Some general simple tips about 3 ph motors please

[Tom Kitta]

The 6 to 7 amps is for 230V and for normal 1ph motor - see:
https://www.emotorsdirect.ca/item/baldor-el3510?quantity=1&tab=specs-tab

Note its tech specs say 8.5 at 115V so 8 amps at 120V - and that is for very efficient motor 1ph small motor (82.5).

compare to more normally priced motor: https://www.emotorsdirect.ca/item/leeson-lm24610?quantity=1&tab=specs-tab

Farm duty "normal enclosure" is same price level https://www.emotorsdirect.ca/item/nidec-fd1cm2pz?quantity=1&tab=specs-tab

I like that website - gives you prices in CAD & also makes me feel rich having so many motors.

Look at PDF here -
https://knowledge.emotorsdirect.ca/...-Motor-Nameplate-What-Information-It-Provides

At the bottom - all you need to known about motors and detailed explanation what design B stands for.

 

[Tom Kitta]

I doubt there is any standard rating for "farm duty" or "inverter duty" or "marine duty" etc. etc. It all feels like marketing talk to me. Where they cannot lie is actual requirements of NEMA - i.e. things such as current ratings or design type etc. Hence why cheap "marine duty" motors can crap out rather quickly. I would not be shocked to see "lathe duty" and "mill duty" motors.

When you ask Baldor what is "farm duty" you get explanation that it feels like a tougher "general purpose" motor for less money... yet they are both design B motors. Nameplates are the same - so what exactly is the difference - any claims that can be proven?

 

[Dabbler]

The amperage differences also amount to design choices made at design time. It is why it is sometimes difficult to match a used motor to a new use.

There are universal motors, squirrel cage motors, wound with litz wire or not, wound with braided windings and straight loops. I've seen many, but not all. yes, it is possible for a 1HP 120V motor to be marked anywhere from just under 8 amps, to more than 14 amps.

The plates aren't always describing the same amps, etiher. there's full load amps, but at what rated capacity? some motors use 80% torque a s the full load amps, while some measure maximum slip before the torque drops to zero. (yes a stalled motor has effectively zero torque, often with destructive current draw).

Some motor plates describe surge amps as the full load - in this case electrical load. That is the current required to start the motor under physical load. This is common for common for 'compressor duty motors. At nearly triple current (rating) they can still be over 90% efficient. Your efficiency is one thing (that is expected load energy versus torque) and the current drqw to start or past the expected load is completely another.

This topic confused me for years. And I took electrical engineering in school. (I'm surprised @Johnwa hasn't waded into this discussion) In U., I worked out many of these efficency graphs - energy consumed versus torque delivered. Some assignments took hours of calculations to make sense of the motor configuration.

 

[DPittman]

Well the chances of me feeling confident that I will pick the right motor for a vfd switch over are pretty slim. Oh well I don't need (or can afford) to do that anytime soon anyhow. I guess what I need to do is some in depth reading of the helpful links provided.

 

[Brent H]

@DPittman - if you are driving your machine with the VFD as the speed control - get a 240 V 3 phase motor that is designed for VFD usage and see what the losses in the motor are as you reduce RPM and then size it so that the losses will not affect your work. I have not seen a “farm duty” 3 phase motor. But I would suggest a drip proof (if there is some motor protection- its in a cabinet) or a TEFC motor that will be more protected from the environment if the motor is out there in swarf central.

 

[DavidR8]

Well the chances of me feeling confident that I will pick the right motor for a vfd switch over are pretty slim. Oh well I don't need (or can afford) to do that anytime soon anyhow. I guess what I need to do is some in depth reading of the helpful links provided.

I bought the motor and VFD for my mill conversion from emotorsdirect when they offered free shipping earlier this year.
They offered excellent advice and helped me select what I needed.
I have no affiliation with the company but wanted to pass along my experience.

 

[Dabbler]

I didn't mean to discourage you. Ther best approach is the one @David_R8 used. Go to a motor supplier with a good service department, and get their advice. You will likely avoid any pitfalls.

I used the motors as supplied with the machines. I measured the no load amps (and verified the machine plate) and filled in the VFD setting for the motor (full load amps) in the setup menu. Mine won't get optimal low RPM torque, but I can use the machine within reason.

 

[Tom Kitta]

Most people go with what Dabbler did - they run VFD with motor they have with settings in the VFD from the motor plate & have no issues when using machine within some reasonable parameters.

In the worst case get a much larger 3ph motor - such as 3hp instead of 1hp - unless you plan on running it under heavy load very slow you will be fine. I can sell you one cheap if you want. Heck I can even sell you a VFD (cheap Chinese) from the bad old days when I did not have a rotary converter.

 

[DPittman]

Most people go with what Dabbler did - they run VFD with motor they have with settings in the VFD from the motor plate & have no issues when using machine within some reasonable parameters.

In the worst case get a much larger 3ph motor - such as 3hp instead of 1hp - unless you plan on running it under heavy load very slow you will be fine. I can sell you one cheap if you want. Heck I can even sell you a VFD (cheap Chinese) from the bad old days when I did not have a rotary converter.

Well "cheap" usually gets my attention but many times I buy cheap because its cheap and then figure out what I really needed and then I aint so smug anymore. I think i need to decide what is right for me first and then I'll look for cheap. And I will likely come looking for you then. Thanks.