Power Supply Adapter Ratings and Country-Specific Voltages

Posted on 2007-09-29
Last Modified: 2013-12-11
Hi experts.
I didn't know where to ask this, and it's not so much a computing question as one that will be known to anyone who has a better knowledge than me as to how transformers work.

I sent an Internet Phone from the UK to a friend in America so we could communicate for free.  It's a cordless one that uses the base set to charge the internal batteries in the handset, and the base unit connects by usb to the computer.

The manual makes no mention of country-specific compatibility of the power adapter that plugs into the mains supply socket and connects to the base unit, and in fact the promotional documentation says "send another of our Internet phone packs to your loved ones, wherever they are in the world and stay in touch for free".

When plugged in, this phone doesn't seem to be charging on the base unit, but works OK when freshly charged AAA batteries are inserted.  On inspection (my phone pack is the same as that sent to my friend), the PSU bears the following ratings:

Mains Adaptor
Input: 230v ~ 50Hz 30mA
Output: DC6v 300mA

When I look at all other PSU's/Chargers for other domestic apparatus like my mobile phones, usb hub, etc, they all show that they accept a RANGE of inputs, eg.  110 to 230vAC ~ 50 to 66Hz.  In the UK we have 230 Volts (+10% 6%) Mains supply at 50Hz.  I believe these are called "switching" power supply adapters (as opposed to "switchable" where you would twist a voltage selector).

I have a rough idea how transformers work, but my question is what the results would be in this scenario where a PSU that is fixed to accept a 230v 50Hz mains supply is plugged into a USA plug socket supplying 110 Volts (-5% to +5%) at 60Hz (I think).

Will it only output half the DC voltage it would with a 230v input, ie. 3v instead of 6v?

If so, then clearly it won't charge the batteries, and more importantly wouldn't damage the batteries or phone, but I'm not clued up enough on power supply frequencies to know how that affects the output.

I know you will wonder this, so I'll answer it for you to save you asking.
Yes, my friend bought one of those simple plug adapters so the pins for the UK style plug pins fit the mains socket in the house there.
I am sure I will be able to source a PSU with USA plug pins and rated to accept 110v while giving the required DC output, but I intend seeking a partial rebate from the UK vendor if this is needed, on the basis that they imply the phone package is internationally compatible without additional purchases.

Thanks in advance
Question by:BillDL
    LVL 91

    Accepted Solution

    you have 2 solutions :
    buy a small  230- 110 V transformer (5 W )
    buy an adaptor 110 V in, 6 V out, 2W min
    i would not connect the 230 V adaptor to a 110 V mains - you cannot be sure it is a switching PS; it can just be a transformer with rectifier.  It will Never work, and can discharge your batteries even.
    LVL 62

    Assisted Solution

    by:☠ MASQ ☠
    Depends on whether the label actually reflects what's in the box.
    On my regular jaunts I have no problem with most transformer/chargers switching between 220 and 110 irrespective of what it says on the box, however I have one charger/adapter for an NTL walkie-talkie set that simply will not charge when in the US but would work fine while connected to the power outlet (not great for a portable device!)  and had to get a Radioshack equivalent (about $10).

    Suggest you just let your friend find out if it works & if not a simple generic adapter should suffice (make sure the polarity of the adaptor jack is correct).

    >>I intend seeking a partial rebate from the UK vendor if this is needed, on the basis that they imply the phone package is internationally compatible without additional purchases.

    I like your thinking :)
    LVL 38

    Author Comment

    Thanks guys.

    nobus, I think you are right about it actually discharging the batteries.  That would tie up with what happened when my friend initially put the phone on to charge.  I'll search for a generic adapter with the correct rating in the US.

    Masqueraid (or is it "Champagne" Charlie Bunson or Bunny Mandelson :-), this is a Tesco Internet phone. They're pretty good at exchanging things, but the Internet phone support appears to be run by a bunch of monkeys, so getting a partial rebate will probably be something of a challenge.  I like challenges, however.


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