adapting 12vdc to 9vdc

BARF! I for will not lift a finger to "save the planet." It doesn't need saving, and if it did "reducing power losses" is not going to do the trick.

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----------------------------------------------------------------------------- Roger Blake (Change "invalid" to "com" for email. Google Groups killfiled.)

"Climate policy has almost nothing to do anymore with environmental protection... the next world climate summit in Cancun is actually an economy summit during which the distribution of the world's resources will be negotiated." -- Ottmar Edenhofer, IPCC

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The question is... what is the original poster's "capacity"?

To expound on this idea, the xx1084 family of regulators would be ideal. Specifically, the AP1084TL-U adjustable regulator. Datasheet:

It's capable of putting out 5A and has thermal shutdown.

The parts list is simple - An AP1084TL-U, 2 ea 100µF, 25volt caps, a

120 ohm and a 750 ohm 1/4 watt resistor, the die cast box, and an insulator - the tab of the AP1084 is at the output voltage.

PlainBill

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One problem with using this part is the risk of destroying it as soon as you start the car: The absolute maximum supply voltage is only 12V, and the alternator puts out more than 13VDC.

This all reminds me of my boom box I built in the early 80s. I used car parts and a gel cell, compatible with car charging systems, which can reach

16 volts. Picture does not show horn loaded drivers.

Greg

Datasheet:

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The 7809 has a max input of 40v from memory.

Rheilly P

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I'd use a 7809 myself, but the part with the low abs max Vin recommended here was a AP1084TL-U.

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I don't understand the problem. I have been using the 7809 etc. for years in the automotive situation without a single failure. It's not exactly rocket science :)

Rheilly P

The problem is that the OP probably knows little about electronics, and is likely to completely botch the project. He'll return to us asking for troubleshooting help.

Excellent idea. 1N400x rectifiers should work.

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No one mentioned putting a string of silicon diodes in series to lower the voltage. Unlike a resistor, the voltage drop would be reasonable fixed. But, no fancy parts, capacitors, etc are required. Sort of crude, but why wouldn't it work? 7 diodes would drop approx 4.2 volts bringing 13ish down to 9ish. Or, maybe 8 diodes to be safe. 13.8 down to 9. Just wondering why no one mentioned the possibility. Heat would have to be handled, but no worse than a three terminal regulator and the heat would be spread across all 8 diodes.

s n

I tried running a small 9V transistor radio years ago at work from a

12V supply. I used a zener and a series resistor. Even with such a small radio the pair got much too hot. The OP plans to power a boom box. At the least he'll need to use a three terminal regulator or a series pass transistor with the zener in the base circuit. Whatever it turns out to be may need a heat sink, must be properly polarized, fused, adequately wired, (so as to not set the vehicle on fire), and I agree with William that this project, although simple to a seasoned technician might be beyond his capabilities. Lenny

Exactly! I have a bunch of 1N4003's in my junk box that I used for any project needing a general purpose diode that can handle some power.

you mention it : the voltage of a car battery varies ... from 14v to 12v or less does the boom box handle 10v to 8v ? or not ? that's why a regulator is needed, except if a regulation is made inside the boom box ? who knows...

--
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Kripton

the ESR Repository @ http://kripton2035.free.fr/esr-repository.html
the Geiger Repository @ http://kripton2035.free.fr/geiger-repositor.html

It's not rocket science, but there are some subtleties:-

A few parts (series 1N400x, series power resistor, parallel TVS) will protect the regulator against +/-100V transients and reverse wiring.

Best regards, Spehro Pefhany

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"Yes, but..." It's much closer to being constant, than it is with a resistor.

snipped-for-privacy@neo.rr.com wrote in news: snipped-for-privacy@4ax.com:

forward voltage drop of a diode varies with current through the diode.

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Jim Yanik
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at
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dot com

Kripton wrote in news:4f1afdb7$0$4206$ snipped-for-privacy@news.free.fr:

you also need FILTERING to reduce ripple(and noise); auto alternators do NOT output straight DC,but pulsating DC.

A regulator IC will reject a lot of ripple and noise. a string of diodes will not.

but hey,it's your boom box.(and ears)

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Jim Yanik
jyanik
at
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dot com

Actually, it makes it worse (percentage-wise).

Best regards, Spehro Pefhany

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