EC Motors

fifty60

Senior Member
Location
USA
How much more electrical noise does an EC motor create compared to a standard PSC motor? Are EC motors as noisy as a VFD?
 

Besoeker

Senior Member
Location
UK
Are EC motors as noisy as a VFD?
We manufacture brushless DC motors and the drives for them.
We also make variable frequency drives.
Although the means of control is different, the basic power circuit is the same. Input rectifier, controlled or not, DC link, and output inverter bridge.
From an electrical noise point of view, I can't see a lot of difference. Chosen installation method can make a big difference for both.
 

Besoeker

Senior Member
Location
UK
Besoeker, do you mind mentioning some of these installation methods?
Normally, for VSDs we use multi-core steel wire armoured cables for buth supply and motor. The armour is earthed (grounded) and acts as a shield. Depending in the location the cable may be run clipped to galvanised slotted cable tray fixed to walls. In a few cases, the switch rooms have a raised floor and cables are run underneath it. We haven't had noise problems.

Where flexibility is required, we use flexible multi-core but it is still armoured but with braiding rather than wire. It keeps the conductors close together and symmetrical.

We don't use steel conduit with individual conductors for this application - in fact we rarely use it for anything. PVC conduit is a non-starter in my opinion.

I know, from this forum (thanks Mr Holt!), you guys can get special VSD cable. I think it is much like our steel wire armoured stuff.
Another thing that reduces noise and is kinder to the motor is output chokes (reactors). It softens the very fast switching edges (the dv/dt).
 

junkhound

Senior Member
Location
Renton, WA
From an electrical noise point of view, I can't see a lot of difference. Chosen installation method can make a big difference for both.
Last sentence very true, but there is a huge difference in electrical noise (EMI) between ec and psm motors. I've designed (part of design team, no single person ever gets to design an aerospace piece of hardware themselves) inverter drives for commercial and military aircraft and spacecraft, and one of the biggest parts of the design job is to get the 'noise' levels down to mil-std-461, and even lower for commercial aircraft.

Ground based, where you can put a fully enclosed motor and everything else in bonded metal conduit is one way to go, but the 'noise' is still there, just that the poco does not have to run comm and nav systems like aircraft.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
How much more electrical noise does an EC motor create compared to a standard PSC motor? Are EC motors as noisy as a VFD?
The way you are asking the questing is a bit like comparing apples and oranges. A PSC motor is not a variable speed motor by itself. So comparing it to an ECM may be a mismatch right there. But some fan suppliers in particular do offer fixed speed ECMs for the simple reason that they are about 20% more efficient than PSC motors. So in THAT context, they can be compared. However then you throw in the VFD issue, which implies you ARE asking about variable speed. In that case, you then have to ask if you mean to compare an ECM to a PSC motor using a VFD? If so, then it gets more complicated.

The only reason to use a PSC motor is because you only have single phase power. PSC motors are ONLY used for single phase applications. ECMs are ALSO designed, for the most part, as single phase. But as mentioned, they are really BLDC motors that have a built-in converter, which, in the versions intended to REPLACE motors in applications typically done with PSC motors, will accept single phase input.

However, if you want to compare them in VARIABLE SPEED applications, then there is no point in using a single phase PSC motor any longer, as they are horribly inefficient (i.e. 60%). There are a few VFDs made for running single phase PSC motors, but they are for retrofit applications where the motor is too expensive to replace. You would be foolish to use one of those on a new design, the VFDs are specialized low volume products and are comparatively very expensive, plus the motor is still going to be inefficient. For variable speed applications being designed from the ground up, you would compare an ECM to a VFD that can accept 1 phase input + a standard 3 phase 230V motor.

In that only viable comparison then, the difference in electrical noise is virtually nil. The noise is for the most part a result of the converter sections being Switched Mode Power Supplies, and both of them are going to be identical. The only possible difference might be in any extra filtering that one or the other might include, which will vary by manufacturer. The ECM will win hands down however based on size and cost.

In comparing an ECM to a PSC motor in a fixed speed application (without a VFD for the PSC motor), the PSC will have virtually no electrical noise, so ANY electrical noise generated by the ECM will cause it to lose in that comparison. The ECM would win on efficiency, but not if electrical noise is your only criteria. Audible noise is possibly the opposite by the way. ECM motors are designed for the most part to replace PSC in fans, so they must have the same audible noise standards. But when using variable speed, lowing the speed often results in less duct noise, meaning the ECM might win there.

Where ECM always loses is in the budget battle. 3-4X the price of a PSC motor in a fixed speed application. Might win against a VFD + 3 phase motor though.
 

fifty60

Senior Member
Location
USA
How does the electrical noise of an ECM operating at a fixed speed compare to an ECM operating at variable speed?
 

GoldDigger

Moderator
Staff member
For variable speed applications being designed from the ground up, you would compare an ECM to a VFD that can accept 1 phase input + a standard 3 phase 230V motor.

In that only viable comparison then, the difference in electrical noise is virtually nil. The noise is for the most part a result of the converter sections being Switched Mode Power Supplies, and both of them are going to be identical.
What about any differences that might come from the ECM motor's electronics being more closely coupled to the motor instead of being located at a greater distance as might be the case with VFDs?
The noise generated might be comparable but the noise radiated could be quite different, yes?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
How does the electrical noise of an ECM operating at a fixed speed compare to an ECM operating at variable speed?
No different, it has nothing to do with the speed. Common mode noise is created as a result of the rectifier pulling current in "gulps" from the AC line and from capacitive coupling in the DC pulses on the output going to the motor windings. That is the same regardless of the motor speed, the pulses are happening at 10-15kHz.

What about any differences that might come from the ECM motor's electronics being more closely coupled to the motor instead of being located at a greater distance as might be the case with VFDs?
The noise generated might be comparable but the noise radiated could be quite different, yes?
Common mode noise? Actually, I suppose a VFD could be worse because of motor lead length if not addressed properly, but all that can be attenuated fairly equally between the two, the technology, as Besoeker said, is virtually identical. In fact, you can by AC motors with the VFDs mounted right on them, making them almost indiscernible from an ECM, albeit the VFD is usually physically larger than the ECM power modules I've seen.

Goulds VFD pumps are like that.
manifold.jpg
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
ECM's are used in a lot of HAVC equipment these days, especially the higher efficiency models. Haven't heard one yet that the fan itself didn't make more noise than the motor driving it, at any operating speed. Many PSC motors are cheaply made and that is why they are noisy in general most of them could be made to be quieter.
 
Top