I see these motors more and more in hvac applications.Are they used because easy speed control.I know before I realized what they were I thought the bearings were bad in the last service call I did.Turns out the drive was faulty.
What an OEM might charge for a replacement part often bears no relationship to what that part should actually cost. Small permanent magnet motors are quite inexpensive, unless you get into a custom-designed one that only the OEM can supply.
At any rate, the "cheap" part refers to the speed controller, not so much the motor itself. To vary the speed of an AC induction motor, you need to vary the frequency of the applied voltage. The electronics needed to do this are MUCH more complicated than the simple SCR phase angle control that will produce variable DC for a PM motor.
I imagine he is talking about the motor in a Trane TWE variable speed air handler (or similar competing product) It is a proprietary design with a motor controller board in the bell cap. When mine went bad I just had the guy put in a regular 1 speed motor. This is basically "air only" so I am not sure what multiple speeds really buys me. The motor and controller board (both seemed bad) went for about $1000. He did the conversion, motor and service call for $275
There are a lot of good reasons for the inverter-controlled motors in HVACR. Let me mention a few here, hopefully without putting you to sleep. They increase system efficiency and offer greater comfort control, such as, by allowing high efficiency modulating gas furnaces to more closely match the heating loads and to equalize the temperature in a building with lower fan speeds between heating cycles. High efficiency 13 SEER and up indoor evaporator AC coils are larger than older 10 SEER coils. Because of the larger surface area and shorter system run times etc., they don’t remove humidity at the same rate as the older coils, so the indoor blower unit is sometimes run at lower speeds to help control humidity levels in the building, even when the T-stat is satisfied. Most older indoor units just used standard 2-speed motors, high speed for cooling and low for heating. The inverter controlled DC motors allow for almost infinite speed control. Many companies like Mitsubishi and Panasonic are using them for condenser fans and for compressors to match BTU output to the cooling load. If you really want to learn more, you can visit another website where I am a member: http://www.hvac-talk.com/ It’s a pro only site and no DYI info, but there are general discussion forums you can search through or join if you want to post questions. Just like here on ECN, if you ask questions, you will get excellent answers.
#172371 - 12/18/0705:53 PMRe: Benefits of a permenent magnet motor?
Well thanks KJay.I am a Electrician with a wandering toolbox.So I don't need any dyi info.You know what they say about the HVAC trade.It sucks on one side and blows on the other.Anyway what I was troubleshooting was a ge ecm or electronicly comutated motor.I guess you could call it a brushless dc motor.Trying to justify the cost of 500.00 motor in a 10 year old carrier unit.
The unit is in decent shape.A little corrosion on the condensor.So I replaced the motor for customer.Granted I am not an HVAC contractor my customer begged me to fix it.
Anyway I was just curious about the little motor.As I have never had to trouble shoot one before.One thing for sure you guys in the heating and cooling business.Sure keep a tight lid on your supplies.Which I envy.That ge motor is patented hence the high price.
Permanent magnet motors are DC motors. They are more expensive than AC motors. Since it is an OEM motor you may have to buy from the OEM, but not in every case. I ran a motor shop for several years and we alway's had some success crossing OEM to standard motors. Take a look at the name plate. Look at the frame size. If, for example it reads 0000012356C it is 56C frame. Now if it reads 56CZ that means it has a shaft modification. Once you are familiar with the standard frame sizes and suffixes, you will get the idea. Any numbers or letters before a standard frame number mean nothing (It's to throw you off). Any numbers or letters after the standard frame size are important. Get a motor catalog and you will find the frame sizes, with all the dimensions. Believe it or not, in many cases there is no modification except for the nameplate. If you can use a micrometer, you can tell within minutes if you have a standard or special motor. Kjay, gave some very good information in the aspects of controlling motor speeds. Personnaly I prefer AC over DC as they can produce full torque at zero speed. Better than DC.
Check www.baldor.com They have some online manuals for the motors and the drives. Have fun.