Hi gents, this is my first post, hello! I haven't done much forklift maintenance but I am an aircraft mechanic so I know one end of a spanner from the other.
I was hoping someone might be able to help out with a problem I have with my forklift, it's a 3 wheel electric Nissan. There's an intermittent problem with power getting to the wheels. I've checked the accelerator control, made sure all of the relays are working and are clean and continuity checked all of the wiring.
The fault happens in fwd and rev, I press the accelerator, the relays click in but the forklift doesn't move. Sometimes, but not always, by putting it into reverse and fwd a few times sets it away. I initially thought it was the safety circuit that prevents switching it on in gear and pressing the accelerator but I don't think it's that now.
I think it's something to do with the microswitches on the rear wheel that control the reversal of the power when the wheel is turned. There are 4 microswitches (2 left, 2 right) which feed into the relays for the fwd and reverse switching, I've checked them and they work fine. With the forklift moving, if I disconnect the connector block it replicates the intermittent fault I have.
So, my questions are; does part of the circuit board control the porting of the power to the wheels and has anyone had this roblem in the past? Oh, one more thing. If the fault is there, by pushing it a very small distance or letting it roll down a slight hill seems to clear the fault and it'll work ok after that for a while.
I'm working blind at the minute because I can't find a wiring diagram would anyone be able to send me one? I am more than happy to pay for it.
Thank you for any help.
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PaulG
look at the possibility that the relays control the trucks SCR speed controllers. Also look closely at the tips of the power relays not seating completely. Are you hearing a SCR hum? Yes the print board does gate on the Rectifiers of the speed control unit.
Well almost all the time they do wear the same on both sides but not always.
As for the micro switches if the motor contactor on both motors are pulling in then you know the control circuit side is working.
Concentrate on the power circuit side, the cables, contacts, brushes, buss fuses etc.
Thanks for the fast responce. Moving the motors slightly made me think about the brushes too, but, would the bushes in both motors go at once? Or, do the brushes have a common connection (maybe the negative side) so if one set aren't working it affects the other? I'll check these next and let you know.
I continuity checked the two sets of microswitches and they are working fine.
Cheers Gentlemen.
it could be the motor brushes being stuck in the brush holders, i've seen this before. You can use a electric motor cleaner(do not use anything else), and spray down the brushes and use a tool and grab the brush lead and pull them out and let them snap back in. Do this a couple of times to see if it helps. Also look at where the heal of the brush is in relationship to the brush holder bracket. If they are worn out it will be even with the back of the bracket or down inside it, if you see this then replace the brushes. If they are protruding out past the rear of the bracket holder then they are probably not worn out and just sticking in the holder. Also check the armature surface, if you see burning where the brushes ride then that is a sign that they might be sticking and arcing too badly burning the armature bars.
One other thing to consider is on these 3 wheel trucks there are usually 2 sets of contactors for each side, a right and left forward and a right and left reverse directional contactor.
check the contactor tips and see if they are burnt or melted. Check the armature of the contactor and make sure it is not worn out, this can cause then to bind and not close completely. If you find this then the contactor will have to be replaced.
Having it start to work properly after pushing it a bit sure sounds like the motor brushes having a problem.
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