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Old 25-02-2005, 02:15
Bill Clinton
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I have an american device which can run off 3 AA batteries, it comes with an included power supply that of course won't work with UK mains. It's output is 5V DC, 300 mA. I have a UK power adapter of which the output is 4.5V DC, 450 mA, the plug from it fits into the device. Will it damage it if I try to use it, it says only to use the supplied power supply, but I want to find a solution other than to continually use batteries. Could the higher amount of milliamps damage it?
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Old 25-02-2005, 10:05
chrisjr
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The current rating of the power supply is how much it CAN supply, not how much it WILL supply

Therefore if the unit only requires 300mA then that is all it will draw, the current is determined by the load not the source.

The only other thing you may need to check out is the polarity of the DC connector. There seems to be no convention on these things. If it's one of the usual small round types with a "hole" down the centre it can have the positive connections on the inner or outer contact (and vice versa for the negative). Pluging a power supply with these connections the wrong way round for the device can damage it.

Another pain in the wotsit is that there are various sizes of these things. One of the more frustrating being two types which differ only in the diameter of the centre contact. There are versions with 2.1 and 2.5mm contacts. They are virtually impossible to tell apart. A 2.5mm plug will fit a 2.1mm socket but that extra .4mm is enough to make it not connect electrically!
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Old 25-02-2005, 12:08
John Currie
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[quote=chrisjr]The current rating of the power supply is how much it CAN supply, not how much it WILL supply

Therefore if the unit only requires 300mA then that is all it will draw, the current is determined by the load not the source.

The only other thing you may need to check out is the polarity of the DC connector. There seems to be no convention on these things. If it's one of the usual small round types with a "hole" down the centre it can have the positive connections on the inner or outer contact (and vice versa for the negative). Pluging a power supply with these connections the wrong way round for the device can damage it.

QUOTE]

The only thing I would add is check on the mains adapter for a small diagram showing the "hole" of the plug and it should have a + or - symbol next to the centre pin indicating polarity.
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Old 25-02-2005, 12:35
chrisjr
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Good point. Look for a symbol on both power supply and the device you want to power similar to...
+ -(.- -
or
- -(.- +
(bit difficult to draw using only text characters but hopefully you'll get what I mean)

Make sure that both are the same.
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Old 26-02-2005, 01:36
Bill Clinton
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Thanks, good job I didn't just plug it in, I'll check for the polarity settings.
Thanks for your information it's been very helpful.
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Old 26-02-2005, 10:34
Richard_T
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what is the device?
it might be worth looking at the input range for the power adaptor as some automaticly sense the voltage and are rated at 110v-240v
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Old 28-02-2005, 00:11
webbie
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You may also want to see if your power adaptor says its output is regulated. This means that its voltage will stay at 4.5V whatever current is being taken out of it up to 450mA. If it doesn't say it's regulated, this probably means that it is unregulated (as they are cheaper!), which means that it will supply 4.5V dc at 450mA. At other current levels, the voltage will be higher. At 300mA it may be 6V or so, and could possibly damage your equuipment.
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Old 02-03-2005, 11:57
sanderton
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You can buy very cheaply adapters with switchable power ratings, polarity and multiple adapter tips. Thay can be lifesavers!
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Old 02-03-2005, 13:41
oldie
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You can also use your existing US power supply with a suitable transformer which converts 230VAC (UK supply) to the US 110VAC supply. I know the US frequency is different from the UK, but this shouldn't matter. www.maplin.co.uk have lots of these in stock at £19.99, saving £20 off normal price. I assume your US power supply still has a US plug on it. If you go down this route make sure that the plug will fit the socket on the transformer. Maplin's part number is VR05F. Any good electrical shop will also have these transformers. Almost any power rating will do, but I doubt if you will find one of less than 50 watts. You don't need anything bigger. An autotransformer will do. You don't need an isolating transformer, it just costs more and for your application you don't need one.
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Old 03-03-2005, 13:13
webbie
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I'm sure I've seen these for under £10 from somewhere. I think it was www.cpc.co.uk but can't find it now! Also, watch for the £4 handling charge is ordering goods under £30.
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