[sdiy] Outside Synth DIY topics but could be of some interest..

Brian Willoughby brianw at audiobanshee.com
Fri Dec 24 00:07:57 CET 2021

On Dec 23, 2021, at 04:02, Roman Sowa <modular at go2.pl> wrote:
> When one of the batteries is more dead than others, at certain current (it may be as low as few mA) it will be too weak to hold and becomes a resistor. It will actually reverse polarity and take most of stack voltage on itself, so entire stack will drop from say 20V to 1V.
> To prevent that you might add ideal diodes over the cells. Those are widely used in solar panels.

Thanks for passing on this technique.

I've noticed that large LED displays - the ones that include a large number of individual LEDs in a combination of series and parallel connections per segment - will often have cross connects between the parallel paths, at the nodes between individual LEDs. My understand is that this allows individual LED components to fail without stopping all current in that series path. Of course, this does require twice the current to flow through the remaining LED(s) at that stage of the series, which would result in inconsistent brightness across all LEDs, but at least it's better than the whole series path in the array going dark.

Similarly, these battery array protection diodes prevent totally dead cells from going reverse polarity, but they do consume a bit of wattage as a product of the diode drop and the total current. Like the LED array workaround, it's not ideal performance, but it postpones complete failure.


> And what a coincidence, few emails later I have found a spam about MAX17220 DC booster, it ideally matches the topic of wringing nearly dead batteries. It starts from 0.88V input and then works until battery is 0.4V dead. Only 4 external components and output adjustable from 1.8 to 5V.
> Once I got a thing from Aliexpress, basicaly a PCB with booster on it and battery clips. So you put a dead AAA battery in and hapily enjoy 5V at its output until poor battery wheeps "please let me go now...".
> It was about $1 IIRC
> Roman

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