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Alternator Charging?

I'm trying to come to a non-physicist understanding of the charging of an alternator. I understand all the parts involved. What I don't get is how DC current coming from the diode assembly to the battery's positive terminal can charge the battery. I don't need to understand the electrochemical reactions in general. My question is a logical one and I'm probably off on the logic. For a 12 volt lead-acid battery the negative terminal is at 0 volts and the positive terminal is at 12. The diagram that I have studied shows a pulsed 0 to 12 volt DC current between the diode assembly and the positive terminal and it is this pulsed DC current which supposedly recharges the battery. But if the positive terminal is at 12 volts then this current flow is the same as it would be as if it was coming from the negative terminal (and thus draining the battery).

Perhaps electricity is just not easy to understand. What would work for me is to say that the voltage coming from the diode assembly is actually higher than 12 volts because it is stepped up when the current is induced in the stator. So in this case the current flow would be reversed from the usual flow of the battery. But this is not what I have read so far. There are limited good articles on this and most brush over how this is accomplished or else the technicalities are beyond my understanding. Any help would be appreciated.

Reply to
Ron Ayoub
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Yes, it is higher. For a car alternator charging a lead-acid car battery the voltage is about 14.4 Volts.

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gareth.harris
Reply to
Gareth

The diodes only allow the current to flow in one direction, into the battery. That keeps the battery from pushing current backwards into the alternator coils when the alternator is not spinning. The diodes also rectify the voltage: the alternator coils make AC, and the diodes turn that into the (pulsating) DC that the battery chemistry needs to charge up.

If the alternator weren't connected to the battery, it could output a lot of voltage, maybe 50 volts at high revs. When it's connected to the battery, the high alternator voltage forces the current to flow into the lower battery voltage. The regulator manages the field coil current to control just how hard the alternator pushes current into the battery.

A "load dump" event would happen if you were cruising along and the connector fell off the battery. The alternator might then push 50 volts into all the electrical gear on the car. All the electronics on a car is supposed to be designed to survive this.

John

Reply to
John Larkin

I think anyone would have problems understanding how you charge an alternator.

Reply to
a7yvm109gf5d1

Just run up to it suddenly, wave your hands, and scream.

John

Reply to
John Larkin

You walk in to an auto parts store, ask for an alternator and whip out your Visa card.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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Don't get even -- get odd! :¬þ
Reply to
Paul Hovnanian P.E.

;-) Ok. Charging was used as a gerund here and not a verb. But it was understably a bit confusing sentence.

Reply to
Ron Ayoub

An open account, or a credit card.

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Greed is the root of all eBay.
Reply to
Michael A. Terrell

"Ron Ayoub" schrieb im Newsbeitrag news: snipped-for-privacy@r24g2000yqd.googlegroups.com...

An alternator is a current source, so the output voltage is resulting from the battery, unless the regulator sees it rising above 14.4v, then the field current is cut out. ciao Ban

Reply to
Ban

But dependent on temperature...

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...Jim Thompson

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Reply to
Jim Thompson

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