NNTP-Posting-Date: Tue, 05 Nov 2002 01:25:42 -0600
From: "Dave VanHorn"
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <7tGLdeAS6fn9EwBv@jmwa.demon.co.uk>
Subject: Re: Best way to power array of LEDs?
Date: Tue, 5 Nov 2002 02:23:56 -0500
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> If the alternator could supply a megawatt, then I'd expect it to be a
> bigger mechanical load than the drive train even with no electrical
> load. When *less* current is drawn, does that mechanical load change
> proportionately, or does the alternator, to some extent at least,
> convert some of its unused capacity to more internal heat?
The alternator is only part of the system.
The voltage regulator does the controlling.
It limits the output of the alternator, both in current, and voltage, to a
When you apply a load, the system voltage begins to droop, and the voltage
regulator applies more current to the alternator's field coil (which is the
rotating one) This causes more current out the stator coils and diodes, and
brings up the system voltage.
You can think of the alternator as a current amplifier, powered by
The alternator will run cooler at lighter loads, since less current is
The engine will be less loaded when there is less load on the alternator.
700W is about 1HP, so that's why you don't really notice it much.
> Well I wasn't thinking of getting something for nothing. I was thinking
> that it sounds too ideal for an increased load on the alternator to
> convert into an exactly proportionate load increase on the engine.
That's the voltage regulator's job, and they do it fairly well.
> If I
> draw less power than the alternator can supply, isn't it just wasting
> some of that power because of the non-ideal properties of the
There's some energy lost in brush friction, bearing friction, moving air
around and such, but it's more or less a constant.
> In other words does a generator precisely convert a higher
> load current into more mechanical resistance?
Both generators and alternators do this, by different means.
Before computer driven engines, you used to notice the loading effect more.
Now, the computer maintains idle at a preset speed pretty well, unless
something's very wrong with the system.