VS HE AC AC motors

[MikeHalloran]

The Web is just full of articles lauding the benefits of High Efficiency Variable Speed AC motors for furnaces and air conditioning. I have one.

It' an Emerson motor, 1/2HP, 1250/var RPM, 230V 1PH 60Hz, built for International Comfort Products, delivered in a TempStar brand air handler, installed by Sears (which doesn't do house air conditioners anymore). It worked great, for six years.

Now it's dead. Well, not completely. The three phases of the actual motor have the same reasonable resistance, and are not shorted to ground. The bearings have more drag torque than I'd like, but are not noisy or gritty, and are 'sealed for life' anyway. It appears that the DSP chip is alive, and bumps the motor in each direction, but can't quite figure out how to make it run anymore. What it's supposed to do is measure the motor's dynamics, and synthesize a 3 phase signal to make the motor run at a switch- programmable constant speed, efficiently.

One of the 560uF/ 250V/ 30mm dia x 35 mm long capacitors associated with the power full wave rectifier showed signs of overheating, so I replaced both of them. No other component shows any sign of overheating. None of the skatey- eight surface mount diodes and capacitors seem loose or look odd. Those diodes and the discrete diodes test okay, in circuit.

I think the motor itself is okay, but there must be a problem on one of the two circuit boards attached. There's a four- position connector on one board that brings in the 230VAC power. There's a six- position connector on the other board that clearly ORs several 24VAC inputs from the thermostat circuits to turn the motor 'on'. There's a three position connector on that second board, the DSP board, that is not connected to anything in the air handler. It's clearly a communications port.

What the Web is _not_ full of, is service manuals for these animals, or information.

I could just give up and replace the motor assembly with a PSC motor, but since the basic motor seems okay, and the components on the circuit boards all look okay now, I'd really prefer to just replace what's broken. If I could figure out or guess what that was.

Has anyone gone deeper into these things, and is willing to conjecture what might be a likely failure point?

Thanks.









Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Sounds like maybe a sensor. The motor starts but because no correct feedback is detected can't continue and shuts back down.

 

[jraef]

Generally, these things are a basic Variable Frequency Drive, converting the 1 phase input power to 3 phase for the motor, and varying the voltage and frequency to modulate speed according to the system demand. I know nothing about this brand, and as you have discovered, they want you to believe it is "magic" so they tell you nothing about it.

That said, if it is a VFD and you lost an input capacitor, its most likely toast. With a bad cap, the DC ripple would have been too much for the output transistors and you likely lost one or more of them. In addition, a bad cap is often a sign that you lost one or more of the input rectifier diodes first. Most newer small VFDs use an IPM (Integrated Power Module), so the transistors and input diodes are all on the same substrate. If it were a stand alone VFD it would cost more to replace that module than to buy an entire unit. The fact that it is a "magic box" from the equipment mfr may make that untrue however because they will maintain exclusive control of your access to it unfortunately.

If you can identify and isolate the control signal that gives the VFD it's speed reference, you may be able to replace it with something off the shelf.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[MikeHalloran]

The only feedback appears to be a 0.15 Ohm resistor near the output transistors. The DSP chip apparently infers both load and speed from that alone.

I'm pretty steamed because the EPA says the cost increment for the magic motor is only $75, and it saves almost that much electricity in a year. The economics of the aftermarket are a little different.

Yesterday, I ordered a PSC motor and cap for $125 delivered, then told the wife that it would be a little less efficient, and was told to cancel that order and order the right motor. So I did. Except today, the only online vendor who listed the magic motor said that the $350 quoted online was for the wrong part. The real right part would cost me $1095.45, if he had it, and he doesn't anticipate having it until at least March.

At least the weather has been relatively cool...



Mike Halloran
Pembroke Pines, FL, USA

 

[jraef]

Holy Moly, that's highway robbery!

Try finding a model number on the motor nameplate and plugging it into this cross-reference worksheet, you might get lucky. I'd also call these folks, they specialize in crossing over OEM motors.

http://www.aosmithmotors.com/concertox/script.exe/aosepc/crm/ccr/crossReference.html

Good luck!

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[MikeHalloran]

I think the whole air handler only cost us $1500.

Been there already. Nobody crosses to this motor.

Emerson
model M55AMCMY205
1/2HP 230V 4A 1 PH
1250/VAR RPM
PT NO HQ108551OEM
MFG NO F98 7
AIR OVER
FRAME 48Y

The air handler is made by International Comfort Products and sold under a dozen brand names, in this case Tempstar:

FAN COIL UNIT
model NFCV3600A1 s/n L984076627
style FCV3600A

-------------------
I'll spend a little while seeking a sensorless vector drive at an affordable price. Failing that, I'll just go back to the PSC motor. The EPA says the difference in energy cost is less than a hundred dollars a year. I'll be dead before an $1100 motor pays for itself.


Thanks for the help.



Mike Halloran
Pembroke Pines, FL, USA

 

[mc5w]

A lot of these "energy saving" technologies have turned out to be losers from a reliability standpoint. Get the PSC motor. Tell her that design E motors have been deleted from National Electrical Code because they were not saving energy because the motors and the controllers burned up too quickly. Tell her that I have been doing electrical work since I was 3 years old and that the right motor to buy is the traditional permanent split capacitor motor.

Also, I did some consulting work for the East Palestine City School District. In the first year of operation of a brand new electrical system they lost about 10% of the T8 bulbs and about 10% of the ballasts. This is partly because the ballasts are cheap junk and NOT using filament heating in an F32T8 bulb is asking for problems.

