Electronically Commutated Motors (ECM)

[charlie b]

A coworker is reviewing a project that calls for ECMs for most of its motors. Many of the motors are 15HP and larger. I was asked whether ECMs have a practical limit to their HP rating, as he had heard that 10 HP was the limit. Two questions:
1. Is there a limit, and if so, is the limit 10 HP?
2. Are higher HP ECMs readily available in the marketplace<?

 

[GoldDigger]

In terms of hardware required, the electronics side will be roughly comparable to a VFD of the same horsepower. The motor will have to be wound for fast rise time pulses.
Neither of these seem to put a hard and fast limit on HP size. But availabilitiy might.

 

[__dan]

My understanding is that ECM motors are mostly a replacement for single phase motors, especially where high torque at low speed and variable speed are required. And they will take over the market in those applications. ECMs replace brushed series connected DC motors in power tools, for the low speed torque.

Smaller ECM motors have PM permanent magnet rotors. PM magnet rotors would be one physical limit on going to higher HP.

In the higher HP you might see servo motors. But that's a range built for special application, very high torque start stop, fast accel decel, and robotic motion control, position control. The limit there is that they are super expensive.

Not the question you asked but why are they going to ECM compared to a regular three phase motors with a drive. It would have to be a high torque low speed and variable speed application (less than a few HP?).

 

[Jraef]

ECMs have the electronic drive that runs the motor built-in. The practical limits of that technology are that the electronics need to survive the heat created by the motor, which in most cases is going to be dissipated into the air stream of the fan / blower it is being used on. Once the motor gets beyond a certain size, the housing technology (essentially a motor frame that IS a heat sink) would become so expensive that nobody would buy one. Most ECMs on the market are under 1HP for this reason, a few go to 2HP. Marathon makes one that is around 4.2HP (these are not standard motor power ratings like in NEMA frame motors), that is the largest I have ever seen. I have no idea what it cost because nobody ever got that far with it, but I bought a 1HP ECM from Carrier a while ago, it was around $1k, which was more than a 1HP 3 phase inverter duty motor and a small VFD would have cost.

The advantage of an ECM is mostly for an OEM that wants a variable speed fan that can run from single phase power, but does not want a complex control panel to have to go with it. So the OEMs will have an ECM made for their fans that has a custom control interface that talks directly to a BMS (Building Management System). The BMS is connected directly to the ECM with a comm signal and sends it a command regarding required air flow, and the ECM does the rest, no control panel. Without that need to simplify, it's difficult to justify the extra cost.

You can get PMAC motors that go up to 75HP that I am aware of (again, Marathon SyMax). The VFD would be separate though and not all VFDs can run PMAC motors, you have to specifically check for that. PMAC motors are used because they have a significant increase in overall efficiency, but significant only if you are attempting to attain some high level in order to attain an "Energy Star" rating on a piece of equipment or a LEED Certificate on a building, where going from 90% efficient to 92% efficient is a big deal.