UL brake rectifier

Replacing clutch and motor brake rectifiers with KEB rectifiers

This post serves as a guide for replacing a DC clutch or brake rectifier with a KEB rectifier.

motor brake rectifier

KEB UL listed rectifiers for DC brakes and clutches


First, why would anyone want to replace their clutch or brake rectifier with a KEB rectifier?  Here are some reasons:

  1. The brake rectifier is a passive device and relatively easy to change out. We’ll outline the process below.
  2. KEB rectifiers are industrial grade and better quality than those supplied with most OEM products.
  3. KEB rectifiers are UL listed – #E308765. Check your current rectifier product – most are not listed.
  4. KEB rectifiers are stocked and ready to ship.


So what are the good rectifier candidates to replace with KEB?  Basically, any brake or clutch using a DC coil.  Here are some examples:

  • Gearmotor or motor brakes from suppliers like SEW Eurodrive, Nord, and Sumitomo
  • Clutches from suppliers like Warner and Ogura.
  • DC brakes from suppliers like Lenze, Intorq, Stearns, and Precima.


 Process for crossing over clutch or brake rectifier:

1.  Download the KEB Rectifier manual

First, for reference, you’ll want to download the KEB rectifier manual which has all the dimensions and ratings.


2.  Double check that the brake or clutch has a DC coil

AC brakes use solenoids and do not need rectifiers.  For more information, check out this post which compares DC vs. AC brakes.


3.  Verify if you need a half-wave or full-wave rectifier

Check the incoming AC voltage and your rated DC electromagnet voltage.  Decide which type of rectifier will give you the correct output voltage.


Please note, this post only applies to standard half and full-wave rectifiers – not overexcitation types which have a time-based component.  Also, 24VDC magnets do not need this type of rectifier and will typically be supplied from a 24V power supply.


Half-wave rectifiers will output:

VDCOutput = VACInput * .45



Full-wave rectifiers will output:

VDCOutput = VACInput * .90


For reference, here is a grid showing the different KEB rectifiers by Type and Voltage rating:

keb brake rectifier grid

KEB rectifier grid



4.  Verify the rectifier voltage and current rating

The listed VACInput on the rectifier should be greater than the incoming AC voltage you are connecting to it.  See pages 4 and 5 of the KEB rectifier manual for the max input voltage ratings.



The amp draw for the magnet can be calculated if the voltage and coil wattage are known.

ICoil = WCoil / VCoil


Make sure the amp rating of the KEB rectifier is greater than the amp draw of the electromagnet coil.  This is also listed on pages 4 and 5.


5.  Verify how the current rectifier is being switched – AC or DC side switching

For more information on the wiring of AC and DC side switching, see page 6 of the KEB rectifier manual.


If DC side switching is used, then you must select one of KEB’s switches rated for 500VAC or less. They will start with either a 02 or 04.


Brake rectifier - DC side switching

The middle terminals of this switch allow DC-side switching


6.  Verify physical dimensions

Finally, verify that the rectifier will physically fit in your terminal box or electrical cabinet.  See page 5 of KEB rectifier manual for dimensional info.




That’s it!   If you have any questions about crossing over your rectifier, feel free to contact a KEB engineer today.

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