Power Board                                                                            Latest change 2017-09-06


In brief:
Discussion of the electronic circuits involved.
Download the zipped Eagle files for PowerBoard. Or the PDF's: Power-Schema,   Power-Board.
Switch to the description of the Bob Control Board.

Schematics and board layouts are drawn with Eagle 7.7.0 Premium. Although I have a licence for larger boards I tried to limit the boards such that they can be handled by the free version of Eagle. As I did not intend to make real PCB's for this project I did not route the boards, I used Eagle just to place the components in a more or less logical way and did the wiring by hand. The Eagle files are likely to contain inapropriate footprints.
Power Board
All electronics in the Foucault system are supplied from one 24Volts battery which is constantly charged by a mains power supply.
In case of a mains power failure the system can run for quite some time from the battery.

Note: Currently a laptop will run the GUI which does graphical presentations and logging. This laptop is not powered from this unit or battery but directly from the mains 230VAC. In the (near) future this laptop is to be replaced by a Raspberry-Pi or the like, which will be supplied from this power supply, but with a different DC/DC converter.

The functions on this board are
- Providing several supply voltages for the board 'BobControl'.
- Monitoring the input and output voltages, and the current drawn or supplied by the battery.
- Temporarely switching off the mains supply power to test the battery status and capacity.
- Reading the temperature sensors on the Power Board and in the Topmount.


PowerBoard-tmb.jpg
Fig 1. Power Board.

The supply voltages are produced by 3 DC/DC converters having an input voltage range of 19 to 36 Volts and output voltages of 5Volt / 500 mA and + and - 15 Volts at 100 mA. See the datasheet of this series.

The input and output voltages are monitored by analog inputs of the Arduino, after voltage division by resistors. The Arduino does 10-bit conversions so we have a resolution of 1 in 1024. The positive voltages refer to GND, the negative voltage refers to +5VD. The +5VD itself is monitored indirectly, as it is the reference for the A/D converter it can be related to the very accurate voltage reference of 2.5 Volts from IC1 datasheet.
For the calibrations I have assumed that the reference voltage is exactly 2.500 Volts and that the dividing resistors also are exact. (which is not, of coarse, but I have no measurement equipment to verify this).

We can state that there is a mains power fail when the PSU voltage drops below the +24Volts level. Normally it should be 0.7 volts above it.
We can deduce a blown battery fuse when the battery voltage is substantially below the +24Volts level. A fuse in a lead-acid battery is of coarse mandatory because in case of some short extremely large currents can flow and will produce a fire hazard.
When the battery current is constantly large and in the charging direction we can conclude that the battery is bad, it may have lost one or more cells.

Temperature measurments are done with Dallas 18B20 digital temperature sensors. One sensor is at this board, the other is at the Top Mount of the pendulum with the Hall sensors. Why temperature measurements? The first idea was in connection to the thermal expansion of the Bob's wire. Afterthoughts indicated that this effect would be very small with a pendulum of this size. But at that time the sensors were in the design already and I decided not to take them out. We'll see....
  
RelayBoard.jpg   RelaySchema.jpg
Fig2. Relay Board.

With relays on an external board driven by Q2 it is possible to  interrupt the mains power temporarely and on purpose to test the quality of the battery. I have not yet decided upon a testing scheme.