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I am quite ignorant in electronics, but I am now building a small off-the-grid installation to be freely cloned (CC-BY) in rural areas of Eastern Poland (and perhaps Ukraine). The vital part of it is the battery bank, which will be built from recycled car batteries etc. So we need some intelligent charger/regenerator/desulphator/monitor/controller to take care of them.

What I am looking is pointing to some low-cost DIY solutions and perhaps some support in prototyping.

The concept is to set up a matrix of batteries (mostly recycled, in various levels of wear) and provide them highly controlled environment - separate chargers, monitoring, on-the-fly desulphation, separate discharge controllers etc. etc. People who will use this design cannot afford buying new batteries, lest replacing whole parallel banks once one unit breaks down. So we shall be dealing with a variety of batteries and the challenge is to make them work efficiently, long term and happily. :-)

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    \$\begingroup\$ This sounds like a big project, and as such, the question is a bit hard to answer. You might get better help when you split your question into smaller aspects. \$\endgroup\$ – zebonaut Jan 25 '13 at 9:49
  • \$\begingroup\$ Note that if you make your charger complex enough, it will be much more expensive than the batteries... \$\endgroup\$ – pjc50 Jan 25 '13 at 10:02
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    \$\begingroup\$ You say "desulphator" - which immediately throws you into the realm of maybe-Science and proprietary magic boxes. While a degree of desulphation of old batteries is possible, and you can buy magic powder which makes them like new [tm] you may find that it's a bit harder than some will suggest. See Battery University for a basic Lead Acid guide. After that, you need to better define your target system to get really useful input. 12V 24V 48V. Dc out, DC to mains converters?. Lighting load/heating load / TV / appliances...? A system using somewhat similar batteries will make life less difficult. \$\endgroup\$ – Russell McMahon Jan 25 '13 at 13:18
  • \$\begingroup\$ Running a 12V base system or maybe 24V will allow flexibility. Batteries can be paralleled via switches and switched in an out without too much drama. If you need many batteries in series and they have different capacities and discharge curves it will be "challenging". \$\endgroup\$ – Russell McMahon Jan 25 '13 at 13:21
  • \$\begingroup\$ Is this still being worked on? I'd like to try the design, but frankly, I need to know much, much more. \$\endgroup\$ – Sean Boddy May 8 '14 at 9:11
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In order to be cheap and work with different recycled batteries it would most likely have to use all the cells in parallel. Every new cell would increase the capacity a little bit.

The simplest way to connect them in parallel is to use some diodes or mosfets to make sure a shorted battery doesn't affect the pack. The circuit is something like this: enter image description here

Of course, the components should be chosen depending on the power requirements.

In some cases it might be more practical to have a board with a microcontroller which controls relays to disconnect each battery in turn every day and checks it's voltage.

Other than that, lead-acid batteries don't need an intelligent charger.

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