The intelligent battery bank Mk 1 explained.
In our preparation for energy self-sufficient settlement, we realised that a reasonable size battery bank is going to be quite expensive - both initially, and periodically, if you need to replace worn-out batteries with new ones.
The key thing is that, if you want to have a decent battery capacity (say, 500 Ah @ 12V) you need several typical batteries to be connected in parallel, or you have to look for specialist, high capacity single battery, which is rare and expensive.
Even if you couple standard batteries, to get the capacity, at the beginning, you will need to replace the whole bank, even if just a single battery gets damaged. Otherwise, you’ll end up with a set of batteries with various capacities (each battery ‘matures’ sightly different way), whch means a lot of parasite currents flowing among them, thus a lot of energy wasted. That is exactly why industrial UPSes (Uninterruptible Power Systems) always have all their batteries replaced - not just the one that failed.
Well, having in mind that we are preparing a solution for people who have strict budget and will likely need their batteries being replaced quite often (continous power cycling instead of stand-by regime), we defined our needs as follows:
We need to have a battery bank capable to adopt various batteries (while all lead-acid type - that’s for Mark I), with various capacity. Ideally, it will adopt recycled batteries, being available at a fraction of cost (in Poland it is ~$7 vs. ~$75).
We need to have a technology to recycle lead-acid batteries, either newly obtained, or those aalready being used, if their capacity drops below accepted level.
The bank has to maintain all batteries equally charged (measured by their output voltage), and to produce designed energy (be it @12V DC, or a multiplication of it, for the serial/parallel combination).
So, thanks to our friends from Warsaw hackerspace, we got to the following design:
- We have two know-hows for battery recycling. One is simply a specialised charger. The worn-out battery is being charged several times, according to the regenerative algorythm. It will help in most cases, at least to keep battery going for a year or so.
For serious cases, we shall use ‘wet’ technology, which uses special regenerative electrolyte, another charging regime and finally, fresh electrolyte replacement. This is rather heavy chemstry, which includes also problems of acid neutralisation and disposal - however, fully doable.
- We have designed a ‘matrix’ of chargers, being independently controlled by the software, taking indvidual care of every battery in the bank. Diagnostics, charging and monitoring will be done real time from a dedicated laptop. This will compensate all individual discrepancies among batteries, making them work like a set of brand new cells. The solution is scalable from 8 up to 32 batteries, which means the possible saving is ~$550 to ~$2200 (Polish price level, again).
Now, what we need to do is:
A. Set up a ‘dry’ and ‘wet’ battery regeneration workplaces, including all necessary consumables and proper waste disposal.
B. Set up a small-scale, 8 batteries ‘matrix’, with control circuits, laptop and software, with internet monitoring access for interested viewers.
C. Get 8-10 disposed car (or similar) batteries, regenerate them, using both technologies and install them in the matrix.
D. Run a mid-term test (up to 3 months), using the matrix for daily activity, batteries being charged from various sources, if possible.
E. Finally, make a report and full-blown documentation and publish it (as we always do) as CC-BY-SA.
In the project, all labor will be provided free. We shall only need to buy electronics and chemical equipment. Batteries - by default - will be bought from the scrapyard.
If you decide to support the project, we shall produce and share quality output that will save every sustainable settler buckets of bucks, and help them to be even less dependent from the battery manufacturers. The solution will be scalable and transferable worldwide.