Author Topic: A Small Experiment - Part One  (Read 859 times)

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Offline German_EETopic starter

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A Small Experiment - Part One
« on: November 17, 2019, 04:48:03 pm »
After watching far too many posts by Big Clive I'm going to try an experiment. The 5 V supply for my desk lamp died this morning and there is no hope of recovery (send no flowers as it was a Viking funeral). To replace it I've ordered off EBay the cheapest 5 V 2 A supply I can find with a Euro plug, the lamp has no exposed metal parts so whatever happens nobody is going to die.

The price, 2.29 Euro with free shipping from China.

When it arrives, sometime between December 15 and January 15 I'll do a PAT test to see if it's safe, check the output on a scope to see if it's clean, then test it under load. That will be part two.

Of course, if you can find a 5 V 2 A supply with one of your local plugs on for less than 2.29 Euro (which is pretty close to the same amount in USD) then please feel free to join in. Let's find out how low we can go and still get something that doesn't kill us.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 
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Offline magic

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Re: A Small Experiment - Part One
« Reply #1 on: November 17, 2019, 07:05:06 pm »
Bonus if you stick a thermocouple inside and check thermals.

Story time: I bought a $10 switchable voltage wall wart rated for 2.5A output. It has no secondary current sense, only primary side over power protection, set to 30W for the highest supported voltage of 12V. If I set lower voltage, it happily delivers more than the rated current. I got up to 4A at 5V.

The secondary rectifier is a standard silicon diode in TO220. It unsoldered itself during that overload test and probably is rather marginal in normal operation too. At 2A we are talking some 1.5W inside a tiny plastic box.
 

Offline German_EETopic starter

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Re: A Small Experiment - Part One
« Reply #2 on: November 18, 2019, 09:18:31 am »
Thermal checks are on the TODO list. As an example of the Chinese way to do business the order was placed on Sunday afternoon German time and by 9pm the package had shipped, that's impressive.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 


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