Hi - First post here. We have an old Clark EC 500 electric forklift that was having the issue of when it would get warm, it would stop working - basically it would not go into reverse or forward until it cooled off. I changed the contacts and it drives in forward now but when I put it into reverse - the contacts engage but there is no power running through them and no "hum". We are actually in the process of moving facilities so, this is not a great time to have it down. I am guessing it is either a burned out thermal coupler or switch, but I can't find a wiring diagram anywhere either. Any help is most appreciated. Cheers!
No one can give you any pertinent info without more from you. Complete model number and serial, capacity and which GE control is in it (a picture helps). That said, if you have one direction with movement, check the micro switches on the bottom of the FWD-Rev contactors and the normally closed tips on the Fwd (If GE control) and the normally open contacts on the Rev.
Hi Bill - Thank you for the quick response. The Serial Number is E235-0186-5041FA It is a Clark EC 500 - 30 It has the Clark EV-1 Control made by GE So contacts on the top right connect when put into reverse but there is no power running through them.
Then as long as the contactor pulls in and you do have forward, then the problem is in the contactor. Misalignment, missing a spacer conductor, the contactor not closing completely. The PMTD actuates both and would not close the contactor if it failed. All the rest of the components are also used in forward so that eliminates them, except for the possibility of the forward contactor NC side.
So you are saying it is not going in all the way and completing the circuit? When I replaced all the contacts on both sides, initially the forward would not work as one of the springs was not allowing it to move in far enough, so I was pretty careful on the other side. I can't quite figure out what is keeping it from moving all the way in to make the contacts connect.
Look at the armature (the moving part) and pay attention to the cone end. There is a guide pin on it, the place where the pin slides through can become packed with dust and dirt over time and prevent the guide pin from going in all the way.
And it seems like it is moving in the same distance when I push on it. I was wondering about that. Any suggestions on cleaning it out? Canned air or something? I just don't know what is going on back behind there....
Hi BillG So - unless there is something I am missing - I don't think the issue is the contacts not connecting. I am seeing the power to the wires into each of those contact centers stay hot when I put in in forward and go cold when I put it into Reverse. It seems like that power needs to transfer from that wire to the back bus and for some reason is turning off when the contacts push forward, leaving only the one post attached to the front bus hot. So when the forklift is shifted into drive - both front posts are hot according to my readings. The post that is connected to CP- S2 which is forward on my forklift stays hot in neutral or forward. The post connected to CP - S1 goes cold when the contacts move forward. Since the CPS1 and CPS2 have the connection to the back post that is connected to the rear bus, there is no power to the rear bus when this happens. It seems like the cable marked CP-S1 should be hot all the time. Hopefully this is clear. Thanks again, Brent
Also possibly relevant - the forklift will "overheat" to where it won't go in gear sometimes. Additionally, if left in gear - it also does something where it basically stops work and won't go into gear either.
When you are using your voltmeter, where are you checking from ---> to, wire numbers please. As I stated before the only difference between forward and reverse are the contactors. As long as the contactor is pulling in all the way, then the problem is with the contactor(s). When you say overheating where and how are you determining that it is overheating? There is only one thermal sensor for the panel and possibly one for the motor. But it does not sound as though you are able to operate it long enough for either one to shut the system down. Is it the SCR control panel or the contactors themselves that are over heating? Give me some history of when (how long ago) and what you were doing at the time of failure. When it won't move do you hear the selected contactor energize or not? What is the current draw at either battery cable when the unit is operating and not.
Hi BillG - And thanks for the quick response again. So - I am checking the current in the contactors grounding to the body through the screw hole for the panel. Here are my diagrams of what is happening - H being hot. I believe that I must not have gotten a good connections with the front bar on the forward as it shows 0 when it really can't be. As far as the other information. When the forklift gets hot as in from the sun or from running a while - the contacts just won't engage. Currently the contacts engage for both forward and backward. It only hums when for forward. When I hot wire the terminal for reverse at the wire CP - S1 then it hums as engergized. Maybe it is a mistake to do this but I wanted to see if the could be a current run through the thing. The intermitent dying has been for a couple of years. We use the forklift during harvest mostly and bottling - so it sits most of the time. I thought maybe there was a burnt contact that was getting worse so changed both sides out. As I said - forward wasn't working when I first rebuilt it as the larger spring for the plunger part needed to be seated to allow the contacts to plunge enough, like you said. I took the reverse one apart again and tried blowing out the hole where the rod goes, but not sure if it did anything. It seems like the wire CP - S1 the front of the contacts should still have power regardless of whether the contacts are going forward enough, shouldn't it? Thanks again!!!
No, this is a two wire system, there is no ground . You may see a voltage from ground to an actual connection but that is due to leakage current from the system (battery, carbon track etc). Look at the diagram for the large studs on the controller (it's printed on the control card opposite the Clark name tag), I can't see it clearly on your picture but the second from the left is - Negative the one to the far right is + Positive. All reference to system voltage are from these two points. You should show either 36 or 48 volts at these two points depending on what battery is in it. An external source (unless it's a forge or steel smelter) will not cause it to overheat nor will normal running, unless it is grossly overloaded. And again how are you determining overheat and what, the controller or the contactors. You will not get proper observations without using the proper test points. Also are you raising the drive wheels off the ground while testing? If not Do it now. Too many mechanics have been killed or injured by a runaway truck while testing.