Troubleshooting Electrical Problems
Sometimes, things we cannot see are difficult to understand. Such is the case with electricity. But, we can certainly see the results of electricity at work. In electric forklift drive control systems, when electricity is able to “flow” properly, the traction motor runs and the forklift operates properly. When that electrical flow is interrupted strange things can happen. Components do not work or work intermittently, fuses blow and in extreme cases, wires can become so hot they could cause the insulation to break down and melt.
This section will guide you through basic electrical troubleshooting. As with any other aspect of service work, it takes time and patience to develop skills. But, if you take your time, read the Service Manual and the Training Manual carefully and follow the steps recommended by CLARK, you will be able to troubleshoot and repair even complicated and involved problems.
The Logic of Electrical Troubleshooting
For some technicians, electrical problems are what they like to work on the least. It’s easier to fix a problem that can bee “seen” as some electrical problems can be elusive. However, if you take your time to carefully analyze the problem and outline some logical steps to solve it, you will find that most electrical problems are pretty basic. Remember for current to work, you need a Battery or a Source for electrical power, a Load such as a motor or contactor and Continuity, which means wires and conductors that are free of resistance. If any of these factors are missing, the circuit is broken and current will not flow.
It’s helpful to have a routine procedure or approach when troubleshooting a problem, a method with which you are familiar and that gives you the most information with minimum time and effort. A general rule of thumb when performing electrical troubleshooting is to: ‘Do tire easiest and quickest checks first. ‘
This approach means looking for the obvious things first, such as damage to wires or buss bars, excessive corrosion on wires and connectors. Fuses should be checked with a VOM meter. Don’t trust your eyes on this check! A fuse that may “look good” may be blown. After this step, you should begin developing a sound “plan attack” before going any further on the forklift. Some of the most frustrating and confusing electrical problems are made more difficult with a haphazard and random troubleshooting approach. It’s important that the checks you make will give you the answers you need. If you test the wrong component, use the wrong test equipment or forget to calibrate a meter, you may get incorrect or useless information. Don’t forget, there is a time to “walk away from the problem”. When that “time” occurs is different for each person but the important point to remember is that it is very easy to become confused when troubleshooting electrical problems. If, after 30 to 45 minutes, you have not reached a solution to an electrical problem, it’s usually a good idea to take a break and walk away from the problem to think about it for a few minutes. This is when you need to go over your “plan of attack” and find out exactly what you know about the problem you are working on.
The CLARK approach to solving electrical problems is to find out what circuits and what components are working properly. This is an “Elimination Process” that leads you to the solution by finding out what is not causing the problem. The most important part of this procedure is to make sure you are using meters or test instruments properly and you are achieving the correct results and readings when you make your test. Always write down your results in case you must relay this information to someone else.
Troubleshoot With Your Senses
Your senses can be used in troubleshooting an electrical problem. Even though we cannot see current flowing through a wire, the effects of it can be seen: Lights illuminate, motors spin, contactors energize and so forth. And, too much current flowing through a wire may cause that wire to feel warm. Touching, sight, and sound as testing methods should be tried first before using test equipment to troubleshoot.
A Troubleshooting Approach
As mentioned before, it is frustrating to try and solve an electrical problem with a haphazard procedure. It wastes time and will sometimes result in more problems. A logical and well thought out plan is the key to quickly diagnosing and repairing electrical problems.
1) Raise Drive lire~m the floor and Block Unit.
2)Evaluate the problem.
This may seem simple but sometimes the problem on the repair order may not be the same as the actual problem. Also, there may be other problems or symptoms that were overlooked. Check not only the listed problems, but also all other components as well. Some may be on the same circuit or may interrelate. This is a good opportunity for you to use your senses as a testing method.
3) Determine the Conditions Under Which the Problem Occurs
Talk to the operator! Does the problem occur after the shift is almost over? Is the truck pulling a grade? Is there sufficient charge in the battery? Were any components or accessories installed recently? What about corrosion? Is the customer washing or steam cleaning the truck? Is proper battery maintenance being observed? Is the battery “boiling over” during charge into the bottom of the truck?
4) Consult the Service Manual
Turn to the appropriate section of the Service Manual for the troubleshooting procedure.
5) Use the wiring schematic to determine the flow of power and which components are in that system. When you have a service problem with an electrical truck, you should make sure the following steps occur:
1) Talk to the operator to verify the problem. Get all the details you can.
