How Long Is That Board? COLUMN BY JUAN C. GRUBE Over the years Tve talked about there being more to testing alternators than just checking volts and amps. This has literally become a soap box issue for me. However, I think we should go back to the first step in alternator testing, checking “volts” and “amps.” When we test an alternator we have two primary variables to check, “volts” and ‘“‘amps.” We cannot check for one variable if we do not control the other. Think of it this way. If we measure the length of something with a tape measure we have to make sure that the start of the tape measure is at one end of the item we want to measure. If we don’t know where the start of our tape measure is located then the length we read on the tape measure will probably be in error. Something that is really eight inches long might measure nine inches if we don’t control where the tape measure is. I realize that this is so obvious that it sounds ridiculous, but checking for “volts” and “amps” is the same. We can’t read one without knowing where the other is. There are two practices for doing this, both of which have merits. First, the traditional method to check for maximum alternator output amps is to apply our carbon pile load until charging voltage is reduced to a control pint. What should this control point be? Nominal static battery volt- age— 13.2 volts. The voltage of a fully charged single battery cell is 2.2 volts. Therefore a six cell battery is 2.2 volts x 6 cells = 13.2 volts. Logically we should apply the carbon pile until our charging voltage is reduced to 13.2 volts, which is the point at which the alternator is charging at its maximum amperage charge rate with no current going into or out of the battery. All the energy is being dissipated as heat in the carbon pile. When we test alternators for maxi- mum alternator output amps we should always use a consistent “control” volt- age, because this is what gives us consistent test results. Our “control” voltage for measuring maximum alter- nator output amps is 13.2 volts. Now that we have agreed on using 13.2 volts as our “control” voltage let me throw in a monkey wrench. I actual- ly prefer to use 12 to 12-1/2 volts which is below nominal battery voltage! Why? It’s called the real world. Because the odds are that your rebuilt alternator will be installed in a vehicle which has a bat- tery that’s not fully charged. I know you told the mechanic to test and recharge the battery before installing the alterna- tor. If you believe every mechanic tested the battery and then put a charger on it for a couple of hours you also believe in Santa Claus! If we’re being honest with ourselves we have to accept this. In my opinion, using 12 to 12-1/2 volts more closely allows you to see the performance of your rebuilt alternator in the same manner that your customer will, with less than a fully charged bat- tery. In the real world, the customer is your end quality control test anyway! The second testing method is just the opposite of the first. Apply your carbon pile load until your ammeter reads the intended amperage rating of the alterna- tor being tested. Then observe the volt meter. It must then be at or above your allowable voltage range. We’re really backing into the specification using this method. You are in the best position to decide what “control” voltage or amperage that you use. But for consistent testing results, use a “control.” Juan Grube is president of JIMCO, Inc., Raymore, Mo.