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noxcuses

Two Motors with one AC Drive

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I'm working on a project where the mechanical guys used two AC motors instead of one motor & gearbox with dual outputs. Ideally, the two motors need to run at the same RPM, but some variance is ok. Since the speed of the pair will be adjusted together, I'm thinking of running both off one AC Drive. The motors are same brand & part number 230VAC .5HP 2A FLA. My plan is to get a drive with 4 Amp cont. output and two 2A (non Solid state) overloads. The overloads will be in parallel from the drive output and status contacts will be wired in the drive enable circuit and PLC. If either of the overloads trip it will stop the drive and signal PLC. I've never done this before and can't find much information on this configuration. There will be at least 4 pairs of these on the system, so panel space and component cost is the reason for taking this direction. Any suggestions? Is this acceptable? Edited by noxcuses

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I've done this with 4 motors on 1 inverter, as long as you have an individual overload per motor, as you say, in parallel on the inverter output, it'll be OK. I've done this on a roller conveyor line.

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We have several setups like this as well (fans and pumps) and it's fine as long as the inverter is sized correctly and each motor is individually protected by overloads. You should not have a problem.

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Just a reminder the individual overloads is not a niceity it is an NEC Code Requirement.

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Another tip. Remember to DISABLE the motor thermal overload function in the drive parameters. You don't need this for multiple motor applications as you are relying on the external overloads to protect each motor. Furthermore, many drives have an external overload function that can be mapped to an input. If you wire the auxiliary contact of each external overload to this input it will shutdown the drive AND give you an indication on the drive display should an overload trip. I find this a useful enhancement when using multiple motors with one drive [in my case have used up to 50 motors with one drive]. My 2 cents.

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Thanks for the tips! I've read that only the bimetallic style overloads should be used, but can't find any that doesn't mount on a contactor. The cost of two contactors and OL relays is about the same price as another drive. It's looking like it will not save any cost or space by running two motors from one drive. What type of OL do you use? Do you use it with contactor?

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Allen-bradley do an adapter for mounting an overload on its own on din rail, part number is 193TAPM or 193TCPM. Scheidner or Telemecanique do them, probably most controlgear manufacturers do as well.

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Where did you read that! We have used motor protective switches for over 20 years for multi-motor protection connected to a single drive. Like these http://www.sprecherschuh.com/products/motorcircuit/kt7/ The only gotcha is to use a good quality dv/dt filter on the output of the drive if you have long runs to each motor. The differential trip coils of the MPS devices can overheat if you don't use the filter.

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Thanks for the info! That is exactly what I'm looking for! What I read was that Solid State overloads do not function properly when placed on the output of an inverter.

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