# Wiring two motors to rotate together



## nolabama (Oct 3, 2007)

what is the application?


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## DaveS (Jan 7, 2010)

The application is for pumping of liquids. The idea is to proportion the liquids 1 to 1. Each revolution is a stroke of the pump. Instead of physically tying the shafts together I would like to wire the pumps to rotate together. I just can't remember how it is done.


Thanks


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## nolabama (Oct 3, 2007)

Are you mixing two different liquids? I have set up a lot of pumps and electric motors in my life and I have never heard of this... that by no means that it can't be done. If they are under different loads - i.e. viscosity differences how is this possible.... the VFD would have to work with the flow meters that measure the liquids to control this... 

I seen/worked on injection systems that are able to mix like this, never wired two motors up that are able to turn at the same revolution however. If the actual RPM level is what your concerned with your gonna need a position sensor on the pump/motor shaft to tell your VFD how to react. 

I am imagining something like a crankshaft position sensor with magnetic pic up would accomplish this. 

As for hard wiring them to do this ... I do not think that is possible.


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## McClary’s Electrical (Feb 21, 2009)

nolabama said:


> Are you mixing two different liquids? I have set up a lot of pumps and electric motors in my life and I have never heard of this... that by no means that it can't be done. If they are under different loads - i.e. viscosity differences how is this possible.... the VFD would have to work with the flow meters that measure the liquids to control this...
> 
> I seen/worked on injection systems that are able to mix like this, never wired two motors up that are able to turn at the same revolution however. If the actual RPM level is what your concerned with your gonna need a position sensor on the pump/motor shaft to tell your VFD how to react.
> 
> ...


 
You're correct, it's not possible, because I've seen it tried. I've seen (2) motors, coupled to a common shaft,being driven by a commom controller, and they still will not match speeds. One leads, one lags, they switch back and forth, one not knowing what the other is doing. You need flow rate indicators for this to work properly. PLC timing will not even work correctly. The pump is going to pump different rates at different temperatures. You need to measure flow.


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## John Valdes (May 17, 2007)

If both motors are 3 phase you can match speed identically. You will need two VFD's with basic master follower logic. Both motors may require an encoder or resolver. But that would depend on the VFD.

I used to provide a demonstration for this exact application.
I had two motors mounted to a mobile stand with both shafts pointing at each other. They (shafts) were about 1/2"-3/4" apart. I had two ABB VFD's connected to each motor and had them programmed to run at equal ratios. 1: to 1:
Then I would tape a $100.00 dollar bill across both shafts and let the participants have the operator station. Stop/Start with ramp and without ramp, Reverse without ramp. Whatever they could do to break my $100.00 bill. No one ever broke one.

So yes. You can make two motors do exactly the same thing, with no error.

The others are taking slip into consideration when indicating this cannot be accomplished. No two motors will run at the exact same base speed on line voltage. Add the inverter, feedback device and properly programmed drives, you now can do it easily.


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## Chryse (Jan 22, 2010)

This is how I would do it if you want to have them both turn at the same time, bear in mind though with the differnt viscosities, you might have higher friction through one of the pumps. Find out the power of each pump you plan to use whether it be a 1500watt pump, or whatever. You need to find the size of wire that will be large enough to feed them both. I would run both pumps to a disconnect that has the capablilty to hold a double pole breaker, or double pole fuses. You need something to protect overcurrent hence the breaker or fuses will suffice. Plug one black wire from one pump into one fuse slot, and the other black wire from the other pump into the second fuse slot. Run a 3 wire that is big enough to hold the amperage of both pumps back to the panel and use a double pole breaker so that at the disconnect, on one side you have 240V coming in, but leaving you have 120V. Only way I can think of to accomplish this.


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## LJSMITH1 (May 4, 2009)

I second John's approach. The only way to account for the manufacturing and application tolerances and variables is to have a feedback loop through an encoder on each motor. This way the VFD can modulate the power to each motor to compensate for fluctuations in efficiency or system variables. The key is to get feedback to each VFD.

Straight line voltage application will not work no matter how hard you try.


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## John Valdes (May 17, 2007)

LJSMITH1 said:


> I second John's approach. The only way to account for the manufacturing and application tolerances and variables is to have a feedback loop through an encoder on each motor. This way the VFD can modulate the power to each motor to compensate for fluctuations in efficiency or system variables. The key is to get feedback to each VFD.
> 
> Straight line voltage application will not work no matter how hard you try.


:thumbsup: Thats a fact.


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