One of my other hats involves advising electronics scrap and
recycling companies, and the repair of all manner of electronics
equipment.
In all of the equipment I have rummaged through I can state the
following without reservation:
I have never seen any sign of damage caused by properly float charged
sealed lead acid batteries.
I have seen lots of serious damage caused by trickle charged nicads.
I have seen some very serious damage caused by lithium iodide pacemaker
cells at end-of-life.
I have seen lots of damage caused by carbon-zinc, and alkaline cells.
Lithium ion cells behave like electrolytic capacitors. They want to
have their initial inrush current limited to about 1C, and they must
have their final charge voltage limited to 4.2V. They will tolerate
being floated at 4.2V for quite a while, but that will ultimately lead
to their capacity being compromised.
A simple backup charger for a LiIon cell would be a constant voltage,
current roll back supply that is controlled by a timer that charges
the cell every time power is restored, and several times a year if
power doesn't fail.
Discharge must be abruptly stopped when the cell voltage drops below
around 2V... the exact value varies by the manufacturer.
-Chuck Harris
Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
On 17 Dec 2015 21:00, "Anders Wallin" <[email protected]> wrote:
First prototype assembled today, tested with 12 VDC SMPS wall-wart supply
and with 12 V lead-acid battery.
Anders
Is the lead acid battery supposed to be there so the unit continues to
function if power is removed?
If do, I believe that the choice of a lead acid battery is a poor one. I
believe that even the sealed ones release very small amounts of sulphuric
acid and when contained in equipment the acid results in damage in the
long-term. I believe that people have reported damage to oscillators like
the HP 10811A even on this list.
I believe NiCd would be a better choice. That said I somewhere read they
were banned in Europe but that might have been for general consumer use, as
I note that they are still shipped in some products - e.g. sone emergency
lights I bought in the UK from Farnell, although the lights were made in
China. One can certainly still buy NiCd cells in Europe.
I don't know if there is any simple way of slowly charging Lithium Metal
Hydride batteries. Commercial chargers from reputable manufacturers have
temperature sensors, voltage sensors and I assume a microprocessor to
determine how to charge them and when to stop charging. You don't need to
fast-charge a distribution amplifier, but I don't know if there's any
relatively simple way of charging them.
Dave.
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