Power Board Latest change 2017-09-06
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
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.
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
Fig 1. Power Board.
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....
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.