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Gear / Technical Help => Remote Power => Topic started by: mfisch on May 17, 2005, 10:10:05 AM
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Anyone here have experience with really big power packs?
I've got a big hungry rig (mac mini + fa-101 + 7" lilliput)
I need 2-4A of power at 18.5V (exactly), and 1A at 12V (11-13V).
My electronics knowledge is fairly rusty, help from anyone who has done this before would be appreciated.
Im thinking the following, any other tested/proven ideas?
2x9.6V WalMart Lion's joined at the hip in parallel (with 1 or 2 spare sets) ---> miniature lion UPS OR switching diode (uninterrupted battery swaps) --> charge pump converter (9.6V --> 19.2V) ---> voltage regulator (18.5V) ---> mac mini
I'm a little worried the setup might not give full 18.5V after conversion and I'm not sure how Im gonna get my 12V for the lilliput, I guess I could carry a small 12V lead pack .....
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try a bunch of 1.2 volt 10000amh D cells from batteryspace.com run them parallel.
my .02
Clint
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I would think you would get the most bang for you buck by boosting voltage to 18v and running a 12v system.
Running 19.2 > 8.5 would not work even w/ LDO circuits. The battery voltage must be at least 1V over what you are dropping it to w/ LDO circuits. More voltage may be required w/ this high of an amperage draw. To be safe you should have at least 3 volts over your desired operating voltage. (digikey doesn't carry any 18.5v regs. so you would have to start w/ an adjustable reg. that would be slightly less efficient than a fixed reg.) I only use LDO circuits so higher voltage may be required w/ traditional VRs.
If you are not comfortable building your own custom circuits.
Find a laptop cig lighter supply that outputs 18.5v (compaq,Acer,IBM)
>cig adapter(or custom boost VR) > mac
12v (i'm thinkin a couple 12A SLA's) >
> lilliput
maybe some wheels to roll it all in on.
I did find some universal laptop batteries but they we only ~50 watts which would give you about 45 minutes @ ~$140 a piece, not an option IMHO
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better solution?
http://www.mp3car.com/store/product_info.php?cPath=21&products_id=94
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+T for the mp3car link
Sure looks like the cheapest DC - DC converter to use for the mini (and it has both my power requirements). I'll look into the efficiency, too bad the cooling looks active -- I wonder if I can retrofit a heat sink instead.
Alas its a SLA solution for sure, I feel like this is doable with lion. Maybe I can find some weirdo 12v cells.
I've actually already got a similar DC DC converter (so Im familier with this setup) -- but that one is 12 --> 12/5 (for my old 500mhz transmeta rig at 5V).
The old rig used half the power (I assembled it all from low power components myself), but, the mini is just elegant ;)
RE: 1200mah lion cells in parallel
I could certainly build my own pack if I was a little more versed in programming/electronics. As far as I know however, its an extremely dangerous feat to discharge/charge lion's without custom matching controller circuitry (which I dont know how to build). This is the reason why hobbyists usually stick to NiMH, SLA, or pre-built lithium packs.