My 4 channel RME Quadmic Preamp burns 4 watts so yours sounds about
right. It is still ok with AA cells at that power.
OK, you can play with all the high tech battery chargers if you like
that monitor, temp, voltage, and pulse away, if you want and many are
real sexy. But for nimh or nicad cells (note, not Lion simply because
I have not looked into them because of the current cost).
If you will monitor the battery on your own and unplug it at full
charge you can get by cheap. Nimh and Nicad batteries start
generating heat at about a 80% charge. Unplug a while after that and
before you burn up the house.
Figure an ideal charge rate of 1C (that means for a rated 2,000 mAh
cell the ideal charge rate is 2,000 ma with a expected charge
efficiency of about 50%). You want to over voltage to get that
current in the batteries, or a min of a 12 volt supply for a 12 volt
battery pack and better yet 15 volts to 30 volts DC. The trick is with
charging that you need a current limiting device to keep the maximum
current at 1C.
In a car with a 12 volt battery it is charged at about 14 volts so you
can use that for a 12 volt battery pack or find any plug in the wall
supply that will give over 12 volts and less than about 30 volts DC.
The cheap method of how to limit current without expensive transistor
devices is called a "light bulb". As current increases a light bulb
will get brighter and limit the current. It gets brightest and can
only pull a max current which is rated as the wattage of the light
bulb. So, 12 volt battery pack at 2,000 Mills equals a 24 watt car
blinker light bulb. Just put one in series with a 14 to 24 volt DC
supply across your batteries and you will not hurt your batteries.
Figure it will charge in 2xc or 2 hours.
The other current limited supply many people have extra around the
house are the power supplies from old laptop computers. Those power
bricks list a max current rating and voltage printed on them. They
can not exceed those limits and will not be hurt with even a direct
short (current limited). If you question if a brick is a current
limited supply just short out the output. If it explodes or burns up
it was not current limited and you can throw it away. So that option
involves a process to beg, borrow, buy an obsolete laptop supply that
no one wants. Then use it to charge a battery pack built with the
expected number of cells. Just do the math of amps x volts = watts and
also remember that a battery cell is a battery cell and always each
cell is about 1.5 volts. Slight changes with different flavors but
not with different sizes, the size is for the current capability not
the voltage.
I hope that is clear and I did not shorten the concept to much.
Rich
(sorry I used the wrong computer so note is not spell checked)
--- In "kennjava" <> wrote:
>
> According to the Mini MP spec sheet
> http://www.apogeedigital.com/pdf/minimp_ds.pdf
>
> ...the power requirements are 6-14 V and 3W consumption. Taking the
> worst-case voltage of 6V, that would imply a current of 0.5 A. (Geez,
> I sure hope the preamp's worth all that current...)
>
> Rich's example of 10 sub-C NiMH cells should power that preamp for 48
> watthours/ 3 watts = 16 hours.
>
> So Rich, what's your $5 solution for NiMH charging?
>
>
> --- In "Rich Peet" <>
> wrote:
> >
> > My recommendation depends on if you build anything at all.
> >
> > In general: amps X volts = Watts. Also amp hours of a battery (usually
> > stated as mAh =1/1000 amps that it will give out for an hour before
> > "going south" (this is a nothern US term to represent where things
> > don't work).
> >
> > Few people other than the laptop people talk in terms of "Watt hours",
> > but the concept works well for recorders too. 10 SubC Nimh batteries
> > will give you 12 volts at about 4 amps. or a total of 48 watt for an
> > hour. aka 48 watthours, note you want something around 10 for an hour
> > of use.
> >
> > This is where the duct (duck) tape comes in, or shrink wrap. Solder 10
> > Sub C cells in series to a connector and velcrow (Sp?) and you should
> > be good to go for more than 4 hours on a charge. Build your own
> > chargers for custom batteries are also an issue if you can not find a
> > 12 volt battery charger for nimh cells I can also recommend a $5
> > solution for that.
> >
> > search e-bay for "sub C nimh" and you will always get hits.
> >
> > Rich
> >
> > --- In "tm957904" <>
> wrote:
> > >
> > > Hi everyone,
> > >
> > > Just a quick question. I have an Apogee Mini MP to use out for
field
> > > recording - great! But Im not sure the best way to power it.
None of
> > > the dealers or distributors have any idea either.
> > >
> > > The unit requires 6 - 14v (i think!) at 1 amp. What do you think
> > > would be a good (cheap) power solution?
> > >
> > > Cheers, any advice is much appreciated!
> > >
> > > Steve Tunnicliffe
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