Motor Amperage

[ascj]

I had to replace two drives on a 90ton Itellipak. We replaced them with Vacon's.

After I finished, I noticed the one motor amping 1/2 of what the other was. So I threw into bypass, same thing. Threw it back, check voltage and frequency. It was the same on both drives. Both motors are identical and sheaves and belts the same.

I got rained out, so I didn't have a chance to tach the drives. I have to return to finish, but any ideas?

[ascj]

I had to replace two drives on a 90ton Itellipak. We replaced them with Vacon's.

After I finished, I noticed the one motor amping 1/2 of what the other was. So I threw into bypass, same thing. Threw it back, check voltage and frequency. It was the same on both drives. Both motors are identical and sheaves and belts the same.

I got rained out, so I didn't have a chance to tach the drives. I have to return to finish, but any ideas?

Sitting on my throne of thought......it hit me. I never checked rotation.

It's been one of those days.:eek2:

[klove]

Good catch.....

[ascj]

So I got back there today. Finished some odds and ends and started her up. Checked rotation. OK Checked amperage at 100% and the one motor is running 25% lower than the other.

So I double check drive setting, checked sheaves, checked belts tension, and a visual of the coils. OK So I tached the blowers at got 721 and 713 rpm. Hmm. Still not making sense. I took motor temps after I let it run for 20 minutes and both motors were close to 10 degrees in temp.

I spoke with maintenance about it, since the log amp draws. They said that unit always had a difference between the two motors. Hmm.

What am I over looking or not understanding?

[Chiller Guy]

Do you think it could be duct work design/installation or static losses?

[chilliwilly]

So I got back there today. Finished some odds and ends and started her up. Checked rotation. OK Checked amperage at 100% and the one motor is running 25% lower than the other.

So I double check drive setting, checked sheaves, checked belts tension, and a visual of the coils. OK So I tached the blowers at got 721 and 713 rpm. Hmm. Still not making sense. I took motor temps after I let it run for 20 minutes and both motors were close to 10 degrees in temp.

I spoke with maintenance about it, since the log amp draws. They said that unit always had a difference between the two motors. Hmm.

What am I over looking or not understanding?

The motors are identicle.

You've checked rotation.

You've checked volts at all the motor terms, and frequency.

You've checked the pulleys for size and cleanliness.

Belt tension and and they're the same type.

This might sound daft but have you made sure the links at the motor terms are the same configuration? Some motors are for international use and sometimes have different configurations for compound windings and the motor tails need to be double checked where they're connected.

Are the motors new or rewinds? if they're rewinds the windings aren't always equally balanced, did you bell them out?

Have you checked the fan impellors for cleanliness?

Have you checked the parameter settings match both motors in the vvf unit?

Length and size of the ducts?

Dirty filters, closed registers/grills or damaged ducts?

[ascj]

The motors are identicle. They are the original motors and are exactly the same.

You've checked rotation.Yep.

You've checked volts at all the motor terms, and frequency.Both brand new VFD's were delivering the same voltage and frequency. Also threw it into bypass, to be sure.

You've checked the pulleys for size and cleanliness.Yep. All the sheaves are the proper size, also matched against tag on blower housing. And yes the are in good condition.

Belt tension and and they're the same type.Checked all belts with my tension tool. I'm running 12 pounds on the belts.

This might sound daft but have you made sure the links at the motor terms are the same configuration? Some motors are for international use and sometimes have different configurations for compound windings and the motor tails need to be double checked where they're connected.Looked at them.......all I saw was high and low voltage connections. The motors does list some other voltages like 200v and such, but didn't see where you needed to change wiring.

Are the motors new or rewinds? if they're rewinds the windings aren't always equally balanced, did you bell them out? As I said, they are original.

Have you checked the fan impellors for cleanliness? The fan blades look ok. Are they clean as new...no, but they don't seem bad. And they both look about the same.

Have you checked the parameter settings match both motors in the vvf unit? Yes and I even ended up copying the one to the other....just to be sure.

Length and size of the ducts?They are big and long....lol. Did I measure the ducts for the system....nope. I wouldn't think that would cause the problem I'm having. But I did preform the CFM test that Trane recommends......and I'm moving enough air.

Dirty filters, closed registers/grills or damaged ducts?The filters are ok, none of the register can be shut off, and visually the ducts look ok......but that doesn't mean any of the liner came loose.

The only thing I could come up with.......is the unit in ducted with horizontal ducts. The blower are only about 4 feet away from where the the duct comes off. The blower that is drawing higher amps is the one that is closest to the side of the unit, where the duct comes off.

Would that do it?

[prorefco]

Have you checked the static pressure in the discharge duct??

[ascj]

Have you checked the static pressure in the discharge duct??

At 100% it's at 1.6"wc.

[btuhack]

How does the ESP compare between the two fans?

[ascj]

How does the ESP compare between the two fans?

How do I check that with two fans?

[prorefco]

Are you saying both fans discharge into the same duct?? even if they do, you might still want to check right at the point where the fan housing discharges on each one...

[ascj]

Are you saying both fans discharge into the same duct?? even if they do, you might still want to check right at the point where the fan housing discharges on each one...

Yes this unit utilizes two blower. They are configured parallel. They don't discharge on each other.

