Educate me on 3 phase power converters

[John Sanford]

Briefly, here's my situation:

Tonite, I'll be looking at a nice (hopefully) Griggio 640 SNAC bandsaw (24" throat, @16" resaw) at a great price. It is powered by a 240v 3 phase motor.

I have two unused 240v outlets in my townhouse, a 40 amp for the oven, and a 30 amp for the dryer. Both are unused, because I have gas appliances. There are no 240v outlets in my shop, aka garage.

So here are the considerations as I see 'em.

1. The townhouse is rented, adding 240v to the garage is a fair option, but not a great one, as it would be $$ out of my pocket.
2. Running a custom "extension" cord from either the dryer outlet or range outlet. Access to the townhouse from the garage is through the laundry room, which is adjacent to the kitchen, so max length of run would be 50' from the range, 40' or so from the dryer.

AND

1. Change the motor to a single phase 240v, if possible. With this option, what size should I go with given the power limitations?
2. Purchasing a 3 phase converter. I have a modest sense of the size I would need (roughly 50-100% the existing motor's HP rating), but no idea what sort of input amperage the converter would need. Nor do I really have a sense of what are the practical differences between a static and rotary converter.

What are the valuable characteristics of a 3 phase converter from the perspective of a home woodshop, and what features would simply be overkill and/or counterproductive?

Note that I can currently get both the bandsaw and a used 3 phase 15hp rotary converter for less than half the cost of a new 24" Italian bandsaw. Naturally, being used, these are transient opportunities.

[Rod Sheridan]

Hi John, a single phase input/three phase output Variable Frequency Drive (VFD) will allow you to run a 3 phase motoer from a single phase source.

It will also do a lot of things such as provide stop/start control, acceleration and braking, and of course if you want, variable speed.

You can find units that will run up to a 3 HP motor with a single phase source.

If your bandsaw has a motor 3 HP or smaller, this is the least expensive, most space saving option available.

I put one on my sawmill so I could use a 3 phase motor on it at home.................Regards, Rod.

[Dennis Ford]

A 15 hp rotary converter would be great, but I don't think you will be able to start it on the 40amp circuit. A 3hp VFD would be my choice (probably cost ~ $300), you could run this off either circuit. That "custom" extension cord will not be cheap but at least it will be yours and not the landlords if you move.

[James Tibbetts]

Since you are renting I would say no matter what solution you choose you will need an extension cord of sufficient length and conductor size to get from the 220v outlet of your choice to the machine. Complete guess, but I think that cord is gonna cost you at least $100.00. A 15hp rotary convertor is way overkill for a single 3 hp motor. I don't know what the VFD units cost, but a static convertor to run a 3hp saw will cost you about $50.00, new, on flea bay. It will run your saw fine, but won't provide the other capabilities of a VFD. Unit should be rated for 5 hp operation.
If the breaker box is in the workshop, (and I had a friend who was an electrician), I would ask the landlord about adding a 220v outlet in the shop. Not a big deal at all. Tell him it adds value to his property and he should split the cost with you!(Good luck with that!)

[Tom Clark FL]

[QUOTE=What are the valuable characteristics of a 3 phase converter from the perspective of a home woodshop, and what features would simply be overkill and/or counterproductive?[/QUOTE]

As my limited understanding of converters goes, make sure your phase converter is 50% larger than the largest motor you plan to run on it. I have had a 5 hp rotary for 17 years, and it works perfectly. Both machines it is hooked to have 3 hp motors.

A friend purchased a 10 hp lathe and a 10 hp static phase convert. It would not run the lathe worth a darn… He purchased a 15 hp static and it ran perfectly.

A static is quieter than a rotary. I mounted my rotary on two sets of rubber feet and it is nearly silent.

[Dave Cullen]

You will need 220V either way. Cheapest "extension" would be 10/3 Romex plugged into the dryer outlet. With a 30 amp 10 gage line you could easilly run a 220V single phase 2 or 3 hp motor or a 3 phase converter for the existing motor. I would bet that a converter would be the cheaper route.

[Kirk Poore]

You will need 220V either way. Cheapest "extension" would be 10/3 Romex plugged into the dryer outlet. With a 30 amp 10 gage line you could easilly run a 220V single phase 2 or 3 hp motor or a 3 phase converter for the existing motor. I would bet that a converter would be the cheaper route.

I concur--get the extension cord. A Teco FM50-203-C 3hp VFD is $196 plus shipping, will give you overload protection and a soft start. The 15 hp RPC is overkill for now, and I don't think static converters are good for the long-term health of your motor.

Kirk

[Ed Aumiller]

Static converters will reduce the 3HP motor to about 2HP... they do not harm the motor, just lowers HP..

Do what James said if breaker box is in garage... otherwise use the extension mentioned by Dave...

Use a vfd for all the extra features, they are worth it... see some of the threads about VFD's on here...

If you are not familiar with 3 phase.... to reverse the motor, swap any two leads...

