Resistance (is futile)

Hi guys and gals! I have my bike torn down to the frame and while it's apart for the fall/winter seasons I would like to do some bench testing of the electrical components to get a good idea on what I should replace before I put it back together. Sounds like a good idea, right? Well, it turns out that I can turn a wrench just fine but when it comes to putting the red and black wires from my VOM on an electrical circuit and understanding what the numbers mean on the screen (and for that matter where my dial should be) I'm at a complete loss.

I just want to be sure that I'm testing this stuff right before I drop a butt-load-o-cash on new used stuff. (BTW the instructions for this thing basically just tell me how to not electrocute myself!)

My VOM has a dial. On the left side it's got (in order moving clockwise from "8 o'clock" position) a circuit tester (I understand that one!); 200; 2k; 20k; 200k; 2m. On the right side of the dial is the voltage meter part (ranging from 2v d.c to 600v a.c.) I get that side too. It's just ohms that I don't get.

My FSM states that "to check the stator coil, connect the ohmmeter between each pair of white wire terminals (3 separate readings). Each reading should be 0.5 ohms +/- 10% at 68 deg." I did that and on the "2k" setting it read 0.5 ohms on all three connections. Did I do that right? On the coil assembly plug (the green and brown wires) the resistance was 89 or some sh&t! However, the resistance between the individual plugs and alt. brushes was pretty low leading me to believe that I need to clean the alternator rotor surface where the brushes make contact (or am I just in trouble on that one?).

If you're still reading (thank you for sticking with me!) could you tell me at which position should my dial be set for an accurate reading? Please?

Oh, and while I'm at it what is the best way (for those of you that have!) to clean the stator/coil assembly and/or alternator rotor?

Any response would be greatly appreciated!

 

Just to clarify, your meter is a needle-type, i.e. not digital? If so, the meter's faceplate should be graduated for the different ranges. Make sure you're looking at the right multiplier. Chances are, your ohms scale is incremented in some division of 2 (20? or 200? or 2000?), with you needing to shift the decimal yourself depending on what range you're working in. A clear picture of your meter would be helpful.

 

0.5 ohm is a very small resistance (virtually no resistance at all) & you should be using the 0-200 ohm range

If I put mine on the 0-200 range & touch the 2 probes together it shows a resistance of 0.3 ohm, just for the leads!

When measuring resistance there is no +ve or -ve lead. They can be connected either way to the item being tested.

 

Adding to what the other guys said.... When measuring resistance you want to choose the smallest range on the meter that is larger than the resistance you are trying to measure.

So, for .5 ohm you set your meter to the 200 ohm range. If you were testing 450 ohms you'd choose the 2K range on the selector.

To be precise you need to know the resistance in the leads (.3 ohm in oldgoat's meter) and subtract that from your reading. When measuring low values having your fingers on the probes will also skew your reading. Test leads with alligator tips can be handy.

 

Thanks everyone for helping to clear things up! Here's a picture of the working parts of my VOM. D'oh, why didn't I post it before?

 

Looks like it is a "Digital Multi Meter" to me DMM

I second what Micarl says. The readings 200, 2K and so on are the maximum readings the meter can indicate when set on that scale. So always use the smallest scale required to get the truest reading. So redo your test but set the scale to 200 this time. (and subtract the resistance reading of your leads)

 

Thanks again everyone! You all really helped to clear it up! Such a great forum.