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Re: 1988 900T alternator out put? Posted by Ari [Email] ![]() ![]() In Reply to: 1988 900T alternator out put?, grlyd, Fri, 21 Sep 2007 16:38:29 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With the car turned off, the battery voltage should be around 12.1 to about 12.6 volts. Turn on an electrical load, like hitting the brake pedal, and the voltage will drop some. A drop to the high 11 volts would be reasonable - much more is a sign of a bad battery.
The voltage on the battery should be around 13.0 to 14.5 volts when the engine is running. Yes, quite a spread. When the engine compartment is cool and the engine running above 2Krpm or so, I'd expect to see around 13.5 or more volts. The engine at idle, low 13 volt range - lower with more electrical loads, like blower motor at speed, headlights on, brakelights on, etc. The alternator output voltage will change with engine speed (higher RPM = higher voltage), temperature (hotter = lower voltage) and electrical load (more load = lower voltage).
As long as the voltage on the battery is 13.0 volts or more when the engine is running, the battery is charging. If you see that the voltage isn't up to snuff, replace the voltage regulator - it's the diamond-shaped device on the back of the alternator. The brushes are integral with the VR, and the brushes wear. Badly worn brushes will results in low alternator output voltage.
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