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Signode
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Location: Lahore
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Switching of Motor Brake, AC Side or DC Side???

03/07/2012 1:22 AM

Dear Frieinds.

This is a general question that in one of our machines, there is a brake motor which brake is 200VDC and powered through a bridge rectifier which input is 230VAC (separate) and motor is for rated 380VAC. I want to get some advice that in such conditions, where should we place/connect the control switch to power on the brake, at input side of bridge (power input to switch then bridge and then brake) or output side of bridge (power input to bridge then to switch and then to brake)?

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kvsridhar
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#1

Re: Switching of motor brake, AC side or DC side???

03/07/2012 2:46 AM

i would recommend that you break the brake supply on the DC side of the bridge rectifier. This will make the brake act very fast. i assume that you do want the brake to act quick since it is a safety device.

The downside is that the DC arc is very severe, and is made even more severe due to the very high inductance of a closed EM Brake. L/R is likely to be 300ms or thereabouts. So you require a good DC contactor with blowout coils. Also, there will be a severe voltage surge, maybe several kV, lasting a very small time, but severe enough to damage electronics and/or the coil insulation. So, you need to put a proper Metal-oxide Varistor across the coil.

If you break on the AC side, the brake could take a very long time to clamp on, defeating the very purpose for which it is there.

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Anonymous Poster #1
#3
In reply to #1

Re: Switching of motor brake, AC side or DC side???

03/07/2012 6:42 AM

great...
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kvsridhar
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#5
In reply to #1

Re: Switching of motor brake, AC side or DC side???

03/07/2012 9:37 PM

Here is a good paper http://download.rulmeca.it/catalogo/macrofamiglia_eng/Electromagnetic_brake.pdf

The delay due to AC switching as compared to DC switching is given here...

Most design decisions are trade-offs. You choose.

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eltech
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#2

Re: Switching of motor brake, AC side or DC side???

03/07/2012 5:04 AM

You can do both AC and DC side.You can also do just the DC and use a bridge rectifier with a suppression on it.
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JRaef
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#4

Re: Switching of Motor Brake, AC Side or DC Side???

03/07/2012 9:21 PM

Most of the time brake coils are switched on the AC side because of the fact that switching DC is problematic.

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TonyS
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#6

Re: Switching of Motor Brake, AC Side or DC Side???

03/07/2012 9:55 PM

Have a look at http://www.seweurodrive.com/download/pdf/9PD0049.pdf it shows connections for both normal and rapid brake applications.

Most crane brakes I have worked on (Igranic, if any of you are old enough to remember them) were AC/DC switched for rapid operation.

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kvsridhar
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#7
In reply to #6

Re: Switching of Motor Brake, AC Side or DC Side???

03/07/2012 10:50 PM

Is that Brookhirst Igranic? i worked for Cutler-Hammer India, and visited C-H Bedford, England. Some people there mentioned BI as the former name. What beautiful products ! The EM brakes are still going strong on hot metal cranes in steel plants in India. Products that were built to engineer's specs....not to accountants' budgets.

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Signode
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#8
In reply to #7

Re: Switching of Motor Brake, AC Side or DC Side???

03/08/2012 5:37 AM

Thanks to all friends for participation.

We need fast action of brake. It measn i should switch the output of bridge.

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JRaef
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#9
In reply to #8

Re: Switching of Motor Brake, AC Side or DC Side???

03/08/2012 11:00 PM

Then pay close heed to kvsridhar's post #1 regarding selecting a DC contactor. You cannot just go out and use a basic cheap AC contactor, most of them are not rated for swithcing DC.

Good luck.

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Anonymous Poster (1); eltech (1); JRaef (2); kvsridhar (3); Signode (1); TonyS (1)

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