impedance meter to test car battery

I'm totally familiar with Thevenin and Norton equivalents. Neither has anything to do with some power source behaving like a *current source*. Why would an alternator or any electric power source be considered a "current source", when it can be modeled using either voltage sources or current sources? Hello? An alternator is only a current source in the same sense that a battery, a capacitor, or a static spark is a "current source". They all deliver current, sure. But so, what? When one starts talking about something being a "current source' in the context of it's output characteristics, that implies that they are saying it's behaving like an ideal current source or similar to one. Which is one that delivers a constant current regardless of load. That most certainly is NOT a car alternator. Cars have VOLTAGE regulators, which is a clue. They behave more like an ideal voltage source, seeking to keep the VOLTAGE within a target rangd. Nor is it like a voltage source in series with a high value resistor, which the village idiot put forth. That is beyond stupid. So sad that we have people here commenting on electronics, when they don't even have a grasp of the very basics of electricity 101.

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Try understanding that neither a Norton equivalent or a Thevenin equivalent is a CURRENT SOURCE, no more so than any battery, any generator, any voltage source is a current source. An ideal current source is one that delivers a specified, fixed, current regardless of the load. An alternator in a car is nothing like that. It behaves more like an ideal VOLTAGE SOURC E, maintaing a fixed VOLTAGE.

takes a special person to be wrong and refuse to admit they are wrong when they only need to look it up and learn something. I'm guessing you know or knew this and had a brain cramp. Now you have dug in your heels and are r efusing to acknowledge that you need to learn or relearn something.

You are the f****it that does not understand that a car alternator does not behave like a current source. Here's a clue. What does every alternator have? A VOLTAGE REGULATOR that tries to maintain a set, constant VOLTAGE, not a constant current. Does that sound like closer to an ideal current source or voltage source?

You really have totally discredited yourself on anything to do with electricity at this point.

trying to maintain a constant voltage. A current

a constant voltage output.

And that is still what they do stupid.

But that's actually not ideal for batteries. I don't know if they have im proved any or not.

Yet here you are pontificating and telling us that an alternator behaves li ke a current source. Go figure.

Certainly it would not be hard to do. I don't know

You should just stop right there.

The regulator limits the output, but we were taling about recovery. when the voltage is low it's operating at full power, in that region it's a current source.

Once the regulator kicks in it starts to pretend to be a voltage source and the battery, which is a voltage source, does a fine job of covering up its flaws.

--
  Jasen.

A Norton equivalent is not a voltage source in series with a resistor. It's a current source in PARALLEL with a resistor. And an auto alternator doesn't behave like a current source in any way shape or form. One clue is that they use VOLTAGE regulators, which make it appear like an ideal voltage source, that tries to keep the VOLTAGE with a small range. A current source would seek to put out a constant current, the resulting voltage, be damned. If it's a current source putting out 1A, and the load was 12 ohms, it would be 12V, if the load was 1200 ohms it would be

1200 volts. Capiche? Doesn't work well for a car.

And equating a current source to a voltage source with a high value resistor in series is just beyond stupid. The higher the resistance, the less like a current source it behaves.

Ok, so now rather than admit you were wrong and move on from there, you are retrenching by trying to ignore what you posted.

You are so much like the Always Wrong who you love to scorn.

--

  Rick C. 

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You seem to not understand the term. What exactly do you mean by "current source"???? Norton equated a current source to other circuits. He didn't define or invent the current source.

So is the alternator a current source or not?

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  Rick C. 

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Hi,

Using an extra current limited charging terminal on the supercap/battery would probably be a good idea to limit the alternator load, but I am guessing at the typical low RPM of an engine that was just started, the alternator won't have enough internal current to damage itself before charging the supercap anyway.

Also the field strength of the alternator stator is provided by the alternator output voltage, so it will be a weaker field if the supercap is at a lower voltage maybe.

cheers, Jamie

Damn, I always get those two confused. I didn't say it was a Thevenin source either.

Tries and sometimes fails. See also "load dump"

And that's what happens in a load dump.

You don't.

like I've been saying all along.

--
  Jasen.

is it important what claims I did not make? I used the wrong term.

It's more like a current source than like a voltage source, in that when open circuit it produces harmful voltages, but when shorted nothing bad happens.

