reef-pi :: An opensource reef tank controller based on Raspberry Pi.

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Quick question for any pi gurus out there. I have enough room in my main unit enclosure to add a 2nd pi3, I'm going to use the second unit to run dosing pumps and a ph probe and plan on running cat5 or 1/8"cables to a breakout box with the pumps in it.

Can I run the second pi off of the existing 12v 2 amp power supply or off the 12v rail on the first pi hat or will it be too much for the power supply to handle?
I'm just trying to keep the power bricks around the tank to a minimum but if I need to add another power supply, no big deal.
 
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Not safely (at least I dont think so). P=IV so if you need 2.5A (max Pi draw) at 5V you need 12.5W (before any efficiency losses) to power 1 Pi. Powering 2 Pis at 5V 2.5A you would need double that (again before conversion efficiency loss). A 12V 2A power supply is 24W. I'd saw you need at least 12V 3A (assuming an 80% loss from the buck converter).

But it is 4am so I could be wrong haha :)
 
MaccaPopEye said:
Not safely (at least I dont think so). P=IV so if you need 2.5A (max Pi draw) at 5V you need 12.5W (before any efficiency losses) to power 1 Pi. Powering 2 Pis at 5V 2.5A you would need double that (again before conversion efficiency loss). A 12V 2A power supply is 24W. I'd saw you need at least 12V 3A (assuming an 80% loss from the buck converter).
Click to expand...

With RPi 3B+, the power draw is around 5.7W under load (with monitor Wifi etc) and 2.3W when idle (link). Zero has much lower power consumption (around 1W). Also, most of the step-down coverter has efficiency > 90%, I thought. If other peripherals connecting to the PS aren't drawing too much, the power supply can easily support 2 RPi 3B+.
 
naoki said:
With RPi 3B+, the power draw is around 5.7W under load (with monitor Wifi etc) and 2.3W when idle (link). Zero has much lower power consumption (around 1W). Also, most of the step-down coverter has efficiency > 90%, I thought. If other peripherals connecting to the PS aren't drawing too much, the power supply can easily support 2 RPi 3B+.
Click to expand...

Thanks, I just used 2.5A as that is the power supply recommended for the Pi. The 5.7W draw is interesting, I never actually thought to look for that. Makes me wonder why do they recommend a 2.5A power supply minimum? If the max current under load is less than 1.2A then a 2.5A is pretty overkill.

As for the converter I did a quick google and most of them advertise 95% but it depends on the input and output voltage. The larger the conversion the greater the loss. I used 80% as a worst case scenario but it could likely be 90.

Either way if the max current draw of the Pi is only 5.7W then yes the 12V 2A supply would be able to handle that easy.
 
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2 amps at 12vdc is 24 watts, 2 amps at 5vdc is only 10 watts. Ohms law. I'm pulling 4.3 watts from the pi, the 5v and 24v power supplies but without any pumps or lights on.
 
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MaccaPopEye said:
Thanks, I just used 2.5A as that is the power supply recommended for the Pi. The 5.7W draw is interesting, I never actually thought to look for that. Makes me wonder why do they recommend a 2.5A power supply minimum? If the max current under load is less than 1.2A then a 2.5A is pretty overkill.

As for the converter I did a quick google and most of them advertise 95% but it depends on the input and output voltage. The larger the conversion the greater the loss. I used 80% as a worst case scenario but it could likely be 90.

Either way if the max current draw of the Pi is only 5.7W then yes the 12V 2A supply would be able to handle that easy.
Click to expand...
This is perhaps my biggest concern when designing aio builds
 
@Diamond1 some things to remember:
- the perma proto or perf boards I recommend are rated for 1.2-2 A
- female -female jumper wires we use has current rating of 1.5 A if they are 28 awg, and 7A if they are 22 awg.
- same goes for solid core wires that we solder as jumpers in the perma proto board. I always recommend 22 awg in guides . Once present , perma proto boards will support 7 amp using these
- lm2596 is rated at 3a, but better design it to run at 2amp or below
- create power rails and draw power from there , instead of daisy chaining , like drawing from pi’s
 
Ranjib said:
@Diamond1 some things to remember:
- the perma proto or perf boards I recommend are rated for 1.2-2 A
- female -female jumper wires we use has current rating of 1.5 A if they are 28 awg, and 7A if they are 22 awg.
- same goes for solid core wires that we solder as jumpers in the perma proto board. I always recommend 22 awg in guides . Once present , perma proto boards will support 7 amp using these
- lm2596 is rated at 3a, but better design it to run at 2amp or below
- create power rails and draw power from there , instead of daisy chaining , like drawing from pi’s
Click to expand...

