🔧🔌 New to Motor World! Need some guidance. 🔌🔧

[priyanktripathi]

I've got this 3-phase 575V motor that we're controlling with a VFD (Variable Frequency Drive), which has been quite the learning curve in itself. But as I was inspecting the motor panel, I noticed something puzzling – there are two brass terminals alongside the power terminals. And I'm scratching my head wondering what those are for. Could they possibly be brake terminals? VFD Power Flex ALB 25B-E1P7N104.

Now, if they are indeed for braking, I'm a bit lost on the next steps. Should I be considering the VFD for braking control, or is it something the motor itself can handle?

Any insights or advice would be greatly appreciated! I'm eager to learn more about this aspect of motor technology. Thanks in advance!

 

[joseph_e2]

Which terminals are you looking at?

DC- and DC+ can be used to build a common-bus arrangement with multiple drives. BR+ and BR- are for connecting an external Dynamic Brake resistor. Does your load need dynamic braking? It definitely does if you're getting bus overvoltage faults. Probably will if it's a high inertia load that you need to slow down under power.

 

[priyanktripathi]

Which terminals are you looking at?
View attachment 69636
DC- and DC+ can be used to build a common-bus arrangement with multiple drives. BR+ and BR- are for connecting an external Dynamic Brake resistor. Does your load need dynamic braking? It definitely does if you're getting bus overvoltage faults. Probably will if it's a high inertia load that you need to slow down under power.

Thank you for replying. i am talking about these two terminals at the motor.

 

[plvlce]

there are two brass terminals alongside the power terminals. And I'm scratching my head wondering what those are for. Could they possibly be brake terminals? VFD Power Flex ALB 25B-E1P7N104.

Are these terminals on the panel, or on the drive? If they are BR+ and BR- on the drive they are for a braking resistor.

When stopping (or slowing) a motor, the motor essentially functions as a generator and power is produced causing the drive bus voltage to spike upward. If the bus voltage gets too high, the drive will fault. To prevent this, you can attach a braking resistor and the excess power will be dissipated across it. This is known as 'dynamic braking'.

Whether you need such a resistor depends on what you are doing. There are a number of factors involved, such as load inertia, how rapidly you are decelerating the load, and how often you are decelerating (ie duty cycle). Something like a blower or pump likely will not need one, but for example a heavy positioner that frequently moves at high speeds with sharp decelerations likely will.

OTOH if these are terminals are somewhere on the panel, not on the drive then they may be the power connections for a mechanical brake. Some motors include a brake which will apply friction to stop and hold the motor unless voltage is supplied. This can be used in conjunction with the dynamic brake -- the mechanical brake is applied when the motor should be stopped and during an emergency stop, but during regular operation the dynamic brake is used instead to extend the life of the mechanical brake.

Or the terminals could be for something else entirely.

tl;dr you haven't told us what terminals you're looking at. 'What two unknown terminals do' isn't much to go off.

 

[joseph_e2]

First thought is thermistor or something to protect the motor. You should try to find a datasheet for the motor. Or see where the wires go to infer their function.

 

[plvlce]

Where does the cable coming off it wire to? Or is it that you're trying to figure out where you should wire it to?

I'd start by looking up the motor literature. Could be a brake, but from my limited experience with Nord I'd guess it's a thermal overload. In the latter case you'd generally wire it back to a digital input on the drive which is configured to generate a fault when it turns off.

 

[priyanktripathi]

First thought is thermistor or something to protect the motor. You should try to find a datasheet for the motor. Or see where the wires go to infer their function.

I got this diagram from the panel cover, is it for thermistor then ?

 

[priyanktripathi]

Where does the cable coming off it wire to? Or is it that you're trying to figure out where you should wire it to?

I'd start by looking up the motor literature. Could be a brake, but from my limited experience with Nord I'd guess it's a thermal overload. In the latter case you'd generally wire it back to a digital input on the drive which is configured to generate a fault when it turns off.

Thank you for replying. I'll go check it. really appreciated.

 

[plvlce]

I got this diagram from the panel cover, is it for thermistor then ?

Yes it is for detecting a thermal overload, in this case not a 'PTC thermistor (TF)' but a 'bimetallic thermostat (TW)' (see Nord catalog pg 117). During normal operation, you will have continuity (< 50 mΩ) between the two leads. If the motor gets too hot then the metal in the thermostat will bend and open the circuit. You then use this as a signal to shut off the motor to prevent it from being damaged by heating further.

iirc Nord drives come with a dedicated digital input for this purpose, but I don't see something like that in the PowerFlex literature. If it were a PTC they have an option to use an analog input, but for the simple on/off of the thermostat the closest I can see is configuring an input as 'SW Enable'.

Alternately depending on how how you are controlling the drive you have other options. If there is a PLC commanding it you can instead wire to that and have it then send a stop command to the drive. If you have a simple 3-wire start/stop circuit the simplest option is just to wire in series with the stop button, although this would have the disadvantage that an overtemp is not obviously distinguishable from a normal stop command, which may hinder troubleshooting.

 

[James Mcquade]

you need to look at the nameplate of the motor and get the manufacturer and motor model number.
they could either be thermal overload terminals or the motor brake.
is there a brake installed on the end of the motor?
if there is, power is required to the terminals when the motor is run to open the motor shaft brake.
call the manufacturer to confirm.
I have seen thermal and brake terminals in place.
james

 

[tripstuf2]

It is for thermal protection, I have many that use this. We typically take an unused input and run it in a loop thru as NC like an estop, that way if motor gets too hot it will stop and will not allow restart until it closes the circuit.