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Some Changes

A project log for Magnificent Moisture Management

I've got a balcony, tomatoes and a micro controller

Michael HaasMichael Haas 04/07/2015 at 12:180 Comments

Spring is coming and the seeds are planted. I've made some changes to the project. Mainly, the MMM is now powered by a 12V lead-acid battery as that's the voltage required by the motorized ball valve. At 7.2Ah, the battery likely is large enough to last all of summer. I have yet to do the math on that. I choose the battery size mainly because it was cheap. Smaller batteries at 2Ah cost around 10€. There seems to be a sweet spot at 7Ah -- I got mine for 15€.

I can easily charge the battery from a battery panel since it's 12V. Amazon.de lists some very affordable solar panels, e.g. 10W at 25€. Cheap chinese charging controllers like the CMP12 start at 8€so this would be an inexpensive, fun experiment.

Unfortunately, these are cheaply made and I read somewhere that they don't even use PWM to adjust the charging voltage. For 15€, you can get better controllers like the CMTP01 or CMTP02 which -- on paper -- do the right thing. Even for those, you can find lots of complaints on your favorite search engine. The original plan was to get a solar charge controller and feed it from one of the random 19V PSUs I have lying around. Since none of the offering seemed good enough, I decided to buy a decidated lead battery charger, the AL-800. I suppose it's better to buy stuff that does one thing well instead of not doing two things at all.

To finally make some progress, I also ordered a DC-DC buck converter based on the LM2596. These can be had for 2€ from China or, in my case, from a German (re-)seller via Amazon for 5€. Along with some fuses, diodes, opto-couplers and transistors, I should be able to prototype the interface for the ball valve soon.

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