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!

MULTIPLE BATTERIES IN CARS

Connection as shown on the attached drawing.

If multiple batteries are required to power consumers used while the engine is not running (a fridge, TV set, etc.), the AH/RC of the battery (batteries) must be calculated so that the battery voltage does not drop much below 11 Volts before the engine needs to be started (for simplicity, and if possible, preference should be given to single battery with sufficient AH/RC).

With reference to ALTERNATOR RATING IN CARS above, 20% must be added to the alternator rating figure for every additional battery (or a battery with substantially higher AH/RC than standard).

BATTERY IN CARS

1. Batteries in most new cars are only about 50% good*, often less. The reason is self-discharge of standard lead-acid batteries and the long time it takes from manufacture to the Customer. Once discharged and kept discharged for a period of time the bateries do not accept full charge again;
* '50% good' means their capacity expressed in AH or RC is only 50%.
2. Replacement batteries are also only about 50% good, for the same reasons as above.

Invest in one of these tools, available from all auto shops, and see for yourself. it gives you a crude indication of the state of your battery; for more precise indication a controlled discharge test is needed.

Exceptions are lead-acid batteries that are kept dry and filled with acid & charged immediately prior to delivery/installation. Another exception are special batteries, for instance some of those with 'spiral' contructions; their cost, however, is usually several times the cost of the standard batteries.

CHARGING SYSTEM

Details to be advised.

EMERGENCY VEHICLES ELECTRICAL SYSTEM

Recently we have been asked to investigate electrical problems in a large fleet of emergency vehicles. These vehicles (some 12 different models) were basic cars - some brand new, some with some mileage already - fitted with additional computers, transceivers, search lights, warning lights, electrically powered medical equipment, etc.
# in about half of the fleet the alternators were found to be inadequate (ref. ALTERNATOR IN CARS in our blog);
# in all of the vehicles the batteries were faulty (ref. BATTERY IN CARS, or MULTIPLE BATTERIES IN CARS in our blog);
# in vehicles with dual batteries the two batteries were connected in a way that promoted premature failure of one of the batteries, leading to the subsequent failure of the remaining battery.
Some of these vehicles required a replacement battery (or batteries) every two weeks. Needless to say, the replacement batteries were also faulty (again, ref. BATTERY IN CARS in our blog).
The additional component's wiring & its termination was not done to the standards applicable to the wiring in the original vehicles, the workmanship was poor, which all contributed to a continuous litany of electrical problems.

ELECTRICAL SYSTEM DESIGN COST SAVING

Details to be advised.