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Help with 12v battery backup circuit

I have a sirius radio that has 45 second memory. The radio is 12v DC. I want to build a temporary battery pack. The reason for this is because if I unplug the radio all memory is lost.

So I want the house and car adapter to plug in to the battery pack and the pack to plug in to the radio. When ever there is an external power source the battery is bypassed. Can anyone help me get started on building a switch that will work like this?

I want to have one 12v dc femail going in and one 12v dv male coming out. I just need help with the switch so that there is no power going in to the batteries etc...

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Bob
Reply to
Bob
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You could use a relay that is operated whenever external power is available. The wiper of the relay connects to the output power to the radio. The contact that is closed when external power is available is connected to the external power source. The contack that is closed when no external power is available is connected to the battery pack.

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Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
dan.hollands@gmail.com
www.QuickScoreRace.com
Reply to
Dan Hollands

Do you know where I can pick up a small 12v relay I would asume15amp max? I found a few bigger ones but a smaller one would be good.

Reply to
Bob

If the voltage of the external power source will be higher than the battery voltage, then: (view in Courier)

+----------------------+ | | +12V>---
Reply to
John Fields

Get a closed-circuit jack. When there's nothing plugged into the jack, the battery provides power to the output through a third contact. When you plug in the wall-wart or car adapter, the plug displaces that third contact, taking the battery out of the circuit.

Good Luck! Rich

Reply to
Rich Grise

On 09/02/2006 the venerable Bob etched in runes:

to build a

all memory is lost.

pack to plug in to the

Can anyone help me

just need help with

Two 1N4001 diodes.

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John B

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Reply to
John B

want to build a

all memory is lost.

pack to plug in to the

Can anyone help me

just need help with

--
Like this?:

news://ag3nu19omnlait7mhu1moigpk9ophjtclf@4ax.com
Reply to
John Fields

Try

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There is no way you will need 15A contacts. it should say somewhere on the radio what is required. unlikely it is more than an amp.

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Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
dan.hollands@gmail.com
www.QuickScoreRace.com
Reply to
Dan Hollands

The two 1N4001 diodes arranged in the 'wired OR' configuration is the easiest and cheapest solution, I have implemented this circuit in commercial applications and works a treat.

Regards Alan

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Reply to
electronic-eng.com 

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Assuming equal drops through the diodes, the battery and the 12V
source will share the current into the load until the battery
voltage drops below the supply votage, at which time the supply will
reverse-bias the diode in series with the battery, effectively
removing the battery from the circuit.  Even better, instead of a
1N4001 in series with the supply, use a Schottky. Something like a
1N5819 would be OK, and it would also be a good idea to put a Zener
diode across the 12V supply in order to soak up spikes, like this,
if you\'re going to be using it in a car:


         +---------------------------+
         |                           |
+12V>---
Reply to
John Fields

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