Syd Curtis wrote:
> Things start to fall into place. I use a Tascam DAT recorder, and the
> advice in the manual is that the light on the charger changes from red to
> green to indicate that about 30 minutes later you can stop charging. Thi=
s
> has annoyed me ever since I got the Tascam: I don't wish to sit watching
> for the light to change so that I know when to start counting the extra 3=
0
> minutes! Why couldn't an apparently excellent piece of equipment indicat=
e
> when the 30 minutes is up.
The problem is it's probably working off battery voltage and in the
latter stages of charging the voltage changes little. And ultimate
voltage will depend somewhat on the condition of the battery pac. With a
old pac it might never reach the equivalent expected voltage after the
30 minute delay. So their way will work for all pac conditions.
The Portadisc has a green led that goes dimmer as it charges. Even
judging when it's out would depend on how bright a light it was in. I
generally only charge in the Portadisc when I know I have enough time to
set it and leave it. Since it's using NiMH batteries a partial recharge
is also ok, and sometimes when out I'll hook it to the car to charge
between sessions.
> > Another characteristic of NiMH re-chargeable batteries: if fully
> > discharged and left for a period of time, the charge will partially rec=
over
> > as the ions migrate to the terminals - this will appear as a partial
> > increase in the terminal voltage of the batteries which may cause the
> > battery level indicator in the Portadisc to show a high percentage and =
fool
> > the user into thinking that the batteries have sufficient charge. Howev=
er
> > this partial recovery has 'no depth' and thus once Portadisc is powered=
up
> > the terminal voltage will drop quite quickly. e.g. on initial power up,
> > might read 99%, then within several minutes of recording drop to 40%.
> >
> I've had just that happen with the Tascam and wondered what was going on,
> fortunately only at home when editing tapes. Now I know.
This sort of thing happens to some extent in most types of rechargable
batteries. I always work on voltage under load. That quickly gives the
true picture.
It can also be a help if you happen to need just a short burst from a
battery to know to turn it off and rest it first.
> I have a couple of rechargeables - "Nicad SC 1600 MAH 7.2V" labelled for
> "Model Engines" bought from a hobby shop that sells them for radio
> controlled model racing cars. These I use externally with the Tascam.
> Before recharging, I use an incandescent lamp to fully discharge them.
>
> Can anyone advise me whether it is likely to be OK to discharge the Tasca=
m's
> rechargeable that way?
Should be ok. The test is how warm they get. If they are getting too
warm to handle it's too fast a discharge rate. If they are not fast
charge types then you should not even get them that warm.
> The hobby shop supplied a charger that works from a 12V car battery. Can=
I
> safely use that to charge the Tascam battery - "NiCd BP-D1 (7.2V, 1.4 Ah)=
" ?
The Hobby shop battery pacs are designed for fast charging and the
charger is probably also a fast charger. You would have to find out if
the Tascam battery was designed for fast charging, not all NiCd's were.
Though most current ones are. You are generally always safe slow
charging if the charger has the right voltage rating, but fast charge
requires the whole system be designed for it. So if the hobby shop
charger has a slow charge that should definitely be safe.
Walt
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