Klas Strandberg wrote:
>
> Thanks, Walt, your info and comments gave me a possibly very good idea for
> the future!
>
> The basic idea with the uncommon Telinga design is to assure the user NEVER
> to be out of power. In only one case since 1982, there was a noise
> generating shortage in the internal accu which made it useless. In all other
> cases, the user has been able to make his recordings, even if the accu has
> been empty and unable to take charge.
I understand the idea behind the design.
Using the 9 volt compartment with a standard 9 volt NIMH battery would
have prevented even that one.
And failed batteries would take a moment to replace. You would never be
in the situation of trying to run by jumpering across a bad battery with
a good one.
> You are right that the charge current is too high in the beginning of the
> process, while it drops in the end. That is because a resistor is the only
> current limiting device. The accus I use are made in Germany, which means
> that I can speak directly to the manufacturer (not as with south-east
> products) and they assure that the accu will not take damage by the initial
> too high current.
Before you get too stirred up the current it gets to is not too high
according to Varta's specs for similar NIMH's. They have not only a slow
charge rate listed, but a safe fast charge rate. That fast charge rate
is not exceeded. I'm perfectly comfortable with the charge current profile.
BTW, putting a ammeter to various chargers is a eye opener. Few, even
the various manufacturer's own charge at the rate they specify in the
specs. It's generally higher, particularly with a flat battery at the beginning.
> A constantly ongoing project here, however, is trying to find a current
> limiting diod or transistor, which limits the charge current to around 10mA,
> even if the charge voltage is only 1,5v higher than the voltage of the accu.
> Then you would get 10 mA charge current regardless of the voltage fed, and
> one could use any DC voltage adaptor between 9 and - let's say - 24 volts.
> But so far, all search has been in vain.
A circuit could be built, but it would be complex, not a single
component. And it can all be avoided by simply making it removable and
standard. Then you would have a large choice of both batteries and
charger types. And since nil labor would be involved in replacing, a
failed battery would not be a big deal. The 9 volt throw away batteries
are available all over the world.
One thing, if it's a external drop in box, put in a diode bridge, that
way either way it's dropped in is ok.
Walt
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