measuring battery or charging voltage is about the same as gauging the fight of a dog by its bark. I think it is great when people take on their own repairs. I love it when they are successful. I dont like it when that success is by chance, and the reason for that is on the odd chance they got it right, it becomes the holy truth. we deal with this every day on this forum regarding hard starts, and now the subsequent fiery death of a xt1200z. the lack of understanding on fuel injection, and electrical, is not mind blowing. Yeah, I said it is not mind blowing. Why? These are very difficult concepts to understand. Better yet, it seems that once someone has a false truth, they shut off any possibility of learning. Awesome, in the sense that it is worthy of awe.
So, what can we learn about electricity that will help us to know that 12 volts measured at the battery means about as little as possible? It's simply difficult. I can't get to the hard stuff without the easy
voltage: the force behind the electrons
amperage: the quantity of electrons flowing past a given point per second (does the work)
resistance: the resistance to the flow of electrons (usually resistance is where the work is done)
so, easy question: Can you have voltage without amperage?
Yes! This is important. When you are testing a battery for voltage you are testing for the approximate force on the electrons. A good example would be if I asked you to lift a one pound weight as fast as you could and then conjectured that at the rate that work was done, you could probably bench 365 pounds.
Can you measure current with your DMM?
Yes and no. Most home use DMM's have the ability to measure small circuit amperage, usually in the range up to 10 amps or so. This means you can't measure the current drawn to light a bulb, or run your fuel pump, or turn the starter. For an Amp clamp DMM, which I am sure a few guys have, they do a great job of measuring to the rated amperage of the tool....but....
Can you see instantaneous changes in values with a DMM?
No, well, not unless you have a really expensive meter, or oscilloscope. Fewer of you have this than you know. What does this mean? well, unfortunately, most DMM's have a really slow resolution. This means that they are sampling data that they display, and usually to the tune of half second intervals. Even if it were .01 second sampling, much of the issues cannot be guaranteed accurate as displayed, and most meters that record peak values dont assure that the peak is the measured vs displayed.
Back to the last one, Resistance. Can you measure it with a DMM?
Yes, and no. You can learn so much a so little from this measurement. A good test would be to measure resistance through a light bulb. They are pretty low in resistance (.3 ohms), but yet generate lots of heat and light and consume electricity. So, how much is too much resistance in a system? Honestly, it could be so little that you think your connection at the DMM leads is at fault. A broken wire with ends that are touching can't carry much for current, but as a DMM tests, it may look like .1 ohms.
What can we measure that will tell us anything?
well, we need to go back to the part of the lesson that we didn't cover. This reminds me very much of teaching high school students. Everyone wants to just "do" without having to learn. That learning thing takes time, and isn't much fun. Ohms law states that the relationship between volts, amps and resistance is:
V=A*R, or for the advanced V=I x R. Voltage on its own is pretty useless, voltage as a result of work being done (amps pushed across a resistance) tells a lot. Using the starter as an example: measuring voltage between the positive of the battery and the positive connection at the starter can tell us a lot, assuming that the information that we get with our DMM is not missing any micro spikes or plummets, and that the bike takes longer than 2-3 seconds of cranking. An oscilloscope would show a wave form (ups and downs correlating with effort to compress each cylinder), DMM will give you a slightly fluctuating number.
How many volts should we have from one end of a conductor to the other? As long as there are not loads (resistance), 0 volts should be "used", so it should measure the same as measuring positive to positive both on the battery, or 0 volts. This test is called voltage drop testing. Because it relies on the relationship of VIR, and does so when there is an active load on the components, it is accurate in diagnosing problems. If any Voltage is measured along this positive conduit, the connections or the relay are to be suspected.
How else can this be used? test batteries with a load. How many volts does it have when cranking? lights on? These are far more important numbers to look at and will tell you the story of your batteries condition far better than any static state voltage test can or will.
Disclosure:
What I have typed above may contain errors. Reading it does not make you an expert. Attempting work on your own vehicle can be hazardous to you or your vehicle. Attempting work without real training can lead to unsafe or damaging conditions. Consult with experts as needed.
