Topic: HungryMan PowerPack Ideas?

[mfisch]

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 .....

[IowaClint]

try a bunch of 1.2 volt 10000amh D cells from batteryspace.com run them parallel.
my .02
Clint

[fozzy]

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

[fozzy]

better solution?

http://www.mp3car.com/store/product_info.php?cPath=21&products_id=94

[mfisch]

+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.