2) Test the truck yourself and begin looking for obvious problems, i.e. damage, vandalism, bad battery, etc.
A Troubleshooting Approach (Cont’d)
3) Have a Service Manual or Training Manual available to refer to.
4) Make sure you have proper equipment such as VOM Meter & AMP Meter.
5) Perform all steps listed in the Service Manual, for the control systems your Unit is equipped with) including discharging the commutation condenser, (if equipped) checking for loose connectors and checking all fuses with a VOM Meter.
As you progress down through troubleshooting the problem, you’ll need to check certain components. Detailed instructions for checking any component can us&&y be found in the Service Manual or the Training Manual. Use common sense and reasoning for any components where exact and detailed check-out procedures are listed. If you use proper test equipment and use the equipment correctly, you should be able to progress through the troubleshooting until you discover the problem.
Basic Test (Tools) Equipment In Troubleshooting
On the following pages, proper use of the Simpson VOM and Handyman Component Tester is pre- sented. Proper use of the Electric Vehicle System Analyzer has been presented at the end of each section on component identification. CLARK stresses that the minimum test equipment to properly troubleshoot an electric forklift would consist of:
1) A high quality Volt-OHM-Current meter as the Simpson VOM or Fluke Multimeter.
2) A Handyman Component Tester.
3) AMP Meter or Stunt.
Front Panel Description Description of front panel controls, jacks and indicators is as follows:
1. Front Panel: 2. Range Switch: -6 The 260 – P Volt-Ohm-Milliammeter is a large, easy-to-read 4-l/4 inch indicating Instrument. Below the Instrument are four controls and eight circuit jacks. Switch positions and circuit jacks are marked in white characters for easy reading.
2 Positions: May be rotated 360 degrees in either direction to select any of the five AC and DC voltages, four DC currents and three resistance ranges.
3. Function Switch: The function switch has four positions: OFF, +DC, -DC, and AC Volts only. To measure DC current or voltage, set the function switch at the -DC or +DC position, depending on the polarity of the signal applied across the test leads. To measure AC voltage set the functions switch to the AC position. For resistance measurement, the switch may be set in either the +DC or -DC position. The polarity of the internal ohm- meter battery voltage will be as marked at the jacks when the switch is in the +DC position and reversed in the -DC position.
4. Zero Ohms:This control is used to compensate for variation in the voltage of the internal batteries, when making resistance measurements.
5. Circuit Jacks:There are eight jacks on the front panel marked with the functions they represent (FIGURE A). These jacks provide the electrical connections to the test leads. The COMMON (-) jack is used (in conjunction with the black test lead) as the reference point for the measurement of all the functions with the exception of the 10 A range.
6. Pointer Adjust For Zero: With the Volt-Ohm-h3iKunmeter in a operating position, check that the pointer indicated zero at the left end of the scale when there is no input. If pointer is off zero, adjust the screw located in the cover below the center of the dial. Use a small screwdriver to turn the screw slowly clockwise or counter clockwise until the pointer is exactly over the zero mark at the left end of the scale. With the indicating pointer set on the zero mark, reverse the direction of rotation of the zero adjuster slightly to introduce mechanical freedom or “play”, but insufficient to disturb the position of the indicating pointer. This procedure will avoid disturbances to the zero setting by subsequent changes in temperature, humidity, vibration, and other environmental conditions. This control is used to compensate for variation in the voltage of the internal batteries, when making resistance measurements. There are eight jacks on the front panel marked with the functions they represent (FIGURE A). These jacks provide the electrical connections to the test leads. The COMMON (-) jack is used (in conjunction with the black test lead) as the reference point for the measurement of all the functions with the exception of the 10 A range.
7. Reset Button: The white button to the right of the output jack is the reset button of the overload protection circuit.
DC Voltage Measurements 0.25 Through 0-250V Range
a. Set the function switch at +DC (FIGURE B).
b. Plug the black test lead into the – COMMON jack and the red test lead into the + jack.
C. Set the range switch at one of the five voltage range positions marked 2SV, lOV, 25V, 50V or 25ov.
NOTE: When in doubt as to the voltage present, always use the highest voltage range as aprotec- tion to the Instrument. If the voltage is within a lower range, the switch may be set for the lower range to obtain a more accurate reading. Be sure power is offin the circuit being measured and all capacitors discharged.
d. Connect the black test lead to the negative side of the circuit being measured and the red test lead to the positive side of the circuit.
e. Turn on the power in the circuit being measured.
f.Read the voltage on the black scale marked DC. For the 2.W range, use the O-250 figures and divide by 100. For the lOV, 50V and 250V ranges.read the figures directly. For the 25V range, use the O-250 figures and divide by 10.
