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mdf



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Topic # 236003 13-May-2018 15:02
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I have a big box of transformers that I have been keeping for *years*. This hardly ever comes in handy, since inevitably there is a mismatch between the volts/amps/pin polarity/barrel connector I have, and what I am looking for.

 

I had a win today, but it did prompt a couple of queries. I was looking for 12V / 1A and I have a couple of contenders. Looking for some guidance as to what is likely to be the best option (this is for a router so pretty much powered on 24/7).

 

I have a big, heavy 12V / 1A Linksys/Cisco that I am almost sure powered a WRT54GL, so is ~10 years old. Unfortunately, this has both a UK plug and is enormous so both requires an adapter and crowds out other things on the power strip.

 

I also have a small, lightweight generic 12V / 1.5A adapter. This is nice and slimline and has a NZ plug. It's not quite the right amps, and I'm assuming uses a different technology to the previous one (something digital vs copper windings?). How worried should I be about the amp mismatch?

 

Does weight = quality in transformers? Which would you use?

 

Given this will be on 24/7, I'm also open to buying a decent one if anyone has any suggestions.


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  Reply # 2015174 13-May-2018 15:20
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The older one uses a transformer, hence the weight, the newer one most likely uses a switchmoded based electronic power supply so is much lighter.

 

 

 

As far as the amp rating, this is what it is capable of supplying, think of it like the maximum speed of a car, you may only need to do 100kph but the car can do 150kpm.

 

You should check the polarity and style of the plug, although it may be a barrel type there are a number of sizes, and the centre pin could be negative or positive, does this match what the device needs, getting this wrong to kill your device.

 

 


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  Reply # 2015175 13-May-2018 15:21
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The amp rating is just the maximum current the unit can supply.  Provided the powered unit needs less than this, it will work fine.


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  Reply # 2015180 13-May-2018 15:21
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Weight means copper transformer which is old. To give them short circuit protection they are badly coupled so have terrible regulation of the voltage. Other than some audio snobs there is no reason to keep them around unless you like poor efficiency and voltages that can be 50% too high.




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mdf



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  Reply # 2015182 13-May-2018 15:25
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Super news, thanks all. Both have the right size barrel and pin polarity. If the higher potential amps aren't a problem, l'll definitely go with the smaller, lighter and generally less inconvenient one.


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  Reply # 2015185 13-May-2018 15:29
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The center pin is a tricky one. A 2.5 mm plug will go over a 2.1 pin but have a crappyty connection and cut out at the worst possible time.




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  Reply # 2015186 13-May-2018 15:31
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There might be quality differences but current capacity shouldn't matter as long as it is equal to or greater. If your device requires 1 amp to operate correctly, then an adaptor rated at more than 1 amp won't hurt anything. The amount of current drawn is determined by the device drawing it, not the capacity of the adaptor. 

 

What is important is the nature of the power being delivered. A router or other sensitive electronics device requires regulated DC. An adaptor that delivers AC, or pulsating DC intended only for charging, will cause much grief. But current capacity is not an issue, as long as there is enough of it.

 

 

 

 





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  Reply # 2015189 13-May-2018 15:37
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richms: The center pin is a tricky one. A 2.5 mm plug will go over a 2.1 pin but have a crappyty connection and cut out at the worst possible time.

 

A very good point. I had only eyeballed it previously. I have just done some judicious probing with the back end of some drill bits. For the original and my proposed replacement, a 2mm drill bit seems to fit (if only just) but a 2.5mm is clearly too big. That sounds to me like both are 2.1 pins?


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  Reply # 2015190 13-May-2018 15:40
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Rikkitic:

 

What is important is the nature of the power being delivered. A router or other sensitive electronics device requires regulated DC. An adaptor that delivers AC, or pulsating DC intended only for charging, will cause much grief. But current capacity is not an issue, as long as there is enough of it.

 

 

Hmm, is there a way of telling the difference? I've no idea what the proposed replacement unit was originally attached to. There are some symbols on the unit but I've no idea what they mean (a solid horizontal line with a dashed line under it; two squares, one inside the other).


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  Reply # 2015210 13-May-2018 16:00
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Routers do not care as they internally regulate down to 3.3 or 5 and 3.3 if they have external USB ports to power. Mine was ok on a car battery till it got way low like 6v once i disconnected the load from it. The ones to watch out for are older style things that have a 5v wallwart but that's rare as now.




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  Reply # 2015211 13-May-2018 16:03
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mdf:a solid horizontal line with a dashed line under it;

 

Direct Current

 

mdf:two squares, one inside the other).

 

Double insulated


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  Reply # 2015212 13-May-2018 16:04
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Here is a link to common symbols. The one you refer to just means DC. Most adaptors are regulated. Anything that previously powered an electronic device should be okay.

 

Edit: The operative term is should be. I guess I ought to add a disclaimer that I can't guarantee anything. I have been mixing and matching old adaptors for years without any problems, but there is always the odd chance something unexpected could go wrong. 

 

 

 

 

 

 





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  Reply # 2015227 13-May-2018 16:25
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I just saw a clever tip that should help: Because unregulated supplies are unregulated, they deliver a higher voltage when no load is put on them. So just measure the voltage. If a supply rated at 12 volts measures significantly higher, like around 15 or so volts, the supply is unregulated. If it is 12 volts, the supply is fine.

 

 





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  Reply # 2015238 13-May-2018 17:01
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Please check if the transformer does not get too hot
Dont want to burn your house down

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  Reply # 2015755 14-May-2018 14:09
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mdf:

Does weight = quality in transformers? Which would you use?

 

Given this will be on 24/7, I'm also open to buying a decent one if anyone has any suggestions.

 

 

I would get a multi-amp class VI efficiency 12V brick and use that. A transformer + linear power supply wastes at least 30% of its total power as heat and typically has little electrical protection apart from the lump of copper and iron it's built from, while a class VI is typically 90+% efficient, has active PFC, and a pile of protection circuitry. I've got a 4A one that runs all my 12V gear with headroom to spare. You can get 5.5mm splitters from anywhere that does alarm-type stuff, they're commonly used for security cameras. So you've got one high-efficiency brick tucked behind a cupboard or something and power for all your 12V gear in one place.

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  Reply # 2015766 14-May-2018 14:26
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Since your linksys requires a UK to NZ power adapter, chuck it in the bin. 

 

Just use the other one. If it works it works.

 

 


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