Three Phase Power Inverter for Stock Feeder

[Ed Weiser]

I just came back from Wm J. Redmond and Son and got a great deal on a Delta Stock feeder, Model 36-856R to put on my 3-hp shaper. It is the "old" color and is described as reconditioned, but in fact is new and in the box with all the packaging and 90-day warranty. Mr. Redmond is selling these for $400. The list price is over $1000. The only problem is that the motor is 1 hp, THREE phase. This brings me to my question. In searching the web I've come upon a number of solid state inverters to convert single phase to three phase (at prices starting about $180.) These are superior to static phase converters (all three leads are powered continuously, instead of just at startup) and less expensive and bulky than rotary phase converters. I have no other 3-phase machines and no plans to acquire any so the inverter would be dedicated to the stock feeder which will be permanently installed on my shaper. Anyone out there have experience with this type of approach? Any advice would be appreciated. And, by the way, Mr. Redmond has quite a few of these stock feeders remaining but is going to ship them back to Delta in "a few days" so if you're interested, I would contact them soon...

Ed

P.S. I have no relationship to Wm. J. Redmond & Son whatsoever.

[Jim Becker]

You might look at a surplus VFD (variable freqency drive) as an alternative to the static inverter as you can sometimes find them quite inexpensively. And if the feeder doesn't already have variable speed...it will have it with the VFD! BTW, you will still need 240v to power it...

[lou sansone]

Although it is tempting to hookup a VFD as has been suggested, my professional advice ( not that it really means any thing but I am an Electrical Engineer who has burned up many things in his life ) is to be carefull with the VFD approach. Technically speaking the VFD's can produce much higher voltage spikes than a normal 3 phase motor is insulated for. I am sure I will get a lot of "feedback" from folks who swear that they run regular "non-inverter duty" motors out there using VFD's , but VFD's are really meant to run with "inverter duty class motors" which have a much higher insulation class than standard 3 phase motors. VFD's are great and I have retrofitted my pattern-makers lathe with one along with a "Reliance super duty inverter duty" motor. This was done primarly because of the great speed control you get from them, rather than the problem of only having single phase and trying to run 3 phase motors. I have a 3 phase shop, so this is not a problem.

I do have a good friend who runs his entire machine shop using the simple static phase converters. He probably has about 10 of these guys all over the place, each hooked up to the particular machine ( CNC center or what have you )They do eventually burn out, but he runs them 8-10 hours per day 5 days a week. My humble advise is to buy the static phase inverter and not to risk damaging the good deal that you have gotten on the power feeder.
regards

[Ed Weiser]

Jim-
Most of the solid state inverters also incorporate VFD's as well. The use of dedicated IC's has apparently made the devices both multifunctional and quite a bit cheaper than inverters once were.

Lou-
My understanding is the problem with VFD's with non-VFD motors is that at lower speeds the fan-cooling works poorly and they overheat. This is apparently more likely on motors running on one-phase power where one-third of the motor armature has no current. I am not interested in the variable speed issue since the stock feeder already had eight speeds and is reversible on its own. I just do not want to go from 1 hp rated to 2/3 hp with a static phase converter.

Ed

[Jim Becker]

Ed. Thanks. I did not know that.

Lou...don't VFDs have the ability to be programed to maintain sanity in their ranges?

[lou sansone]

Ed. Thanks. I did not know that.

Lou...don't VFDs have the ability to be programed to maintain sanity in their ranges?
Jim
Yes and no. You can program all types of things into them like "acceleration and decelleration ramps" which are really great. I especially like the "decel" circuitry on the lathe because it lets everything come back to a nice rest rather than slamming off or coasting to a stop. You can also program the top speed and all of that, but the problem seems to be in the actual phase generation circuit. There is some "majic" going on with the switching circuit the tends to produce voltage spikes as high as 3-4 times the incomming voltage. One of the interesting things about the VFD's is you can overspeed the normal motor by 25%. That means you can get somthing like 2500 rpm out of a 1750 motor! Hey, if it was just a junky off the shelf 3 phase motor then I would say "go for it". But since it is really part of the whole assembly I personally would not risk it.

