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Electronic AC > DC transformer

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RazorM

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I have a Radio Shack cordless phone which is rated as: 12Volts, 300mA & 8Watts. Where the center pin is +.

This was for an input voltage of 110volts.

I've moved somewhere that has 220Volts output now. I've been using a converter to step down the wall voltage (220 > 110) but found taht the converter heats up quite a bit & it's plugged in 24 hrs a day for the phone...

I've tried to find a AC>DC transformer that matches the original, but have had no success.....

So what parameters need to fall in what range? I suspect the voltage must stay at 12V ideally & the current can be slightly lower but preferably slightly higher??

or is this oversimiplified?
 
RazorM said:
I have a Radio Shack cordless phone which is rated as: 12Volts, 300mA & 8Watts. Where the center pin is +.

This was for an input voltage of 110volts.

I've moved somewhere that has 220Volts output now. I've been using a converter to step down the wall voltage (220 > 110) but found taht the converter heats up quite a bit & it's plugged in 24 hrs a day for the phone...

If you have the correct 220/110V transformer the phone power supply should be getting no hotter than it did previously, it's running on exactly the same 110V supply.

Bear in mind, these PSU's normally do run hot.

I've tried to find a AC>DC transformer that matches the original, but have had no success.....

So what parameters need to fall in what range? I suspect the voltage must stay at 12V ideally & the current can be slightly lower but preferably slightly higher??

or is this oversimiplified?

Just buy a regulated 12V PSU, as long as it's higher than 300mA it will be fine (and they all are likely to be higher), these sorts of PSU's are likely to be switchable to different voltages , and may well be switchmide - making it light and cool running. But make sure it's a regulated one, the non-regulated ones are totally crap!.
 
I've seen many 220/110V wallwart autotransformer with 3*4cm dimensions, rated for 50VA! (US made) It run up to +70Cgrad without problems. I hope You have some similar type, NOT a triac-downconverter.The triac-type converter start to work over 50...100W power, and recommended only for ohmic loads (hair dryer,etc.).
Most of case the cordless phone base station contain internal regulated 9V supply, so the cheap universal wallwart supply will work.
 
Regulated or non-regulated PSUs

Looked at several PSU's around here & none of them mention in words "Regulated" or "Non-regulated".....should I be looking for symbol of some sort?

sorry if this is a simple & stupid quiestion....so many elec. gods here....
 
Re: Regulated or non-regulated PSUs

RazorM said:
Looked at several PSU's around here & none of them mention in words "Regulated" or "Non-regulated".....should I be looking for symbol of some sort?

If it doesn't say, it's not regulated - if it's regulated it will say, usually either regulated or stabilised.
 
Regulated

I suppose than if I watched it w/ a volt-meter i would see an unstable needle pointer if it was unregulated right? ...& vice versa for a regulated one....
 
Re: Regulated

RazorM said:
I suppose than if I watched it w/ a volt-meter i would see an unstable needle pointer if it was unregulated right? ...& vice versa for a regulated one....

No, with a stabilised PSU you will see 12V when it's set to 12V, with an un-stabilised one you will get something like 18-19V off load.

As Sebi says, it's quite possible that the phone has it's own regulator, but for the slight extra cost I would always go for a regulated wall-wart.
 
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