How To A ferrite bead can clamp the inrush current

Dom

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Aug 6, 2011
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I stumbled across this, but it seems that putting a ferrite bead on the mains wire has solved the fuse blow.

My Roksan Caspian M2 was blowing fuses in the IEC fuse holder on the back of the amp. On the back it says 2 amps and apon inserting a 2 amp slow blow mini fuse, would end in a failure and blow the fuse.

I had 2 options, either 3.15 amp slow blow or a 2 amp curly slow blow. However there's a third option.

If I put a ferrite bead on the mains wire that plugs into the wall, the effect is that it clamps the surge and stops the blow. Now I can use the intended fuse for the amplifer, 2 amp slow blow Bussmann.

So what I am trying to say is that the resistive properties of just one ferrite bead will protect your gear from transients and stop fuses blowing.

I hope this helps people.
 

Sliced Bread

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Jul 28, 2010
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Not long, just a few on and off's.
I’ve never had a fuse go on my HiFi either.

It sounds like you know what you’re doing so I’m glad you’ve found a solution. Just for my education is this because you have a mains issue or is it because your driving difficult speakers into high volume (or maybe another cause entirely)?
 

Dom

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Aug 6, 2011
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I’ve never had a fuse go on my HiFi either.

It sounds like you know what you’re doing so I’m glad you’ve found a solution. Just for my education is this because you have a mains issue or is it because your driving difficult speakers into high volume (or maybe another cause entirely)?
I don't have a mains issue and I dont listen at high volumes. Its when turning on an amplifier and goes it goes into stand-by, it would blow the fuse. So there is a large over current in the kila amp region, and its enough to blow the fuse. I don't the science well enough to explain.

They are 4Ohm speakers, with a sensitivity of 86dB.
 
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abacus

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Sep 24, 2008
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Something not right there, is the voltage low in your household? Also when did you have the electrics last checked in the house as there may be some loose connections, best to contact Roksan as it’s possible that the capacitors on the Roksan power supply are beginning to fail?
Finding a bodge to try and fix something that should not happen in the first place is not the best way to go about things.

Bill
 

Dom

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Aug 6, 2011
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Something not right there, is the voltage low in your household? Also when did you have the electrics last checked in the house as there may be some loose connections, best to contact Roksan as it’s possible that the capacitors on the Roksan power supply are beginning to fail?
Finding a bodge to try and fix something that should not happen in the first place is not the best way to go about things.

Bill
Hi Bill.

I had the electrics and outlets checked and they replaced the fuse box. Yes, I contacted Roksan, which is owned by Monitor Audio and they recommended a 3.15 amp fuse even though 2 amp is actually written on the back of it.

It's possible that the capacitors on the power supply are failing. I would get them replaced, but i'm hesitent. It takes time and the money which would be in the hundreds. My old Roksan K2 had a problem and it cost me £400.

Your right Bill and should probably consider there's a problem.
 
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nopiano

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Feb 15, 2009
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Mmm, unfortunately my electrical knowledge doesn’t extend to understanding this, but maybe an expert can confirm it’s not just coincidence and that ferrites do achieve this.
 

abacus

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Hi Bill.

I had the electrics and outlets checked and they replaced the fuse box. Yes, I contacted Roksan, which is owned by Monitor Audio and they recommended a 3.15 amp fuse even though 2 amp is actually written on the back of it.

It's possible that the capacitors on the power supply are failing. I would get them replaced, but i'm hesitent. It takes time and the money which would be in the hundreds. My old Roksan K2 had a problem and it cost me £400.

Your right Bill and should probably consider there's a problem.
If you don’t want to update the fuse rating (Although as you have been told this is fine by Roksan there should not be any problems) you can get anti-surge fuses which have a little extra resilience over standard slow blow. (Motors for example usually need these due to initial high start-up current, so may be worth a try)

Bill
 
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If you don’t want to update the fuse rating (Although as you have been told this is fine by Roksan there should not be any problems) you can get anti-surge fuses which have a little extra resilience over standard slow blow. (Motors for example usually need these due to initial high start-up current, so may be worth a try)

Bill
True, and I very much doubt a ferrite bead is going to affect current delivery or solve the issue of fuses blowing.
 
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shadders

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Hi,
At 50Hz the reactance/impedance coupled to the mains wire will be negligible.

Do you use powerline communications devices, or is there severe RF on the mains ?

Regards,
Shadders.
 

Dom

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Hi,
At 50Hz the reactance/impedance coupled to the mains wire will be negligible.

Do you use powerline communications devices, or is there severe RF on the mains ?

Regards,
Shadders.
No Shadders I don't get RF on the mains or use a powerline communications device.
I looked it up ferrite beads online and some people said it could help. Others said it would saturate. Anyway i'm not knowledgeable on the science.
 

shadders

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Nov 19, 2009
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No Shadders I don't get RF on the mains or use a powerline communications device.
I looked it up ferrite beads online and some people said it could help. Others said it would saturate. Anyway i'm not knowledgeable on the science.
Hi,
Can you post the ferrite bead details or a link to the vendor selling ?

Did you put the ferrite bead around the Live, or Neutral, or the entire 3 core mains cable ?

Regards,
Shadders.
 

shadders

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Nov 19, 2009
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Hi,
I am surprised at the large inductance for the device, but still, at 50Hz it will present 6.2ohms impedance, and for 240volts (RMS) will still allow 38amps. (neglecting the other components reducing this).

It would be surprising that the extra impedance is such that it will reduce the surge current by just enough to stop the fuse blowing.

If Roksan are suggesting the a 3.15amp fuse is ok, and this works 100% of the time, then maybe they under specified the fuse in the first place with the initial production.

Regards,
Shadders.
 

Dom

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Aug 6, 2011
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Oh ok Shadders, thank you for the information. I don't claim to understand what you are saying.

FYI, i'm using a Marshall 2 amp fuse and I think they are rated at 100a breaking.

GAK
 

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