NOTE: Turn offthe power to the circuit and wait until the meter indicated zero before disconnect- ing the test leads.
Direct Current Measurement
Direct Current Measurement 0-1mA Through 0-500mA Range
Direct Current Measurement 0-1mA Through 0-500mA Range (Cont’d)
a. Set the function switch at +DC (FIGURE C.)
b.Plug the black test lead into the -COMMON jack and the red test lead into the +jack.
C. Set the range switch at one of the four range positions marked 1mA, 10mA, 100mA or 500mA.
d. Open the grounded side of the circuit in which the current is being measured. Connect the VOM in series with the circuit. Connect the red test lead to the positive side and the black test lead to the negative side.
e. Turn the power on. Read the current in milliamperes on the black DC scale. For the 1mA range, use the 0-10 figures and divide by 10. For the 1 0mA range, use the 0-10 figures directly. For the 1 OOmA range, use the 0-10 figures and multiply by 10. For the 500mA range, use the 0-50 figures and multiply by 10.
f . Turn the power off and disconnect the test leads.
When resistance is measured, the INTERNAL batteries B 1 and B2 furnish power for the circuit. Since batteries are subject to variation in voltage and internal resistance, the Instrument must be adjusted to zero before measuring a resistance, as follows:
a. Turn range switch to desired ohms range.
b. Plug the black test lead into the -COMMON jack and the red test lead into the +jack.
C. Connect the ends of test leads together to short the VOM resistance circuit.
Resistance Measurements (Cont’d)
d. Rotate the ZERO OHMS control until pointer indicated zero ohms. If pointer cannot be adjusted to zero, one or both of the batteries must be replaced.
e. Disconnect shorted test leads.
Measuring Resistance a. Before measuring resistance in a circuit, make sure the power is off to the circuit being tested and all capacitors are discharged. Disconnect shunting components from the circuit before measuring its resistance. b. Set the range switch to one of the resistance range positions as follows (FIGURE D):
1. Use R X 1 for resistance readings from 0 to 200 ohms.
2. Use R X 100 for resistance readings from 200 to 20,000 ohms.
3. Use R X 10,000 for resistance readings above 20,000 ohms.
C. Set the function switch at either -DC or +DC position:
Operation is the same in either position except if there’are semi-conductors in the circuit. Adjust ZERO OHMS control for each resistance range.
d. Observe the reading on the OHMS scale at the top of the dial.
NOTE: The OHMS scale reads from the right to left for increasing values of resistance.
e. To determine the actual resistance value, multiply the reading by the factor at the switch position. (K on the OHMS scale equals one thousand.)
Resistance Measurement of Semiconductors/Diodes&CR’s
If there is a “forward” and “backward” resistance such as in diodes, the resistance should be relatively low in one direction (for forward polarity) and higher in the opposite direction. Rotate the function switch between the two DC positions to reverse polarity. This will determine if there is a difference between the resistance in the two directions. To check a semiconductor in or out of a circuit (forward and reverse bias resistance measurements) consider the following before making the measurement:
a. The polarity of the internal ohmmeter battery voltage will be as marked at the jacks when the switch is in the +DC position and reversed when in the -DC position.
b. Ensure that the range selected will not damage the semiconductor.
C. If the semiconductor is a silicon diode or conventional silicon transistor, no precautions are normally required.
NOTE: The resistance of diodes will measure differently from one resistance range to another on the VOM with the function switch in a given position. For example, a diode which measures 80 ohms on the R XI range may measure 300 ohms on the R X 100 range. The difference in values is a result of the diode characteristics and is not indicative of any fault in the VOM.
77/75/73/70/23/21 Series II Multimeter
Readings are shown on the liquid-crystal display. If the input is too large to display, OL (overload) is shown and the entire bar graph lights. Select the next higher range. The “Replace Battery” is dis- played when about 100 hours of battery life remain. Replace the battery. Bar Graph The bar graph shows readings relative to the full scale value of a measurement range. Polarity is indicated. The bar graph has a much faster response time than the digital display. Standby If the meter is on but not used for an hour (20 minutes in diode test) the meter enters “Standby” to extend battery lift. In standby, the meter shows bar graph segments. To resume operation, turn the rotary switch and press the push-button.
For more information, please download the manual: