I suspect that my battery does not receive enough power from the generator. How do I verify that? I know that involves a voltmeter, but what are the exact things I'm measuring and how?
I have a Skoda Felicia 97 1.3L, battery is standard and 1.5yo. Idle RPM seems to be a little low, but that's a separate question once I have proper data from the question above.
First thing is to check the Battery, see my post here.
Provided your battery is good, the following will let you know about the alternator.
Start the vehicle and let it idle. The voltage should be about 2 volts above open circuit voltage.
You can also do a loaded voltage output test. Turn on the high beam headlamps, AC on high, rear defogger etc. Bring the engine RPM up to 2000 RPM and check the voltage at the battery. It should be at least 0.5 volts above open circuit voltage.
You also need to check for AC ripple to make sure the diode rectifiers are still good. Put you meter on AC volts put the black lead on the battery ground and the red lead on the output lead of the alternator. You shouldn't have more than 0.5 AC volts, if you do the alternator is bad.
Most auto parts stores in the USA will check you battery and alternator for free. No idea what's available in Russia but it's worth asking.
If you'd like to see if your alternator is working, first you need to know what your battery is reading with the engine off. Put your multi-meter on vdc reading and test your battery. It should be about 12.6vdc if in good shape. Next start your engine. Your reading at the battery should be somewhere around 13.1-13.6vdc. It may even be a bit higher than that right after start-up (say in the 14vdc range), then settle down into this area. It may fluctuate a little bit (like .1-.2vdc), but nothing erratic. Most vehicles have what is called an "idiot light" in the instrument cluster which will come on if the alternator is not producing the amount of voltage it needs to sustain the battery and keep the engine/accessories running. It's really the difference of voltages, off vs running, which you're looking for to assure your battery is charging. If you put your multi-meter onto the battery and it is discharging (voltage constantly dropping), you need to look at your alternator as a source of mischief. If your battery is not charging up to snuff (around the 13.1-13.6vdc) arena, it could also be a source or problems.
You're measuring voltage. Idle could be related to the battery as well, since the battery might be lacking. Post results once you've found out. If it's not (from memory) around 12 or higher, then it's slowly degrading. Charging it does fix it temporarily, but it will die out eventually.
