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Modifying a battery powered light to hardwired.

Bamse

Nov 9, 2018
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Apologies in advance if this is a bit simple for these forums but I'm new to this and this looked like a good place to ask.

As above, I have a motion activated battery powered indoor light and want to hard wire it so I can stop wasting batteries.

I have a AC to DC adapter rated to the current voltage and current and Im going to solder the the wires to the positive and negative battery contacts in the light itself.
My question is, should I be adding a fuse in the circuit and if so, can I have a recommendation of what type to use please?
The light runs off of 4 AA batteries at the moment.

Thanks for looking.
 

duke37

Jan 9, 2011
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Welcome to the forum, you are doing right to start with low voltage, low power equipment. You can work up to lightning generators slowly.:)

Look at the current demand of the light and select a fuse somewhat bigger than this. You probably need a 100mA one or so. A delay fuse that is one marked T may stop stop the fuse blowing at switch on.

I assume the light contains electronics. If so, get the polarity right.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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You didn't say what the rated voltage and current for your motion-sensitive light is. Four alkaline chemistry AA cells provide 6 V DC when fresh. The current available from AA cells is typically less than one ampere, so if your AC to DC power supply is a "wall wart" delivering 6 V DC at no more than 1 A (6 watts), you probably don't need a fuse. Such devices are self-current-limited by design.
 

Bamse

Nov 9, 2018
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Thanks for the help and the suggestions guys

The light is led so very low power the manufacturers spec state that is 0.7 Watts at 6 volts so I work that out to be 0.12amps.

It does contain a small circuit board

It's interesting you say the batteries provide 6 volts when fresh. After the batteries have been used for a week or so the light starts to intermittently switch itself on and off and I'm assuming this is because the voltage has dropped as the batteries have depleted somewhat. This of course won't be an issue when it's hard wired.

Also, I'm not sure what a Wall Wart is? I would be using a standard Ac/DC mains to 12v power supply.

Thanks again all :)
 

duke37

Jan 9, 2011
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A wall wart is a lump which plugs into the mains and outputs a low voltage in its tail. Such a device is used in most low powered equipment as the equipment can be standard, only the wall wart needs to be changed for different power supplies.
They give isolation - they will not give a shock on the output. Most have coaxial output plugs and may have the centre pin positive or negative. More modern ones are usually centre pin positive. Note that some wall warts do not have rectifiers inside and produce AC. Just look at the specification.

Edit: The battery will provide 6V so why not use a 6V wall wart? You could even try a 5V USB supply.
 

BobK

Jan 5, 2010
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Also, I'm not sure what a Wall Wart is? I would be using a standard Ac/DC mains to 12v power supply.
If you connect it directly to a 12V supply, you won't have to worry about powering it any more, it will be dead.

Bob
 

Bamse

Nov 9, 2018
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If you connect it directly to a 12V supply, you won't have to worry about powering it any more, it will be dead.

Bob
True, but if you look at the link for the 'Wall Wart' I posted then you'll see it's adjustable to 6v. That is clearly what I meant but wrote 12v in my first question. I'll try to be more concise in future questions :)
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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I like to qualify my answers with weasel words like "maybe," "probably," and "your mileage (or kilometers) may vary" because no one here can be responsible for what original posters do, or how they do it, with the answers we provide. This is a hobby forum. You are responsible for your own disasters if such occur.
 

Bamse

Nov 9, 2018
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And they do, quite often
Which is why I'm asking questions here :)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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It is also quite possible that your switched power supply, even on 6V may still more than 6V.

If I were you, if check it.

Rather than soldering the wires to the battery terminals, I would make some fake batteries. I have used a piece of dowel with screws in the ends. The fake batteries can then be inserted, with the power wire slid under the appropriate screws. This allowed you to easily change back to using batteries again.

There is a chance that your device uses a tapping between batteries for some reason. If it does, then simply connecting a power pack as you are planning may not be successful.
 

Bamse

Nov 9, 2018
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Thanks, good advice about checking the actual voltage
I've seen people using dummy batteries but I don't need to be able to swap it back and forth plus, I can always bypass the battery compartment completely and just soled the wires directly to the positive and negative on the board itself I assume
 
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