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Dc Fork Lift


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We have a 20+ year old 72V DC fork lift and some time back the speed controll failed so we bought a new one with, I think. The latest tech. We fitted it in accordance with the manf instructions and nothing worked , not even the "on" LED.


Many of us checked the wiring and I spoke to the manf but could find no fault. So finally sent it back for checking but when the manf checked it they found it worked ok. So it was sent back to us and we refitted it and of course it did not work.


One of our electricians removed the field and arm connections from the controller whilst it was fitted to the fork lift, applied power and the On LED worked. So Power off, refit the arm connections, power on and the LED worked. So power off, refit the field, power on and the LED did not work.


Power off remove field, power on and the LED worked.


Now for the fun bit.



Leave the power on connect one side of the field and the LED stays on. Tap the other side of the field to the connection and the LED stays on. Fit the other side of the field properly and still the LED is on.


Sit on the fork lift ( to set the seat switch ) release the hand brake and the machine worked.


The above was about a month ago and so far the machine has continued to work as it shoulld.


I realise that flashing the field in some way activated the controller but why? The only thing that I can think of is that we wired the field 'in reverse" ( both sides of the field float) I did ask the manf but recieved stoney silence.


Two more points. All connections were very clean so no chance of a faulty connection ( they were checked many times) and we are using 2* 36v motors in series.





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  • 2 weeks later...

Hi Terry


After a lot of thought, I still can not give you an answer on this at all.

It sounds like there is an over current shut down that was activating within the controller.

Reversing the field, or flashing the field should not have any impact that I can understand, so no answer form here!!


Best regards,


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