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Using correct rating fuses

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its been discussed before at great lengths...  Fitting the correct fuses is so important,  mains fuses are not to be misinterpreted that just because it’s triggered never assume that you can use a higher rating.  Mains fuses or any in line fuses are there to protect against instantaneous current surges that are very likely to short and damage power drivers or in an even of a component failure that’s “forced” a condition to put a rail supply in direct path to 

 earth or neutral.   With mains fuses,  engineers will factor in what’s normal usage that’s safe and what’s not normal and unsafe, hence the fuse rating limits. 

Nearly all Hifi equipment and power electronics will supply a DCV,  to do so somewhere along from the mains there will be a fullwave bridge rectifier that uses four diodes to switch the AC cycles to enable DCV rails.   Any fault or failure here, can result in seriously safety concerns,  normally blowing a fuse or worst  tripping the buildings mains breaker or the RCD.  

I hate going out to these faults,  usually you need to access dangerous mains voltages,  sometimes I’m playing around with full 30A 3 phase, sometimes 2 x 30A single phase,  now these are areas of the product you do not want to have live and dicking around with a MM.  When I was training at Kodak,  I was fault finding in an area call PD&C ( power distribution and control) this area is so dangerous, one slip and you end up in another life!  I learnt a while b4 this training how to stay safe by relating to basic electronics theory and what can  be measured during “power down”.   In a test for fault finding, out of a a number of students,  I was the only one to fault find and finished 1st to find all faults successfully in this PD&C area where the equipment powered up and usable,  but because of my unconventional way of fault finding, it really didn’t suit the requirement for the circuit to be switched on and follow the 240VAC with a MM to demonstrate and show where the breaks were, so the trainer failed me in the spot!  Not that I give a rats,   Name of the game is to stay alive!  Today that training would have changed due to OH&S.  

 

So here is a typical mains fuse example that I go to: 

 

customer says the machine was operating, then she heard it go “bang” power goes out,  product is dead, cannot be switched on.  She was told on the phone to check the RCD on the side of the product and also the breakers on the wall.   Both have been tripped, she switches them to power up, still no power to the product, service order registered,  out I go on site.   

Here we find that the 8A sand filled fuse has blown,  you can’t see any signs of component failure, yet it blew a 8A mains fuse to a SMPSU.   Normally in this case you’ll see something that’s blown,  blackened areas or damaged tracks, but here no visual sign of damage.  So with power off, you can traced where 240VAC goes using basic ohms law with a MM.   it’s isn’t far from the mains I discover that one side of a full wave bridge has a short on the positive terminal to the AC input.  Now a short is a short,  whatever rating fuse you use, this is going to pop them all full stop!  Some will argue that I shouldn’t be fault finding components like this and it should be taken out of circuit, well check the pics I’ve done that as well, this bridge rectifier is faulty, however way I use those probes for polarity, a short is a short!  A working bridge will have working Diodes that will conduct one way and not the other! 

It’s so important to use the correct fuse, higher ratings can also damage surrounding component, and Ive seen this done!  Some techs will uses a nail so whatever is faulty like in this instance would have demonstrated visually what’s faulty!  But you don’t need to go there, experience will tell you there is no need for that!  Especially if it’s tripping the building RCD breakers.   

 

 

 

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That's right.

You don't want a fault situation that can end in a fire.

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4 minutes ago, LogicprObe said:

 

That's right.

You don't want a fault situation that can end in a fire.

The product has and area that also operate at around 185C.   There’s one thing about Japanese equipment is they don’t compromise on safety,  there are multiple non contact thermal fuses triggering at 200C in series in case a heater element driver stays permanently on!  Then there is a thermopile to monitor that unit,  it’s part of the Accreditation to operate in EU. 

 

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Yes.

I'm a big fan of Japanese product..............................but only if it is also manufactured in Japan.

as for the EU standards............a lot of it is pie in the sky.

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10 minutes ago, LogicprObe said:

Yes.

I'm a big fan of Japanese product..............................but only if it is also manufactured in Japan.

as for the EU standards............a lot of it is pie in the sky.

Thermopiles was a requirement due to the Buckingham Palace fires,  the standards was raised so this shouldn’t happen, however it seems that companies inside EU don’t even operate to this standards; case in point: Notre Dame 

 

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