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Motor questions about direct replacement mount and practicality of changing fixed speed motor to VFD

davidaj

Plastic
Joined
Feb 19, 2024
Location
Calhoun, TN
I have the pictured Grundfos pump that circulates a glycol (I assume) solution for 4 closed loop geothermal heat pump units. It is driven by a Baldor 1.5 HP single phase motor (model: 84Z04007). The motor recently quit running when called for by one of the heat pumps. I verified voltage to the motor but it will not turn on. I assumed it was the capacitor but the nice guy at the local motor repair shop says that the capacitor is fine and definitely not the problem. He said that these motors are typically replaced instead of repaired, and he pointed out that the unit is 17 years old. There is a definite burned electrical smell coming from the motor. The shaft turns very easily and smoothly.

As I've not done much with motors like this before, and I like to be educated, I've got the following questions:
  • The motor is listed as having a 56C frame. Am I correct in understanding that that refers to the dimensions of the mount part of the motor? Does that mean that any 1.5 HP 56C frame motor will/should mount directly onto the pump assembly frame without modification? In other words, do I have to buy a direct replacement Baldor 84Z04007 motor, or just a 1.5 HP with a 56C mount and the correct spindle size?
  • If any appropriately sized 56C frame motor will work, would this be a potential candidate to be replaced with a VFD motor? I ask this for two reasons. First, we typically only run 2 of the heat pump units of which this was supposedly sized to run 4 at a time so I feel the pump is oversized for what it is being used for now, and thus likely not very efficient in this use case. Second, this motor is in a closet off of a 30' X 40' meeting room. The motor is so loud when it runs that it is highly distracting to those in the room. Because of that, I always try to precool the room in the summer and preheat it in the winter to reduce the runtime of the motor when the room is in use. I'm thinking that if I could replace the motor with a VFD, I could slow it down when people are using the room and likely reduce the sound level considerably.
  • If you agree that this could be a good use case for a VFD drive and motor, I'm open to any advice on that with the caveat that I'm trying to keep this as budget friendly as possible. I see a lot of reasonably priced VFD controllers on Amazon. Am I insane for considering one of these reasonably priced options? Same thing for motors. Am I just setting myself up for failure if I don't use a name brand pump like the Baldor that originally came with it? Any and all thoughts are very much appreciated..

Thanks so much.

David

Pump and motor (minus the capacitor)
Entire pump.jpg
The motor faceplate
motor label.jpg

How the motor mounts to the pump assembly. Also demonstrates how the spindle on the motor connects to the spindle on the pump.
Mounting method.jpg
 
56c is a common face mount size. As long as shaft diameter/length/keyway are correct I would replace with a three phase and vfd pump. Or at least a two speed motor. Just make sure it rotates in the correct direction.
Swimming pool pumps are going three phase with a dedicated vfd timer. Most pool pumps are oversized so the builder never gets a call back about underpowered pumps. I would bet your system is the same way before shutting down 1/2 of it. Lower rpm is lower amps and lower pressure. In pools the pump can lose prime, so the first five minutes is run at high speed then. it drops to a lower running speed.
Is the compressor and fan multi speed? If so the pump rpm can be tied to that change.
Bill D
 
Pumps are often a good vfd application since as you said the flow can be adjusted. I used a multi stage booster pump to get decent water pressure at my house for 10 years or so. The single phase motor died at some point as yours did. I needed something quick and found a 3 phase motor with the same frame and rpm. I also had a used vfd laying around. The setup was very reliable for 6-7 years till I got a higher pressure government water source.
 
Cheap VFD's off ebay can be very poorly made chinese imports which may be ok, but also maybe a source of issues.
A brand name VFD is not much more money, and will probably give you a lot less heartache.
Check out "AutomationDirect" or "Marshall Wolfe". You'll also get tech support as well.
True industrial suppliers.
Bob
 
Any 56C motor frame will bolt up. C Face and shaft dimensions are all the same with 56C frames.
Are you saying that the shaft diameter, length, and keyway will be the same on all 56C frames? Seems like that would mean that any 56C motor would be a direct replacement for any other 56C motor. Is that correct? Rotation direction might be an exception, I imagine.
 