--
  Jasen.

Doesn't matter. Both Norton and Thevenin are wrong the way you want to use them. There is no such thing as a "Thevenin current source". Thevenin ju st said you could equate any given DC circuit to a voltage source and a res istor. Norton said you could equate any given DC circuit to a current sour ce and a resistor.

You seem to want to make a distinction between a current source and the The venin equivalent.

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I don't know that. I was simply saying that combining a rather large cap w ith the battery an alternator may produce excessive currents. If nothing e lse it may blow a fuse. I believe that is what happened in my truck when s omething shorted to ground. A wire fried burning up it's insulation but th e repair shop never could explain what shorted. Meanwhile the 160 amp fuse blew. I think this could happen with the super cap as well.

--

  Rick C. 

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  -+- Tesla referral code - https://ts.la/richard11209

Whoey Louie wrote in news: snipped-for-privacy@googlegroups.com:

An alternator is typically a fixed voltage device. It is a fixed voltage POWER SOURCE. Which is to say that it IS indeed a current source, all the while refusing to generate a voltage higher than its designed setpoint. Constant voltage, current varies with load.

So if it is below spec rpm, it will not behave properly and will appear to act differently than ideal doctrine.

IDK what you're talking about. I was responding to the posts that claimed an auto alternator behaves like a current source. It doesn't, it behaves similar to a voltage source. A current source would be trying to maintain a fixed current. An alternator/VR maintains a fixed VOLTAGE.

Nonsense. It's no more a current source when delivering 100 amps than it is when it's delivering 5.

The VR is always operating.

it starts to pretend to be a voltage source

Heh genius. You claim that an auto alternator behaves like a current source with a high value resistor. I say you're full of baloney, it behaves like a VOLTAGE SOURCE. I can give you the model using a voltage source. Take an ideal voltage source of value 15V in series with a

0.025 resistor. With a load of 1 amp, the alternator puts out ~15V. With a load of 100 amps, it puts out 12.5V.

Now provide us with the values for your current source and high value resistor that you claim model it.

Agreed.

It is a fixed

Well, like I already said if you want to talk about that definition of "current source", then so too is a battery, a cap, or a lightning bolt. But when someone brings up something being a current source in the context of electrical engineering they usually mean that whatever they are talking about behaves like an ideal current source, which we use in EE, which is source that maintains a constant CURRENT, regardless of what load is on it. That isn't an alternator, which behaves like a voltage source. You can model it with an ideal voltage source of about

15V and a low value resistor in series of about 0.025 ohms.

all the while refusing to generate a voltage higher than its

Agree.

Give me a break. I assume we are talking about a working alternator operating within it's normal range.

See also "load dump"

Oh yes I do. I'm waiting for Rick to give us the values for his ideal current source and the high value series resistor that model how an alternator behaves.

Try that and see. And since when are we talking about disconnected alternators? shorted alternators? The discussion was how a working, normally operating alternator behaves in a car.

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se them. There is no such thing as a "Thevenin current source". Thevenin just said you could equate any given DC circuit to a voltage source and a r esistor. Norton said you could equate any given DC circuit to a current so urce and a resistor.

hevenin equivalent.

Since you know so much, give us the values for the current source and high value resistor that you claim model an alternator......

I can give you the VOLTAGE source model, take a 15V ideal voltage source in series with a 0.025 ohm resistor. So, what value ideal current source and what high value resistor do we use with your model?

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with the battery an alternator may produce excessive currents. If nothing else it may blow a fuse. I believe that is what happened in my truck when something shorted to ground. A wire fried burning up it's insulation but the repair shop never could explain what shorted. Meanwhile the 160 amp fu se blew. I think this could happen with the super cap as well.

You need to read the posts you respond to as well as your own. I never made the claim you say I did. You meanwhile incorrectly said a current source is not equivalent to a voltage source in series with a high value resistance.

Just read the posts quoted above. It's that simple, Always Wrong.

--

  Rick C. 

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  --+ Tesla referral code - https://ts.la/richard11209

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It is a current LIMITED power source that is voltage regulated. The current limiting comes from the internal resistance of the Alternator's windings. Compare it to a lab grade bench power supply. You can set the output voltag e, and it will go into current limiting to protect itself.