3 phase power solutions

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I know that this has been discussed to death on other forums, but why not discuss it to death here and keep the pageviews in-house? 😁

So, I'm kinda shopping used table saws and am faced with the ol' quandary - do I want to deal with a 3 phase machine? 

Most people don't have 3 phase on tap and many resort to either Rotary Phase Converters or Variable Frequency Drives, both of which seem to have pros and cons. 

RPCs typically have a bigger up-front cost, but can be used with multiple machines... but there are also matters of noise, energy efficiency and convenience (always flipping two switches instead of one). 

VFDs can have a lower up-front cost and some nifty features like speed control and braking... but each machine needs a dedicated unit and they seem to be practically limited to ~3HP for most residences (because of single phase input limitations [I could be wrong here - I don't know what I'm talking about and the info online is a jumble] and the costs of units rated to support 5+ HP). 

I guess that I'm curious to hear the thoughts of those that have done either/both. I also still have some questions on either approach and they're basically around sizing - 

For RPCs, do you need an idler motor that's significantly lager than the motor that you want to run (some say 2x the HP)? 

For VFDs, can a ~3HP VFD practically support a 5HP machine, in this case, a saw specifically? 

TIA! 
Can’t answer your questions directly as my only experience is with a VFD on a 1HP motor (and it works fabulously with speed control). 

One of the things I’ve read that makes sense to me (especially when looking at used tools) is that used 3-phase tools seem to sell for cheaper than their single phase counter parts. I’m told/am guessing that this is due to a smaller pool of buyers. That said, the price difference may be significant enough that adding the cost of a solid VFD may still leave the tools cheaper than its single phase counterpart. It seems 3-phase tools are also beefier and more solid…that may be a good thing or a bad thing based on how much room you’ve got and how you plan to move them. 

Again, I’m limited in my VFD experiences but based on what I’ve done to this point, I’d be actively considering used 3-phase tools and a VFD going forward…especially if the price is right!

I’ll be following to get info from those with more experience on the matter!

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".

Yeah, the cost of 3ph machines on the used market can be really attractive and it's definitely one of the big reasons that this is even a question for me. I've certainly come across a few Unisaws (among other things) that would be really tempting, if they were just a little closer (why does everything good have to be a 4+ hour drive from me?! 😭) 

An interesting option that I ran across overnight is the DIY option for an RPC - basically an add-your-own-motor kit. A quick look through my area shows some seemingly suitable 10hp motors in the $200 range. With the kits in the $150-250 range, that's an attractive price to address multiple machines and do so at full power (at least within the scope of machinery that I'm considering). 

Oh, and the gist of what I've come to understand on VFD sizing is: you can run an undersized VFD, 'specially if you don't think that you'll bump your head on its power ceiling very often... but don't get too silly with the undersizing. If this is correct, I think that the 5hp tables would be fair game with a decent 3hp VFD. What I've been seeing on a lot of these motors is an FLA (full load amps) of ~12, whereas these 3hp VFDs are rated for 10-10.5 (with many able to provide 50% more for 60 sec and 100% more for a brief spurt). I can't speak for others, but I think that would cover me just fine.  
Makes sense to me, but I don’t have the experience to speak to it. 

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".

Looks like this may be interesting for me... I've never ventured down the 3 phase path, but I happen to have it "on tap".... well at least one outlet squirrelled away in a corner of the workshop,


If your first cut is too short... Take the second cut from the longer end... LBD

I got so busy that I never had a chance to follow up on this. 

I ended up buying a 5hp, 3 phase Unisaw at auction for a pretty good price. After a bit of researching, I ended up with a Hitachi VFD bought from Wolf Automation (https://www.wolfautomation.com/vfd-3hp-230v-single-phase-12a/) The VFD is advertised as 3hp, but spec'ed at 12a, which is the FLA of the motor on my Unisaw. 

Wiring power to the VFD and from the VFD to the motor was cake. Figuring out how to re-use the power switch to start and stop the motor took a little more time, but was pretty simple once I understood the basics of the switch type. 

So far, the saw has been humming along beautifully. There is a bit of a VFD whine that I think I might be able to tune out, but it's not bad enough that I've bothered with looking in to it. 
I have a factory 3ph, 5 hp motor on my 18" Delta wedgebed planer and I bought the cheapest VFD I could find that would support 5hp, accepted 1ph input power and had a return option.  So far it's worked great but I've yet to try and plow of 1/8" of thickness from a 16"+ wide maple slab so when I'm ready to (and several are close to being done air drying), that will be the real test!