From: Johannes Wolf (mp2100_at_mail-gw.estec.esa.int)
Date: Thu Jun 17 2004 - 08:21:01 PDT
DO NOT REPLACE THE BLOWN FUSE IN YOUR CIGARETTE LIGHTER ADAPTER WITH A
BIGGER ONE!
If you can answer my simple question with YES, there is an easy explanation:
Q: Do you use a rechargeable battery pack in your Newt?
If so, the Newt will start with fast charging as soon as you plug in
external power (in your case the cigarette lighter adapter).
The charging current is mainly dependent of the voltage you apply.
Assuming 7.5V the current can go easily up to > 1 Amp.
Your cigarette lighter adapter was rated for 300 mA -> that does not mean
that it will LIMIT the current to 300 mA, but the voltage regulator inside
the adapter is not capable of delivering more (electrical ratings and power
loss -> thermal reasons).
Thus the blown fuse prevented your adapter from being damaged and therefore
your Newt as well!!
You should be happy about that!
Remember that the usual fuse for the car cigarette lighter is rated at 10
AMPS!!!
SOLUTION:
a) you do not charge your Newt battery pack while plugged to the cigarette
lighter (first replace the blown fuse with one that has the same current
rating and characteristic e.g. slow, medium or fast), safest is to remove
the battery pack completely - or you use the battery tray with alkalines
instead
Since the Newt has a current consumption of 50 .. 100mA + the consumption of
the PCMCIA cards that you use you will stay below 300mA which matches with
your adapter (while running on batteries you can check the actual current
for your Newt e.g with the battery monitor of AVIs BD)
b) you get a proper adapter that is voltage regulated at 6 .. 7.5V and has a
current limitation to max. 1.3 Amps or at least a max. current capability of
1.3 Amps. Then you can also charge your battery pack inside the Newt.
and not to forget
c) you get 4 high capacity NiMH cells (available with 1300 or even 2000 mAh)
and put them into a Newt battery tray. For recharging them you can use any
commercial charger that can be supplied with 12V from the cigarette lighter.
If you are not sure it is always safe to apply a voltage of 6V only, because
then the charging current is limited due to the smaller voltage difference
between battery and power supply.
In any case: if you have some measuring equipment that you can measure the
characteristics of your black box power supply, there is no voodoo and no
risk at all.
The tricky part is that the Newt was designed to use a power source that is
current limited (i.e. it reduces the output voltage as soon as the max
current is reached)
This means that only a power supply with characteristics that are comparable
to the original supply will guarantee most efficient charging of the Newt
battery pack.
I hope this was not too sophisticated.
Cheers
Johannes
> -----Original Message-----
> From: newtontalk-bounce_at_newtontalk.net
> [mailto:newtontalk-bounce_at_newtontalk.net]On Behalf Of MKow1234_at_aol.com
> Sent: Thursday, June 17, 2004 4:21 PM
> To: newtontalk_at_newtontalk.net
> Subject: [NTLK] After-market power adapter / Aftermarket voodoo
> [It's dangerous to mess with Newtons and odd power supplies!]
> The output voltage should have been listed in DC volts, not AC.
> Newton AC adapters are plentiful and dirt cheap, so there's no need to go
> with some off-brand adapter that might harm your Newton.
> ------------------------------------------
>
> Incidentally, I recently tried a science experiment in my car,
> attempting to
> run one of my MP 2X00s off of a Radio Shack cigarette lighter
> adapter. The RS
> car adapter has a switch to adjust the voltage output from 3-12
> volts (I set
> it at 7.5 volts, of course). Output current for the device is rated at a
> maximum of 300 mA. My MP ran just fine off of the adapter -- for
> about two
> minutes. I blew one of those dinky-assed fuses inside the body
> of the adapter plug.
>
>
> I'm trying to figure out why the fuse blew, and the best answer I
> can come up
> with is that the Newton's load on the circuit was too great for
> the adaptor
> to handle (Reminded me of the old garage band days, when I
> discovered that one
> could not connect an infinite number of speakers in a series circuit to a
> guitar amplifier rated at 8 ohms! But I digress...) I suppose
> that I could place
> a LARGER fuse into the RS car adapter, but that would probably
> mean that a
> secondary fuse under my car's dashboard would then fry out. If
> any electrical
> engineers out there have a suggestion, please post a response. In the
> meantime, I'm thinking a DC 12 - AC 120 power inverter is the
> kludgy solution to
> charging the Newton on camping trips this summer.
> Matt K.
-- This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries Official Newton FAQ: http://www.chuma.org/newton/faq/ WikiWikiNewt for all kinds of articles: http://tools.unna.org/wikiwikinewt/
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