Electronics > Beginners
Tips to measure mains transformer and survive?
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vk6zgo:

--- Quote from: Fungus on November 04, 2019, 03:48:02 pm ---
--- Quote from: vmallet on November 04, 2019, 01:07:32 am ---I have a 110V->220V consumer transformer (I am in the US) with a three-prong socket for the 220V output. What would be the right way to proceed and what safety tips should I follow to make sure I don't win a trip to the heavens?

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a) Wire it all up with a 1A fuse and long wires on the primary side of the transformer, connect the multimeter to the output.

b) Plug the whole thing into a plug strip - one with with a switch on it.

c) Plug the plug strip into the wall then use the switch to power on the divice. Don't look directly at it, wear ear plugs.
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With respect, ---it's a transformer, not a nuclear device!

I will admit that the series fuse is a good idea, but I was more concerned with making sure the Mains to primary connection was secure.
Inserting a fuseholder into that simple circuit makes for a less secure connection, unless you go to great lengths to fit the whole assembly in a box.

Over many years of working with transformers, I have never seen one which has a direct short across the primary .
The usual fault condition is a shorted turn on either primary or secondary (or an open circuit winding).
In such cases, the existing turns limit the current drawn from the Mains.

Faults with transformers just let the magic smoke out, they don't fly apart.
Series wound electric motors, --------now, there's another thing altogether!

--- Quote ---
--- Quote from: vmallet on November 04, 2019, 01:07:32 am ---I would like to measure its output voltages.

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Or...

Read the label on the side: It says 12.5V and 18V  :)

nb. The voltages will depend on the load you apply to it, you only get that voltage with a particular load. I wonder where it might tell you that information....

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"Reading the label" doesn't tell you anything about the transformer's condition, though!
DTJ:
A handy tip for working on mains powered devices is to unplug the power cord and stick it in your pocket when working on it. If the cord plug is in your pocket then you are (generally) safe to poke around moving test leads or wires. It's easy to get side tracked and forget that the gear you are working on is live.

Another tip when doing testing like above is to use the back of your hand or fingers to test to see if something is (thermally) hot rather than your fingers which if the surface is live could 'grab' the live material.
exe:

--- Quote from: DTJ on November 05, 2019, 02:18:04 am ---It's easy to get side tracked and forget that the gear you are working on is live.

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Yeah, happened to me multiple times :(
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