I just finished to assemble the Bucket Wheel Excavator (42055) set, I inserted new batteries in the battery box and tried to power it up.

The LED on the battery box blinks for a millisecond almost imperceptibly, and nothing happens.

I now wonder what could be the problem, I tried with several different batteries without luck, tried to clean the metal parts, but still nothing.

How can I understand if the problem is the battery box or the motor?

  • Did the motor function before you inserted it into the model? If you didn't try that, you'll need to disassemble the model far enough for you to try it without any possible load. If you have somehow locked the gearing, then the motor will probably give up to prevent burnout. – user9308 Jan 8 '18 at 10:43
  • No I haven't tried it before. I'll do some test – Fez Vrasta Jan 8 '18 at 10:43
  • Even if there are blocked gears, you should be able to hear a small "click" as it takes up the strain. – user9308 Jan 8 '18 at 10:49
  • No I can't hear anything at all – Fez Vrasta Jan 8 '18 at 10:49

First: check battery condition. Are all 6 batteries fully charged? Or for non-rechargeable batteries: are they all functioning (new, not expired, no chemical leaking damage)? If one single battery is dead or defective, it can prevent current to pass. If you have another set of fresh (or fully charged) batteries, try using these (but see also the step below).

Second: verify proper battery placement. The Lego battery box requires the batteries in each sub compartment to be oriented the same way (all tops pointing in the same direction - no battery should have "inverted" orientation). Check that you placed the batteries in the battery box with the right orientation and with the proper polarity (as indicated in the battery box).

As a side note - I always put a piece of plastic sheet ribbon (used in gift wrappings) in each side of the battery box compartment prior to adding batteries; this facilitates subsequent removal of depleted batteries. You can remove the last battery by pulling both ends of the ribbon.

Third: verify that the battery box works properly. If batteries are healthy and battery polarity is correct, then first test the battery box unattached. The orange slider has 3 positions: on-off-on (either 'on' reverses the polarity for the motors attached). When the slider goes left or right (either 'on' position), the green indicator LED light should remain on. When the slide goes into the middle position (off), the LED indicator should remain off. If this fails, contact Lego to supply you a spare battery box.

Fourth: verify that the motor works properly. It is wise to test the battery box and motors prior to assembling any motorized model. If you know the motor previously worked, and you have access to another unused motor, test your battery box with that other motor. If the battery box doesn't manage to operate the motor, try using another battery box if you have one at hand. If that other battery box works, then contact Lego to supply you a spare battery box.

If neither battery box operates the unloaded motor, then contact Lego to supply you a spare motor.

  • 1. I specified that I tried several different batteries, new and not. 2. my battery box fits only 3 batteries, all 3 oriented the same way. 3. The LED doesn't stay on... I guess it is – Fez Vrasta Jan 8 '18 at 16:50
  • @FezVrasta there should be 6 batteries in total, 3 in either compartment of the battery box. If the green LDE indicator light never stays green, even with all batteries in, then your battery box looks indeed defective. – ShutterFreak Jan 8 '18 at 18:52
  • oh f**k, I didn't realize I had to put other batteries the other side! It works! Damn I'm such an idiot ahahah – Fez Vrasta Jan 8 '18 at 18:57

As Phil B suggests you really must start by testing a motor by itself from the battery box. This will confirm whether that battery box is working or not.

My experience in Radio Control has taught me to test each "electrical" bit one at a time and in a logical sequence starting from the power source until the fault is identified.

For the future it worth testing electrical things like the motor and battery box before they get "built in" to a complex model.

  • Thanks for the advice, there's nothing between the battery box and the motor, they are linked directly and the battery box turns on manually, no radio controls. What I wonder is if it is normal for the battery box led to not stay on while the battery box is powered? – Fez Vrasta Jan 8 '18 at 12:30
  • When no motors connected to it, the led should stay on. The led can go out if faulty or too many motors are attached... – Michael Verschaeve Jan 8 '18 at 13:05

Do you have another battery box from another set you could try? You could purchase the motorization set to have a spare battery box and some other useful components. However, I think I own at least 50 battery boxes, I have never experienced any issue with them. Likewise, I never have experienced any issue with motors that are new. What also could be the issue is that you have made a mistake in a building step somewhere which causes the drivetrain to block. The motors and battery box have circuitry in them so they shut themselves off if too much current is drawn, which happens when motors are blocked. I would test this with all switches in neutral and then see if the motor spins freely. If this is the case you'll have to test every function, see what blocks where and resolve it with the aid of the building instructions.

  • I already tried to run it with all the functions set to neutral. I can't hear any sound at all from any part of the set... – Fez Vrasta Jan 8 '18 at 10:37
  • Take the battery box out, and one motor. Connect those, hold the motor in one hand, and see if it works when you turn on the battery box. If yes, the problem is in your build as per this answer. If no, there’s either something wrong with the battery box, the motor, or the way you inserted the batteries (or the batteries themselves, but since you’ve tried several this is unlikely). – Phil B. Jan 8 '18 at 10:43
  • If you can demonstrate issue with a motor or the battery box, lego support will be happy to send you replacement parts... – Michael Verschaeve Jan 8 '18 at 10:51
  • I don't think there's anything wrong with the construction, as last resort test I tried to manually rotate the gears connected to the motor and they rotate just fine (obviously with a bit of difficulty because of the motor not being turned on) – Fez Vrasta Jan 8 '18 at 11:39

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