We had always used accumulators. When I was a kid with this tiresome “current = 10% capacity” procedure. It took years ’till we finally got a “quick charger” – but that was only for the AA-cells. (My parents still have this one. And also their “C/10” charger.) Today you have a good chance to avoid those single rechargable batteries at all. Everything has some kind of built-in Li-Poly and charges from USB. And those wall warts will live longer than the phone they came with. But eight years ago I had demand for a “classic” solution.
In my job it absolutely makes sense to know the whole Conrad catalogue. It is much more versatile than Farnell, RS, etc. pp. – you get your resistors, connectors, perfboard and the whole arsenal of tools there. (When I need components for something really meant for mass production I usually look at Schukat – if they have loads of something in stock, there is no need to look any further for pricing and availability… Just look at their pricing for CR2032s.)
…so when I was looking for “my new charger” I stumbled over an evaluation board from a small company called BTI: http://www.bticcs.com/
Of course they claimed to have an edge over all competitors and that their “Computerized Charging System” or CCS (the company -founded to specifically sell this product- is 26 years old now) would significantly enhance the lifetime of your rechargeable batteries. What made me take notice however was the other feature: the board would charge anything with just minor modifications of the circuit. And it would charge series connected cells as one package.
If you want to read all the negative opinions head for this part of the internet (in german). A patent is mentioned there too – Google links to Espacenet, if you are searching for official translations. I preferred to take andvantage of the features, like just being able to cahrge salvaged Li-cells put into an RC car or using just those cells to charge my phone along the way and ignored the noise.
The evaluation board’s article number, 150065 is mentioned here, seems to be a dead link by now. But here’s my charger anyway:
The board fits into a Hammond 1593-series enclosure, which is available anywhere and cheap. It also has the advantage of having removable front panels, so it is easy to work on.
To make this usable by others, without reading the datasheet, I choose to use a connector with four contacts and integrate the resistors for nominal voltage and voltage limit in the battery holders. Additionally there is a switch to choose two different current limits (which I called “AA” and “AAA” as this is what the others would charge exclusively).
There are some jumpers inside to determine in which dimensions the capacity of the accumulators roughly lies. Normally there is no need to change something there.
The heat sinks are there, because there is enough room. No further justification necessary – the cooler semiconductors stay the longer they live.
As a power supply I choose a 15V 2.4A DC (so it’s 36W) mains adaptor. The worst case scenario (until the present day) was two paralleled 16650s – and i didn’t even get close to one amp then.
And the advertising messages?
It charged anything I thew at it. Charging multiple NiMH AAs in series works, but as my collection is quite multifarious I prefer charging single cells while wathcing TV (from commercial break to commercial break).
The algorithm is also very soft on the cells and will report the crippled ones to you. If I decide to use a crowbar then, I just hand those cells over to a Sanyo NC-MDR03W, which came along with some 1st generation eneloops. This type of charger just forces current into the cells on a “do or die” basis then – and the current and heat can occasionally get a few extra charges into worn out cells, before they fail completely.
(Yay! No reference here – first post without template. Just realized that this part was missing so far to get the whole picture. 😉 )