# Vfd Or Rpc For Triumph 2000



## quickcut (Sep 2, 2016)

Good day all. 
I have a Colchester triumph 2000 lathe that I am taking home. My supply at home is 2 phase . That is phase to phase 380v, phase to neutral 220v. I would really like to keep the control system as original and therefore would like an opinion on using an 3phase inverter on two phases , or a RPC into the invertor or just a straight RPC. Th original motor is 7.5hp 380volt and starts DOL.  The motor runs continuously and the machine has clutches for transmission 
Some input please, thanks
charles


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## dieselshadow (Sep 2, 2016)

In my opinion, rotary phase converters are outdated technology now. A VFD can easily be used to convert your power into the needed power. You may be able to do it with zero modifications to your machine as well. 

It may be harder to find a special 2-3 phase rotary converter as well.


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## Eddyde (Sep 2, 2016)

Hi Charles,
I've been looking into getting a Lathe around that size and face the same problem, except different voltage (230/115). This is what I've learned so far: You have to double the size of the VFD if you are using it to convert single (2 hot legs is still called single phase, not 2 phase) to three phase, so you'll need a 15 hp VFD, these are very expensive Also you'll need to modify the controls on your machine as the power switch must go to the VFD and the VFD directly to the motor, and if you have a coolant pump you'll need a separate VFD for that as well. 
For RPC I think  you'll need a 10hp to start a 7.5 hp motor, with no or light load. Also could be pricey if bought new, but can be made from a surplus motor, so could be had much cheaper. Another option would be to change out the motor in the lathe to a single phase one, although I think  5hp is about the upper limit for single phase motors (could be different in the 380v world), which should be fine as long as you don't need to take huge cuts for high speed production.

I assume the RPC into a VFD scenario would be to get finer speed control? Personally, I don't think that would be necessary as those lathes have lots of gear range. I had a 6 speed lathe for 20+ years and always managed speed wise, Hp, that's another matter.

Hope that helps,

Eddy


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## mksj (Sep 2, 2016)

There are some inexpensive VFDs that are rated for 10Hp/7.5Kw single or 3 phase input and 380VAC systems. Just a bit unclear on your voltage standard, in general VFDs do not step up the voltage beyond the line voltage, with the exception of 120VAC models. Probably the easiest solution if you want something simple and will not break the bank would be to check with the eBay model below. There should be RPCs that will do what you want, that are specific to your country's electric grid, but will be more costly. As Eddy noted, usually 3 phase VFDs models are derated x 0.6 for single phase input, so you would need a 15Hp model in most cases. If you use a DC filter choke on the DC bus, the derating is around 0.7-0.8 x the rated output. You might also check with Gohz below, I am not aware of any 380VAC single phase to three phase VFDs.
http://www.ebay.com/itm/TOP-QUALITY...RIABLE-FREQUENCY-DRIVE-INVERTER-/122001986268
http://www.gohz.com

One thing that one needs to consider, is that an RPC requires no modifications to machine, on the other hand, a VFD's output is not intended to be switched with contactors and is made to be a direct connect to the motor, especially if you are using sensorless vector setting. So there are changes needed to the lathe controls, and one also needs to consider if there are any 3 phase pumps used on the machine. It may be possible to use a VFD in the V/Hz mode, simply to provide 380Hz 3 phase, and use it to power the lathe as is, but you would need to contact the manufacturer to see if the unit will work as such.


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## quickcut (Sep 3, 2016)

On further investigation it appears that the motor can be connected for 220v 3phase.(delta) It is going to be a bit of a fiddle with the contactors as they will require the two hot legs. The pump I will change to a 220volt single phase as I have one. The largest 220volt single phase VFD without really looking and braking the bank is 4.0kw. Would this be adequate for thye 5.5 kw motor as I am really only do-ing light  machining. I could increase the acceleration  time to say 5 seconds and the machine spindle is engaged via clutches. Thanks for all the input so-far.


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## Eddyde (Sep 3, 2016)

Are you thinking, by decreasing the voltage requirement of the motor the VFD will be able to supply it with more power? That's not going to work as the motor is still going to draw the same wattage, If you decrease the voltage the amperage draw will increase thus the wattage requirement will remain the same. A 4.0 Kw. inverter would not be adequate to run a 5.5 Kw. Motor, at best it would just shut down, at worst it could burst into flames. Even the 7.5 Kw. inverter is too small to run a 5.5 Kw motor if you are using it to convert single phase (2 hot legs) to three phase. you must derate it by .6  (some even say .5) thus 7.5 x .6 = 4.5 still not enough to power the motor. You will need a 10Kw. 380v VFD to safely run that motor.


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## Eddyde (Sep 3, 2016)

dieselshadow said:


> In my opinion, rotary phase converters are outdated technology now. A VFD can easily be used to convert your power into the needed power. You may be able to do it with zero modifications to your machine as well.
> 
> It may be harder to find a special 2-3 phase rotary converter as well.


In all respect, RCPs are not outdated technology, they do only one thing, convert single phase to three phase, but they do it simply and reliably. They require no modification to the machine and you can run multiple machines off one RPC.
A VFD does give you more control over the motor but that may not always be necessary. Also, they do require modifications to the machine as you must connect them directly to the motor, not through any switches, relays etc. In order to use the machines controls, they must be wired to the VFD. A VFD can only run one motor.
I'm Not saying one is better than the other, they just offer different solutions that may fit one situation better than the other.


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## dieselshadow (Sep 3, 2016)

Eddyde said:


> In all respect, RCPs are not outdated technology, they do only one thing, convert single phase to three phase, but they do it simply and reliably. They require no modification to the machine and you can run multiple machines off one RPC.
> A VFD does give you more control over the motor but that may not always be necessary. Also, they do require modifications to the machine as you must connect them directly to the motor, not through any switches, relays etc. In order to use the machines controls, they must be wired to the VFD. A VFD can only run one motor.
> I'm Not saying one is better than the other, they just offer different solutions that may fit one situation better than the other.



Agreed. I was simply stating my opinion. 

A rotary phase converter is inefficient compared to a VFD. But if you are simply powering up multiple machines at once, than it can be a good compromise to a home shop utilizing 3 phase equipment. They are also nice if you can't handle modifying the original wiring on the equipment. Besides the inefficiency of spinning another motor (essentially that's what a RFC is), you also have to listen to it run, and you lose some floor space. A VFD is small, virtually quiet, and can be mounted just about anywhere due to their size and weight. 

 For these reasons, in my humble opinion, the RFC is a bit of outdated technology. But it still has a purpose here. I wasn't trying to "kick it to the curb" so to speak.


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## mksj (Sep 3, 2016)

Agree with Eddyde, most likely an under rated VFD will shut down and you will get a fault code. You could use a 7.5Kw 3 phase VFD if you add a DC choke, the VFD indicated above and others on eBay is ~$250 shipped and rated at 7.5Kw single or 3 phase input, they are available in 220V and 380VAC versions. This would be the least expensive option that I could see.


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## quickcut (Sep 3, 2016)

The correctly sized vfd it will be.  I will post further when all is up and running. Thanks again for all the input and especially for pointing out the pitfalls.

charles


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