Author Topic: Fuse / Breaker size question  (Read 480 times)

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Offline shanezampireTopic starter

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Fuse / Breaker size question
« on: July 10, 2019, 03:15:09 am »
Hypothetically lets say you have a 24vdc 5a 120w power supply and you want to make a bench top variable power supply. You run it to the variable control module, potentiometers, binding posts, etc. Of course you want to put a fuse / breaker before the binding post (I assume that's the correct place) and I assume you want one after the 120v main line coming in.

My question is what size do you use?

Online calculators say Fuse rating = (watts/volts) x 1.25

So you would need a 1.25a fuse or next size higher to main line coming in

and you would need a 6.25a fuse right before the binding post

If this is correct ... wouldn't it be better to just stick with a 5a fuse OR one them Resettable Push Button Thermal Circuit Breaker Panel Mount to be on the safe side?



 
 

Offline MosherIV

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Re: Fuse / Breaker size question
« Reply #1 on: July 10, 2019, 06:41:49 am »
Quote
So you would need a 1.25a fuse or next size higher to main line coming in
Sounds about right. Try a Timed or antisurge type due to the inductance of the transformer.

Quote
Of course you want to put a fuse / breaker before the binding post (I assume that's the correct place)
Why? What are you trying to protect?
It would be better to put the fuse on the output of the transformer to protect both the transformer output and the psu circuit.
You would expect a bench psu to have current limiting and set that to some value to protect the circuit under test/development.
Bench psu should be capable of withstanding a short circuit by limiting the output current to the current limit. They should also be able to deliver the rated current or current limit continuosly.
 


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