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.
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.
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.
Klas.
>Klas Strandberg wrote:
>>
>> Walt,
>>
>> A NiMHy cell has 1,2v nominal. Five of them in series make 6v, the stereo
>> DATmic needs 5v to work well, it's only 1v to go and I consider that too
>> little. Using 5 cells also means that you don't get any warning. Within a
>> few minutes, the output goes from full to nothing.
>>
>> Six NiMHy in series make 7,2 volts, which is sufficient. But to charge it,
>> the voltage of a NiCad 9v battery is too low.
>>
>> It's a choise - using 5 cells to make it possible to use a NiCad battery for
>> charging, and pay for it by means of poorer distortion figures and lower
>> running time, or
>> being stuck with using dry-cells for charging. Dry-cells have 1,5v per cell,
>> as you know.
>>
>> If this is a problem, I can make you a 10mA current limiting charger using
>> two NiCad batteries.
>
>I understand you need all the voltage available. 7.2 volts.
>
>As I noted I'm using a 9 volt NIMH battery that's higher voltage. At
>least one company makes these. Obviously they add two more cells to the
>stack as their voltage is rated 9.6 volts, approximately the same
>voltage as a 9 volt alkaline. That provides a good charging battery for
>yours that's rechargable itself, and it will run the Telinga just fine,
>as would a alkaline 9 volt. This battery fits in the battery
>compartments of all my 9 volt devices. I'll be using this battery to
>power my modified SASS, where it will be fit in a standard, accessible
>battery compartment (I got one that Shure uses in some of their
>equipment by ordering the parts).
>
>I looked into all this before buying the Telinga, the battery setup was
>a big stumbling block to my buying, I've been burned by custom batteries
>in equipment before. Leaving some expensive piece of equipment suddenly
>useless. So I wanted to completely understand what was there. I checked
>in detail Varta's specs on their custom cells. Once I had the Telinga I
>measured the actual charging currents that a Alkaline 9 volt battery
>gave the internal battery. I already had one of the Plainview Batteries,
>so measured what charging current it gave the internal battery. Both new
>alkalines or the Plainview NIMH give the internal battery considerably
>more charging current than 10mA, highest at the start of charge and
>tapering down to near zero at full charge. But well within Varta's fast
>charge specs. Both batteries charge the internal in about the same time.
>So, yes, I do charge my Telinga with a rechargable NIMH 9 volt battery
>and have done so since nearly the beginning. I agree, charging with the
>7.2volt NIMH or Nicad 9 volt batteries commonly available would not work
>well, you would only get a partial charge. The one I use gives it a full
>charge, same as using up a alkaline.
>
>Just as a regular Alkaline can run the Telinga, the Plainview NIMH can
>run it. In fact there are quite a few brands of NIMH and Nicad 9 volt
>batteries that have the same voltage as your internal, I've not run into
>any 6 volt ones. If the handle was equipped with a regular 9 volt holder
>any of these batteries would work fine.
>
>The battery I use is available here:
>http://www.4gdo.com/9nimh_batteries.htm
>This battery has been available for several years. I use the charger
>they sell with this battery. I have tested some other NIMH chargers and
>they actually can charge the battery if their unloaded voltage is high
>enough, though at a slower rate.
>
>There are two issues that bothered me. One was the use of throw away
>batteries, which I solved as per above. The second was a custom battery,
>not available locally, at the distance I am it would take time to get.
>And, being custom is vulnerable to being discontinued. This problem
>would be easily solved by designing the Telinga with a standard battery
>compartment that would take batteries of the regular 9 volt form factor.
>Batteries of as good or better specs than the custom are available in
>NIMH from a number of suppliers, and in a pinch a alkaline would fit as
>well. I've even got a couple old nicad "9 volt" batteries that still are
7.2volts.
>
>The 9 volt battery compartment of the Sennheiser MZA14 phantom power I
>have in front of me, for instance, takes the battery drop in longways,
>uses spring contacts rather than snaps, and it's 23mm x 30mm That sort
>of size should fit fairly easily in a handle design. Then the battery
>would be a standard type, recharging could be done externally. There's
>very little chance standard 9 volt batteries will go away anytime soon.
>
>I have considered pulling the electronics from the handle, and
>designing/machining up my own handle with the necessary holder. But I've
>got way too many projects. It may suddenly become a very high priority
>when the battery fails. I'm hoping that's a while yet.
>
>Walt
>
>
>
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