Ahhh what a nice sunny day for a cruise.
If only the bloody car would start, that is! Ran fine yesterday.
Battery is almost new and reads some 11.6 volts before I started it up.
Started it up with the help of the battery from my other car.
At idle I read about 13.6 - 13.7 on the battery, 13.7 when I rev it.
Took it for a little cruise, voltage didn´t change. Normally it goes to about 14.5 volts when charging so I figure the alternator is dodgy (my 100 watt headlights may have finally killed it off!).
Is this an accurate assumption?
Now to replace it...
Looked up alternators in the EPC and I find 70, 90, 100 and 120 amp versions. Would any one of these fit?
Is this another of those "the bigger the better" situations?
Would be nice to have the correct part number handy when I´m searching for my alternator tomorrow :-)
My C20LET is the early 1992 type with the early type idler/cam belt etc.
No, that battery at 11.5V is as dead as a dead cucumber.
The voltage out of the alternator varies with the battery voltage to a degree. With a pretty charged battery, expect it to be around 14.4V. However with a battery as flat as that, expect it to be about there!
The voltage difference between the battery + the alternator output is what causes the charging current to flow. The chargin current rises with repect to the difference in the two voltages. So if the battery is at 11.5V, and the alternator output was 14.4V, the charging current would be greater than when the battery was 13V, and the alternator voltage was 14.4V
The alternator output is a contsant current source, rather than a set voltage output. When the battery is so low, the charging current is limited before the alternator voltage output has reached it's full output.
Hope that makes some sense to you.
What was the voltage across the battery when you returned from a run, with the engine off? You need to check that current is not being drawn from the circuit when the ignition is off. It could be the alternator, but I'd want to do a few easy checks first.
Check the battery voltage with the ignition off. I presume it's dead again.
Disconnect the battery negative terminal, and charge the battery up. With the ignition still off, connect an ammeter between the negative terminal and chassis to see if any current flows. If it does, then it's the loom discharging the battery, and not the alternator being dodgy.
If not, then connect the baterry back up again, and measure it's voltage. The voltage should be 13V, or there abouts for a well charged one.
Turn the engine on, and check the battery voltage again. With the battery charged, the alternator output should be about 14.4V
It doesn't sound like a dodgy alternator, because I would expect it not to charge at all. The fact it's putting 13.5V out over an 11.5V source means it's whacking out a fair bit of juice...
I just did a little more testing.
Plugged in my charged battery off the other car. Voltage initially 14 volts with engine running, and as time went by (engine still running) the voltage actually dropped....!
Conclusion: Dodgy alternator :-(
The low-voltage battery seems to charge thoroughly when I put it in the other car, so on the plus side the battery seems to work okay.
Is there any way to match a Bosch part number against GM part numbers?
My dodgy alternator reads...
0 120 488 192
K1 > 14V 28/70A