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Replacement of Power Packs
-not a simple choice
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Contributed by Puddledud.
Replacement Power Packs - not a simple choice
Need a replacement
power pack aka wall wart for a device? By far the best option
is to locate a battery pack which is original equipment and
designed for the device in question. Otherwise choosing an
appropriate replacement power pack for a device might not be
as straight forward as first thought. There are many
things to consider before a choice can be made with
These factors - as I
recall them - are:
- the mains voltage
where the device will be used
- does the frequency
the supply is designed to operate under match that of the
This is often
50 Hz or 60 Hz sometimes supplies are marked to operate at
either 50 or 60 HZ.
- the magnitude of
the voltage supplied by the power pack
- is the output AC
- is the centre pin
positive or is the centre pin negative?
- some are tiny,
others are large and there are some bizzare pin sizes and
connector layouts out there.
power rating of the
device being powered:
- while a 1 amp
supply will drive a device needing just 200 mA there is a
potential danger in using such a supply for, in the event of a
malfunction in the device to be powered, it might then be able
to draw more power than its design parameters allowed for.
Conversely putting a 400 mA supply to do the work of a 1 amp
supply is likely to result in burning out the plug pack. In
that case the user had better hope that at least it burns out
gracefully and doesn't cause a fire because it could.
REGULATED or UNREGULATED
An UNREGULATED supply is designed to provide more or less the
expected voltage if the mains voltage is as expected and if the
load applied is as expected. Such a supply when tested may deliver
a significantly higher voltage than specified. This voltage may
drop or settle down under load.
This UNREGULATED plug pack may also provide a higher than expected
output voltage due to there being a higher than expected mains
voltage present. Where I live the mains is nominally 240 volts AC
but when tested it is found to be usually over 245 volts AC. This
means that an unregulated plug pack used here will always deliver
a higher than expected output voltage.
A REGULATED plug pack is designed to deliver the specified output
voltage and will internally adjust the output until it meets the
output voltage specified.
the nature of the device to be powered
If the original supply was a basic no frills UNREGULATED supply
then the device to be powered may take precautions to cope with a
range of input voltages but on the other hand if the original
supply was a REGULATED one then using an UNREGULATED supply with
the device could lead to damaging the device.
Some supplies may be marked c.c. which I think means constant
current and this is likely to be a further factor that needs to be
considered when looking for a replacement power pack for a device.
It may be associated with devices containing rechargeable NiMH
A check list:
It is always necessary to identify:
• The mains voltage
• The mains voltage frequency
• The plug pack output voltage type
• The magnitude of the output voltage
• The physical dimensions of the plug pack connector
• The polarity of the plug pack connector
• The amperage expected by the device to be powered
• It may also be necessary to consider whether a c.c
(constant current) power pack will be needed.
Devices often - nearly always - specify the voltages either on a
compliance plate on the powered device itself or beside the
insertion point for the plug pack connector. Sometimes a search on
the net will locate such information too. The best source of such
information is the original plug pack - if it is available.
It is excellent practice to always choose to use a REGULATED
supply in preference to an UNREGULATED supply as this goes some
way to catering for the situation, which is frequently
encountered, when little is known about the design parameters of
the device which is to be powered.
It is always good practice to test the output of a plug pack using
a multimeter to make sure that it does deliver the voltage
expected and not one several volts different before connecting it
to the powered device for which it might be intended. At the same
time check that the voltage on the centre pin of the connector is
the polarity expected.
When a new plug pack is fitted to a powered device it is also a
good idea to keep an eye on it while it is running for a while
because one reason for needing a new power pack in the first place
could be due to the powered device attempting to draw too much
power from the plug pack and so causing it to burn out.
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First posted in January 21, 2014
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