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Power Connections

Page history last edited by Zonker Harris 6 years, 1 month ago

The considerations

  • The height under a module (one plate and one brick tall) is only 1/2 inch (12.5-mm).
  • Connections should be polarized, to prevent reversed connections.
  • Connectors should be easy to mate and to uncouple with one hand.
  • Should be able to carry at least 250-500 milliamps, sustained load.
  • Should be difficult or impossible to short the pins. 

 

The candidates

  • Molex .062" series connectors (stiff to connect, but can be adjusted)
  • RCA Phono (stiff to connect, harder to tune, exposes user to power)

 

The prototype

  • Using the molex .062" series connectors
  • ~6" sections of 20-24 gauge red/black twinlead between connectors.
    • 20-gauge wire will supply power better to more MoCs.
    • a small ring of heat shrink to hold the two pairs close to each other. 
    • two pairs join at most connectors, just one pair at the ends of the harness.
    • red for positive, to the "pointy end" of the connectors. Black for negative. 
    • consistent polarity is important, since many folks will use LEDs instead of lights
      (Some folks may also use Arduinos, which will burn out if the polarity is backwards.)
  • Male shell, and female pins on the cable harness.
    • reduces chances for shorting the pins on the power cable.
  • Power source and MoCs use female shell and male pins.
    • power source can "stub-in" to any open port on the cable harness.
    • power should NOT be turned on until its connected to the harness.
    • MoCs can connect to any connector on the cable harness.

 

Male pins (still need to be soldered and crimped). Soldering will provide long-term reliability.

 

Female shells, with/without the locking tabs. The male pins in the female housing makes it easier to test your connections with an ohm meter, or alligator clips to a power supply.

 

The zig-zag style will make storage easier.
Using heatshrink where two wire pairs meet provides strain relief. At some point, you need a attach a USB connector/cable to supply power to the cable, and thus to the MoCs.

male shell and female pins

These make up the power cable harness. (Shown are the two end connectors). This way, the power pins are protected against accidental shorts.

 

Molex shells come with bend-back tabs, to lock them into metal chassis. I have cut them off for this application, to save room, and for easier handling. I was getting scratches on my hand while trying to make connections with one hand.

 

Presumptions

MoCs should have  4"-6" of cable hanging below, so you can connect the model with one hand while holding it up with another. (This still needs some "real world" testing and feedback. Holding the model and making connections with one hand would be easier with longer leads under the MoC, but then you need to stash that extra cable under the MoC as you set it down.)

 

Protoyping the design

 

Cribbing bricks can be used while you build up your module, to help press bricks and plates into place. Once the module is built, you should remove the cribbing.

 

 I've built some basic bases, using the 1x4 arch brick design, so I can see whether the idea is really practical. So far, the test results are good, but only if the cribbing bricks are removed from the underside of the module. (The 18-gauge power cables below aren't supple enough to try to scoot them around to accommodate cribbing bricks below. Especially if you're placing a module into a spot between other modules already in position. You could use 20-gauge power cables, but you might not be able to supply power to as many modules.)

 

The power harness can be run in a straight line "down main street", or zig-zag as needed to put power under a group of modules.

 

The basic power harness could have 4 to 16 connectors. (I don't want to do too many, since some modules might want 150-250 milliamps each.) This harness uses male Molex connectors, with female pins, to minimize the chance of something under a module shorting out an unused connector.

 

The power feeder connections, as well as the power pick-up for the modules, will use the female connector shell and male pins. The power feeder can connect to any open connector on the power harness. And, it'll be easy to use alligator clips to connect test-power to your modules as you are developing new lighting designs.

 

The arched bricks make it easy to route the power harness under the modules. Using a single Technic Peg per side has been sufficient to hold the modules together, but they are not needed if you have a good, flat table for your display. (A large sheet of 1/4" plywood can fit in your car, and provide a flat base for a small-to-medium sized display.

 

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