# Info on Temco Rotary Phase Converters?



## vocatexas (Jun 5, 2019)

Finally, after a long delay, I'm on the road to finishing my shop. I'm going to need a rotary phase converter to run my equipment, and I had priced a converter from American. However, there is an bi-monthly auction not far from me, and last night I noticed they had their listing for this months' auction up. On the list is a Temco phase converter of the size I need. It appears new or barely used. I'm going to call the auction owner, who I know, and see if he can provide any details on the unit tomorrow. 

Does anybody here have any experience with Temco phase converters, either good or bad? If I could save a grand or so, it would really be helpful, but I don't want to buy this thing and then find out there are issues I could have avoided with my original choice. Saving money is great, but spending twice I'd rather avoid.

The unit in question is a Temco AC29.  https://temcoindustrial.com/temco-ac29-rotary-phase-converter-29-kw-40-hp.html


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## MikeInOr (Jun 5, 2019)

"TEMCo's TRU-WAVE™ technology is a signature feature found only on TEMCo phase converters. TEMCo's TRU-WAVE™ Phase Converter produces a three phase sinusoidal waveform, generated from a single phase source, offset at 120°. "

LOL!!! What a bunch of BS!!!

Looks like a standard balanced rotary phase converter to me.  I am sure it will do what it is supposed to do just fine.  There really isn't any magic in RPC's, they all pretty much operate the same.  There are RPC's that use capacitors to balance out the legs and those that don't.  A balanced RPC will have more consistant voltages across the three legs which is a good thing.

I built my balanced 10hp RPC about 20 years ago... and it is still going strong... even though it does not have "TRU-WAVE" technology... LOL!!!  I am converting all my 3 ph machines to VFD's now that VFD's are affordable for the common man.  I am sick of listening to my phase converter run and soft start greatly lowers start up amps!  Above 10 hp and VFD's aren't really cost effective vs a RPC though.  What is the largest motor you are going to run?  If 10 hp or under I would HIGHLY reccomend going with VFD's.  If your largest motor is over 10 hp then I understand why you would go with a RPC.


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## Ulma Doctor (Jun 5, 2019)

unless you are using equipment sensitive to voltage differences, you are not gaining anything by purchasing an expensive RPC

most lathes, milling machines, grinders and drilling machines can operate on an unbalanced RPC

you can build your own! cheap!

https://www.hobby-machinist.com/threads/rpc-simple-design-unbalanced.12712/ 

this design has been tested on over 50 units, the first one was built more than 20 years ago and it still runs today!


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## vocatexas (Jun 6, 2019)

Mike, I've read a fair amount on phase converters, but very little on VFDs. I had been told that on very old electric motors a VFD could damage them. I've got a 10 hp motor made in 1917 and a 5 hp from 1942. In total I'm going to be running a lathes with a 10, a 5 and a 2 hp motors and at least one mill with two 5 hp motors. Do you think VFDs for each would pay off or would a single RPC be better? The advice I'd been given was to go RPC, but I'm still open for suggestions.

As far as the 'Tru-wave technology', yeah, I know that's mainly hype. It's just that this is in a local auction and I might be able to pick it up for pennies on the dollar.


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## Eddyde (Jun 6, 2019)

Yeah, a bunch of sales hype for sure, but the unit does look solid and reliable. I'd definitely grab it at a reasonable price.
For the setup you describe I would go with the RCP. I use both RPC and VFDs in my shop. RPCs are pretty much plug-n-play, no need to modify the controls on the machine and are more cost effective for larger horsepower and multiple motors. VFD's do offer more control over the motor such as direction & speed control, torque limiting and overload protection, but can only power one motor per VFD, if you have a second motor on a machine, like a coolant pump or feed, you'll need a second VFD. Also you must wire the machines controls and motor to the VFD separately, no switches allowed between the VFD and motor. However they are worth it for machines where you really need the extra control. Also note, if you are using a VFD for phase conversion, you must derate it by a third so for a 10 hp motor you will need a 15 hp VFD.


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## MikeInOr (Jun 6, 2019)

1) *Will the current electrical panel in your shop handle the Temco 40hp RPC?*  According to the specs on their website that RPC requires a 80amp circuit.  Can you put an 80 amp circuit in your electrical panel?  If you can not install an 80 amp circuit in your electrical panel that would put the TEMCO out of consideration "FOR ME".  For the motors listed a 20hp RPC would be overkill and a 15hp RPC should be perfectly acceptable.  Smaller RPC's use smaller circuits.

2) Would I trust a TEMCO phase converter?  I know Temco has been around for quite a few years.  I have never used, seen, or talked to anyone that has used one of their RPC's.  If it were my money I would absolutely have no problem purchasing the Temco RPC at a considerable discount.  I would venture the Temco is as good as ANY brand of phase converter and I would would snap up a deal on one in a heartbeat.  The price of their RPC's suggest they use quality contactors and quality capacitors rated for well above the required voltages... if not they would be out of business.  As for the flowery marketing language... I just find it funny!

