PTRider wrote on 04/23/09 at 19:16:05:Voltage regulator
directing the alternator output? It just regulates the voltage, doesn't it? The voltage (the alternator output) goes to whatever takes it...low battery, lights, etc.
Yes, a high voltage will soon boil a battery dry.
Here's one test. Measure the battery voltage across the battery terminals with the engine off, after recharging the battery if necessary. A digital voltmeter gives a better reading. Start the engine and measure the voltage across the battery terminals again with the engine running at good speed (the 5000 rpm test is great...what does 5k sound like???). If the voltage is lower with the engine running the charging system is bad, either the alternator or regulator is bad. If the voltage is way too high, the regulator is bad. If the voltage is normally high, up to 15.5 volts as Gort specifies, then the charging system is OK and the battery doesn't hold the charge, the battery is junk or something is draining the electricity away. By the way, a (nominal) 12 volt system should never be 12 volts--that indicates a 50% discharged battery. 12.6 to 12.8 volts is a full charge (2.10 to 2.13 volts per cell). Up to 15 volts is needed to force the charge into the battery for a short time. (Right now I have a tired battery that recharges great but loses its charge when sitting for a couple of days. I'm seeing if it can be rejuvenated by
desulfating with a
Battery Minder trickle charger & desulfator. If it doesn't reclaim this battery in a month or so, I'll buy a new battery.)
I use the word 'directing', figuratively. The circuits in the VR 'sense' that the battery is low, and open an electrical path from the ALT to the battery for charging purposes. When the VR malfunctions, it can act randomly and stop the battery from ever seeing current from the Alt, or always see it, or sometimes see it but at the wrong times, and so on. Now I must qualify this by saying that the systems I have tested and repaired were designed as I have described. It may be possible that someone has newly redesigned this circuitry in some way I have yet to see, but I doubt it. But anything is possible.
Concerning saying that if the battery voltage is lower with the engine running than when the engine is off, which means the charging system is bad; I have seen malfunctioning charging systems put anywhere between 12 to 13 volts into a battery that reads 12 volts when the engine is off. But that isn't enough. The system should have a good 14 volts when the engine is running, at idle. Mine does, however I gave the Suzuki factory shop manual test numbers at 5000 RPM because its always best to quote from the factory specs whenever you are trying solve an electrical problem.
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