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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