[lou sansone]

Jim-
Most of the solid state inverters also incorporate VFD's as well. The use of dedicated IC's has apparently made the devices both multifunctional and quite a bit cheaper than inverters once were.

Lou-
My understanding is the problem with VFD's with non-VFD motors is that at lower speeds the fan-cooling works poorly and they overheat. This is apparently more likely on motors running on one-phase power where one-third of the motor armature has no current. I am not interested in the variable speed issue since the stock feeder already had eight speeds and is reversible on its own. I just do not want to go from 1 hp rated to 2/3 hp with a static phase converter.

Ed
Ed
That is another issue that also a concern, but from all that I have studied about it, the insulation class and voltage breakdown is the real motor killer.
I have a 1 hp power feeder and in low range you can't stop it. The other thing that I have found will happen is your feed wheels will slip before anything else bogs down.

[Bruce Page]

Ed, I have used the same "static" converter on my 3 phase lathe & milling machine (5hp & 2hp) for many years, without incident.

They are cheap, and in my experience, reliable.

[Rick Lizek]

My local electric motor company sells Baldor VFD and they have a model that actually runs on single phase 120 volts for motors 1 hp and under. I saw it hooked up to a small drill press and it's pretty slick as it give variable speed and a host of other options such as soft start and can actually double the rated rpm of a motor. I did buy a bigger one to run a bridgeport and while it's a bit tricky to program the first time it's a great way to go. While the forums are great sources of ideas I still go to ly local technical expets and the manufacturers tech help and usually compare several sources as sometimes details get over looked. Typically I find the local guys can offer better service when in a bind as I can bring it over or they can swing by the shop, so I dont mind paying a bit extra for the local service.

[Steve Stube]

Ed, if it were me, I would buy a VFD for this application and find one for ~$100.00. I have 8 VFD's in my hobby shop and know they are a great way to power up 3 phase equipment even in those cases were you don't need the variable speed capability that they are so suited for. I have used static converters, rotary converters (I still have 3 HP and 5 HP units but no longer use them) and the VFD's already mentioned, the VFD's are the best. VFD's produced after about 1996 provide a balanced and clean (no spikes) 3 phase output.

general comments;

some VFD's are 115 V single phase input and 115 V 3 phase output. I have one feeding a 115/230 volt inverter duty 1 HP 3 phase motor. Not real common but available.

230 volt single phase input VFD units are generally available in fractional HP models up to 3 HP, above 3 HP you generally have a 3 phase input requirement but by derating a drive you can work around that to go to higher HP.

some single and 3 phase VFD's are multi voltage. Examples can be found for 115 v single phase input with 230 v 3 phase output and others are 230 v single or 3 phase input and output 460 v 3 phase.

sometimes it is desirable to provide an additional fan for cooling the 3 phase motor where extended run periods at reduced speed are encountered as the motor fan at reduced speed can not cool adequately alone.

very old motors may not be suitable to VFD use without employing the soft start feature due to brittle insulation on the motor windings.

most VFD's (all of mine) are capable of at least 120 Hz operation (twice rated motor speed) but that doesn't mean that the particular motor or what is powered by the motor can handle such a speed increase. Above 60 Hz, know what you are doing to be safe. Some go to 400 Hz. - scary!

Plug stopping and instant reversing are also available with VFD's as with 3 phase power but in most cases does require an additional resistor kit to soak up the heat.

These are my observations and experiences FWIW.

[Ed Weiser]

Steve-
Thanks for your comments and experience. The rating of the stock feeder I need to power is 1.5 kvA at 3400 RPM and 1.2 kvA at 1700 RPM. I believe this is within the range for 1 hp solid state motor controllers I have found. The brands that seem most affordable are Hitachi and LG. The Leeson and Baldour controllers are very expensive. I have not found any controllers for 1 hp, however, less than about $180. Any suggestions where else to look?
Thanks again.

Ed

[Steve Stube]

I like shopping on eBay.