Another battery charger question

Inserting a few diodes in the "sense" lead to the regulator will raise the charging voltage 3 silicone diodes will raise the voltage by aprox 2.1 volts - close enough to charge an 8 volt battery with a 6 volt regulator.

Reply to
clare
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Reply to
guillemd53228

Hmm ... if an 8V battery were a *true* 8V -- yes. However, since the 8V lead-acidej battery is four nominal 2.2V cells, that will really be 8.8V charged, and closer to 9.6V under charge, depending on temperature, so you want to boost that regulator's output by 3.6V -- about five diodes total.

And it would be nice to have a current limit in the regulator chip too, just to be safe. :-)

Enjoy, DoN.

Reply to
DoN. Nichols

I saw a link to a torrent of electronics books:

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Reply to
Michael A. Terrell

The problem with gas is that it's compressible. The result is you lose the pressure x flow = voltage x current = power analogy, which holds for liquids, but not gases.

Reply to
Ned Simmons

the problem with liquids is they do no compress. You can always run more current though a conductor and the "speed of electricity" doesn't change. In that respect, current is more like a gas.

They're all analogies, but the gas one seems to have fewer holes than the liquid one.

If you try to model a capacitor with a tank and then use liquids or gasses to represent a difference in potential of the charge, the liquid analogy doesn't work.

Reply to
Cydrome Leader

I can't think of a property of electricity that's analogous to compressibility. Do you have one in mind?

If you increase the flow of either a liquid or gas thru a pipe the velocity increases, but the liquid's flow increases in a linear fashion - not so for the gas. So I=E/R goes to hell for the gas.

I've never seen an electrical analogy based on gas. Got a pointer to one?

But a hydraulic accumulator makes a good enough for the analogy capacitor.

Reply to
Ned Simmons

In the liquid analogy, the equivalent to voltage is pressure, but you can't compress a liquid, you can compess a gas and you can force more charge into a conductor, just like with a gas.

Again, no analogy is perfect and they all fall apart depending onw how much you want to prod at them. Take for instance this scenario- I want to transmit one coloumb of charge across a wire- no problem.The size and length of the wire really don't matter. What if I want to flow 1 tablespoon of water across a 100 foot garden hose? what goes it may not even come out. The liquid and gas molecules themselves have volume and must move to go anywhere, unlike with electricity where the electrons going in a wire are not the ones going out and you're not moving any materials.

Not off hand, but this guy really gets into the topic

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if you get really bored there's more complaining

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I'd disagree. You can always cram more gas into a vessel, but only so much liquid, no matter what the pressure. I can't stress it enough, but all these analogies do fall apart, I just feel the gas is more accurate than the liquid one for most folks.

Reply to
Cydrome Leader

On 3/3/2014 3:01 PM, Cydrome Leader wrote: ...

That isn't really true, either. Real liquids are also compressible, just must less so. And, you'll eventually reach the same pressure in a given volume with either.

Reply to
dpb

The point of this analogy is to relate something you can't see to previous experience handling a familiar fluid. Water is everywhere, while the PV=nRT behavior of gases isn't so intuitive. jsw

Reply to
Jim Wilkins

[...]

The best "capacitor" analogue using the "incomplessible fluid" approach that I've heard described is a divided, two-port tank with a deformable barrier (think sheet of rubber).

| | +----+ +----+ | | | | | /-----\ | +-/ \-+ Barrier, partially deformed | | | | | | +----+ +----+ | |

Pump fluid ito one side and it pushes fluid out the other side... and "stores" energy in the deformed barrier, up to a maximum which is reached when the fluid on one side of the barrier fills the tank. This barrier will, when outside pressures abate, attempt to return to its equilibrium state, with equal fluid volumes on each side of it.

Hope this helps...

Frank McKenney

Reply to
Frnak McKenney

Pretty good.

And the analogy for current through an inductor is RPM stored in a flywheel.

Enjoy, DoN.

Reply to
DoN. Nichols

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Reply to
mahamahafarhat

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