Charging Systems

Charging systems are required to make up the volume of current used in a complete circuit. A complete circuit draws current proportional to the resistance it encounters while flowing within an electrical conduit (wire). A charging system has a permanent magnet alternator or an electromagnetic alternator, or a generator. We will clarify each one however they all 3 produce a flow of electrons or current.


An easy way to understand this electricity flow thing is to think about an air tank (battery) an air compressor pump (generator) conduit piping or tubing (conductor or wire). You can fill up an air tank and go anywhere with it as with the 12 Vdc battery. If you have 12 pounds of air pressure in an air tank and 12 volts of dc electricity in a battery they would act in the same manner.


To generate this dc electrical flow of electrons (amperage) we need to rotate a pump which is the generator in this case. Electrical energy is made obvious by the changing of a magnetic field next to a coil of wire. As a magnetic field becomes present something happens in a coil of wire and when the field is collapsed or moved away from the coil a spark of electricity emerges. This is like walking over carpet and touching metal to get a spark. Just combing your hair will generate a potential voltage of 2000 volts and that's why you get a spark. This is one good thing to know now, 100,000 volts (100Kv) will jump a gap in air one inch (1"). So the voltage is gained by compressing electrons within a confined storage system (battery).

The picture on the far left is a common generator, a generator produces D.C (direct current) as the shaft is rotated by a belt frictionally attached to the pulley. A generator can be rotated by any power source at any speed, the faster the pulley is rotated the more dc voltage you get. For example; at 200 revolutions per minute 5 volts is present at the two lug terminals on the generator case housing and at 400 rpm 10 volts dc, 600 rpm 15 volts and so on. Once it rotates fast enough the voltage goes higher and higher so it needs the regulator on the far right to regulate the amount of voltage that is charged into a 12 Volt battery.


We know that electrons are volume and referred to as current, those added up in a volume produce a measureable voltage. Voltage is like pressure in air tanks so if you take two tanks and connect them together with a pipe or tube the air pressure would travel from the highest pressure tank into the lower pressured tank until the two were equal. That is how current travels also, a 12 volt battery that has 12.59 Vdc (E) or electromotive force cannot be charge from a charger producing 12.59 Vdc. The charging source voltage needs to be higher, when the voltage output from a battery charger goes to 12.6Vdc the battery will only charge or accept more volume of current until the battery goes to 12.6 Vdc which takes only a small amount of charge.


For example on a battery charger there are current settings, 12 Vdc and 2 amps, 15 amps, 50 amps or a hot start 200 amps. If you use a DVOM to check the output voltage of the charger you will find at 2 amps charge rate the voltage output is 13 and at the hot start 19 Vdc or so. you can see that more pressure in volts from the charger the more volume of current or amperes will flow from the higher electrical pressure (E) into the lower pressure battery. When you hook up battery cables directly to a generator it will turn and become a motor.

A generator has permanent magnets which are simply permanent in the aspect of a block of metal or some magnetic piece that has a magnetic field. An alternator in an automobile is different which we will detail later in this text. Alternators simply produce alternating current or AC exactly like what you have in your house and that has to be turned into or changed to direct current. A regulator does not change the AC to DC it regulates the voltage into a battery. A rectifier (diode) is used to rectify the alternating current into direct current. The middle picture is a magneto or magnetron type of charger, that means it has permanent magnets that are alternated in polarity when assembled into the pulley housing, 1 north, one south, one north one south and so on. As this pulley is rotated the magneto charging produces an alternating current that needs rectified into dc and then it can be stored within a battery.

Stator and Components


This set of components are commonly found on most lawn mower small engines, they are a good example.

In the picture above there are two rings, these are called stator rings in most all applications but they are called an alternator in the john Deere parts book. This application in the small engine produce an alternating current (AC) and have one copper wire wound around the metal pieces of the round ring. As a magnet is passed by these metal pieces wound with wire a spark is produced containing alternating current. Alternating current cannot be stored and has to be converted into DC (direct current).

In the picture above there are two round ring looking pieces, they are called stator's normally by most all mechanics but in the parts book for a John Deere D-120 it is called an alternator. Go to our Part Name page of this site to look what things are called by other manufacturers. That is the one very important issue when trying to find the part you need.


As seen in the picture one stator has two wire ends, it is made from one copper wire wound around pieces of metal and ending up looking like a ring of wire. As magnets pass by the individual coils in the ring the alternating current is produced and can be measured on the AC setting of the DVOM. Also a resistance can be measured with the engine off on the Ohm scale of the DVOM.

The Stator's in the above picture look like rings with two wire ends. This is simply another form of a coil of copper wire. One piece of copper wire is wound around and around blocks of metal until they form a ring. These two are examples found in most all small engines and is called an alternator in the John Deere D-120 parts book. Technically this ring is actually called a stator in most all other generic mechanical applications. That's why when looking up parts for your equipment you need to know what that manufacturer call the piece your looking for and you can go to the Part Name page of this site and look up some generic parts always needed.


This stator with one wire can be tested easily, if your stator is on your piece of equipment and your battery fails to charge then you can un plug the two wire ends and run the mower. Since the stator produces AC (alternating current) you will need to set the DVOM dial on the AC setting 100 volt scale and run the engine. The AC voltage should be between 26 Vac and 40 Vac. If it is below that your stator is not working properly. The reason you need a minimum of 26 Vac is because when changed into DC it is chopped in half meaning @ 26Vac the maximum voltage in DC would be 13 Vdc. At 13 Vdc the battery will charge very little but would maintain most likely.

Think of the AC electricity as a wave in the ocean, when you look at a wave in the ocean from the side it has a top peak and a bottom peak. Half the wave is on the topside of the horizontal surface of the water and half is below the water surface. This is a full peak to peak wave view and when the wave is said to be 15 feet the entire peak to peak is around 30 feet. 15 feet + and 15 feet -. AC electricity looks exactly like that on an instrument called an oscilloscope and has a 0 horizontal line and peak to peak in the vertical axis. So when a wave is chopped half it's height is effective and that's what happens to the AC wave on the oscilloscope. A 26 Vac peak to peak will only give you 13 Vdc which is under the 13.2 potential the battery could maintain. 

I went out on a service call for a situation of the engine not rotating when the key switch is turned to the start position, as seen in all the battery voltage tests normally you will find between 12.59 to 13.07 Vdc when measuring a good battery. This one measured 12.6 Vdc on the DVOM but as the key switch was rotated to start position the battery voltage dropped to 6.96 Vdc and within a second or so dropped even further to 4.54 Vdc. This indicates that under a load the battery voltage is dropped to whatever is on the meter. This battery has lost it's capacity by being run down and not sufficiently charged. Even though the no load test was good this battery failed at the load testing. We are going to replace the battery and test the charging system.

We have purchased a new battery from NAPA and unwrapped it, you can see the battery voltage is 12.56 which is less than the battery measured in the previous pictures @ 12.6 Vdc. The new battery started the engine immediately with no hesitation and as you can see the charging system voltage brought it up to 14.13 Vdc as soon as the engine started. This is an indication that the charging system is charging the battery. This reading can be between 13.5 Vdc and 18 Vdc to show that your charging system is working.