selecting the right fuses

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beatnik

Well-known member
Joined
Oct 18, 2009
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Location
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Sorry, I know this could be such an obvious argoument. But I really can't figure it out. I searched on the forum, but didn't get precise answers.

The question is about how choosing the right mains fuse for various projects.

I don't know, what type (slow or fast blow), what value, and especially in what the value is based (power transformer VA, power supply or audio circuit current drawing,....???)

For example, the gyraf GSSL project calls for a 315mA slow-blow fuse. What this exact value is based on?h

Thanks in advance
 
Funny, a similar question was asked in the Mibuzz built threat.

Here is an answer 'tomcat' posted: ::)

Following info copied from another thread to help you to calculate the fuse by yourself

---
I decided to email Triad Magnetics and I'm glad I did. Their engineering manager responded quickly with this information...

"Since the VPT36-690 transformer is rated at 25VA (Volts times Amps), the theoretical input current would be 25VA / 115V = 0.217A or 25VA / 230V = 0.109A.  However, this does not include the magnetizing current or inrush currents – so we generally recommend the fuse be rated at 1.3 to 1.6 times the theoretical input current.  It is very important that a Slow Blow (time delay) fuse be used to allow for inrush currents that exceed the fuse rating to prevent nuisance fuse blowing."

This seems like a very good guideline for fusing the transformer.


... hope this helps.

Regards,

Chris
 
this is exactly what I was looking for! many thanks!
always something new to learn from this great forum!
 
Please note that many factors influence the optimal selection of fuse; for example, toroidals have generally a larger magnetizing current, the actual value of smoothing caps can make a significant difference on the inrush current even if the steady-state current is the same, and also beware not all fuses are equal, even if they bear the same slo-blo (retarded) designation.
All in all, there's a certain amount of trial and error involved in the process.
 
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