where does the power go?

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Newz2000
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Re: where does the power go?

Post by Newz2000 »

Thanks Robert and Stephen, it's good to know how that works. My suspicion has been confirmed in that the pulley on the generator turns nearly freely when there is no need for electricity to be generated.<p>What happens when equipment in the car draws more current than the generator is rated at? Does it begin to overload the generator in the same way that an electric motor or speaker gets overloaded (coils burning out and such), or does the extra current come from the battery?
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Chris Smith
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Re: where does the power go?

Post by Chris Smith »

Matt <p>The extra current comes from the battery.

The coils in the generator are self regulated, in that they are designed to put out their max current, with out overheating.<p> The fan in the generator or alternator are designed to run full bore, and remain at a constant temperature and current with out causing harm. <p>Only poorly designed generators should fail in the manner you suggest, or ones that have poor insulation and short out as the wires warms up.<p> They have a test for commutators called the “growler” and it looks for things like this. <p>On the alternator, you use a ohm meter to ground on the field windings, and set it at upwards of 20 megs or more. Any reading is interpreted as a short and will most likely fail under load.
Robert Reed
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Re: where does the power go?

Post by Robert Reed »

Matt<p>The modern day (modern being going back 30 years) alternator systems are usually fused (or resetable breakers) at 40 amps on most cars.Generators ?-- going too far back in time to remember, but I would suspect they had similar protection. There is no single automotive load I know of that is fused for more than 25 amps. That is the fuse rating and not the normal load current. However lumping many loads together could draw considerable current. It would probably be rare to have a situation where you would pull this much current (WITH FACTORY INSTALLED EQUIPMENT). Any overload of each individual item would be disconnected by its own fused circuit. When a system 'bolt down short' occurs, then the alternator protection comes into play. The only real major problem will occur if a fault develops in the unprotected heavy (#4) battery leads.
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Chris Smith
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Re: where does the power go?

Post by Chris Smith »

Robert<p>On VWs it was quite common to over draw the circuit because it seems every one needed more head lights than VW provided. <p>I recall a common problem when two 100 watt driving lights were added to the fray, on top of all the other hippy equipment that VWs suffered, and you could see the lights go green, and stay there after the excess current in the battery was used up. <p>From my dinosaur memory also, I think the CB was built into the regulator for dead shorts mostly.<p>However modern Alternators have a unfused direct cable between the battery and the alternator. Its size limitation is the only fuse. They smoke real nice when screwing up.
Newz2000
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Re: where does the power go?

Post by Newz2000 »

What started our (my brother and I) interest into this subject was that he burned out two generators. The first one went after a month of using the car, the second one went 15 minutes after the first (expensive fuse). He had to buy a new generator (the first replacement was a spare he had on hand) and then we replaced all of the wiring. 10 seconds after starting it the regulator smoked.<p>I wasn't there for that last part and he IMd me and said, "I think the regulator blew up." I asked him, "Why do you think that?" He said, "I heard a noise and then smoke came out of it." I replied, "Yep, I think you're right on with your diagnoses; it blew up." He ended up fixing the regulator and put it back in. It made it only 8 seconds this time. So we went through, traced everything out and could find no problems. Since the regulator looked *very* old, he decided to replace it with a new one. The new one blew.<p>Finally, after much pounding of fists and gnashing of teeth, he realized that the new generator didn't have insulation between one of its terminals and the outer metal of the housing. He was able to fix it and the place where he'd purchased the generator and regulator traded his blown regulator for a new regulator without complaint. (can you imagine a local shop stocking two regulators for a '67 beetle?) Now it seems to work fine.<p>It's had a somewhat happy ending. Of course, with project cars, there realy isn't such thing as an ending.<p>We're wanting to add some more electronics equipment (sensors and a mcu-based computer, maybe some fans) and we're curious what happens if we overload. I appreciate the informative answers.
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Chris Smith
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Re: where does the power go?

Post by Chris Smith »

IF the system is working correctly, the battery will carry any load that the generator cant. <p>IF this persists, the battery and alternator will come to a balance point, and your lights and such will suffer from a brown out. <p>BUT, under normal conditions it wont burn out anything. <p>The brown out could damage other Sensitive equipment, but the car and generator should survive just fine.
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