wiki/ GroundTeamHome/ launch tower power interface board

Electronics - Power Interface Board

The Power Interface Board is used to bring all electrical connections in the LTC box to one location, create a common ground, and then go out to all the devices in the box. Additionally, this board will allow an operator at the LTC box to visually see that all connections are good and the system is operating.

General Notes

Circuit Choices

Decision Tracking

Some of the decisions on this portion of the project were debated - here's the reasoning:

  1. Use this board to star the power

  2. Using this board creates a star topology for power. This is negative because wires could be running extra distances.

  3. Having all the connections in one place will make the box cleaner.
  4. Having all the connections here means we can monitor the system health.
  5. Ultimately seeing the connections are good is more important than the starring - so we'll go with this board.

  6. Power converters on the board

  7. In the past power converters have been off-board devices so if they burnt out they could be replaces without making changes to circuit boards.

  8. No power converter has actually fried so this requirement may be necessary.
  9. By putting converters on the board we can save a lot of space and get reduction in LTC container box.
  10. If we're building a "power board" it makes sense to have everything related to power on it.
  11. In the end the small size of power converters we found fit really well with the board size and if something fries - we'll just de-solder it (so all parts have through holes). Also, we should put sockets onto the board and not actually have the converters mounted but we forgot to order sockets.

  12. Umbilical power at 24v

  13. The decision to put power converters on the board resulted in not being able to find an 18v DC/CD converter.

  14. The decision to upgrade to a 24V converter was made because the rocket can handle it and the part was very robust.

  15. Use the solar charger load terminals

  16. The solar charger has three sets of terminals - solar panel, battery, and load. In the old launch tower the load was not used to feed the system - instead system draws right off of the battery.

  17. The load terminals may get cut off by the charger when the voltage drops to (say) 10V. However, we want our system to be able to run itself off the battery even if the battery gets down to 9V or 5V. For this reason, we can't afford the system to cutoff power so we will continue to NOT use these terminals - and instead run the system directly from the battery.

  18. I/O screw terminals distributed around perimeter

  19. The screw terminals are located to put them closest to their actual device - limiting cable length. This required the layout of the box to be figured while this board was developed and could be a slight problem if the layout got changed int he future.

Design Reference - July 23, 2012

Here are the current schematic and layout designs as of July 23rd, 2012. This design was submitted as the final production run. Major changes have occurred on the board compared to June 18 version and final description of board and choices are above.

Eagle files available in the GIT repository "launch-tower".

Design Reference - June 18, 2012

Here are the schematic and layout designs as of June 18th, 2012. This shows the general idea of bringing all the power into one location with LED indicators. Left here as a reference comparison to final version.