I'm pretty sure that DC power supplies must be chosen with care, to be
matched to the appliance or machine in question. My daughter has a
CD-RW Station burner, made by EXP, and has lost the power supply. I
have a lot of DC power supplies accumulated over the years, including
some where you can choose the voltage...but how can I determine which
to use with this machine? I'll go to the manufacturer's website, but
I'm betting it won't have the answer to this one (except maybe to buy
a replacement, which is OK, but might be more complicated and slower
than necessary). Thanks!

Hi bbb

When matching up DC power supply units to the equipment that requires
them there are four separate things to be aware of:

* the required voltage;
* the required current;
* the polarity of the supply;
* the physical shape of the plug and socket.

Voltage
This normally varies from about 3V to 12V DC.

Current
This can vary from as low as 100mA up to 2A or even higher in a few
cases.

Polarity
The DC connector will have two terminals, one of which is considered
positive and the other negative. It's obviously crucial to ensure that
these are the right way round.

Physical
Although many manufacturers use standard round-pin sockets for their
DC supplies, there are some that use proprietary forms. If this is the
case then finding a generic replacement is going to be extremely
difficult.

So how to tell which of the above combinations your device requires?
Well fortunately there is a global standard set of symbols designed to
detail exactly that. This should be either printed or moulded into the
plastic of the device, close to where the DC input socket is. Voltage
(and current if applicable) should be simple to identify as they will
be printed simply as (for example) "DC 9V, 400mA" -- note that the
Amps rating is often left off as most devices can draw the required
current as long as the voltage is correct.

To identify polarity you have to understand how the plug and socket
are designed. Essentially the plug is like a cylinder, where its outer
wall is one electrode and the inner wall the other. The universal
schematic diagram identifies which of these are positive and which are
negative, and both examples can be seen at
http://www.cyberpowersystems.com/phonesaver/faqs.htm (scroll down
about one screen).

So to answer your question, at the very least you need to match up the
voltage and polarity of one of your spare AC-DC adapters to the
voltage and polarity required by your daughter's CD-RW burner. The
only real stumbling block you might encounter would be if the
manufacturers have used a non-standard shape for the plug, in which
case you might find yourself forced to buy a new power supply direct
from them.

If you find that none of your adapters seem to have the right output,
you might also find that you're able to order a custom adapter from
http://www.globalspec.com/SpecSearch/SearchForm?Comp=2249


I hope this gives you the information you were after, however please
feel free to ask for clarification if necessary.


Regards
iaint-ga


Google searches performed:
AC-DC adapters
DC input symbols

---

Request for Answer Clarification by bbb-ga on 29 Nov 2002 00:02 PST

OK, I've found this: Underneath the unit, there's a sticker with info,
including this: 12V 1.5A DC .... So we know the voltage and amperage.
I also see a symbolic drawing near the DC input, which shows -- now
that I know what to look for (!) -- that the outside of the pin should
be negative and the inside positive. Among the 30 or so (!) DC
converters I have, I see a lot with 12V, but haven't found one yet
with 1.5A -- though several are 1.25A... and a lot are 200mA (which
seems puzzling, since it's so far from 1.5A). Most also have diagrams
the polarity  of the pin (and in most of those cases, the outside is
negative.) So I'm partly there, in terms of figuring this out....

Wow. Thanks very much for what certainly seems like a very thorough,
very clear, and very useful answer. The unit in question (a CRW-940, I
see on the bottom) does seem to have a round DC input, which is good.
I'll look into the rest and see what I can figure out....
Thanks!!!!!!!

I also have a pile of power cubes. Almost half are ac instead of dc.
When in doubt, I use a bit lower voltage or current rating, often with
good results. Using a higher rating (either voltage or current) may
damage the cd burner but lower voltage and higher current is usually
safe.   Neil

To neilzero:
Thanks. Useful to know this. By the way: I believe I burned out some
computer speakers by using the wrong "power cube" (handy phrase, which
I never knew).
bbb-ga

It's not puzzling that some of your power supplies are as low as 200mA
- they're simply designed for items with lower power consumption.

Your 1.25A adapter might be adequate for intermittent use for a short
while.

I couldn't find higher than 1.25A on the Radio Shack (.com) website
but higher power adapters are available. From the British site
maplin.co.uk I found:

"A range of high quality fixed voltage regulated mains adaptors for
personal computers, radios, calculators, video games, cassette
players, small TVs and battery operated equipment. The adaptors
feature short circuit protection, plus automatic thermal and overload
cut-off. The regulated output ensures a constant DC supply with
minimal ripple. The output is via a flying lead with ... a 2.1mm plug
only. Polarity is centre positive when the ‘+’ symbols on the output
lead are aligned, and is reversible.
12V 1.5A order code JC93B  and the price would be GBP 24.99 incl tax.

As you know the voltage and current required, any good electrical
retailer should be able to find you an approrpriate power supply. Be
sure to specify *regulated* - an unregulated power supply supply gives
its rated voltage only at its rated current, and at lower currents the
voltage can rise. The round DC power plugs come in a multitude of
sizes, but are pennies each from component suppliers, so an
appropriate supply that has the wrong plug can have its plug changed
cheaply.

Owain