they are about a hundred bucks per horsepower. So a 30Hp is $3K, a 40 hp is about $4K, etc.  

Or you can build your own, just depends on your application.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: flyingparks on September 10, 2021, 07:54:52 AM
Thanks guys. I saw some pretty inexpensive ones that I thought were too good to be true. Sounds like its not. The saw, I believe, is 3HP. I'm trading some work for it and it seems like a really good deal. Especially if I can use it! I'll keep you updated.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: DMcCoy on September 10, 2021, 08:34:59 AM
I tried building my own and yes it worked but balancing the legs was difficult and the motor had a whine to it.  I then went to a VFD, much better and smooth(no whine), buy a higher rated one than you need, mine was at par and overloading was an issue if I remember correctly.  Finally I got a rotary inverter from US rotary.  I wished I had started here, no problems since.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: JRWoodchuck on September 10, 2021, 11:06:38 AM
I built my 15 hp from a kit I already had the motor for $115 and Im pleased with it. If your thinking of adding more 3 phase tools to your collection I would go rotary converter and build it a bit bigger. But if your thinking this is the only 3 phase tool then the vfd should be good. 
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: Larry on September 10, 2021, 11:52:38 AM
Three ways to make 3 phase power.  Static phase converter, rotary phase converter, and VFD.  I have all three in my shop.  Each has advantages and disadvantages.  The static is cheap but only delivers 2/3 of the power needed.  Rotary's deliver full power, but are expensive, large, and make noise.  VFD's are small, quiet, and can vary the frequency for variable speed.  

What is the horsepower and required voltage for your saw?  I did a quick search and saw one with a 120v 3 hp motor which would be problematic for a converter.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: Joe Hillmann on September 10, 2021, 03:12:28 PM
I was once in a shop that had 3 phase tools and only single phase power.  Some how the owner wired the lathe and Bridgeport together.  Whichever tool he wasn't using he would wrap a rope around some part of it that spins when it is running, then he would pull the rope to start the tool spinning at the same time he would turn on the switch to the tool.  Then he would just let that tool run with no load.  As long as that tool was running the other tool could be started and stopped with just the switch and it ran smooth and normal.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: Don P on September 10, 2021, 03:18:47 PM
And that's pretty much all there is to a rotary.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: scsmith42 on September 11, 2021, 06:46:27 PM
In my experience, under loads 50% or greater than the rpcs rated hp, an RPC will not produce full power as compared with line power or a generator. 

Case in point, I run my 15hp 480v Woodmizer twin blade edger off of a 30hp Phase-a-matic RPC. Occasionally it stalls when edging 9/4 or thicker oak. When we run into this problem and switch the power source to my generator instead, no problems at all.

Usually for a single motor, a VFD is the least costly option. For multiple motors, an RPC becomes more viable. If I have multiple loads I prefer to wire the output from my RPC to a 3 phase load center, and then wire the equipment to that so that the circuits are protected.

If you opt to build your own converter, Cronin sells kits that make it easy to do so. For your donor motor, higher RPM is better, so a 3600 rpm electric motor is a better choice than a 1725 rpm one.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: Don P on September 11, 2021, 06:57:54 PM
Scott, can you do a "stories I've heard" vs real world experiment next time you're in the stall situation? Turn on another 3 phase motor and let it idle... does that act as a "flywheel"?
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: scsmith42 on September 11, 2021, 07:02:33 PM
Scott, can you do a "stories I've heard" vs real world experiment next time you're in the stall situation? Turn on another 3 phase motor and let it idle... does that help act as a "flywheel"?
Sure. I can do that this week

Options include a 3hp RAS, 7.5 hp jump saw, 10hp air compressor or 15hp lathe and dust collection system.

The RAS, jump saw and lathe would be in an almost no load situation, so would probably be the best choice.

My RPC was recently rebuilt and we just checked all of the caps last month, so it should be in like new condition.
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: flyingparks on September 12, 2021, 12:11:35 PM
Thank an again. Once I get the unit Ill keep you all updated. I wont know the voltage until I get it. Should be this week
Title: Re: Phase Convertor for Mafell Bandsaw
Post by: Al_Smith on September 12, 2021, 08:12:08 PM
Once again I'll just say I do weird stuff .I'm somewhat of a savant electrically speaking ,just saying not boasting .My shop is 200 amp single phase 120/240 volt  .From there to a large service  panel and from there 100 amps going to my machine works .There to two 10 kva single phase 480 to 120 hooked  up reverse with the  primarys hooked up series and the secondaries in parallel making 480 single phase that runs a 5 HP three phase motor as a rotary with run capacitors .To that using a 3 phase 480 to 240 volt transformer I get the  3 phase 240 volts .Plus a single phase 240 transformer with an augmented boost making around 268 volts which will fire 277 volt lighting .
That home built rotary has never failed me .At the moment it's running around 7 HP with the largest motor being 3 HP .As a rule the rotaries if built correctly will start up to the size of motor it's built from and run up to 3 times that amount providing they aren't larger than the rotary . I've lost track of how many of those things I've cobbled together but none have ever failed .You can get the plans right off the internet .