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02-11-2012, 07:13 PM   #1
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DIY K-5 Power Supply from 12V battery

I just finished making a power supply for my K-5 based on the one at this link: DIY Power Supply for Pentax K5 DSLR . The directions Bob gives are great and I highly recommend it. The SWADJ3 regulator device allows you to dial in the voltage you need for the device in question. For the K-5, that's 8.3VDC.
I was thinking of getting the AC adapter for my K-5. However, I also needed something that I could also use in the field when camping or observing at my telescope. So I modified Bob's design by putting a cigar lighter plug on it instead of the AA's he showed in his blog post. I have several rechargeable jump start batteries for cars with cigar lighter plugs on them that I use to power my computerized telescope. They are 12VDC and contain 17AHr of power. So with the cigar lighter plug I can power my K-5 for extended periods and for long exposures using 'bulb' mode without fear of draining my main camera battery.
This solution offers a lot of flexibility as I can now provide extended power virtually anywhere and it cost a lot less than the KAC-50 AC adapter!

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02-11-2012, 08:29 PM   #2
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Noice!
02-11-2012, 09:34 PM   #3
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Very good.
02-11-2012, 11:16 PM   #4
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Would you mind posting a picture of the jumpstart batteries you refer to? I wouldn't mind building one of these PSes for astro photos.

thanks,
Jack

02-12-2012, 12:39 AM   #5
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I'm surprised there aren't similar devices like this already on eBay or DealExtreme.

I hope some small electrical manufacturer from Shenzhen in China is reading this thread...
02-12-2012, 09:27 AM   #6
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I've gotten some 'Shenzhen' power supplies/AC adapters in my day and I prefer building my own with quality parts! ;-)
02-12-2012, 09:29 AM   #7
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I have several, but they are nothing special. Just Google "jump start battery" or use that term in an Amazon search. Just be sure it has a cigar lighter socket and you'll be good to go. Also look for AHr rating. Some come with a lot of extra junk like radios, etc. I just went with a basic battery or one with an air compressor which seems to be getting common on these devices.
02-12-2012, 11:10 AM   #8
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That's quite excellent!

I was wondering if there's any more detail guide on wiring and stuff? Even the DIY link is a bit too brief for me to figure out all the pieces.

02-12-2012, 07:11 PM   #9
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"I was wondering if there's any more detail guide on wiring and stuff? Even the DIY link is a bit too brief for me to figure out all the pieces."

Nope. You have it all. Don't worry, once you have the pieces in hand, it is clearer. The 3 piece plug has uniquely marked sides so with that in hand and the DIY article w/pictures as a reference, you'll get it. If you want to test your circuit before soldering, add one of Dimension Engineering's "breakout boards" to your order. With that, you can plug in the SWADJ3 regulator and clamp wires into a fixture holding it. It's only $10 more and is quite handy for testing your circuit. You can get the SWADJ3 and breakout board here: 3A Adjustable step down switching voltage regulator.

By the way, the block box in which I placed the regulator is Radio Shack's smallest project box and only cost a few dollars. An alternative I considered was some 3/4" PVC pipe with end caps. The SWADJ3 fits into it nicely. I opted for the box because I had an extra one on hand.
02-12-2012, 08:15 PM   #10
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Thanks, I think I'm going to have to add this to my to-do list. I think I would like to make the power input side to be modular so it can be powered by other DC source or the cigarette plug.
02-13-2012, 03:04 AM   #11
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That's a neat solution.

One could also achieve it using a standard DC-DC converter e.g. this with a 9V output and then dropping the output through one silicon diode (e.g. 1N4001) which would give you around 8.4V.

Locating the connector was a good piece of work
02-16-2012, 05:38 AM   #12
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QuoteOriginally posted by peterh337 Quote
Locating the connector was a good piece of work
Indeed! I've thought about building my own for a while, but without the connector this wasn't possible. I even considered hacking the AA tray of the BG-4 grip and attaching an external supply that way. Thankfully I can abandon that idea and just build a proper supply with the proper connector.
03-06-2012, 07:22 AM   #13
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Finished up my supply this morning. Works like a charm. Even took out the batteries in the camera to make sure it was actually working off the supply. It's a fairly quick project IMO, but I did take some extra time to make sure I did it right so I didn't screw up my K5. Thanks atnbirdie for creating this thread so that I could discover the correct connector to use with this project. That's been my missing link for a while.
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03-06-2012, 09:06 AM   #14
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Is that a 35mm film container you're using? If so, then that is really... dare I say it... empowering!

In all seriousness, I'm going to have to try to make one of these.

I have one of those large 12volt battery jump starter units. It should power the K-5 for hours.

Last edited by mtansley; 03-06-2012 at 09:11 AM.
03-06-2012, 09:42 AM   #15
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Yup. I was looking around trying to find some kind of enclosure for the regulator and connections and thought that would work well.....I think it does.

I'm still a little concerned about the fact that the regulator can be adjusted. Worried about it getting changed somehow and screwing things up. I'm entertaining the idea of removing the potentiometer from the regulator, measuring the resistance that is giving me 8.3V out of the regulator, and then replacing the potentiometer with a fixed value resistor. Then no worries about accidental voltage changes. No rush to do that just yet, but if I do go down that path I'll post back here with how that goes.
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