Powering the Observatory

Providing power - the problem

The reasons for manaing the power to the observatory are varied:

Ability to operate through or recover from a power cut
Ability to handle the wet and humid external conditions
Ability to power the rotating dome section
Ability to power diverse voltage and current ranges, from very low to potentially quite high
Optional - abilty to remote control and or reset the power - tends to drive the 'operate through a power cut' requirement

this one: https://www.amazon.com/dp/B082MFJDK2?psc=1&ref=ppx_yo2_dt_b_product_details. Actually the spec says 4A at 24v so should be plenty to charge the dome battery. I had another one from Aliexpress at 140W but couldn't get it to work. This one worked first time and seems quite efficient.

The building power supply

The dome is a 2.7m wholly fibreglass dome at the end of a garden, standing on stilts. Its within the reach of a domestic mains spur so was connected via armoured cable to a RCD protected dual plug outlet bolted to a stand off the floor in the dome. The mains is then fed to a wall-mounted 7-way mains extension. This provides the mains requirement - the dome PC, the remote control switches for battery chnagrgers, inspection lamp, glue gun and monitor for working in the dome.

The remote control mains switches are TP Link Kasa domestic switches that integrate to a phone app and also to Alexa digital assistant. This happens handily to provide a means of turning on at dusk and turniong off at dawn. The building is also mounted with two solar panels - a 30 Watt panel mounted south-facing at 45 degrees inclination and a vertically mounted 100-Watt flexi panel. Since that panel is vertical it will provide more power at lower sun heights like during winter but for a shorter length of time.

Solar power

The solar panels provide their power to the low-voltage power board. This board has a number of key components:

MTPP Charger - high efficiency battery charger rather than the cheaper and less efficient PWM chargers
12V Automotive Voltage regulator 0 accepts 0-40v and put =s out a regulated 12v, up to 6A
12v Power fused connection box - leds indicate for blown fuses for each connection.
Bolt points for unregulated power in ( solar and ground )
Bolt points for charger connections to the 70AH car battery
Insulated board to mount it to...

The low-voltage power is distributed

Powering the rotating Dome

The Electronics

The controller is an ESP8266-01 wifi module which is programmable using Arduino tools. It's a 3.3v device so the device bottom left in the picture is the 5v to 3v3 regulator along with another 12v to 5v regulator to manage the power drop from the 12V supply. The ESP is the red/blue led device with the visible wiggly wifi aerial. It is tiny but consumes between 50-250mA depending on WiFi activity. To the middle is the i2c expander. This turns an industry-standard 2-wire 10 bit serial control signal into an 8-bit parallel set of signals, 1 bit for each input or output required. Bit 0 is used for nothing but flashing a LED at a 1 second interval to indicate life. Another bit provides the control to the MOSFET transistor buffered through a 2N2222a NPN transistor that powers the solenoid lock and is protected by a flyback diode. Two are the switch inputs to the controller and two more are outputs to the motor controller that configure the H-bridge motor driver. The section at top right provides the switch signal inputs and the signals from the manual switches that are then fed to the motor driver unit through the 6-pin connector. The code is available if interested at Github. As mentioned, it implements the ALPACA interface which can be operated manually via curl commands, it also supports remote debug over telnet, remote firmware update through the browser and remote querying for state from the browser.

Cost

The system cost was relatively low.

£85 for the MpTT charger from Amazon.
£40 2.5mm^2 x-section cable rated at 15A 12v - 50m coil -
also including Amazon, Ebay and B&Q
£24 12v Automotive voltage regulator - also Amazon.
£12 8-way marine fused distribution box - Amazon
Automotive battery charger.
TP-Link wifi mains switch
12v to 8.2v DC/DC converter for DSLR power

Risks and issues

Operation

Responsive Embed

Create a responsive video and scale it nicely to the parent element with an 16:9 aspect ratio

Final disclosure.

All the drivers (observing conditions, safety, dome controller, shutter controller ) are all built and operating with Voyager, I have finally debugged the shutter control logic for full automatic operation from the Voyager manual and automatic interfaces while all the time the manual switching has worked like a dream... What I find most satisfying is the way the spring tensioners move in and out like pistons as the winch drives the shutter up and down and they take up the slack at varying poiunts in the system. And that its a whole lot quieter than the manual process before. And it means I can think about leaving the dome to finish an imaging session on its own. As long as the dome power lasts out.

Test code samples


curl -v http://espdsh00/status
curl -v -X PUT -d"shutter=open" http://espdsh00/shutter
curl -v -X PUT -d"shutter=close" http://espdsh00/shutter
curl -v -X PUT -d"shutter=abort" http://espdsh00/shutter
curl -v -X PUT -d"latch=powered" http://espdsh00/latch
etc..

Skybadger Observatory

Links