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#1130: Tickling the Electrons

Original Air Date: 07.23.2011

   Best Moment

This week on Car Talk, are you ready for some wacko theories? Dennis in California puts Tom and Ray to the test, pondering his friend's contention that the best way to charge a dead car battery is by turning on every accessory in sight. Is there anything to this notion of "tickling the electrons"? Elsewhere in Wackyland, Jenny is convinced that her Civic has a harder time starting when its gas tank's not full; Linda needs to retro-fit her ATV to make it a good Summer sled-dog training vehicle; and mechanic-turned-sculptor Coby learns what happens when you add a few extra tons to a half-ton pickup. All this, plus some choice Last Words, and lots more, this week on Car Talk.

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This Week's Puzzler

3rd Open: Mail--The Poem ??Tom Green??s Auto?? and Puzzler Apology 1:50 Find out!

Last Week's Puzzler

2nd Open: Mail. ??Last Words?? 2:15 from 0128. Also used in 0629) Find out!

Show Open Topic

Gas conservation idea - brick in the gas tank.

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The beauty of alternators is:

by Anonymous

...that the charging current sent to the battery does NOT go through the brushes like it did in the old days of DC generators. ALL of the battery charging current comes from the STATOR (the part that does not turn), and since it is alternating current, it has to go through the diode bridge to get turned to direct current. The brushes of the alternator only carry a small amount of current FROM the battery to create the rotating magnetic field which sweeps over the stator to make the lecktristaddy flow!

Favorite Moment: When Click said the brushes in the alternator carries the electrical current TO the battery. It made me fall off the toilet in amazement as I screamed "NOOOOO!"

The purpose of an ammeter

by Anonymous

The caller with the charging question is mostly right. The purpose of a dashboard ammeter is to show when the battery is taking or giving up charge. The positive battery lead is the only place in the electrical system that can have current going in either direction. Current goes out when the battery is called to supply all or some of the power. This gives a negative current reading on the ammeter. Diagnostically, if the car is running and the ammeter is negative, the alternator is not keeping up with the load and the battery is helping. If the ammeter is very positive, the battery is taking charge rapidly. If the ammeter is slightly positive, it is taking charge slowly. The caller said the ammeter was reading slightly positive at high idle. Battery was taking charge slowly. With a depleted battery, this would indicate the alternator is not able to sustain the voltage necessary to rapidly charge the battery (various reasons are possible). The caller says turning on a load (the blower) causes the ammeter to go more positive. That must mean the battery is taking on charge faster. This indicates the act of putting a load on the alternator (the blower) has caused the alternator/voltage regulator to increase alternator output, which at this point has increased the voltage on the battery thereby increasing the current charging the battery. With the addition of more load (the headlights) the alternator is asked to put our more power. It puts out more power to run the increased load, but cannot sustain the high voltage necessary to maintain a rapid charge on the battery. As the caller described, by adding the headlights, the ammeter went back down accordingly. This behavior will vary based on the vehicle design and condition. It may not always be the case that adding load to the electrical system will increase the battery charging rate. If you are fortunate to have an ammeter, you can adjust the idle and loading to maximize the charging rate shown on the ammeter.


Famous Last Words...

'There's no way this could possibly go wrong.'

The Ford Is My Auto, I Shall Not Want Another

One man's ride is another's affliction.

Novel concept for increasing MPG

Hey, it worked for the toilet!  Let's try it on the car.

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