PF525 EM Brake control ??

milmat1

milmat1

"It Can't Do That !"
Location
Siler City, NC USA
Occupation
Controls Engineer
Friends,
I have a PF525 VFD 1HP 480V drive. At the last minute they changed the motor to a break-motor.
I have 480V in the VFD cabinet obviously, but I have no control voltage. no 120 or 24V at all. And no space to add a XFMR./PSU.
I need to operate a brake contactor for the EM brake from the PF525. The PF525 onboard 24V+ is only good for like 100ma or so.
We could use either the Opto-outputs (50ma max) or the R1 relay output. But I would need a 2-pole contacvtor with a coil consumpsion less then 100ma..

Any ideas on how to get out of this corner i have been painted into.
 
There are some contactors out there that have special electronic coils which can be controlled via 24VDC from PLC outputs, then use the line voltage for the actual coil energy. Essentially they have an internal interposing circuit inside, saves you the step. I know for sure AB has them, I’m pretty sure Siemens does too and if those two have them, the other major players will too. Finding them on the shelf may be a challenge though.

But still, you will need another box willing that contactor in it.
 
What brand of drive is it? There might be a way to use a CT/relay combo to release the brake when it picks up amperage on one leg. I've done a ton of work for Matot, the cargo elevator which all had the same brake motors. But they never used drives. Interesting issue for sure. If it's a YASKAWA drive I can definitely help you design something.
 
herding_cats said:
What brand of drive is it? There might be a way to use a CT/relay combo to release the brake when it picks up amperage on one leg. I've done a ton of work for Matot, the cargo elevator which all had the same brake motors. But they never used drives. Interesting issue for sure. If it's a YASKAWA drive I can definitely help you design something.
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I'm betting you're more than capable with about any. Parameters and auxillary contacts don't vary much other than what they are called and how to get there.

It's an PF525.
AB I think.
 
Thus using relay coil at 480v then to contactor coil at 24vdc? Prob easier to find relay than a contactor.
 
 
The PF525 already can control the brake contactor, the problem is that he has no source for control power to operate the contactor….

The smallest low energy contactor I could find has a 3W 24VDC coil, but 3W at 24VDC is 125mA of current, too much for that on-board 24VDC source within the drive. I also could not find a low current interposing relay that has 600V rated contacts (A600) to be able to use the 480V coil on a contactor. I really think you are going to have to hang a small CPT on the outside somewhere. Or open up the motor and remove the brake coil.
 
 
herding_cats said:
there are plenty of tiny relays that you can use to step up to a higher coil mA rating, or to 24ac/dc whatever. Use this to control a larger relay, then to control a real high voltage contactor. This relay rated at 5mA, 5 vdc:

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But the contacts on that relay are not rated to switch 480V, which is the only thing he has to power the contactor coil. That’s the core problem.
 
I know that. You use this tiny relay to control the coil of another relay, then use that relay to control the coil of the contactor. It's cascade relay wiring. The drive only sees the load of 5mA on that tiny relay card effectively controlling the main 480v contactor.

Do you want me to draw out the schematic?
 
He has no other voltage to power the relay to switch the 480. You keep missing that fact. He ONLY has 100mS of 24VDC, and 480V available. You can have as many interposing relays as you want, it doesn’t make it work if you have nothing you can switch.
 
You mean mA, not mS? That would be milli-second. I drew up the schematic but the file is too large to upload.

I will explain: The tiny relay card is directly connected to the drive. That coil rating is 5mA which will work.

Then, use the contacts of that relay card to control another cube relay, lets say rated at 24 vdc, 1 A

Then, use the contacts of that cube relay to control a 24 VAC power source connected to a full size mechanical contactor, be it 2 pole or 3 pole depending on the requirements of the electromagnet in the brake. Presto. You have control of the brake with 5mA source.
 
 
You would need a 277x24vac transformer as well to make it work. Or a 480x24vac. Both are available in 40VA (typical HVAC transformer, $16 or so)
 
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