[prorefco]

So, are you saying they both have pressures of 1.6 " at 100%??

[bob_scheel]

The only thing I could come up with.......is the unit in ducted with horizontal ducts. The blower are only about 4 feet away from where the the duct comes off. The blower that is drawing higher amps is the one that is closest to the side of the unit, where the duct comes off.

Would that do it?

Yup! Just let me get it clear. You are saying that the air entering the plenum which the two fans draw from is ducted so that most of the incoming air hits the higher amped fan? If this is true then it is very easy to have a static pressure difference between the inlets of the two blowers and thus one fan is doing more work (and consuming more energy) The other possibility is that one of the fans has its output restricted somehow. Could be anything from a pc of sheet metal to a pc of cardboard or duct insulation folded over.

[ascj]

So, are you saying they both have pressures of 1.6 " at 100%??

1.6" is my supply static. I was going to try to test static at the discharge of both fans, but discharge of the one fan is behind the electrical controls panel.

[ascj]

Yup! Just let me get it clear. You are saying that the air entering the plenum which the two fans draw from is ducted so that most of the incoming air hits the higher amped fan? If this is true then it is very easy to have a static pressure difference between the inlets of the two blowers and thus one fan is doing more work (and consuming more energy) The other possibility is that one of the fans has its output restricted somehow. Could be anything from a pc of sheet metal to a pc of cardboard or duct insulation folded over.

Let try to picture it for you. This is a Trane Itelllipak. I will be explaining it, if you were looking down on it with the supply towards the top.

The return comes in on the bottom right. The bottom left is the economizer. Then you have 2 sets of filters. Followed by the evap coil. Then you have both fans, side by side. 10"-12" away from them you have the hw coil. 24" after that you have the supply duct coming off the left side.

The left side blower is the higher amperage blower.

The filters were clean, the evap coil gets cleaned every year, and the hot water coils were pulled and cleaned about a year ago.(I posted about the method we used).

The only units I have ever serviced with parallel blowers are Trane's 90ton+. But they have all been downflows and the amperages pretty much matched.

[btuhack]

Found this, part of it pertains to side discharge intellipaks. see p8-9.
http://trane.com/Commercial/Uploads/Pdf/1102/20%20-%20130%20tons%20-%20application%20brochure.pdf
If all else fails, move the s/a duct to the other side. HeHe.

[ascj]

Found this, part of it pertains to side discharge intellipaks. see p8-9.
http://trane.com/Commercial/Uploads/Pdf/1102/20%20-%20130%20tons%20-%20application%20brochure.pdf
If all else fails, move the s/a duct to the other side. HeHe.

According to that, I'm ok. With hot water heat, supply section panel on fresh air side of unit closest to the condensing section. Which I am.

[jdcoolj]

I'm gonna take an educated guess and say the motor on the controls side of the unit is drawing more amps than the motor on the opposite side. if so, it is the design of the unit. when the unit is not economizing the return dampers are wide opened and the outside air dampers are fully closed. naturally the fan closest to the return dampers is going to steal more air than the other, causing more of a load on that motor. there is a good chance if you put the unit into service mode and go 100% outside air, the opposite motor would draw more amps. Thats one reason why the I-pak was redesigned. the I-pakII design is very similar to the McQuay.

[ascj]

I'm gonna take an educated guess and say the motor on the controls side of the unit is drawing more amps than the motor on the opposite side. if so, it is the design of the unit. when the unit is not economizing the return dampers are wide opened and the outside air dampers are fully closed. naturally the fan closest to the return dampers is going to steal more air than the other, causing more of a load on that motor. there is a good chance if you put the unit into service mode and go 100% outside air, the opposite motor would draw more amps. Thats one reason why the I-pak was redesigned. the I-pakII design is very similar to the McQuay.

What's funny is the motor on the economizer side is pulling high amps. And I did mess with the dampers to see what would change and it wasn't much.

But with that said......this has been keeping me up at night.:LOL: Late last night it hit me......if my memory serves me right, I think one side of the unit has double up evap coils. Meaning the one side is double the depth compared to the other. Im not sure if that is the case, it just seems to ring a bell. I still have to return to mount the VFDs keypads in the electrical compartment. I let you all know.

[btuhack]

bring your camera

[griz]

not sure about this but is the return fan running

[ascj]

not sure about this but is the return fan running

No power exhaust installed on this unit.

[prorefco]

Well, regardless of all else said here, the bottom line is, one fan must be moving more air than the other for what ever reason....

[ascj]

Well, regardless of all else said here, the bottom line is, one fan must be moving more air than the other for what ever reason....

I agree......just want to know why. I can't stand not knowing.

[griz]

you need to talk to JAY GUY

[brooklyntech]

Fan closest to supply duct plenum would be drawimg more amperage because of supply duct opening. Opposite side fan is discharging right into a interior cabinet of unit across hot water coils, the coils a creating resistance to air flow-not lot but I would guess enough to give u the difference u are seeing???? P.S. At the end of the day does it really make a difference or are u just anal? Then again I'm the same way, it would bug me 2.

[GT Jets]

I have had to adjust sheave sizes to counteract this phenomenon in a unit that was somewhat undersized for the system....When both fans ramped up to 100% with a duct static of 1.25", one would fault out on high amps, found it to always be the one with the "cleanest" duct run.....

GT