Voltage Switching Unit (VSU)


EHC-5 and 6 cranes run on 24V to reduce the current thereby reducing the wire size used to power the crane.

The Voltage Switching Unit (VSU) automatically switches the auxiliary battery between two states:

  • Charge State – (crane off) the aux battery is in parallel with the chassis battery to charge
  • Activated State – (crane on) the VSU switches the aux battery into series to supply 24V to the crane hoist and pump motors.


Reference the diagrams below and these steps to wire the VSU.

  1. Connect the longest (26 ft, 4 ga welding) wire to the chassis battery positive terminal using a 150A slow-blow automotive fuse within 12″ of the battery.
  2. Connect the two battery lugs to the auxiliary battery (red tape or marking denotes the positive terminal). A standard maintenance free automotive battery is best (avoid deep cycle batteries).
  3. Connect the Tweco and 3-pin connector to the crane wiring. Insure the crane ground is making good contact to the chassis ground.
  4. Connect the shortest (8 ft, 4 ga welding) wire from the VSU to the chassis ground.

NOTE: Do not connect equipment and lights to the auxiliary battery since the terminal voltages shift between 12V-ground and 24V-12V. The example below would be supplying 24V to the equipment whenever the crane is actuated.



The attached document notes the voltages at various points inside the VSU for ease in troubleshooting.

VSU Troubleshooting

Attachments -

Last Update: July 14, 2021  

July 14, 2021   984   webmaster    Information Bulletins    
Total 0 Votes:

Tell us how can we improve this post.

+ = Verify Human or Spambot ?

Log In is required for submitting new question.