BD3 Brake Power Supply specification and manual

BD3 Brake Power Supply is intended to interface mains supplied eddy current brakes with dynamometer controller. It is used to keep brake current at level required to get desired torque. BD3 offers one or three phase mains input and fast demagnetization circuit for quicker brake response. With BD3, typical dyno brakes will deliver full torque output under 0.2s and will completely turn off under 0.02s. Fast brake response is especially beneficial in dynamometers with low inertia, such as engine dynamometer or hub dynamometer.

BD series brake power supplies comparison

Safety precautions

  • Device should be fixed on hard, flat surface in well ventilated area.
  • Device must not be exposed to vibration.
  • Device air flow must not be obstructed.
  • No foreign objects should be inserted into the device.
  • Life threatening, high voltages are present in the device. Make sure that it is disconnected from mains power supply before doing maintenance work.
  • Device is equipped with high voltage storage capacitor. Before servicing the device, after disconnecting power, wait 15 minutes for the capacitor voltage to drop to safe level.
  • Device is intended for installation by qualified personnel.
  • Device should be protected from access by unauthorized personnel.
  • Device should be protected from moisture. It mustn’t be used when wet.
  • Device should be protected from ingress of conductive contaminants. It shouldn’t be operated where metal grinding or cutting dust is present in the air.
  • Device mustn’t be powered without assembled enclosure.
  • Device installation doesn’t require enclosure disassembly.
  • If the device is not working correctly, makes disturbing noises, emits burning smell, it should be immediately powered down. Please contact the manufacturer for repair.
  • All dyno metal elements must be connected to safety ground. Any short circuit of live wire to dyno chassis must result in circuit breaker opening. Use of RCD breaker is advised for additional safety.
  • Device power supply must be protected with over current circuit breaker with B characteristic. The breaker value should be selected to minimum that is sufficient to supply the brake.
device variantone phase supplythree phase supply
BD3 – 22.5A25A10A
BD3 – 45A20A
Maximum circut braker values


Supply1 or 3 phase
L-N 100-230VAC
L-L 100-400VAC
Continuous current ratingBD3-22.5A:
22.5A @ 40°C ambient temperature

45A @ 25°C ambient temperature
40A @ 40°C ambient temperature
Brake discharge methodFast discharge with storage capacitor
Switching frequencyAdaptive, up to 4kHz
Brake current controlControlled with microcontroller in closed loop
Dimensions22.5A: 14cm x 15.5cm x 12cm
45A: 26cm x 23.5cm x 11cm
Current target controlProgrammable current range
Galvanically isolated PWM input, 15Hz – 4kHz, 4V – 8V, higher input voltage allowed with external resistor
Galvanically isolated CAN bus interface, CAN-BUS 2.0B, 500kBit
DiagnosticsCAN bus:
Brake current
Power stage temperature
Switching frequency

Additional information possible in future with firmware updates
Operating ambient temperature−20°C ÷ 50°C
Operating humidity0% ÷ 95% without condensation
ElevationUp to 1000 m.a.s.l.
Mass22.5A: 1.3kg
45A: 3.3kg

Device connection

PWM IN-PWM input negative
PWM IN+PWM input positive
CAN HIGHCAN bus high
CAN LOWCAN bus low
N / NMains supply neutral
L1 / LMains supply phase
L2 / NNeutral for 1 phase connection
2nd phase for 3 phase connection
L3Mains supply phase
CAPACITORDischarge capacitor connector
BRAKEEddy current brake connector
Terminal1 phase connection3 phase connection
N / NN – NeutralN – Neutral
L1 / LL – PhaseL1 – Phase 1
L2 / NN – NeutralL2 – Phase 2
L3L3 – Phase 3
Example connection for 1 phase and 3 phase power supply

WARNING! Voltages in the device are life threatening.
All connections should be made with the device disconnected from main supply.
Connecting the supply is allowed only when the device is safely installed and it’s enclosure is assembled.
Storage capacitor keeps dangerous voltages present in circuit for 15min (250uF) or 30min (530uF) after mains disconnection.
Wait for capacitor to discharge before servicing.
PWM and CAN circuits are isolated from dangerous voltages and are the only circuits safe to touch when the device is powered on.

Capacitor and brake wiring should be routed away from sensitive circuits (i.e. load cell cable). If separate routing is not possible, shielded wiring should be used.

Typical required cross section of power cables is:

  • 2.5mm² up to 17A
  • 4mm² up to 23A
  • 6mm² up to 30A
  • 10mm² up to 40A
  • 16mm² up to 50A

Discharge capacitor

The device uses discharge capacitor for storing brake demagnetization energy and for filtering mains input voltage. Typical voltage present on the capacitor is 325VDC for 230VAC supply or 564VDC for 400VAC supply. When the brake is quickly discharged from high current, capacitor voltage will temporarily rise up to 1000V.
Capacitor and brake wiring should have 1200V insulation rating to provide adequate safety during discharge voltage spikes.
For fast demagnetization to work properly, the capacitor must be sufficiently sized. Minimum required capacitance value can be calculated using the calculator below.

Eddy current brake peak current

Eddy current brake inductance

Magnetic energy in brake

Minimum capacitance
ModelInductance [mH]Nominal current [A]
Frenelsa F16-16012318
Frenelsa F16-GR18422
KLAM CFK-50077019

BD3 must be always operated with discharge capacitor connected. Operating the BD3 without the capacitor can lead to device damage not covered under warranty.

