kendrickg
Member
You all were very helpful when i asked about a VFD / dynamic brake problem so i had to ask the forum about this. I understand that this is a plc forum, but you all are some of the best diagnosticians in the world!!
Had a forklift repairman come down for $90 and hour for 10 hours and he couldn’t figure it out. We have an early 80s raymond Electric forklift that goes into full speed as soon as you tilt the joystick. Happens in forward and reverse. The drive motor contactor cycles on and off giving the motor full power during the one cycle (about 0.5s on and 0.5s off) . It is an SCR type drive system, with a "main SCR" and a "commutating SCR", and two main rectifiers. WE have a junk lift that i have been swapping parts from, so i swapped all the SCRs, rectifiers, control box and main capacitor. The repairman tested all the scrs and recs and said they were fine. What would cause the motor contactors to cycle on and off, it should be on all the time during motion and the scrs would vary the power to the motor. There is separate forward and reverse contactor, but they are both affected by the cycling problem.
The problem started when we had to push a machine up a slight grade into our building. The lift was straining for about a minute and we smelled a kind of burning resistor or transformer smell. When we got into the building the lift started doing this immediate full speed condition. We used the lift an hour later and it worked fine, and continued using it for two weeks. We stressed it again and a cable lug going to the rectifiers fried and the immediate full speed condition returned. This time it didn’t "go away". I replaced the cable and and rectifiers but the problem was not repaired what so ever. So, we replaced all kinds of parts on the lift and no results. We might as well buy another lift instead of having another idiot technician come out, but the lift has low hours for its age and has never given us any problems. Any thoughts?
Had a forklift repairman come down for $90 and hour for 10 hours and he couldn’t figure it out. We have an early 80s raymond Electric forklift that goes into full speed as soon as you tilt the joystick. Happens in forward and reverse. The drive motor contactor cycles on and off giving the motor full power during the one cycle (about 0.5s on and 0.5s off) . It is an SCR type drive system, with a "main SCR" and a "commutating SCR", and two main rectifiers. WE have a junk lift that i have been swapping parts from, so i swapped all the SCRs, rectifiers, control box and main capacitor. The repairman tested all the scrs and recs and said they were fine. What would cause the motor contactors to cycle on and off, it should be on all the time during motion and the scrs would vary the power to the motor. There is separate forward and reverse contactor, but they are both affected by the cycling problem.
The problem started when we had to push a machine up a slight grade into our building. The lift was straining for about a minute and we smelled a kind of burning resistor or transformer smell. When we got into the building the lift started doing this immediate full speed condition. We used the lift an hour later and it worked fine, and continued using it for two weeks. We stressed it again and a cable lug going to the rectifiers fried and the immediate full speed condition returned. This time it didn’t "go away". I replaced the cable and and rectifiers but the problem was not repaired what so ever. So, we replaced all kinds of parts on the lift and no results. We might as well buy another lift instead of having another idiot technician come out, but the lift has low hours for its age and has never given us any problems. Any thoughts?