Thanks. I'll try the design with 6 X 9volts first to hear if there's
less noise, then build the battery packs. It would take quite a while
to charge 4 bat packs using my one, $80 MAHA charger so I'd need to
find some cheaper, good, 12 volt NiMH pack charger for the phantom
supply to be excursion practical. No luck when I searched for that
before. So its, 3 pounds of batteries for a 4 ounce recorder, Klas's
friend's supply or back to the Roll's. :-) Rob D.
=3D =3D =3D
At 12:21 AM -0600 11/27/05, Allen Cobb wrote:
>For current measurement, I still rely on my trusty old Fluke,
>which isn't cheap, but nowadays you can probably get very cheap
>DMMs (digital multimeters), perhaps even at radio schlock.
>
>As a matter of fact, here's one that lists for $6.95:
>
> http://tinyurl.com/a9lk9
>
>With any reasonable digital meter, you can just take a VOLTAGE
>reading (after the cell has cooled to room temperature) for a
>fairly accurate way to match cells. Although you're not
>measuring current, if all cells have gone through identical
>charging and cooled for the same length of time, then they
>should have identical initial voltages. Technically, of course,
>the entire discharge curve should be matched, but that's a bit
>excessive.
>
>You could also read current through a small resistor, or even a
>momentary dead short across the battery in current mode, but I
>wouldn't recommend that unless the meter has a peak-reading
>(latching) mode so you can touch the terminals VERY briefly. And
>cheapo meters may have very little current handling capacity.
>However, with AAA NiMH batteries, the internal resistance is
>fairly high, so current dumping isn't all that risky.
>
>Please note that some kinds of batteries, especially NiCAD and
>Lithium, can dump current tremendously fast (almost no internal
>resistance), and could even explode if you do something like
>this when fully charged. For safety, or if you're not sure of
>the battery type, don't do the dead-short test! Use a 10k
>resistor, or such. You're really only after a relative
>measurement anyway...
>
>One advantage of rating the cells by measuring their voltage
>(which should correlate to energy density in a given
>form-factor) is that it's non-invasive. Current measurements,
>unless done with a large limiting resistor, will be depleting
>the cell as you measure it, perhaps leading to misleading
>results.
>
>Four 12V packs in series sounds very reasonable (and
>convenient).
>
>ac
>
>
>Allen Cobb
>
>http://acobb.com
>http://shakespeare.acobb.com
>http://timbreproductions.com
>
>
>-----Original Message-----
>From:
> Behalf Of Rob
>Danielson
>Sent: Saturday, November 26, 2005 4:55 PM
>To:
>Subject: RE: [Nature Recordists] DIY 5X9v bat phantom supply
>
>
>At 4:08 PM -0600 11/26/05, Allen Cobb wrote:
>>FYI - Most 9V batteries I've dismantled contain 6 cells that
>are
>>close (about 2mm shorter) to AAA cells.
>
>Of course! Duh,..!$#! So maybe I wasn't too far off target with
>the
>2/3's size AA NiMH's. Mike says we'd need to measure the current
>of
>each cell to match them. Got a link for something cheap to
>measure
>current? After that, I only feel confident about charging NiMh
>with a
>MAHA charger so that could mean four, 12 volt (4 X 10 X 1.2)
>battery
>packs. Mike or Allen, see any problem with using 4 packs
>serially?
>Rob D.
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
________________________________________________________________________
________________________________________________________________________
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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