As successful industry specialists we would like to give operators a little advice on repairing their forklifts and avoiding rapid subsequent breakdowns (and stress!). The advice we have written below is simplified and by no means exhaustive. The intent is to provide managers and operators with a basic overview of forklift breakdowns. We want to identify the most common causes in order for you to repair your forklift quickly and efficiently. You will see the forklift is quite a complex system! Often rapid subsequent breakdowns mean the underlying cause has not been found. We hope this information will help your team, but use it at your own risk and always seek professional advice when dealing with problems associated with your forklifts.
Firstly why do most forklift breakdown? Well there are a number of reasons. Let’s have a look at the major factors, but to do so we have to look at the forklift system as a whole.
The four major components in a forklift are: the contactor (relay), the electric motor, the electronic controller and the battery. Unfortunately a failure of any four of these components will cause your forklift to stop working.
Lets look at the contactor:
The contactor in most forklifts acts like a relay which activates and deactivates the high current power systems. Because operations of the contactor are at high current levels, this causes arcing and therefore the contactors slowly get worn or warp out of shape, leading to failure.
Having worn or warped contactors will cause a voltage drop across the contacts, to compensate the current increases. This causes fluctuation in the delivered power levels which over time will harm the forklift motor and the controller.
The most common cause of contactor related faults is poor operation of the forklift.
Frequently switching the forklift on and off, or mishandling causes this kind of wear. Did you know most forklift manuals advise not to simultaneously lift whilst moving? Operation of the drive motor and lifting motor simultaneously places very large demands on the electrical system. Not waiting for the forklift to initialise properly (before the operator starts putting in control inputs) means a sudden surge once the system is ready to go.
The contactor is the cheapest of the system parts to replace, so they should be inspected regularly and maintained.
Let's look at the electric motor:
The electric motor will heat up as part of its normal operation. DC motors use a set of carbon brushes. Whilst the brushes wear they produce carbon powder, this powder slowly blocks up all the cavities inside the motor. With months or years of continuous use, the cycle of heating and cooling of the electric motor will cause the insulation of the electric motor coils to become brittle and deteriorate. At some point the lack of insulation and large amounts of carbon dust on these coils will cause the electric motor to short circuit between the exposed copper and motor housing. This short circuiting often causes undesired power surges and consequently damages the electronic controller. Eventually the controller will fail which will stop the forklift from operating.
Often when there is a short circuit in the forklift motor there will be some significant heat produced, so there is a fire risk and if the forklift operation isn't ceased immediately parts of the motor or controller can melt or sustain damage beyond repair.
Short circuiting can be identified by smoke that smells like electrics burning. This may be coupled with possible unusual/undesired operation of the forklift itself.
When repairing a forklift that has fallen victim to a short circuit, the contactor, motor, controller and the battery must all be individually checked. A common fault is to replace the controller only (without fixing the short circuiting motor). This may allow the forklift to operate normally for a small amount of time before the heat build up caused from the short circuit damages the motor or controller again! A short circuit type of failure is the most common type of failure that we see.
We recommend getting your motor rebuilt by a reputable company, this will ensure another failure of this type won't happen again for quite some time!
The controller itself.
The actual controller although built to withstand specific design environmental and operating criteria may fail in time due to any number or multiple components failing. This may be due to vibration, temperature variations over a long period of time, excessive condensation associated with rapid environmental changes (work inside/outside the cool-room/freezer, exposure to rain), or simply parts approaching the end of their design life.
This is one of the least likely scenarios, so we recommend you always get the motor and battery checked as well!
With time as the battery ages or approaches the end of its design life, cells in the battery will begin to die or some cells may start leaking. This has the effect of increasing the systems current to compensate for reduced battery voltage. As more and more cells of the battery die the subsequent increase in the current will reach a level where the controller can't cope causing the controller to fail (as it is operating outside its designed parameters). This stresses various components. In our experience we find controllers can fail when two or more battery cells have failed. The forklift body is designed to be electrically neutral, so it does not have a positive or negative charge. Leaking cells can cause your forklift body to become charged – which can cause sensors and other types of electronic circuitry to operate erratically. Battery checks should be conducted as part of your routine maintenance program for this reason!
Replacing only the controller without checking the battery will again allow the forklift to operate normally for a very short amount of time before the controller fails!
Finally we have put together a little forklift checklist:
PLEASE NOTE - ALL THE OPERATIONS DESCRIBED BELOW HAVE TO BE PERFORMED WITH THE FORKLIFT BATTERY DISCONNECTED!
1) Check the battery:
a) is the voltage at nominal level? (most commonly 24, 36, 48, 75, 90, 110 Volts)
b) any visible damage, acid leaks?
c) remove and insulate the battery from the forklift and conduct a power leak test: The battery casing should not be positively or negatively charged, just neutral.
d) test battery plug and socket for corrosion, burns and conductivity.
e) acid level?
f) battery temperature?
2) Check the contactor:
a) are the contacts moving freely?
b) are the contacts in good condition?
3) Check the motor:
a) are the brushes excessively worn?
b) check for a short circuit between the brush holders and the motor body
c) what is the level of electric resistance between the motor body and the winding?
d) is the motor full of dust?
e) is the rotor moving freely and smoothly?
4) Check the cables and terminal lugs connecting the controller to the main terminals:
a) is the insulation melted, damaged? if yes, replace the cable
b) are the lugs discoloured because of corrosion or overheating? if yes, replace the cable
5) Check the multi-pin plugs for broken wires or damaged pins.