Thanks for the heads up. I plan on using 22awg for all the wiring except for the wires running from the head unit to the pumps. For those I'm leaning towards cat5.
 
Hey everyone. New to the forum and to Reef-Pi. I e encountered a lot of hurdles and the learning curve I’m still climbing. I’m having a problem that I just can’t figure out. I have been able to install and login and start ReefPi. When I go back to my project the next time, I can’t seem to get the server to open. I did everything including a purge and reinstall. When I check the status, It shows me this:
a2059df2e1b9e3e228c1a4a34a79c006.jpg


I know it has to be something simple, but I just can’t see it from where I’m standing. Maybe one if you super users can give me a hand past this hurdle? A possible related issue is that I cannot seem to get my ssh to connect. I never have been able to. It’s selected in options. Ive Double checked everything.
 
pdisner said:
Hey everyone. New to the forum and to Reef-Pi. I e encountered a lot of hurdles and the learning curve I’m still climbing. I’m having a problem that I just can’t figure out. I have been able to install and login and start ReefPi. When I go back to my project the next time, I can’t seem to get the server to open. I did everything including a purge and reinstall. When I check the status, It shows me this:
a2059df2e1b9e3e228c1a4a34a79c006.jpg


I know it has to be something simple, but I just can’t see it from where I’m standing. Maybe one if you super users can give me a hand past this hurdle? A possible related issue is that I cannot seem to get my ssh to connect. I never have been able to. It’s selected in options. Ive Double checked everything.
Click to expand...
Looks like https is turned on, I recall reading another thread here about it causing a problem.
 
Tidal Gardens
pdisner said:
Hey everyone. New to the forum and to Reef-Pi. I e encountered a lot of hurdles and the learning curve I’m still climbing. I’m having a problem that I just can’t figure out. I have been able to install and login and start ReefPi. When I go back to my project the next time, I can’t seem to get the server to open. I did everything including a purge and reinstall. When I check the status, It shows me this:
a2059df2e1b9e3e228c1a4a34a79c006.jpg


I know it has to be something simple, but I just can’t see it from where I’m standing. Maybe one if you super users can give me a hand past this hurdle? A possible related issue is that I cannot seem to get my ssh to connect. I never have been able to. It’s selected in options. Ive Double checked everything.
Click to expand...
Don’t reset database or reinstall reef-pi. What version you are running ? Can you copy paste the reef-pi log , I can’t see the address it’s binding to. Also let us know how your trying to access reef-pi , from which device and at address in your browser you are trying ?
 
I had shared this earlier in the thread, the ph build I am running does not have voltage isolation. Though this has allowed me to develop the support for this chip in reef-pi, and helped me understand my daily cycle, the result was highly dubious. I would always get ph from 6.7 to 7.8. Here is my past 30 days pH chart
Highest pH during late afternoon,
Screen Shot 2018-11-14 at 11.59.18 PM.png

And lowest pH during early morning (values that is just not possible)
Screen Shot 2018-11-14 at 11.59.06 PM.png

This is the historical trend.

Screen Shot 2018-11-14 at 11.58.53 PM.png

After some reading and double checking here in the chemistry forum, it was clear that this is unrealistic and this is also a common probelm with the ph sensors. They are very sensitive to a host of things . From calibration to temperature correction to stray voltage sensitivity in reading, there are many things that can go south. @Roberto_b also pointed out this .

Today I had the time to upgrade the ph monitor with electrically isolated ezo carrier board. I had few goodies that I ordered in past from whitebox labs (including a Tentacle t3 board for pi), and this is the same thing I have recommended in the adafruit guide as well.

3FC100E4-2819-4C62-9127-8A9F20D93796.jpeg

The carrier board comes with its own pull up resistors, which makes the circuit required for pH monitor to nothing. The perma proto board only serves the purpose of 5V+ and GND rails. I2C pins from Pi is directly connected to the carrier board.
After upgrade, I powered up Pi, and the I noticed an immediate jump in pH. Last night during this time this reef-pi logged 6.8 , now its 7.7. I am excited, let's see how the data looks after 7 days of operation. The build itself is running fairly well for several months now. No significant stress for pi zero with less than 1% CPU usage,.

Screen Shot 2018-11-15 at 12.04.22 AM.png
 
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