Is a 500w switching power supply enough for a 400w motor at high draw+additional power supply questions.

Thread Starter

Cyrus Mingley

Joined Apr 18, 2020
92
I have a 24v 400w bldc motor and planning on using it for a lathe, turning small aluminum parts. I'd have the tool move at a very slow pace as to not stress the motor by removing a lot of material very quickly. It probably won't run at full capacity, but lets say I load the motor to the absolute max. Will it draw past its rated 16.6 amps or will it max out, slow down, and stop until the load is lessened? I have to note that the motor has a potted speed controller built in, does this have a system that will limit current draw? If it does draw past 16.6 amps, will it burn the coils out, and if it reaches past the power supply's rated output, what will happen? The power supply has overcurrent protection but is this for input or output? Is it even possible to draw more than the power supply outputs or will it just not draw any more?
 

Thread Starter

Cyrus Mingley

Joined Apr 18, 2020
92
I have a kollmorgen cti 187-2 bldc motor with a built in speed controller. I'm wiring it to a 5k ohm potentiometer. (Yes, the same one I've been asking about for a bunch of my past questions). I found a wiring diagram (kinda).
1589259949358.png
This is all well and good, except the wire for the control circuit was cut at some point leaving me with wires. The problem with this is the diagram has a 3 pin connector, with red blue and white wires for the potentiometer. Apparently there's also a two pin connector, for braking. This is only pins, so there's an unaccounted for wire here. There are three wires left after wiring the potentiometer. A brown wire, a green wire, and a black wire. Any ideas on what they do? Two shut off the motor when connected, what about the other? One of these has to be connected to the same pin as another wire, right? Thanks for any help, this motor is a relic with very little helpful information on the web.
 

MisterBill2

Joined Jan 23, 2018
7,035
My guess is that the green wire is a frame ground , and that is simple to verify with an ohm meter, just check for continuity between the green wire and any bare metal you can find on the motor.
If the motor runs when you connect power to the red and black leads then you may not need whatever function those other wires provide. So at that point, just insulate the ends and leave them until you discover their function.
And about the power concern: a variable speed motor starting at no load and low speed will not have an inrush current near the maximum specified draw, which is at full load.
 

MisterBill2

Joined Jan 23, 2018
7,035
Most motors have a constant power rating and in addition a peak power rating. Peak power is time limited in almost every case. So if you overload the motor momentarily it should not suffer.
Switching power supplies over-current protection is on the output current and an excess load will either result in foldback current limiting, where the voltage drops to limit the current, or they go into a shut-down mode and the power must be switched off and back on to reset them. And you could always get a cheap ammeter and wire it in line so that you would always be able to see the motor load.
 

Thread Starter

Cyrus Mingley

Joined Apr 18, 2020
92
My guess is that the green wire is a frame ground , and that is simple to verify with an ohm meter, just check for continuity between the green wire and any bare metal you can find on the motor.
If the motor runs when you connect power to the red and black leads then you may not need whatever function those other wires provide. So at that point, just insulate the ends and leave them until you discover their function.
And about the power concern: a variable speed motor starting at no load and low speed will not have an inrush current near the maximum specified draw, which is at full load.
Thanks, I just tested it and the green is not a frame ground. The only thing I can find is that it’s continuous with the green wire on the hall sensor circuit. It’s marked as “h-“ which is the negative lead.
 

MisterBill2

Joined Jan 23, 2018
7,035
OK, so the green wire is not a frame ground connection. That implies that the color coding is not a standard code, meaning things need to be traced and checked, no presumptions or guesses. But if the motor is already able to run and the speed control functions correctly then you are all set.
Question: are the pictures and diagrams in post #2 of your motor? Or just some similar looking 400 watt motor ? No green wire appears on the pictures, is why I ask.
 

Thread Starter

Cyrus Mingley

Joined Apr 18, 2020
92
OK, so the green wire is not a frame ground connection. That implies that the color coding is not a standard code, meaning things need to be traced and checked, no presumptions or guesses. But if the motor is already able to run and the speed control functions correctly then you are all set.
Question: are the pictures and diagrams in post #2 of your motor? Or just some similar looking 400 watt motor ? No green wire appears on the pictures, is why I ask.
The picture is my picture and the diagram is for the exact model I have, so it’s pretty confusing. Somewhere in that main cord with the 6 smaller wires there’s an unaccounted for wire
 

MisterBill2

Joined Jan 23, 2018
7,035
OK, then the whole thing is rather puzzling indeed. That green wire might be for production line tests that every motor gets. I think that you mentioned that the connectors were cut off, meaning that some useful clues are missing.
BUT if the motor runs as needed then it should be OK for lathe duty up to the limits of it's capability. And the really good news is that with spinning it up instead of just switching it on to full speed there will be no serious inrush to overload the supply.
 

Thread Starter

Cyrus Mingley

Joined Apr 18, 2020
92
OK, then the whole thing is rather puzzling indeed. That green wire might be for production line tests that every motor gets. I think that you mentioned that the connectors were cut off, meaning that some useful clues are missing.
BUT if the motor runs as needed then it should be OK for lathe duty up to the limits of it's capability. And the really good news is that with spinning it up instead of just switching it on to full speed there will be no serious inrush to overload the supply.
Yeah, the connectors were cut off before I got it. Alright, I’ll test it with a low amp fuse just in case. Thanks for the help!
 

MisterBill2

Joined Jan 23, 2018
7,035
Yeah, the connectors were cut off before I got it. Alright, I’ll test it with a low amp fuse just in case. Thanks for the help!
Possibly the green wire, connected to the Hall sensor, might be a speed signal output for some external function. In that case, just insulating it and keeping it out of the way should be enough.
 

Thread Starter

Cyrus Mingley

Joined Apr 18, 2020
92
Possibly the green wire, connected to the Hall sensor, might be a speed signal output for some external function. In that case, just insulating it and keeping it out of the way should be enough.
Interesting, once my power supply arrives I’ll test it and if it works without it I’ll leave it and insulate it
 
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