New power supply for old lego motors

November 13, 2013 11:47 AM

I have a bunch of old Lego 71427 motors (seen here) and a battery pack (I believe part 5293) that was stored for a decade with the batteries inside, with predictable results. Easiest way to make these usable, short of tracking down the long-discontinued original battery pack?

According to the Lego FAQ "you can use most of the 9V elements" with the current power supply with the "8886 Power Functions Extension Wire".

A) Does "most of the 9V elements" include the motors I have?

B) If so, do I need to replace all the old wires with the new type, or can I get away with just buying one to connect the first motor to a new power supply, and then daisy chain the rest using the old connectors? (The connectors I have look identical to the current ones on the female end, but on the male end have four regular studs instead of the current two-studs-plus-rectangular-4-pin-connector.)

posted by ook to Sports, Hobbies, & Recreation (5 answers total)

If this is the battery pack you're looking at, it's a nine-volt unit. Assuming that that battery pack was made to work with your motors (which I think it was, I remember having both of them together as a kid I think) any assemblage of batteries that outputs nine volts should be able to power those motors. In alkaline AA terms that would be six batteries wired in series, or eight in NiMH rechargeable AAs (well, seven and a half but round up to eight; NiMH batteries are 1.2V nominal rather than the 1.5V of alkalines).

Assuming you want to go with rechargeables, the simplest thing to do would be to get an 8-battery holder like this one or this one (the second one comes with a built-in switch) and figure out a way to wire it up to your motors. You could perhaps even build a battery enclosure out of LEGO, or attach some LEGO to a store-bought holder to make it integrate with your stuff if you want. You could also use 9V batteries but their capacity will be tiny and they're harder to find as rechargeables.

It wasn't clear to me which motors on the page you linked were your model, but an image search for the part number indicates that they're these square jobbies that I remember from my own childhood. The contacts for those are on the black two-by-two on top. That'll be a little difficult to directly wire something to, though you might have a LEGO-specific connector in your collection somewhere, or perhaps you can scavenge something off of your bad battery packs. If not, this image suggests how you might remove the contact panel and solder in some regular wires.

That's how I'd approach the problem. Good luck!
posted by Scientist at 12:36 PM on November 13, 2013

The old wires could be connected to other wires exactly the same way as the old motors, so as long as the new wires can connect to the old motors (and they look like they do, and LEGO says they do) then they can also connect to the old wires.

Looks like you do need at least one new wire to connect actually connect to the new battery pack, though.
posted by ckape at 2:18 PM on November 13, 2013

Take a Lego connecting wire with the square connector on each end, cut it in half, and splice the dangling end to whatever other device you want, like a generic battery pack. Encase the whole thing in Lego bricks, with the connector showing on the roof, and you've got a custom battery pack.

These motors and wires were used by the "RCX" era Mindstorms kits, if that helps.
posted by alexei at 2:58 PM on November 13, 2013

You might check BrickLink or similar. If I found the right part, looks like you can get an actual replacement for ~$1. You said "short of replacing" but this is pretty cheap to have an actual replacement part.

Plus all the fun that comes with minimum orders! I picked up so many extra parts for my son trying to get that one wing piece I was missing...
posted by caution live frogs at 9:31 PM on November 13, 2013

Response by poster: looks like you can get an actual replacement for ~$1

That's for the instructions for the part, not the part itself, sadly. :) Best I've seen for the old device is on eBay for $20, which is about double the cost of the current-generation one...
posted by ook at 10:42 PM on November 13, 2013