I have seen the same problem with some yellow solid state chargers for forklift truck batteries. These had a tendency to burn up in part because the dealer forgot to install a 3-phase inductance in the branch circuit.

A lot of these technologies turn out to be cheap Chinese junk. You need to stay at least 2 fads behind.

 

[jraef]

Hmmm... interesting that the motor says it is 1 phase. Where did you come up with 3 phases earlier in your posts? If it is 1 phase, it most likely IS a PSC motor, because those are the only 1 phase motors that can be controlled with a VFD.

So if indeed your motor is still good, maybe you can just replace the speed controller for it. This is one of the few VFDs for PSC 1 phase motors I know of.

http://www.hoffmancontrols.com/products.php?ID=23

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[MikeHalloran]

Jraef,
from the _outside_ of the motor _assembly_, it looks like a 1ph motor. It has 3 connectors. One carries 230/60/1 into the metal shell bolted over the blind end. One carries three or four 24VAC 'gate' signals from the thermostat logic. Those signals also feed a separate circuit board that simplifies the field wiring and carries a relay that gates the 240. The third connector is clearly a diagnostic connector that connects to ... I don't know. It's not connected to anything in normal service.

When you trouble yourself to remove that metal shell from the blind end of the motor, you find two circuit boards within it, stacked up with a bunch of heavy duty through-pins.

The board adjacent the motor has the 230V input connector, two big caps, two smaller caps, connections to a full wave rectifier (square module bolted to the shell), a good size toroid and a couple of rectangular devices that I can't quite figure out. It's clearly a rectifier and filter.

The other board, adjacent the shell, has the diagnostic connector, the 24VAC logic connector, a good size DIP package and a 168-ish pin SMT package, some glue logic, and lots of SMT discretes. It also has six power FETs that feed three wires. Those wires are the only connection to the actual motor.

The motor wires have flying push-on connectors so you can separate the controller from the motor. Disengaging them and measuring the motor itself shows no conductance to ground, and about the same resistance from any one terminal to the other two terminals. Spinning the motor shaft produces an AC voltage across any two of the terminals. I.e., it's got a permanent magnet rotor, and three field windings connected in a delta. It's a three phase motor, and it seems to be in good condition.

Which brought a thought. I found two sensorless vector controllers 1PHin/3PHout for less than $200, and downloaded the instructions. Both of them make a point of stating that they get hot in normal operation, which doesn't impress me much, but they are known brands.

There's not enough room in the air handler for either one, so I'd have to splice on a decent box, punch a couple of holes through, and add a couple of relays with 24VAC coils to switch the driver's inputs, which are programmable for damn near any other kind of logic or linear signal but the 24VAC that thermostats use.

The PSC motor is looking like a better choice, though it would be fun to screw around with the motor if I had time.

Mc5W,
thanks for the input. I'm not real impressed with the reliability of energy saving technology, or any other government mandated technology, either.

Itsmoked,
with DSP, we don't need no stinkin' sensors. We do need some engineers who can design to cost without giving up everything else. Okay, I suppose, technically, it's a _great_ design, because it lived through the 5 year warranty, by a small margin.

All,
thanks for the help.



Mike Halloran
Pembroke Pines, FL, USA

 

[jraef]

Huh.
It does indeed sound like a 3 phase motor, but it is interesting to me that the nameplate states it as a 1 phase. I had no idea that a motor with an integral drive would be so labeled. Must be something new in the industry, maybe because, as you said, there is no way to separate the drive from the motor anyway. So the "1PH" on the nameplate is only indicative of the input power source, not the internal motor winding design.

I'd rather see the truth on the nameplate.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[waross]

I'm with you on that jraef.
Mike What voltage is generated? It may be residual magnetism, or it may indeed be a magnetic rotor. That would make it a synchronous motor. Or a generator if you need one.
tabletop in the other post may be able to use it for his dirt bike.
Seriously, have you confirmed that it is indeed a permanent magnet rotor and not residual magnetism that's generating the voltage?
yours

 

[davidbeach]

jraef, that truth was on the nameplate. From the description given the item would only accept a single phase input. The truth that really needed to be on the nameplate was that it was a drive motor combination. From a connection and code enforcement standpoint though, a nameplate calling it a 3 phase item would have caused no end of trouble.

 

[MikeHalloran]

Well, it cogs just a little. When I first spun it, I thought the bearings were, uh, tight. Not gritty, like a failed ball bearing, but more like a dry Oilite. When it had been de- energized for a day or two, it seemed easier to spin, and seemed to coast longer. Perhaps it was remanent magnetism that had faded, or perhaps it was my memory that had faded. Stuff happens.






Mike Halloran
Pembroke Pines, FL, USA

 

[jraef]

davidbeach,
OK, maybe "truth" was a bit harsh, so lets just say the "whole truth". I agree with you however that too much information can be just as bad as not enough, especially when dealing with the general public.

Much as I would, Mike has delved into this thing much more than the average John Q. Public would have. Engineers are like that I suppose. Interesting lesson though.

It reminds me of my new favorite quote:

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' (I found it!) but 'That's funny...'"

 

[davidbeach]

Nice quote.

 

[MikeHalloran]

Since it's an OEM component part, and so far not sold even as a service part, I don't think the usual labeling requirements apply.

So far I haven't tried using it as a generator with a load stiffer than a voltmeter, so it may not actually be a PM rotor.



Mike Halloran
Pembroke Pines, FL, USA