PeachParts Mercedes-Benz Forum - View Single Post - Can I test for and fix an overcharged battery?

G-Benz · #8 06-18-2004, 01:13 PM

From a physical perspective:

Jackd said it first...a battery will not hold an overcharge. It is designed to produce a nominal 12V at a certain rated current draw, period.

Because a battery will lose the ability to maintain the required current at that voltage for an extended period, the alternator is designed to replenish the battery and allow it to do its job while the engine is in operation.

The alternator is pulley driven, so the rate it will do so is dependent on engine speed.

By itself, the alternator is incapable of maintaing a steady voltage stream under varying loads...that's what the voltage regulator is designed to do. The voltage regulator is also designed to apply more voltage as load demands deem necessary.

When the voltage regulator fails, it either prevents the alternator from providing sufficient voltage or too much voltage. When the alternator fails, it simply does not provide adequate current.

When too much voltage is applied to the battery via the alternator/regulator, the battery electrolytes begin to boil. The worst case scenario will be a battery explosion!

When my regulator went out, the voltage was 17.5 at the terminals...the smell of sulphuric acid venting out of the battery caps was my first indication of a problem.

If you have an overvoltage problem, it can create a variety of electrical weirdness.

I don't know what year your car is, but the regulator is an external component on some alternators, and internal on others.

The internal ones are integrated and require alternator replacement...