Replace 9v square battery with mains connection?

noshankus · 04-02-2011 10:28AM #1

Hi All,

I have a box which basically just keeps a small LED alight. The problem is that I use a small square 9v battery to power it and the battery runs out every ~ 2 months. It's a huge pain to get to it and replace the battery, but I have a mains cable right beside it that I could use.

My question is, how could I go about this, and preferably small and cheaply.

I understand that I'll have to step down the mains and maybe have a transformer to change from AC to DC.

Is there anything out there that would do this all in one go and come in a small package?

Many thanks for your help and ideas!

noshankus · 04-02-2011 10:36AM

Hmmm, what about one of those small transformers for lights in a dresser for example. You know the ones that light up a sitting room dresser... they're small and might work?

drBill · 04-02-2011 10:48AM

Any old mobile phone charger should do the trick. Most of them put out less than 9v so (presuming you already have a resistor in series with the LED) you might need to change the resistor to maintain the same brightness.

And you don't really need to change from AC to DC, AC will still light a LED - although there will be a slight flickering/shimmering effect which may or may not be noticeable.

noshankus · 04-02-2011 11:05AM

Interesting and a good idea!

Could I essentially open the charger up, attach the live/neutral wires straight into it and chop off the end of the charger wire and attach the wires directly to the contacts where the battery connects?

Or am I being way to naive?

meercat · 04-02-2011 01:07PM

No need for transformer
There are mains operated smoke and heat detectors available from your local electrical wholesalers
They also have a battery backup.
http://www.safelincs.ie/Kidde-9HI-Mains-Powered-Smoke-Alarm/

noshankus · 04-02-2011 01:58PM

Haha! Brilliant!

This will work a treat

Replace 9v square battery with mains connection?

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