I finally got around to installing a set of fuses and a terminal strip on an old computer power supply that I had. 3.3V @ 20A, 5V @ 16A, 12V @ 16A, thus the need for fuses! I also added a small digital voltage regulator that you can see in the bottom left of the pic, so I have a variable power supply that I can step down to a specific voltage if necessary.
Thanks for viewing!
Robin

Raspi & Gertduino UPS

I have purchased a couple of Arduino boards that are made specifically for the Raspberry Pi and they are named after their inventor Gert van Loo, Gertduino. The specs, software, and manual are available via this link.

It is a great platform to work on the inter-communication between the Raspi and the Arduino. I'll be using this combination to further develop my battery monitoring system for my Raspi UPS.
The Arduino will have a 3 level response:
      1)  My plan is to have my Raspi backup battery charged via the solar panels.
     2) The Arduino will monitor the battery voltage. If there is very little sun, or too much load, then the arduino can switch on the 110VAC battery charger to charge the batteries back up.
     3) The Arduino will continue to monitor the battery voltage, and if there is no sun AND no utility power, then the Arduino will safely shut down the Raspi if the voltage drops to a preset level. If the voltage continues to drop, the arduino will shut off as well.
     NOTE: The advantage of the Arduino is that it can safely recover from a power outage, where the Raspi may not. So the Arduino will power back up and when the battery voltage reaches a preset level, it will power up the Raspi.
     ARDUINO vs GERTDUINO: I like working with the Gertduino since it is mounted on the Raspi that it communicates with. However, I've been able to communicate with a regular Arduino Nano as well, so this would be the device I will use as my Battery Monitor, freeing the Raspi GPIO pins for other uses.

Raspi Block Heater Control

Well, I have a Raspberry Pi controlling a 5VDC relay, which in turn controls a 120VAC Relay which can then turn my vehicles block heater on & off. For those of you who don't live in the colder Northern climates… a block heater is an electric element that is positioned within the water jacket of your automobile engine. When the temperatures drop below -10C to -20C, the engine is cold, the engine oil is much thicker, the battery loses some of its capacity, and starting can be difficult. When we talk of plugging our cars in, we're referring to plugging the block heater in to provide heating (much like a hot water kettle) for the engine so that it will be much easier to start at those frigid temperatures. My first attempt:

You can see the Raspberry Pi in the upper left hand corner, and the 2x5VDC relays (blue) just above it.  The 5VDC relays can safely be driven from the Raspi's GPIO pins and they can safely trigger a 120VAC relay that will power the block heaters. You can see the 2 x 120VAC relays on the DIN rail just above the 3 white/grey circuit breakers. There is an advantage to using these relays (commonly known as ice cube relays, because they are about that size), and that is 1) there is an indicator light to tell me if it is powered on and 2) there is a manual lever that I can move to manually activate the relay for troubleshooting purposes. Also, if for some reason, my Raspberry Pi was not running, I could manually activate the relays to power the block heaters continuously to ensure my vehicles start in the morning. There are 2 sets of relays to power 2 different block heaters in 2 vehicles.

The only problem with the above setup is that if there is a power failure during the evening, the Raspi's SD card may become corrupted and not restart when power is applied. I find this happens on occasion and I assume it is because the SD card is being written to when the power fails.

So version 2 includes my thoughts on a UPS that I've talked about here on this blog. I've installed a power supply (upper right) and 6 x AA batteries in a holder mountain just above the Wall Adapter on the right.

Now the 12VDC wall adapter powers the power supply (small circuit board to the upper right of the DIN rail) through a 1N4007 diode. Also the 6 x AA (6 x 1.5VDC = 9VDC) batteries are tied to the power supply as well through a 1N4007 diode. Normally when the wall adapter is working, it's diode is forward biased and the power supply is supplied by the wall adapter. Should the House Power fail, the voltage will drop until it reaches 8.3VDC (9VDC from the batteries - 0.7VDC to forward bias that diode). At this point the Raspberry Pi power supply will be powered from the batteries.

Our power outages occur fairly frequently (several times a month), however they are short lived. I am hoping this battery pack will last me thru the winter…..grin.

I'm running the WebIOPi software which allows me to have the block heaters turn on and off via preset times, as well as through a webpage on my smart phone or tablet. Thanks got to Eric Ptak (trouch) who is the author of this wonderful software, WebIOPi

Raspberry Pi UPS

I've had an ongoing issue with my Raspberry Pi's corrupting the SD card if the power failed during a write cycle, at least that's my assumption. On occasion, after a power outage, I cannot access the Raspberry Pi and have to reboot it. By watching the terminal display, it often indicated a kernel panic and I know that I have to re-write the SD card. About 10% of the time I cannot and have to throw the SD card out.

Most often, it seems that the power outages last for a brief period of time. So I went looking for a short term backup solution. My first thought was to go with rechargeable batteries, and I may still follow this route, but for now I've settled upon standard alkaline batteries to provide my short term coverage.

I've come up with the following circuit to prevent power loss to my raspberry pi's. I use a 12VDC wall adapter together with 6x1.5VDC (AA) batteries. Both feed the 10-30VDC > 5VDC power supply through diodes. My reasoning is that as long as the wall adapter is working, it will supply the voltage & current to the power supply, since the battery diode is reverse biased. If I lose utility power, the wall adapter voltage drops to zero, and then the battery diode becomes forward biased and supplies the voltage and  current to the power supply.

I have sourced the power supplies & wall adapters from China. 6 cell AA battery holder from my local electronics store and using 1N4007 Diodes to provide the isolation.