Cheap VFD's off ebay can be very poorly made chinese imports which may be ok, but also maybe a source of issues.
A brand name VFD is not much more money, and will probably give you a lot less heartache.
Check out "AutomationDirect" or "Marshall Wolfe". You'll also get tech support as well.
True industrial suppliers.
Bob
Thanks for pointing me in the right direction of suppliers that those-in-the-know would use. Much appreciated. I will be contacting them..
 
Swimming pool pumps are going three phase with a dedicated vfd timer. Most pool pumps are oversized so the builder never gets a call back about underpowered pumps. I would bet your system is the same way before shutting down 1/2 of it. Lower rpm is lower amps and lower pressure. In pools the pump can lose prime, so the first five minutes is run at high speed then. it drops to a lower running speed.
Is the compressor and fan multi speed? If so the pump rpm can be tied to that change.
Bill D
I was a licensed solar contractor in Florida before moving to East Tennessee. In an attempt to reduce electrical consumption on top of what we helped our customers produce, we helped several of our solar photovoltaic clients replace their existing 1 speed pool pumps with 3HP Pentair VSD pumps. By running them longer but slowing them WAY down we were able to move the same amount of water per day at a greatly reduced kWh count. This had the added benefit of being whisper quiet compared to the noisy pumps we replaced. In some cases we could reduce total household consumption by 25% if I am remembering correctly. I believe we were reducing the pump consumption by 80% or more. That past work is probably what got me thinking about replacing this pump with a variable speed one. The difference is that those pool pumps were fully integrated with the VFD and timer so it didn't require matching a motor with a VFD as I'm having to do this time, and needing to ask questions to make sure I get it right!

To your other question, these heat pumps do not have variable speed compressors and fans.
 
If you look at the label on top of the cat no. it says thermally protected. This means that there is a thermistor inside that will open if the motor over heats. Some times these thermistors will not reset to the closed position and will stop the motor from running. I have in a bind cut out and bypass these resistors to get the motor up and running just make sure your motor starter heaters are set on the lower side to give you some protection.
 
I replaced my single speed 1.5 Hp pool pump with a 1 hp vfd driven one. Instead of a constant 3,600 rpm I run it just under 3,000 rpm to give it enough flow and pressure to run the pool sweep machine that crawls around inside the pool. Pressure is about 12PSi instead of 15-20. Watts is about 1/2. Flow is not noticeably changed with no flow meter. After a couple hours on high it switches to around 900 Rpm and runs hours at low pressure lower flow but enough to filter things. That takes under 100 watts.
Bill D
 
Are you saying that the shaft diameter, length, and keyway will be the same on all 56C frames? Seems like that would mean that any 56C motor would be a direct replacement for any other 56C motor. Is that correct? Rotation direction might be an exception, I imagine.
Correct. 56 is the NEMA frame size. C indicates it has a C face (which is how your motor is bolted to the pump). If the motor shaft was special it would have a Z designation (so would be 56CZ). NEMA designations/dimensions are standard so that any NEMA 56C motor will interchange dimensionally including all shaft dimensions.

All 3 phase motors are electrically bi-directional, and most single phase motor's rotation can be changed, but not always.
 
This has not been specifically stated here, but for the OP if you want variable speed via VFD it must be three phase motor when replacing the existing one.
Thanks. Fortunately, I was aware of that. I ended up speaking with a very helpful individual at AutomationDirect.com who guided me through what I needed to order. Their website does a great job of allowing one to filter down to only the few appropriate choices, but it was helpful to get his opinion on a specific brand and model of VFD and motor once I'd filtered down to the workable options. My experience with them so far has been very positive. Fast shipping too - the parts should be here the day after tomorrow!
 
If you look at the label on top of the cat no. it says thermally protected. This means that there is a thermistor inside that will open if the motor over heats. Some times these thermistors will not reset to the closed position and will stop the motor from running. I have in a bind cut out and bypass these resistors to get the motor up and running just make sure your motor starter heaters are set on the lower side to give you some protection.
Is there a simple way to see if that is the culprit? Is that was I'm looking at here in the center-ish part of the photo?

Temperature switch.jpg
 
Take the cover off it should have two wires. Check continuity it should show closed. if it shows infinite ohms its open. Then just connect the two wires together. The ones I have seen are usually inside but this could be it.
 








 
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