Batterys and Voltage Question

Hello, im new here (made my account 2 hours ago) so hope i have asked this in the right place.

im planning on building a speaker rucksack, i.e modifing some speakers into a rucksack. now the speakers i have chosen to mod into the bag are mains powered but i want to power them with batteries.

The speaker adaptor looks like this...

http://i40.tinypic.com/71h9at.jpg

and reads "Logic3 AC/DC ADAPTOR CLASS 2 TRANSFORMER, INPUT : 230V 50Hz, OUTPUT : 15V 1200mA MODEL : D57-15-1200"

I have 2 batteries which combined i think i could use to power the speakers, they look like this...

http://i43.tinypic.com/3321buv.jpg

http://i39.tinypic.com/1691c78.jpg

Small light coloured one reads "VALVE REGULATED RECHARGEABLE BATTERY, HGL3.2-6, 6V3.2Ah/20HR, CYCLIC.

Big dark coloured one reads "SEALED MAINTENANCE-FREE RECHARGEABLE BATTERY, UL3.4-12(12V,3.4AH/20HR).

As i understand it the speakers run off of 15V 1200mA and the batteries together will produce 18v. this is too much power for the speakers so i need something to step down the power to the right voltage for the speakers.

what do i need to do this? a certain component, resistor maybe?

any help would be greatly appreciated, thanks :)

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110100101108 years ago
oining the 12V suggestion of anyone else it may run on the 6 V one up to some volume (and have distortion if you try to go higher) or on any source of between maybe 9 and 15 V lead acid batteries can give high current if short circuited and make a lot of damage. add a circuit breaker of few A in series with the battery
superrob (author)  110100101108 years ago
by circuit breaker could i put a fuse between the positive of the battery and the speakers? also what rating should this be? thanks.
you can. a fuse provides the same protection about 4 - 7 A should be ok
superrob (author) 8 years ago
Ok, i just hooked up just the 12V battery to the speakers and they powered up and gave pretty reasonable sound, however not as good quality as when plugged into the mains. out of interest i just put my multimeter onto the mains adaptor, set the multimeter to DCV 200 and it gives a reading of 21.0, does this mean the mains adaptor is actually giving out 21V? Im not sure i trust this? if its true could i just attach both batteries to it and have 18V going into the speakers? thanks for all the help so far.
lemonie8 years ago
Have you tried it with the 12v battery (just to see)?

You need a voltage regulator, there might be one in your mains-adaptor. Perhaps you could hook-up the batteries to the mains-adaptor without disabling it's mains function?

L

t_0220.jpg
he can connect to the batteries a plug identical to the one of the mains adaptor
I don't quite understand what you mean? L
there is plug on the mains adaptor he can add one like that to the battery now he can use the speakers with either one
guyfrom7up8 years ago
it should work fine off 18 volts, but don't hold my word for it. Like Tool Using Animal and Lemonie suggest, I'd suggest trying it off of just the 12volt battery, first. Make sure you get polarity correct!
The absolute voltage on such things tends not to be overly critical, I'd suggest just attempting to run it off of 12 V and see if it works to your satisfaction.