hmmm.. looking at a charging/alternator problem.
DC amp meter shows only around 1 amp charging.
AC amp meter shows 4 to 5 amps charging,
volt meter shows 14 volts.
can the high a/c current show the high voltage but still not charge the battery?
I am wondering if the diodes are bad.
anyone have any experience with this?
Full Version: charging system question.
QUOTE(crash914 @ Jul 2 2007, 09:05 PM) 
hmmm.. looking at a charging/alternator problem.
DC amp meter shows only around 1 amp charging.
AC amp meter shows 4 to 5 amps charging,
volt meter shows 14 volts.
can the high a/c current show the high voltage but still not charge the battery?
I am wondering if the diodes are bad.
anyone have any experience with this?
How did you connect the amp meter? How many amps is it rated for? Just curious...
The diodes (there are three of them) work to convert the AC current to DC. AC is a sine wave and DC is flat. depending on which diode goes you would be charging the same voltage but only half AC and half DC. Really need an O scope to check diodes or an alt/battery tester that checks diode ripple.
Yes... the alternator can be making voltage and not charge the battery if it has a bad diode. In fact, it would ruin the battery in short order.
An alternator makes current that swings from positive to negative with every rotation of the armature. The 4 diodes are one-way valves that only allow the positive current out to the positive post of the battery, and allow the negative current back in from the negative post (for those Electrical Engineers and Physicists out there, yes I know the electron theory, but this is practical electronics, not theoretical). When you have a bad diode, it will short out. That means the "valve" in the diode is stuck in the open position. So negative current is connected to the positive side of the battery 1/4 of the time. This will make the battery discharge 1/4 of the time. Batteries don't like this much, and they will die from it in short order.
I personally would pull out a Oscilloscope and look for a negative wave to show up on the positive side of the battery. Or you can just look for AC volts across the battery.
Or just pull the alternator and have it checked at your FLAPS.
An alternator makes current that swings from positive to negative with every rotation of the armature. The 4 diodes are one-way valves that only allow the positive current out to the positive post of the battery, and allow the negative current back in from the negative post (for those Electrical Engineers and Physicists out there, yes I know the electron theory, but this is practical electronics, not theoretical). When you have a bad diode, it will short out. That means the "valve" in the diode is stuck in the open position. So negative current is connected to the positive side of the battery 1/4 of the time. This will make the battery discharge 1/4 of the time. Batteries don't like this much, and they will die from it in short order.
I personally would pull out a Oscilloscope and look for a negative wave to show up on the positive side of the battery. Or you can just look for AC volts across the battery.
Or just pull the alternator and have it checked at your FLAPS.
I will try the ac volts....my meter goes from 0.1 amps to around 400.
I could swap the alternator...but that is work.
I knew I should get an old oscilloscope...ebay here I come...new tool....
I could swap the alternator...but that is work.
I knew I should get an old oscilloscope...ebay here I come...new tool....
I think what Clay is saying is, the positive half cycle charges the battery and the negative half cycle discharges the battery, thus there is no net charging. Not a good thing to allow for any length of time. Diodes do tend to fail often. The ones used in my high amp alternators are avalanche diodes.
The Physicist.
The Physicist.
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