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Resistance needed to drop from 13VDC to 9VDC

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#26 steveeb

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Posted 04 April 2009 - 03:44 PM

I know it's a really old thread, but the last 3 months have been quite hectic and I haven't had time to finish this little project. I'm just now getting back to it.

I'm about to order the two caps suggested (10uF and 22uF) but I noticed that you can get these things with different voltage ratings. What voltage rating should I get? I'm thinking 16V should be fine, or should I go with 35V to be safe?

#27 walt r

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Posted 04 April 2009 - 10:11 PM

If the cost and size of the two caps are close I'd go with the 35V.

#28 b1gred

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Posted 05 April 2009 - 08:09 PM

16V caps will work (as long as you don't have any surges in your primary (13.8V) supply. 35V is overkill, but will offer a bit more protection (which will be un-necessary if your primary supply is regulated (or a battery)).

#29 steveeb

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Posted 24 April 2009 - 03:14 PM

Thanks for everyone's help. I used a 4-pin fan connector from my computer scrap pile. The regulator chip fit perfectly and I was able to connect the capacitors thru the other end (see pic). I had a bunch of computer RAM heatsinks laying around which was also a perfect fit for the chip.

I measured the input at 13.1V and the output was exactly 9.0V. Perfect. Thanks again.

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#30 PJ Anway

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Posted 24 April 2009 - 06:47 PM

Steve,
Would you mind making a little schematic of your setup with chip and capacitor numbers.

Thanks,

#31 steveeb

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Posted 25 April 2009 - 12:45 AM

I went with the larger capacitors per Artic Eddie's suggestion. I used the link provided by CCS_Hello for the schematics and edited it accordingly. I used the 4-pin fan connector (a 3-pin connector is too small) to bring it all together. Everything fit nice and snug and it sure beat soldering everything together.

The "Red" wire is the unregulated input (pin 1), the "Black" wire is the ground (pin 2), and the "Yellow" wire is the output voltage (pin 3).

It really couldn't be simpler. With this setup, I guess I could just pull out the 7809 and replace it with another regulator (e.g. 7805 for 5V or 7812 for 12V) if I wanted to change the output voltage.

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