Absorber compatibility

To be suitable for use with BD3, the absorber insulation must withstand temporary voltage spikes up to 1000V. Typical absorber wire insulation is rated to withstand 2kV – 8kV from turn to turn. Good design can further increase breakdown voltage of whole absorber. If you’re not sure if your absorber have suitable breakdown voltage, contact your manufacturer.
Following absorber brands are confirmed compatible with BD3:

Absorber brandFactory insulation voltage test
Pentar Kloft5000V
Elektromex Centrum1000V

To keep your absorber insulation healthy for longest, adhere to following guidelines:

  • Don’t overheat the coils
    • Don’t exceed nominal current
    • Don’t power the brake which is not rotating
    • Run the brake idle for some time after heavy run to allow it to cool down
  • Avoid mechanical damage to the coils
  • Keep the moisture and mold away
  • Avoid coils contamination with dust or fluids

Programming and operation

Best way to connect BD3 brake interface with DC1 dynamometer controller is via CAN-BUS. Twisted pair cable must be used. 120Ohm terminating resistor must be placed on bus ends. On the DC1 end, built in resistor can be used. For more information refer to Wikipedia page on CAN bus.

Example BD3 CAN bus setup

Example CAN bus setup for BD3 require:

  • Speed: 500kbps
  • Send BD3 control message: checked

Enable terminator can be checked if CAN bus has one end in DC1.

CAN idDescriptionFormat
0x160Programming communication from DC1 to BD3
0x161Programming communication reply from BD3 to DC1
0x162Control message with desired current information [16bit current fraction 0x0 ÷ 0xfff0 big endianness][ channel 1 ]
[ channel 2 ]
[ channel 3 ]
[ channel 4 ]
0x163-0x166BD3 status message [each field 16bits, big endianness]
0x163: channel 1
0x164: channel 2
0x165: channel 3
0x166: channel 4
[ output current 10mA/bit (45A version) 5mA/bit (22.5A version) ]
[ output switching frequency 100Hz/bit ]
[ power module temperature 0.1°C/bit signed ]
[ reserved ]
BD3 CAN communication reference

Example CAN inputs configuration file for 22.5A version on channel 1.

BD3 interface should be configured with BD3 Tool before use.

BD3 tool
  1. Detected device list – click on the device serial number to configure it
  2. Scan again for BD3 devices – if the device was powered or connected after running BD3 tool
  3. Assign BD3 device to channel – the BD3 will know which current it should provide and on which id it should send status message by using assigned channel information
  4. Set current range – sets device to provide fraction of BD3 nominal current (45A or 22.5A)
  5. Upgrade firmware – button is enabled if firmware in BD3 can be updated
  6. Log window – shows information what’s going on in communication between DC1 and BD3.


Up to 4 BD3 interfaces can be connected to DC1 dynamometer controller. Each one of the BD3 interfaces must be assigned to distinct channel. Each Torque Controller in DC1 sends desired brake power fraction (0.0 ÷ 1.0) through CAN bus if “Send BD3 control message” is checked.
Example data flow:
Torque Controller 1 in DC1 -> CAN bus message 0x162, channel 1 -> BD3 programmed to channel 1 -> CAN bus status frame 0x163 -> DC1
Torque Controller 2 in DC1 -> CAN bus message 0x162, channel 2 -> BD3 programmed to channel 2 -> CAN bus status frame 0x164 -> DC1

Current range

The connected eddy current brake nominal current must be programmed into BD3 interface. With use of this information BD3 interface adjusts effective output voltage to keep your brake safe. Over-driving your absorber coils with current higher than nominal for some time can lead to coils damage!

Example eddy current retarder specification.

Retarder electrical characteristic is connected with following equation:

  • rated voltage = coils circuit resistance * current rating

If one of the parameters is missing in the specification, it can be calculated from other two.
Example current range calculation for F16-120 absorber and BD3-22.5A:
Current range [%] = absorber current rating [A] / BD3 current rating [A] = 15.5A / 22.5A = 0.68 = 68%

Absorber nominal voltage rating

Supply voltage on L-L terminalsDesired absorber nominal voltage
230VAC or 400VAC192V

Lower than desired absorber nominal voltages are supported, however:

  • Current fluctuation around desired current target will be higher (average current will still be at desired value)
  • As a result of higher current fluctuation there will be higher absorber torque output pulsation and electrical noise emission

If you have absorber with lower than desired nominal voltage it would be the best to rewire it for higher voltage. Absorbers are usually made with 16 coils rated to 12V. Rewiring the absorber for higher voltage will require to connect all these coils in series (16*12V = 192V).
If absorber rewiring is not possible and current control is not satisfactory, BD3 power supply voltage can be lowered with use of transformer.


Producer guarantees that the device is manufactured according to accepted craftsmanship practices and it meets the applicable standards. Correct device operation is guaranteed for 24 month period starting from date of purchase.
Guarantee does not cover damages caused by improper installation, usage or non compliance with instruction manual.
Device is intended for installation by qualified personnel. Device final performance and suitability for particular application is dependent on the user and thus it is not guaranteed by the manufacturer.
These specifications are subject to change without notice.