# I want to operate a DC brake for crane hoist - KBPC3510 rectifier

Discussion in 'General Electronics Chat' started by PRAVEEN SHARMA, Jan 9, 2016.

1. ### PRAVEEN SHARMA Thread Starter New Member

Jan 1, 2016
1
0
Mods edit:
This thread was split form -- Full bridge rectifier.

Hi everyone,

I want to operate a DC brake for crane hoist. Brake rating is 24V DC, 80W rating max. Can i use KBPC3510 rectifier. What AC voltage transformer to be used. how much VA rating to be used. Please help

Jul 18, 2013
10,859
2,525
Measure the resistance of the brake coil and this can then calculate the VA required.
A transformer va from your numbers is around 100Va.
24vac secondary, no Cap required.
Max.

3. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Transformers are labeled for AC voltages which are RMS (Root Mean Square). Given an RMS voltage, you multiply that by the SQRT(2) ≈ 1.414 to get the peak voltage. You need a little bit of headroom for the diodes in the bridge rectifier and a bit more if you want to use a voltage regulator.

So:
$24= \sqrt{2}V_{ac} - 1.4$
$\left(\frac{24 + 1.4}{\sqrt{2}}\right)=V_{ac}$
$V_{ac} \approx 18 \text VAC_{rms}$

If you want to use a voltage regulator then bump the AC voltage up a bit to say 20 VAC.

Jul 18, 2013
10,859
2,525
For a brake you do not need smoothed DC, place a reverse diode across the brake help retain it.
Max.

5. ### chuckey Well-Known Member

Jun 4, 2007
75
10
Depending on how the DC is being switched to the brake, it would be worth while to incorporate a back EMF diode or some sort of snubber across the switch.
Frank

6. ### panic mode Senior Member

Oct 10, 2011
1,329
305
you definitely need a diode across brake and this needs to be placed as close as possible to the brake coil (not 30m away or where PSU is). note, this diode need to be reverse biased (cathode to +ve side).

24VDC is industrial standard and you don't need to make own PSU, you can get cheap industrial PSU which will have approvals and other features that may be useful (like short circuit protection etc).

if you are making your own PSU, yes you can use that bridge rectifier, with up to 1000V and 35A it is more than big enough (an overkill actually - something rated for 60V and 5A would also be fine).

Jul 18, 2013
10,859
2,525
He already has the bridge, and 24vac control transformers are common.
Max.

8. ### ian field Distinguished Member

Oct 27, 2012
4,459
792
Crane hoists usually use DC braking.

2 push buttons for up and down. each button is single pole changeover. both buttons pressed or both buttons released shorts the motor winding.

Just to get started - say both NC contacts go to battery negative, and both NO contacts go to battery positive. the motor is strung between the to moving contacts. Any time both switches are in the same state; both ends of the motor winding are connected to the same battery terminal.

Last edited: Jan 10, 2016

Jul 18, 2013
10,859
2,525
Doesn't help the OP, he evidently has a 24VDC 80w brake to operate. Could be a 1ph or 3ph motor.
Max.

10. ### crutschow Expert

Mar 14, 2008
13,508
3,385
Actually, you do want the diode at the PSU switch so it suppresses the spike from the wire inductance as well as the brake inductance.
Remember that the purpose of the diode is to provide a path for the inductive current when the switch opens, and that path includes the wire inductance.

But if you switch the AC voltage to control the brake then you don't need any added suppression diode since the bridge diodes will serve that purpose.

11. ### panic mode Senior Member

Oct 10, 2011
1,329
305
you can have both but if one must choose, imho it is better to have diode at the load. otherwise you are burning contacts and stressing insulation of the wires and load.