This is VERY IMPORTANT....Be sure to remove the blade before powering up ANY 3 phase motor for the first time as there is a chance the motor will start in the reverse direction.
This can cause damage if blade comes off due to guides, brushes, etc catching from the blade going the wrong way... This is VERY IMPORTANT....

[Jim Neeley]

While Romex may be the cheapest, each conductor is a solid core of copper rather than being copper strands. As such it is not suitable for installation where the cord will repeatedly be flexed (as when rolling up and unrolling) as it will, over time, fatigue and may fail, resulting in a hazardous condition.

If you can "permanently" mount it in the wall, it will be fine.

Just my $0.02.. YMMV.

Jim in Alaska
(also EE)

[Jeff Duncan]

I agree with Jim, Romex though possibly cheaper, does not make for a good extension cord. It may cost a few bucks but you can make your own extension cord to handle whatever you need. I have one in my shop that's 50' of 4 wire 10 gauge SJ cable with a plug on one end and a receptacle on the other. I use it to run my edgebander which is in a separate storage space next to my shop. SJ cable is much easier to handle than trying to roll out Romex.

As far as the saw goes there are as you mentioned different options. As it's a Euro machine be careful if looking for another motor. Euro machines tend to have Euro motors, which do not necessarily have "Merican counter parts. Comes down to how the motor is mounted and pulley bore sizes. If the motor was supplied here by the importer, (which also sometimes happens), then you'll have a standard motor. In that case I would price out a suitable single phase replacement as one can often find affordable motors through CL and e-bay.

good luck,
JeffD

[Rod Sheridan]

You will need 220V either way. Cheapest "extension" would be 10/3 Romex plugged into the dryer outlet. With a 30 amp 10 gage line you could easilly run a 220V single phase 2 or 3 hp motor or a 3 phase converter for the existing motor. I would bet that a converter would be the cheaper route.

Do not use Romex as an extension cord, it's against code.

You do not need a 10 gauge extension cord, the largest needed would be a 12 gauge cord, or a 14 gauge cord if the current is 18 amperes or less for your VFD.

Regards, Rod.

[David Kumm]

How RPC are rated varies by company. Some rate at highest HP to start, other by light load and they need to upsized. I would overengineer the extension cord if going any distance. A big bandsaw with 16" resaw will need full power, especially if it is the Griggio with full cast iron wheels so I would not go static. A three hp VFD might even be a little light depending on the amp draw of the motor. I don't know about Griggio but the 3 hp listing on some Italian machines is at 50 HZ so you may be getting a 3.6 hp motor that pulls more amps than the vfd can handle. Don't get the vfd until you see the motor plate. You may be OK in that the VFD overload capability might be high enough to handle the short term needs. If you intend to do a lot of resawing of long boards yiou will want to upsize the vfd. Dave

[John Sanford]

So, an update:

IF I go down this path, I will take the extension cord route. I'm figuring I'll make up or buy a 50' 8 gauge cord using SOOW cable. Overkill? Perhaps, but it insures that my breaker is "sized to the wire" w/o downsizing the breaker, and I can trample/coil the cord without worry.

I got a look at the bandsaw, it's an older one w/o any dust collection from the factory, but it does have a foot brake. I was unable to see the motor plate. The saw is fitted with Carter disc guides, looks like these. It has spoked wheels, not solid, and strangely enough, comes with an extra wheel.

The seller is offering the Bandsaw, a Vega 1553 lathe w/ the inverter package, and an RPC built using Baldor bits for $2500. The Vega has some surface rust on the bed, face plates, spurs, and some significant rust at the bottom of one end of the base. The saw has some slight surface rust. I haven't seen either run, but I was able to turn the bandsaw wheels and the lathe by hand, so they aren't frozen.

I am torn... the saw is actually physically bigger than I was thinking of getting in my present and forseeable circumstances, i.e. I consider moving with the beast in the future with some trepidation. The lathe is going to need some cleanup, and the RPC may not be useful for me (I just don't know enough about them...), the plug that it currently has on it is wired for a 50amp circuit. On the flip side, it IS an Italian stallion that humbles my Big Box 14" Delta. 48" of spindle turning length would be a big upgrade from my current Jet Mini-Lathe, and if the RPC will do the trick, all I'll need is the big extension cord...

Any input would be appreciated...

[Michael W. Clark]

If you buy it and don't want the RPC, let me know. I assume a 15hp RPC will start a 15hp motor?

[John Sanford]

If you buy it and don't want the RPC, let me know. I assume a 15hp RPC will start a 15hp motor?

Not as far as I've been able to determine. The RPC HP rating needs to be 50% to 300% larger than the motor(s) it's going to start. How much bigger depends on the nature of the service the motor is doing. "Hard starting" motors need more HP from the RPC.

I'm not sure what size this RPC is, it's not the 15hp one mentioned in my first post. Physically, it is pretty big, but since it's the very first RPC I've ever seen, that doesn't mean much. For all I know, a .5hp RPC could be just as big.