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#1130: Tickling the Electrons

Jul 23, 2011
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.

Show Open Topic

Gas conservation idea - brick in the gas tank.

This Week's Puzzler

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

Last Week's Puzzler

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

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12 Comments

The purpose of an ammeter

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.
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Who's a 'Yankee'

Heard during today's show that you were mildly surprised when the guy from Illinois identified himself as a 'Yankee'. Guess you haven't heard of the hierarchy of 'Yankee-ness'. It goes as follows: Outside the U.S., a Yankee is anyone from the U.S. In the U.S., generally, a Yankee is anyone who resides north of the Mason-Dixon Line. North of the Mason-Dixon Line, a Yankee is anyone from New England. In New England, a Yankee is anyone from Boston. In Boston, a Yankee is anyone who eats pie for breakfast. There you have it. Peter Lee Milwaukee, WI
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A new Player?

Do you suppose "Maureen Briology" will become a new member of the Car Talk Staff?
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A bunch of sissies?

Tom and Ray: Love your show, have for years, laugh out loud funny and educational. During the Stump the Chumps segment, one of you blurted out the phrase "a bunch of sissies". I was surprised. In my youth it was used as an insult to mean a male that was not manly, but acted like a woman, feminine or gay. It is also an insult to females since it implies that femininity is the less desirable state of being. Maybe we can all find a new phrase.
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Show Review - 1687

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dog team

When talking to the lady from Alaska you faled to mention that cars to day can't be towed at hi speeds and a long distends she will haft to hall it on a trailer My wife and I listen to your show every sunday at 10 & 2 in the pickup on sirius raido this is in Wyoming . Know more needs sead
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dog team

When talking to the lady from Alaska you faled to mention that cars to day can't be towed at hi speeds and a long distends she will haft to hall it on a trailer My wife and I listen to your show every sunday at 10 & 2 in the pickup on sirius raido this is in Wyoming . Know more needs sead
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Show Review - 1690

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need more meat

i am pretty tired with all the filler on the show. let's get on with talking about cars. the name of the show is 'car talk.' that should give you some direction.
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Above & beyond

At the recommendation of my regular repair shop, I went to Summit Transmission and Jerry Kubitsky. My shop was puzzled by the "issue" with my transmission and said Jerry is the best transmission guy in San Diego. Well, they were right. Not only did he take extra time (with patience) to explain the detail of the problem. After he thought is was resolved, there was still a question. Instead of being satisfied with the result, Jerry took more time and effort, on his own, to further research the issue. He found a remote issue and spent another 10 or so hours redoing things, and another $300 or so in extra parts. I (and most others) would have been OK with the first fix or would have never known the difference. I am so grateful that he went above and beyond the expected and the basic repair. I am now confident my jeep will be with me for many more years. I love that jeep and want to keep it awhile longer. Jerry was fabulous, patient, and honest.
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WHY IT WORKS :

Waveaction has it right! P=IxE (Power = Current x Voltage). The Battery will only draw an amount of current proportional to the difference between the charging voltage and the discharged battery voltage, and will absorb the Power at this Current level. As you demand more power from the Alternator (lights, fan, radio), the additional Current demand will cause the Alternator to increase its Output Voltage in order to increase its Current output. This causes the Voltage difference between the battery and Alternator to become greater, which allows more current to flow, and charge the battery slightly faster. At some point of loading (adding the heated seats, rear window defroster, and electric dashboard Hibachi), the Alternator can no longer keep the voltage level up with the massive current draw, and when the system voltage falls below the battery voltage, then the already stressed battery is pressed into service, and supplies current to the system.
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There must be 50 ways to spell you, Coby . . .
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The beauty of alternators is:

...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!
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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!"
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