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Automatic switch from battery to ac-dc?

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revans

New Member
Ok I'm working on a portable speaker project at the moment using the Amp6-Basic amplifier from 41Hz audio amp kits

I'm running it off both battery power and ac-dc and would like to be able to rig it so that it runs off battery when there is no wall power available, but then when a 12v ac-dc adapter is plugged in it will automatically switch to that.

Could anyone please help me out as to how I would be able to do this?
If you'd like/need more details, just ask. Thanks.
 

BeeBop

Active Member
Ok I'm working on a portable speaker project at the moment using the Amp6-Basic amplifier from 41Hz audio amp kits

I'm running it off both battery power and ac-dc and would like to be able to rig it so that it runs off battery when there is no wall power available, but then when a 12v ac-dc adapter is plugged in it will automatically switch to that.

Could anyone please help me out as to how I would be able to do this?
If you'd like/need more details, just ask. Thanks.
Just use a jack which has a switch built into it for your adapter to plug into. The switch disconnects the battery. These jacks are quite common.
 

revans

New Member
OK so now I've found a suitable jack...could someone please explain how these work and how I would go about wiring it up so that when no adapter is plugged in battery is used and then when I plug a 12v adapter into the jack it switches over to that?
 

audioguru

Well-Known Member
Most Helpful Member
What are you doing with a little car radio amplifier that has only 11 Watts per channel into 4 ohms?
The battery in a car will power it for days.
A car battery charger will charge the battery plus power the amplifier so a switch is not needed.
 
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BeeBop

Active Member
OK so now I've found a suitable jack...could someone please explain how these work and how I would go about wiring it up so that when no adapter is plugged in battery is used and then when I plug a 12v adapter into the jack it switches over to that?
One of the contacts on the jack will disconnect when you push a plug into the jack. That contact goes to your battery, the other side goes to your power in connection. When there is no adapter, the path from the battery to circuit is complete, and your cct uses the battery. When you plug in an adapter, the battery is disconnected, and the adapter feeds your cct. Hope that makes sense...:)
 

revans

New Member
@audioguru: It ain't a car radio, it's a portable boombox/ghetto blaster/speakers :D
something along the lines of this: Portable Amplifier and Speaker Box Mod by MetkuMods

@BeeBop: Umm, I'm sort of 50-50 on the making sense bit. How are you meant to connect the amplifier and battery via the socket, when the socket has three terminals, and you really need four? (+/- to amp, +/- to battery). Must you double up on one terminal?
 
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BeeBop

Active Member
@BeeBop: Umm, I'm sort of 50-50 on the making sense bit. How are you meant to connect the amplifier and battery via the socket, when the socket has three terminals, and you really need four? (+/- to amp, +/- to battery). Must you double up on one terminal?
The - is (usually) the ground connection. So the - of the jack, battery and circuit will all be connected together.

The other two connectors on the jack are like a switch. One side is connected to the battery, the other the circuit. When you push the plug into the jack, then the switch opens, disconnecting the battery.
 

revans

New Member
Sweet as, I've got it now :D Thanks for your help, BeeBop.
However, if you'd like to continue your great work I've got another question ;)
Would it be possible for that dc jack to power 2 different circuits? Both use 12v so it would sort of be like running them in parallel, if possible? I've have illustrated my very probably stupid idea with my unbelievable paint skills. (see attched file). Thanks.
 

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audioguru

Well-Known Member
Most Helpful Member
The amplifier is rated at 25 "Whats" per channel. When the battery is 14.4V (impossible) and the volume is turned up way too high so the output is horribly distorted square-waves with 10% distortion into a 4 ohm speaker.

With a fully charged 13.8V lead-acid battery then the power is 14 Watts into 4 ohms at clipping.
How will you carry a lead-acid battery? It is very heavy.
 

revans

New Member
@audioguru: Honestly, I didn't really understand the meaning or relevance of anything you said except the last line ;)

Anway, the SLA I'm probably use is 5aH and weighs 1.8kg. I'm not sure about the total weight with speakers and plywood enclosure but it should definitely be <10kg which should be pretty manageable. (btw I'm not looking to carry it everywhere, just want to be able to carry it, say, down to the beach or out into the garden.
 
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audioguru

Well-Known Member
Most Helpful Member
My beach sound system had two midrange/tweeter satellite speakers at 4W each and a sub-woofer at about 8W.
It had 12 AA Ni-Cad rechargeable battery cells producing 7.2V.
It played loudly all day.

Your sound system might sound like mine but it will be slightly louder and weigh much more. They will weigh much less if we use modern Ni-MH AA cells.
 

revans

New Member
You have a point there, but...as I am running it off both ac-dc and battery, I decided that I wanted to only have only one set of external cords associated with the speaker system (i.e I didn't want to have to use a separate battery charger). With an SLA battery, I can use this circuit: 12V powered, 12 V battery charger which will enable me to use one 12v ac-dc adapter to both power the amplifier and charge the battery.

Also: Anybody got anything to say on my double power thing (see post with awesome paint drawing)
 
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BeeBop

Active Member
Sweet as, I've got it now :D Thanks for your help, BeeBop.
However, if you'd like to continue your great work I've got another question ;)
Would it be possible for that dc jack to power 2 different circuits? Both use 12v so it would sort of be like running them in parallel, if possible? I've have illustrated my very probably stupid idea with my unbelievable paint skills. (see attched file). Thanks.
Yes, that would work...:)
 

BeeBop

Active Member
Wow... I wasn't expecting that :D I suppose the current for each circuit would add up. So say if circuit #1 drew 2 amps and circuit #2 drew 1 amp I'd need at least a 3A 12A AC-DC adapter?
Yes, and some headroom would be nice. Depending on what the circuits are, they could use more current on start up than in opperation....
 
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