Thursday, May 24, 2007

ALTERNATOR IN CARS

How to ensure your alternator rating is correct for your car, including additional equipment & your driving routine.
1. Ensure your battery is fully charged;
2. Disconnect cable from Alternator + post (take care, the cable is live - if unsure, disconnect the Battery + terminal first, reconnect after! Insulate the cable terminal to prevent short circuit);
3. With respect to your electricity usage write down your worst prolonged driving condition, even if it happens but once a year (for instance driving for several hours at night, in hot weather, rain, pulling a trailer. This equals low beam, air cond in 'medium', fog lights, wipers, stereo, rear defogger, etc.. Less than, say, half-an-hour situations need not be considered);
4. Attach an ampmeter to the battery positive cable as shown on the picture (negative cable can also be used, if more convenient);
5. Start the engine, turn everything on you have written down under item 3 and hold the rpm on about 1500, or higher;
6. If they are powered by electric motors, wait for the radiator cooling fans to be turned on (or turn them on by bridging their relays);
7. Write down the highest reading on the ampmeter;
8. Turn everything off (ignition switch last);
9. Add 20% to the figure obtained under item 7 and THAT IS WHAT YOUR ALTERNATOR MINIMUM RATING* SHOULD BE! In most cases you'll discover that the rating of your alternator is well below that figure, and that's where most of the charging problems are hidden (for multiple batteries system calculation ref. item below);
* RATING = current output of the alternator shown on a label. Usually indicated as, for instance, 80A
10. When finished, reconnect your alternator (with the engine NOT running).
Take care - same as item 2!

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