Ok, so Hottest 100 is around the bend and I want to rip the 12V batt out of my girlfriends car to power a suitable radio. To be clear, I'm thinking a radio something like this:

http://img519.imageshack.us/img519/3685/l14390027lx9.jpg

Right. So assuming this radio runs on 8x C batteries, which is pretty typical, that's 12V - should be alright to hook-up, amirite? I will chuck 3A fuse inline on the positive terminal just in case.

Anyone have any success with doing this? Car radio and speakers not really an option because of short timeline.

You have to make sure it's a similar amp output.

I went in a different direction and made my own boom box.
I got an old JVC MP3 head unit I had lying around and bought some 6 inch sony speakers, as well as a small sealed 12v battery and chucked in in a wooden box I made up. I also got an aerial on the top.
It just plugs into a cigarette lighter and I usually just run it off a battery booster pack I got from supercheap.

It actually sounds pretty sweet.

Why wouldn't you buy a $130 of C batteries to last the entire day?

Just out of curiosity, where will you be taking this setup?

Just out of curiosity, where will you be taking this setup?

To a park. Don't want to blast the s*** out of everyone, just want something guaranteed to last 8-10hrs - how many C batteries would that take you reckon?

Supercheap are selling these for $49
http://www.supercheapauto.com.au/media/21172/2664-jump-start_117x132.jpg

about 8?

what makes you think a car battery will run a radio longer than C cells?

C-cell = 8ah

8x8 = 64ah

a typical car battery will probably be half that or less.

just use normal alkaline batteries, they'll be fine.

http://www.powerstream.com/battery-capacity-calculations.htm

Car radio and speakers not really an option because of short timeline.

What do you mean by that? Are you saying there's no radio in your car and not enough time to install one or not enough time to rig up your own boom box style radio using car gear?

I had a car battery running an inverter + my laptop for a few hours one night during a black out with no signs of the inverter bitching about low batteries. Also I believe car batteries produce hydrogen? gas but is that only when they're being charged or also when they're being used? Either way I'd keep it away from sparklers & candles & s*** if you go down that route.

If it were me I'd just take along a few value packs of C cells, seems easier than carting a car battery around, possibly spilling the acid, you're going to a park, parks have kids, soccer balls, footballs, cricket balls and idiots who could stumble all over your s***.

edit: get one of these and get a workout while you listen :p

last edited by whoop at 01:08:28 20/Jan/09

You also forgot they are f***ing heavy

I made it. Radio was 8 C-cell radio for $35 from K-Mart.

64Ah is reasonable, but a car battery half-less - a car batt is like 1700-2000+ Ah I thought.

Anyway, worked like a treat. Did a nice mod with proper clips and a 3AG-type 3A inline tamper-proof fuse. It all wraps up nicely into the original battery compartment (you can no longer run the radio on batteries).

http://img159.imageshack.us/img159/6708/n5055086711227705350yq6.jpg

can't believe you wouldn't just use energizers
hilarious

I made this about three weeks ago for a fishing trip



the solar panel was about $170 from jaycar but has no problems pumping out nearly 20vDC @ 1.5A
so I have that into a DC - DC charger, 12v 7.2Ah battery - 2x USB <-> 12v fused sockets to power the iPhone & speakers

it will run all night on the battery no worries and charges while running all day no worries

Nice one tequila. Yeah I've seen those solar panels at Jaycar and thought twice about wasting some money on them - but so far I have resisted :-D

20V @ 1.5A is very solid! You're giving me ideas already. I didn't realise they had that kind of performance.

I don't know much about electricity but when I measured it with a multimeter (on a cloudy day) it registered 18.7v and wouldn't budge from 1.5A

something tells me its probably capable of more than 1.5A but its 'resisted' somehow, possibly using a resistor

once again, dont know much about electronics - just enough to play with DC and know I probably wont kill myself

its a 10W panel, they had other types there for cheaper but they were about twice the size for the same kind of power output

^ That's actually pretty damn awesome tequila!

Do they have those kinda setups for noobs? Ie you go to jaycar, and purchase, and plug in ipod/speakers.

yeah pretty much, the solar panel just has two wires (+ & -) coming off it, so I just plugged that into a small dc-dc charger (also from jaycar, about $20)
then i plugged that into the battery (also from jaycar, $30~ - heaps of different sizes)
then I knew I had a reliable 12v source and I just grabbed a couple of those 12v <-> usb output things (also jaycar, $7.95 each) and wired them directly to the battery (they're internally fused)

then i can just plug in anything thats got a USB power cable (ipod, iphone etc) -
so then I went into dick smith and found a set of suitable speakers which run off USB ($20~) and they're 4 watts

perfect for use in a tinny or just chilling on the beach @ camp site etc

some pics - http://unix.org.au/~brett/projects/solar/
battery was 6Ah not 7.2

made the little tray from scrap wood, going to finish off the enclosure when the mrs isnt looking (got wood chips all over the floor of the apartment already)

last edited by tequila at 10:17:36 29/Jan/09

64Ah is reasonable, but a car battery half-less - a car batt is like 1700-2000+ Ah I thought.

uh nowhere near.

car batteries are all about pumping out HEAPS of amps for a short period.

RC you can use to convert back to amp hours, RC = number of minutes a battery can pump out 25 amps before the voltage drops off (aka before deep discharging the battery).

so to work out amp hours you can just do

AH = (RC * 25) / 60

so for an 80RC battery (which is pretty large) its only about 33AH.

the one you had there was probably more like 35RC so about 15AH. you would have been better off with a D cells.

Ah well, it works like a treat and the car started straight away after using the radio for a day, so no sweat. Plus, it was fun, and that's priceless, amirite?

its pretty funny from where I'm sitting

but I can appreciate the desire to play with toys/electronics
I only went the solar route for fun, I could have quite easily chucked 4 x AA's in my speakers too

I agree pinky, wheres the fun in just chuckin in the batteries. Also, your probably more likely to have a car battery (thats probably gonna be pretty charged up if its in a car) than 8 of those other batteries, that you would have to replace all the time.