charging system blues
I've marked agree on the above two posts because a new battery will still get run down if its not getting recharged.
went back with a meter & had batt volts at each check. i'm thinking "damn amp meters"
Are you saying that everything in the system is showing 12 Volts????
The ammeter shows whether the battery is charging or discharging. If everything is at 12 Volts, especially with lights on etc, then battery voltage is getting everywhere with no loss.
The questions then are:
Why is your voltmeter showing just 12 Volts?
Is the Battery down to 12 Volts?
Is the Alternator putting out only 12 Volts?
Or is your voltmeter bad?
Except when starting, all of the power comes from the alternator, and the alternator should be putting out at least 13.7-14.7 volts.
Internally, a charged battery is 12.5-13.2 volts. So it does provides no current once the alternator is running. It draws power only while recharging.
Your car may or may not have a problem. The only thing you posted that suggests a problem is that you are measuring 12 volts at the battery terminal, and elsewhere too???
As far as the ammeter showing charging: That's normal after starting.
The ammeter showed higher current flow with increasing rpm from idle. That's also normal.
When the battery is charged, the ammeter should show no current in either direction.
The voltage will drop every time it hits resistance or is used to drive something (that something can be a motor, a chemical reaction in the battery, or a lamp). The test light doesn't show how much voltage.
It could be your voltmeter is bad or not getting good connections. Test it against a known voltage like a 9volt battery.
Then recheck the voltage at the Battery terminal and the voltage at the alternator output terminal. They should be very close to the same voltage.
You can do this when the engine is off just so you can see. if one is 12.8 the other should be about 12.8 Volts. If not either something is wrong, or the test probes didn't have good contact with clean surface.
With the engine running, observe the ammeter and measure voltage at the Battery and at the alternator output. The voltages should be within a few tenths of each other.
IF voltage is within a few tenths, then there may not be a problem in the wiring. Verify with some load tests. Move on to figuring out why the voltage out of the alternator is low.
IF there is a voltage drop of 0.5 or more,
there is too much resistance somewhere and it is important to figure out where. In this case, measure the voltage at each connection you can have access to. The first easy one is the starter relay. Then the connectors.
Testing with load. AJ is correct that without any load, there will be no voltage drop. So, once the battery is charged, it will be harder to trace a problem if there is any. You can turn on the headlights, and look for voltage drops on the alternator out put wire and connections. Then turn off the motor and do the same for the battery wire.
Another way to look for resistance is disconnect the battery positive and the alternator output wire. Then measure resistance in the wire. Same deal, work back to the firewall if it shows a lot of resistance. Then remove the bulkhead connectors or go underneath the dash and measure resistance.
Do this methodically and write down every reading and what it is across. Then you'll know if it is the wire from the battery to the starter relay, or relay to bulkhead (includes the fusible link), under the dash, or in the alternator output line and its connection at the bulkead.
If the wiring route is getting confusing. draw yourself a diagram.
Feel free to download and modify
Understanding Charging Systems with Ammeter
