Another battery charger question



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
http://amasci.com/miscon/whyhard1.html
if you get really bored there's more complaining
http://amasci.com/miscon/elect.html

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.
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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.
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wrote:

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
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[...]

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...
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    [ ... ]

    Pretty good.
    And the analogy for current through an inductor is RPM stored in a flywheel.
    Enjoy,         DoN.
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But past a certain point, the analogy doesn't hold water - - - - .
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RogerN wrote:

Water hammer, ie. the inertia of the fluid moving through the pipe. Its not a perfect analogy, but then none of this electricity is like water and pipes is perfect, but it conveys the general behavior.
Jon
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Toro has some good educational stuff on their website, including a basic primer aimed at teaching technicians enough "electricity" to troubleshoot mower and tractor wiring: http://www.toro.com/customercare/commercial/education/pdf/09170sl.pdf They also have a hydraulics primer that is pretty good: http://www.toro.com/customercare/commercial/education/pdf/09169sl.pdf
----- Regards, Carl Ijames "Tom Gardner" wrote in message
Thanks for all the replies and knowledge. My other battery charger is a one pound electronic machine. It works OK, supplies 2, 6 and 12 amps and has all sorts of buttons and lights! What it won't do is charge a totally dead battery...thus repairing the old Craftsman. It displays: "BAD BATTERY" and I have to hook-up jumper cables from another vehicle to get a few percent of a charge to get the electronic charger to work.
I also confess I don't know enough about electronics. Is there a good book to start with that isn't too stupid yet not over my head? I think I can still learn stuff.
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"Tom Gardner" wrote in message

If you're interested in battery charger electronics you can look up some voltage regulator circuits. You can use an adjustable voltage regulator, such as an LM317, by setting the output voltage to what you want the maximum charge voltage to be, you can use it to charge a lead acid battery. By adding a resistor, low ohms and enough power for an amp or so, you can have the regulator lower the charge current while the battery gets nearer to full charge, like the lead acid battery chargers do.
I read some interesting charging information about the "Battery Tender" maintenance charger, useful if you want to keep your seasonal batteries in good condition through the off season. I found a PDF file that, on page 4, shows the voltages that the battery tender operates at, "absorption charge" to 14.5 and maintenance charge of 13.2V. http://www.powerwerx.com/download/Product_Instructions_Waterproof_800.pdf
Also, something I was interested in for boat batteries. Get a gasoline small engine and mount an automotive alternator, then you can have a portable battery charger that should be capable of some fairly high current. For Gunner's 8V batteries, I read about modifying the voltage regulators for alternators (the kind that have external regulators). IIRC, the basic idea was to control the output by controlling the power going to the rotor. That way the alternator, with the right voltage regulator, could be used to charge 8V batteries on up to 48V golf cart or fork truck batteries.
http://www.smartgauge.co.uk/alt_mod.html http://www.madelectrical.com/electricaltech/howitworks.shtml
RogerN
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If you start playing with homebrew battery chargers this is a good meter to monitor the voltage: (Amazon.com product link shortened)93695849&sr=8-3&keywords=innova+meter
Digital meters aren't reliably accurate to one count, so "13.8V" could be anywhere from 13.70 to 13.99. This one should reduce the uncertainty to 13.79 - 13.81. Mine is quite accurate but I can't promise another will be as close.
The lighter plug is safer than clip leads and you can put an outlet for it in the homebrew charger's front panel, or use the lighter outlet in the vehicle. This device is powered from the 12V input and unlike a DVM doesn't have internal batteries to run down if left on for days. It draws 8mA from the car battery, most of that probably for the display's useful backlight. jsw
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wrote:

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.
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    [ ... ]

    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.
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On Wednesday, February 26, 2014 8:56:26 PM UTC+2, Tom Gardner wrote:

Now you could get all in one from Hello World Magazine. The Hello World Mag azine is a free online magazine which deals with fashion, beauty, homemade craft, recipe, entertainment, study, traveling and much more only for you. It would change your lifestyle. http://www.helloworldmagazine.com
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