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Replacement of Power Packs
-not a simple choice



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Contributed by Puddledud.

The article

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 confidence.

These factors - as I recall them - are:

supply voltage:

- the mains voltage where the device will be used

supply voltage frequency:

- does the frequency the supply is designed to operate under match that of the local mains?
  This is often 50 Hz or 60 Hz sometimes supplies are marked to operate at either 50 or 60 HZ.

output voltage:

- the magnitude of the voltage supplied by the power pack

direct or alternating output:

- is the output AC or DC

plug polarity:

- is the centre pin positive or is the centre pin negative?

connector type:

- 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.

Constant current

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 batteries.

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.

Hints:

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.


Regards,

Puddledud



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First posted in January 21, 2014 (140121)

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