Do All Alternators Operate Similar ?

My car alternator charges more at faster speeds and higher rpm. Are all alternators similar in this regard or are there alternators available that operate
just as well at low speed and low rpm.
You can run your battery flat if you are stuck in a three or four hour traffic jam at night with your lights on and barely moving forward. This gets worse in cold weather.
I was just wondering if there were alternators available that charge well at low rpm.
Thanks in advance Denny B
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My '94 Crown Vic does this, too. When there's a load on the system, as with lights and blower and rear defrost on, the voltage level will go down 10 to 15%. I had my mechanic check this last week. He reported that the alternator is only charging 65 amps at idle, though the alternator is rated to put out 95 amps. He figures it's a bad diode in the alternator, since it only happens under load at idle. The charging is just fine when there are RPMs on the engine. Since a new alternator is $350 installed, we agreed that I'd just keep an eye on it for now and watch to make sure the battery light isn't coming on at any point. (BTW: I trust this guy totally. He's never once steered me wrong in the 10+ years I've been going to him) Once the spring comes to the forsaken lands here and the blower and rear defrost aren't being used all the time and I don't need lights to drive to and from work, the load on the alternator will be much reduced and I can probably drive through the summer with it. I'll likely get a new one in the fall.
Hope this helps.
Bob.

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most alternators drop slightly in output voltage when idling, however this should really be an insignificant amount on a correctly operating alternator and sitting at idle for a lengthy period of time even with your lights on should still charge your battery, so if it doesn't, then either you have too much load on your alternator or its probably got a burnt diode or similar charging fault. alternators with certain faults may indeed continue to charge but not as efficiently. and of course once this happens your alternator will have to work twice as hard to keep the battery voltage topped up so its life-span from this point onwards is probably very short. have it properly checked and replace as necessary, you might get stuck somewhere. steve.

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Hiya all,
I would have considered this to be normal operation. Every vehicle I've ever had charges better when off idle, including the Chrysler (sorry, I do still have the Granada) that's now only two weeks old. The headlights get marginally brighter when all the switches are on and the revs are increased.
If you're stuck in traffic turn your headlights off and sit there with just the sidelights on, switch 'em back on when you move at any sort of speed.
Three to four hour traffic jam!!! find a different way home from work or get a train man! It'd be cheaper to get a hotel than idle the way thru' all that fuel.
pottsy
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(...)

That reminds me of the power crisis in California. They said that if everyone would just shut off his lights on the cars, they would save enough energy to prevent the power outages. Unfortunately, cars don't usually come with power cords.
Jeff
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It is kind of like a water pump. The faster it goes, the more juice it can put out.

Sounds like a problem either with the battery or the alternator or maybe voltage regulator. While an alternator should produce more electricity at higher RPM, it should produce enough electricity at low RPM to run the engine electronics, ignition, CD player, lights and charge the battery.
Now, if you have one of those truck with the rack of lights at the top and another at the bottom, and you're using all of them, well, that is why you can't keep the battery charged.

Yeah. Most of them.

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water pump huh? actually your wrong, years ago before alternators were invented or used cars made use of dynamo's, which did this exact thing, provide more power with faster speed, however with modern electronics which demand an acurate regulated voltage and current flow this would only serve to eventually burn out the components it is powering, which is why we use alternators designed to provide a steady voltage regardless of engine speed, true the voltage can sometimes drop at a slow idle speed and when under load from headlamps etc but as mentioned before this should be a signifficant amount.
steve
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correction..........INsignifficant amount...............i was tired..

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(...)

The electronics limit the voltage, of course. However, you can't reach the voltage (and current output) if not enough energy is coming into the alternator (i.e., the alternator is turning fast enough). The electronics themselves don't generate electricity, they can only regulate what's there. So the faster the alternator is turning, the more electricity it can generate (which really means that at the output voltage, it can generate more current going faster, because the output voltage is regulated by the electronics).
Jeff
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your just guessing arn't you jeff, do you know how an alternator works? or did you get a starters guide to home electronics (ages 3 - 5 yrs) and figgure that qualifies you to argue your point.????? alternators have a cut-in point, IE they need to turn a minimum speed before the regulator will transfer the voltage to the battery, this is designed because at an extremely low engine speed the alternator may only kick out 10 or less volts and this fed into a battery holding 13.5 volts and above will have an opposite effect of charging, so therefore it needs to supply in the region of 13 - 15 volts and a regulated feed (IE amps) in order to maintain a healthy charge. at the other end of the scope, if it wasnt regulated then you may find anything up to and over 16-18 volts which will not do todays modern electronics any good whatsoever. so therefore alternators are designed to provide the same voltage and current flow once the alternator has kicked in. if yours isnt doing this, or the fluctuations are over + - 1 volt then i would say its faulty.
steve "pissed and can't be arsed"uk
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snipped-for-privacy@sprint.ca says...

Often, people will get a replacement alternator, and not notice the pulley is different. If you put on a replacement alternator and the pulley is larger than original, you will have problems. Some rebuilders don't worry about the difference, as long as the amp rating is right. Had this problem on an 82, they gave me a v8 alternator instead of a six. Alternatively, you can look at other alternators for your application and find one with a smaller pulley if you do a lot of idling. Many of these high capacity alternators the kids are putting on their cars to power their sounds systems use a small pulley.
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The smaller pulley simply speeds up the rotation of the alternator, which is exactly what happens when you come off idle. The real need here is to fix the problem.
Either you have an excessive load or you have something wrong in the electrical system. First, check all the electrical connections at the alternator, battery and grounds. A loose connection will cause the charging system to lose efficiency. If that all checks ok, have the alternator load tested.
CJ
says...

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