Project Dick Grayson: Yes Gary, my friends are electric...

 You might remember that I have 3 power-related please: Tom II, plus Dick Grayson and Harry Hart which I rarely talk about. Today I want to introduce Dick.

While Tom has been the dumping ground of much of my time, Dick is where I actually started, to wit, seeing what I could do with used Lithium Polymer cells (or LiPo for short). These proved far more complicated than I'd expected, and needed a lot more care and planning that I'd expected, so it's been slow going and progress has been glacial so for most people it's kinda boring.

Thing is, LiPo is a pretty exciting tech. It's high-density so you can pack a lot of juice into a small space, and it can respond to peaks in load demand much, much faster than Lead Acid. Problem is they have this habit of catching fire and exploding if you mistreat them so they're not for the faint of heart, or those who are uncomfortable at the thought of asbestos underwear.

The complexity comes from making sure they stay in their safe voltage zone, and because they live around 3.7v, you need to string a few of them together to get a useful voltage. Dick is built around a 4-in-series platform, or 4S. 4 x 3.7v is 14.4v, so you need to adjust your input voltage to meet their charging requirements, then control your output to the level you want. It's not as simple as devices built for 12v automotive systems which can handle a wide range, so you need an input controller, and output controller, than a Battery Management System (BMS) to handle the cells themselves. Dick has all of that, and the little red box in the middle with lots of thin wires keeping the heart of the thing civilised and regulating the internal voltages so that everything charges and discharges nicely.

This what's called a "prismatic" 4S (which just sounds achingly cool, but meajs that each "cell" is made up of a number of 3.7v cells rigged in parallel. This allows for some variance in the internal capacity, so a single cell can fail without taking out the entire string.

Right now Dick is running my old 12v Inverter for testing. I can feed it 24v, and it will regulate that down to 19v, then to the 16.8v charging current. There are 3 variable outputs, one set for 19v, another for 12v (regulated to be safe to feed various server and comm's equipment) and the central feed that sits at ~13-16v for less sensitive gear like my Victron Inverter. It takes a wallop of juice to charge (~60-80w), but it also stores a herculean amount of juice for something built out of old Dell batteries; I don't have tested figures yet, but it should come out to ~210Wh.

Theres a lot of refinement to be done, but when I'm happy with my testing I plan on lashing everything down with hot glue and tape, cutting holes in the hollowed out Makita case for the plugs, then sitting it between Tom II and the various loads as an intermediary. It will handle the peaks in my load, then trickle back from Tom II at a sane, sensible rate to reduce the strain on the Lead Acid batteries. Then I'll adjust Tom II's thresholds to cut out sooner and increase his overall lifespan. I'm calling it a "LiPo-Gel Hybrid" system which I reckon should overcome some of the major limitations of both technologies in a pretty cost-effective manner. Over the next few days I'll be testing to prove the concept, evaluate the actual capacity, then I'll transition to my "Production" testing environment... Assuming nothing catches on fire. 






We finally see the Raspberry Pi come into the picture. The Pi has been both a blessing and a bane - the EPever solar controller uses Modbus (RS485) for communication and telemetry, which needs conversion to a data format PC's and so on can read. They helpfully provide (sell) a Modbus <-> USB converter, but the drivers for that aren't pre-compiled, or even production-ready. I've burned more hours than I can count finding a revision that will actually compile in Raspbian, which has meant learning a boatload about how to compile a driver and load it in the first place. Someday I'll find a better way, but for now at least I can pull data from the thing without plugging in directly so that's a win... 


And yes, those are heat sinks off an old dead motherboard I'm using to keep the RPi cool. 

No, I'm not ashamed by that, they were free. 

And more importantly, they work :P

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