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Forum: Do-It-Yourself
07-05-2013, 09:39 PM
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Guys, you can probably get away with using any 8V DC adaptor (plugpack, wallwart, whatever) if it can continually supply at least 2A, and up to 6 or 8A for very short periods (such as writing to flash).
Now, unless you know what you're on about, it's almost impossible to find either of these two specifications for any given plugpack, and not even then!
So as a "rule of thumb", may I suggest the following :
1) Buy a good quality adaptor.
I prefer the old, transformer-style adaptors, because although they're heavy and huge (!!), there's almost nothing that can go wrong with them, especially in comparison with the smaller and lighter switchmode supplies. Plus, it's almost impossible for the mains voltage to appear on the output, whereas switchmodes have exactly that issue.
Put another way, the technology level of switchmode adaptors is in the same ballpark as transformer plugpacks were in the 1980s. Trust me on this one - I've designed plugpacks for commercial vendors.
2) Use the heaviest wire you can to attach the lead to the Digikey plug. I'm not talking jumper cables, but certainly use braided multistrand wiring in preference to solid copper (it's more flexible and has far more surface area). If the cable is rated at at least 2A (and preferably 4-8A at 120V or 240V), then you shouldn't have too many problems.
3) Keep the cable as short as possible.
Yeah, I know, when you really need to use an adapter for the camera, it's always too far away from a wall outlet or generator lead or whatever... But you're far better off finding an extension lead for the adapter than making a longer DC cable!
But let's say 2 metres (~6 feet) long as a kind of compromise, and then every extra metre you add to that length, expect the power handling to degrade by 50%.
So, let's say you use 3m of high-quality, braided 10A cable, with an 8V/4A power supply. You would to expect the camera to see a maximum current source (while keeping the voltage the same) of less than 5A due to the cable, which means roughly 2A to the camera. Now, that might work - but it will probably give you problems in very cold or hot weather, and you would expect to see file saving problems at maximum camera load. Which is kinda important to the picture taking process, I understand!!
I hope this makes sense to everyone interested. I've grossly oversimplified things to avoid writing a book here on connecting DC supplies to high-power cameras like ours (mine's a K7). If anything doesn't make sense, I'd be happy to explain further.
Again, I hope this really helps everyone.
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