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ammo box radio
swanny - 15/8/16 at 10:29 AM

this is a dumb question so apologies.

im making an ammo box radio and have a mini amp (3a) and a 12v 7ah battery.
rather than fry the amp is there a simple way to use these two together?

Thanks

paul

r1_pete - 15/8/16 at 11:21 AM

If the amp is 12v there is no problem, a higher voltage supply will do damage, but an appliance will only draw the current it needs.

swanny - 15/8/16 at 11:40 AM

ahh. But when i roughly connected it up i quickly got some warm wires and a very smelly (and non working ) amp, so i'd presumed that i'd fried it with the battery

gremlin1234 - 15/8/16 at 11:43 AM

as he said, if radio is designed for 12v no problem.
but do use a 3A fuse in line.

ps a 7amp hour battery, will theoretically supply 3 amps for a little over 2 hours.

in reality, you wont be using it at max current, so should last longer.

gremlin1234 - 15/8/16 at 11:45 AM

quote:
Originally posted by swanny
ahh. But when i roughly connected it up i quickly got some warm wires and a very smelly (and non working ) amp, so i'd presumed that i'd fried it with the battery
give us a photo of the amp, or its spec
was it connected the right way round?

swanny - 15/8/16 at 12:00 PM

this one

gremlin1234 - 15/8/16 at 12:32 PM

that has a power input of 12V 2A, so you should use a 2A fuse.
it is also centre positive for the power connection, (test the connector you are using)
when you tried it, did you have any speakers connected?

swanny - 15/8/16 at 01:30 PM

yes i had speakers connected. i will get a fuse and test the connector

thanks for the help, much appreciated

paul

BenB - 15/8/16 at 04:33 PM

Are the speakers the right impedence for the amp?

02GF74 - 15/8/16 at 07:44 PM

At full whack, assuming your spkrs can take it, that amp will be drawing 16 A, thr piddly battery may struggle.

Unless you want to shake the neighbours windows, you probably need no more than 30 w , i assume speakers will be inside the box.

Re. burning, doesnt sound good, if there is no load, i.e. spks not connected then it should draw little current. Best fit a small value fuse eg 2a before reconnecting. Did you have any input signal to it?

BenB - 15/8/16 at 09:29 PM

It'll handle it fine to begin with. I fly r/c and use i.c. starter motors pulling 20+ amps from a 7Ah battery. I've even jump starter a Nissan Micra using one. The issue at 16a would be duration. Especially as you're not supposed to drain the battery too far....

gremlin1234 - 17/8/16 at 09:41 AM

quote:
Originally posted by 02GF74
At full whack, assuming your spkrs can take it, that amp will be drawing 16 A, thr piddly battery may struggle.
amps have for so long used fictional measurement of 'peak music power output', which in this case is 200W, regardless of the 2A 12V =24W max input.
in real numbers its probably about 2x8W

swanny - 20/8/16 at 08:29 AM

Cracked it, i had the connectors the wrong way round. Never mind you live and learn. Fuse and new amp on the way! May be to try and find a better battery with longer life. Not sure if I'll find one small enough without big bucks, but it may well spend most of its time on mains. I suppose for camping trips I could use a solar charger

Thanks for replies. First ever electrical dabble.

gremlin1234 - 20/8/16 at 09:55 AM

before changing the battery, try it out, see how long it runs for