3) Will you save money with a RPC?  If I were to buy a 40hp phase converter to run Seven 3 phase motors in my shop I would add a 3 phase panel and run 3 phase wiring through out the shop.  This would be costly.  By contrast all of my VFD's plug into my existing 1 phase 240v wiring.  When comparing costs I would factor in the 3 phase distribution wiring.  If I decide to move a machine I don't have to worry about whether a 3 ph outlet is close (My shop has a very generous amount of 240v 1 ph outlets).

4) How comfortable are you with wiring?  My father was an accomplished electrical engineer and I very comfortable pulling my own wire and rewiring my own machines.  A RPC will not require any rewiring of your machines.  Just plug them into your new high dollar 3 phase outlet and press the Start button.... you are good to go!  By contrast in almost every case adding a VFD to a machine REQUIRES some rewiring of the machine.  The first rule of VFD's is that there are no switches or other controls allowed between the VFD and the 3 phase motor it is running.  Cutting the power between the VFD and the running motor can cause permanent damage to the VFD.  This also means that a VFD is required for every 3 phase motor on a multi motor machine.  Rewiring a machine for a VFD is quite straight forwards and this board is a great resource... but your comfort level with wiring should be a consideration.

5) Are VFD's safe for older motors?  It seems like it was about the early 2000's that someone reported high frequency spikes from VFD's can cause arcing through the bearing of motors with un-insulated armatures leading to premature bearing failure.  The root of this concern has to do with the functionality of power transistors (IGBT's and Mosfets).  In SOME conditions when turning off a power transistor (done 60 times a second for 60 hz power) a very short (microsecond) spike in voltage can occur which can in rare cases cause a arc through the bearings in old motors with un-insulated armatures. The current associated with the microseconds spike is pretty much nonexistent so it has no effect on the electrical portions of the motors.  Since that report the characteristics of power transistors and the controlling electronics have progressed immensely!  I have several old 3 phase machines dating back to the 40's and 50's with specialized (irreplaceable) motors that I run on VFD's without concern.  For example one of my favorite and most used woodworking machines is a 1947 7.5hp Redstar radial arm saw.  It is a beauty and a pleasure to work with!  If the motor on it were ever toasted the whole saw would be worthless.  I have no qualms about running it on a VFD.  Quite the contrary, with the soft start of the VFD the initial inrush current is a small fraction of what it would be starting the motor with a RPC or 3 phase electrical service.  Less current = less heat = less stress on the 70 year old insulation in the motor.

6) Functionality - The number one advantage of a VFD is the gained functionality of the machine you are using.  Being able to set the spindle and feed speeds of a lathe or mill to virtually any RPM you want is a VERY nice feature.  It reduces belt changes and allows you to tweak speed changes on the fly.  If you are getting chatter on a cut just tweak the speed with the VFD a bit until the chatter goes away.  On my radial arm saws and table saws the soft start and electrical braking are also very nice features that I have come to really appreciate.  The electrical braking of your lathe spindle allows for MUCH quicker stops during operations like single point threading.  I love being able to start my wood working saws without the lights in the shop and the house flickering.  The soft start function is not only healthier for the machine it is also healthier for the entire electrical grid all the way back to the power generation station (not that my hobby machine use will make a noticeable difference but it all adds up!)

Everyone's needs are different.  These are the off the top of my head things I would consider when deciding between RPC's and VFD's.  I welcome other members to add to my list of considerations to make it more complete.


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## Eddyde (Jun 6, 2019)

MikeInOr said:


> I am sick of listening to my phase converter run.
> Above 10 hp and VFD's aren't really cost effective vs a RPC though.



Note, VFDs aren't silent, they have cooling fans that can run continuously. My 7.5 hp HY brand VFD is quit loud, louder and certainty more annoying than my RPC. A well balanced RPC should be pretty quiet.


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## markba633csi (Jun 6, 2019)

Mike: I have heard that the winding insulation can break down on some older motors from VFD spikes- in addition to the bearing issue
Of course, the varnish they used back then could have been marginal compared to todays polyurethane and other materials, but lots of folks run with VFDs and old motors;  I haven't heard of any sure fire way to identify the weak motors
Mark


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## MikeInOr (Jun 6, 2019)

markba633csi said:


> Mike: I have heard that the winding insulation can break down on some older motors from VFD spikes- in addition to the bearing issue



I wonder what the reasoning behind that theory is?


My understanding is that many of the newer IGBT modules have built in tuned snubbing capacitors to pretty much eliminate the transient spikes found in older IGBT's and VFD's.  With the newer VFD controlers on a single chip and the improved IGBT modules I wonder how much of a problem transient spikes actually represent in modern VFD's?


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## markba633csi (Jun 7, 2019)

Probably not much, haven't heard or seen any reports of this for a couple years now


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## vocatexas (Jun 7, 2019)

Good info, guys. I'm trying to digest it. If you have any more, fire away. I haven't committed to anything yet.


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