Noobs next project (Lego): convert battery powered to DC?

Thread Starter

Todd W. Roat

Joined Jun 7, 2015
Back at it for new project but little electricity and circuits experience. I purchased one of those large LEGO displays you see at Taregt that contain lego toys, light, and a motion sensor that triggers the lights coming. Kind of cool. But it takes 26 D-cell batteries to run it! No wonder they never worled when I was in the stores.

I would like to convert this to a basic plug DC. Below are the pictures of the relevant battery wiring and the small circuit board used.
As always, all input welcome so I dont fry it.

As Im typing this Im think is the board might not even be needed. Not exactly sure what it does. Rewiring for direct power LED lights might be enough. Guess I should bite the bullet and buy 24 batteries to at least see what all the functionality is first huh.

Pretty sure it sat quite until you motion sensor (top of the one picture/wired) triggers, lights up, and maybe some noises.



Joined Sep 9, 2010
... it takes 26 D-cell batteries to run it!

The first step is to figure out how all those batteries are connected. Are they all in series, giving ~39V? Are some in parallel?

If you're lucky, the whole thing might run off a typical laptop power brick - the AC adapter. These put out about 19V and several amps of current.


Joined Oct 15, 2009
More than likely the large amount of batteries is so the display lasts a long time (the season) or whatever so employees aren't always tasked with replacing batteries daily..

As wayne said.. you need to see how all the packs are wired to determine the voltage and current requirements for the supply....

blocco a spirale

Joined Jun 18, 2008
From the board, it looks like the 6V packs are in parallel (via diodes) so 4 cells should be enough to test it and a 6VDC power-supply is all that's needed to run it. I presume the large number of cells is simply there for longevity rather than to serve some unusual power requirement.

Unplug all the battery holders from the board (the 6 plugs on the left), snip the leads off one of them, connect it to a 6VDC power-supply and plug it back into the board in any one of the six empty positions. It probably won't need more than a couple of amps.
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