Phase converter question.

Little Bill said:
In the factory I worked in, we the electricians/technicians had to work on some of the equipment. We had those Tajima machines. I didn't know what kind of machine the OP had when I posted earlier, but I think an RPC would work. The motors are DC and are step motors. The machine is computer ran. You put a programmed disc in and set the parameters and it takes off. I never took the time to see what the 3ph was doing. My guess is just to divide/balance the load.
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If motors are all DC then seems reasonable it could be supplied with single phase, though the power supply may be designed for three phase input and only supplying it with single phase may overload portions of it would either need to be oversized or use a power supply of proper single phase input rating.
 
Typical VFD is designed to run a single motor or a group of motors that will all be fed the same output at same time.

There is other "inverters" out there that would work as power conversion equipment that can handle varying load conditions not directly governed by the inverter.

VFD's don't handle switching (on or off) of their output very well, and they don't handle non motor loads very well either. But they are only producing an output that is somewhat crude AC wave that a motor will work with, and the drive does depend on feedback from the motor to know how to respond to somewhat minor changes in loading conditions. Other items won't work so well on a VFD because of how it works, it is not a general purpose type of power converter, it is converter that is designed to interact with a specific type of load.
 
The two motors I'm thinking of were, one ran the heads in an X & Y direction, the other ran the needles up/down. It's been a few years so I may not remember everything about them.
 
The X/Y motors appear to servos, which would make sense, so they don't even see line power.

Reiterating my guess- there are no actual three phase motors involved, just many line-to-line connected power converters and small motors. It probably could be rewired to take a single-phase 240v feed if someone wanted to take that on.
 
Lots of phase conversion systems depend on the connected load for correct function.

A three phase motor connected to a mechanical speed control presents very different characteristics to the supply line than a VFD running a 3 phase motor.

So knowing exactly what sort of three phase load you have is necessary to select proper phase conversion.

Many VFDs take 3 phase input, but will function at reduced capacity with single phase input.

This us why I stand by my recommendation that you get an electrician who understands phase conversion on site to understand the innards of your machine.

Forum rules prohibit DIY assistance, which IMHO would include modification of your machine to accept single phase (if possible). In general the mods permit general questions such as 'what should I buy/plug in' to make something work, but as soon as the thread veers to 'how do I reconnect this widget ' it will get shut down, with good reason!

IMHO the least expensive route to getting your machine functioning will require internal modifications, figuring out what bits can run single phase and what bits require 3 phase, then selecting the best way to get three phase for those bits. That modification is not something a free internet forum can support.
 
zbang said:
The X/Y motors appear to servos, which would make sense, so they don't even see line power.

Reiterating my guess- there are no actual three phase motors involved, just many line-to-line connected power converters and small motors. It probably could be rewired to take a single-phase 240v feed if someone wanted to take that on.
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Correct me if I am wrong, by rewiring the equipment to utilized single phase would that not make any safety certification invalid?
 
winnie said:
Lots of phase conversion systems depend on the connected load for correct function.

A three phase motor connected to a mechanical speed control presents very different characteristics to the supply line than a VFD running a 3 phase motor.

So knowing exactly what sort of three phase load you have is necessary to select proper phase conversion.

Many VFDs take 3 phase input, but will function at reduced capacity with single phase input.

This us why I stand by my recommendation that you get an electrician who understands phase conversion on site to understand the innards of your machine.

Forum rules prohibit DIY assistance, which IMHO would include modification of your machine to accept single phase (if possible). In general the mods permit general questions such as 'what should I buy/plug in' to make something work, but as soon as the thread veers to 'how do I reconnect this widget ' it will get shut down, with good reason!

IMHO the least expensive route to getting your machine functioning will require internal modifications, figuring out what bits can run single phase and what bits require 3 phase, then selecting the best way to get three phase for those bits. That modification is not something a free internet forum can support.
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"figuring out what bits can run single phase and what bits require 3 phase, then selecting the best way to get three phase for those bits."

This would still require a phase converter of some type and would not actually solve my situation.
 
Thann37 said:
"figuring out what bits can run single phase and what bits require 3 phase, then selecting the best way to get three phase for those bits."

This would still require a phase converter of some type and would not actually solve my situation.
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Yes, you might still require a phase converter of some type. But the analysis might determine that the bulk of the loads are single phase loads, and that there is a single motor which requires 3 phase power, or some other variation on that theme. Running a motor from a VFD fed from single phase is in general much less expensive than running a general purpose phase converter, even though the VFD has a certain limited built in phase conversion capacity.

(A VFD works by rectifying incoming AC to high voltage DC, then synthesizing three phase AC power to run a motor. But a VFD is limited to running motors only, not general purpose 3 phase loads.)

-Jonathan
 
Most machines that need three phase have a three phase motor and the rest of controls are single phase. When you hook it up to a rotary phase converter you make sure that the controls are not powered by the made leg of the roto phase. If there are not any three phase motors on the machine under discussion here then there isn't any reason that it can't run on single phase.
 
kwired said:
If motors are all DC then seems reasonable it could be supplied with single phase, though the power supply may be designed for three phase input and only supplying it with single phase may overload portions of it would either need to be oversized or use a power supply of proper single phase input rating.
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Quite possible. I have a customer that has Italian machines, all of the drives are single phase in, although the entire machine is three phase. They are just balanced between the phases.
 
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