[NTLK] Re : Is model H2200 the only model of AC adapter

NewtonTalk newtontalk at pda-soft.de
Tue Nov 13 20:16:49 EST 2018

>> Never use a third party AC adapter for a Newton or an eMate. Never ever.
>> Chances are almost 100% you'll fry your little green friend within a
>> of milliseconds.

> Could you elaborate a little more about it? I?m asking, because there no
> detailed info about that statement. Why I couldn?t use ANY 7.5Volt, 1.2
> adapter with Newton?

The main reason is that what you find on an AC adapter's label isn't
necessarily what said adapter will put out. Very often the voltage you find
there means they'll guarantee the voltage won't drop below this value even
if the specified maximum current is drawn. This doesn't necessarily mean the
voltage will be the same if NO current is drawn. I have some cheap
unregulated multi-voltage supplies that, with their switch in the 7 Volt
position, will put out around 10 Volt when no current is drawn. A healthy
Newton will draw around 20...30 milliamps after you turned it on. For an
adapter that can supply a couple of amps, this is almost the same as no
current. Connecting such a supply would beam your Newton into Nirvana in no
time. This is the most frequent reason for what I describe here:


You can, of course, measure the voltage before you connect the supply to
your Newton for the first time. This will improve your little green friend's
chance of survival significantly. But since it will take only a couple of
milliseconds for your Newton to die, it will not guarantee survival unless
you check the supply voltage (Newton already connected) with a storage
oscilloscope at the moment you plug the adapter in the wall socket. Or
(Newton not yet connected) at the moment you plug the adapter in the Newton.
Overvoltage will kill Newtons very fast. So you must ensure they never see
any. Not even for a millisecond.

Another thing the Newton power adapter does, which many off-the-shelf
adapters don't do even if they're decently regulated, is folding back the
current limit if the output voltage gets too low. This is how Apple's
engineers prevented harm to your adapter and, as a consequence, to your
house, if the Newton, due to some internal defect, tries to draw more power
than it should. If the voltage reaches 4 Volt due to an excessive load, the
maximum current must be limited to 100mA instead of the 1200mA that are
normal. The more the overload reduces the output voltage, the more limited
the output current must be. With 0 Volt (something's shortened out in your
Newton) the current must be limited to 0 amps. Short-circuit protected
adapters will do the latter. But not all adapters are short-circuit
protected. And even if they are, you don't know if they adhere to the 4 Volt
100mA specification.

You won't necessarily kill your Newton by connecting a third party adapter.
You can be lucky. As a matter of fact, back when I had my first OMP and no
knowledge whatsoever about Newton hardware, I used it with some AC adapter I
found in my drawer because the original one in the box had an American plug.
Well, I was lucky. The adapter was decently regulated, and the Newton never
attempted challenging its current limitation by shortening it out.

Original Newton adapters are still available and not even all that
expensive. Especially if you take into account what it would cost you to
have your Newton repaired and get a second adapter after the first one
killed it. So why take a chance!


-- Newton software and hardware at http://www.pda-soft.de

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