Henry Guenter is a former service manager for Massey Ferguson.
Many people are reluctant to tackle electrical problems in farm equipment. They can’t see the current passing through the wires, which can make it challenging to diagnose.
Overcoming this fear of the unknown starts with understanding the basics of diagnosing problems with electrical circuits. At the least, it might make it easier to pick up the right part when there is a problem.
Basic tools
Current is the flow of electrons along any conductor, such as a wire. It is measured in electrons per second, or amperes. If working with oil, it would be called gallons per minute.
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An amp meter, hooked up in series into the circuit, measures amperes. Because all the current goes through the gauge, it is important to use the right gauge. A 50 amp gauge will not handle the battery wires going to the starter, which can have 500 amps going through them.
The force required to move the current through the wire is measured in volts. The switch might be turned off so no current is flowing, but if the battery is hooked up, the force is still there.
Volts can be measured with a voltmeter hooked up across the battery posts. It will show battery voltage whether or not something is running off it. There can be volts without flow, but there cannot be flow without volts.
Sometimes a poor connection is not evident. Put a voltmeter on the two points in the connection, such as the battery post and the cable connected to it. If the connection is good, there will be no reading. Be careful here. A bad connection can blow up the gauge.
The resistance to this flow between two points is measured in ohms by an ohmmeter, generally the sharing meter body with the voltmeter. It has batteries in it that send a measured amount of current through a conductor, such as a wire. Be careful to disconnect other sources of current from the conductor before attaching the ohmmeter. It is used by putting the leads from the gauge on each end of the conductor.
All conductors have resistance but if there is an opening somewhere, such as a break in a wire, it will show infinite resistance. This is the best way to measure a connection. If there is no resistance when measuring from post to wire, it is a perfect connection. Any reading means a poor connection. An infinite reading is no connection at all.
A person can sometimes tell whether there is a poor connection in a machine’s wiring by checking if it is getting warm or has corrosion on its terminal points. A wire that is too thin for its job can get hot because it has a lot of resistance to current flow.
Battery
The battery stores electricity and is used in every circuit. When buying a battery, assume it is ready to go.
The maintenance-free battery has a long shelf life and is not nearly as subject to overcharging as the older style units you had to service. It is made of different materials.
Wet, charged batteries can “self discharge” in 90 days at room temperature.
When storing batteries, remember a fully discharged battery will freeze at -8 C. A fully charged battery won’t freeze until it gets to be -59 C.
When a battery is discharged too much, it becomes sulfated. These can be brought back with a slow charge of one or two amps. If they are being charged too fast they will start heating. When that happens the plates will warp and cells will short out. Slow charging can be used to check what shape the battery is in by how much charge it will take.
The charging of a sulfated battery can take as long as 100 hours. If the battery is left too long in a sulfated state it will get hard and it will never come back, but don’t give up right away.
To test a battery, the best method is to put a load on it. It is well worth the money to buy carbon pile. Set the load on the battery to three times the rated amperage for 20 seconds. The voltage on the battery should not be lower than 9.6 volts at any time during the test.
Taking care of the battery will make it last longer.
- Keep it clean. It is common for the battery to discharge through the dirt accumulated on the battery’s top.
- Do not cycle it too often. This happens frequently if lights have been added to the system and the alternator isn’t big enough to handle the load. If the charger must be left on overnight so the combine can start the next morning, it cycles the battery. Every time this happens it takes life out of the battery.
- Do not overcharge. This likely happens where there is a malfunctioning regulator. Once I had a combine that had a poor connection from battery ground strap to the frame. Since the regulator was reading battery voltage through the ground, it kept on reading as a low battery. As a result it charged as much as it could. This caused the electrolyte to turn into hydrogen and oxygen gasses, which washed down the plates and weakened the battery.
- Do not undercharge. This causes some of the plate surface to sulfate and harden, which reduces the capacity of the battery. This will be noticed when trying to start a machine on a cold morning. The reserve is less than it used to have.
Battery replacement
When buying a new battery consider two things – cold cranking amps and reserve capacity. CCA refers to the number of amperes the battery can deliver at -18 C for 30 seconds. Reserve capacity is the number of minutes a battery will deliver 25 amps. In hot weather, the engine is just as hard to start as in cold weather. Generally, the more expensive a battery is, the more CCA and reserve it has. I have also noticed that the heavier a battery is, the more CCA it has, even though the rated amperage is the same.
Charging circuit
The alternator and regulator go together and should be tested together. On the back of the alternator are three terminals or variations. There will be an output terminal, which has a wire going to the battery, maybe through the solenoid for the starter. It also has a ground terminal. It is grounded to the frame of the alternator. There should also be a regulator terminal.
I recommend getting a book on the subject or a repair manual. I will run through two tests to show how simple it is.
With all accessories and circuits off, attach the voltmeter at the regulator and the ground. It should read less than 0.1volts. A high reading indicates a shorted diode or key switch. With only the key on it should read two to three volts. With the engine running, it should read 15 volts. When the voltmeter is switched to the output terminal, the voltage should drop one volt. For the battery to charge, the regulator terminal needs to be one volt higher than the output terminal.
If you are brave enough to take the alternator apart, the diodes can be checked with an ohmmeter.
Starting circuit
The starting circuit consists of a switch and the starter. The starter uses a lot of current so it needs a relay switch that can handle a heavy energy flow but needs only a small current to switch it on.
The relay in this case is a solenoid switch, and is usually found on the starter. There are two posts on the solenoid, one connected with the battery and the other to the starter. Inside the solenoid is a plunger with a big washer on one end and two coils of wire wrapped around it.
When the ignition switch is turned on, it sends a current through both wires, making it a powerful magnet. This pushes the washer against the two posts connecting battery to starter.
When the engine starts, one of the two coils of wire around the plunger gets fed current in the opposite direction so the plunger is not magnetic any more. A spring pulls it back, disconnecting the starter circuit.
The starter circuit is easy to test, but make sure the machine is out of gear. Have someone sit in the operator’s seat. Put a jumper wire from the battery post on the solenoid to the small post going to the ignition switch. This eliminates the wiring and the ignition switch.
If that did not solve the problem, put a jumper directly across the two big posts on the solenoid. This will eliminate the solenoid.
I hope your machines start as well as your new year.
