2way Circuit Breaker instead of melting fuse inside amp - a good idea? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd January 2011, 08:03 PM   #1
diyAudio Member
 
Join Date: Apr 2010
Location: Germany
Default 2way Circuit Breaker instead of melting fuse inside amp - a good idea?

Hi all

I'm building a powerful Sym-A-Sym like amp at the moment and break my head about profer fusing of the amp.

I used LT spice to simulate what would happen if one of the rail fuses tripped and was shocked to see that the absence of the positive rail makes the output go to the negative rail. This is not a nice behavior. After an overload condition I could have serious DC at the output. Now I'd have to rely on a DC protection circuit - given installed and it works.

I think about using 2way circuit breakers as fuses to solve this problem. If one channel trips the other one is forced off as well.

They are designed for AC mainly but can switch some DC, too.

According to the datasheets I'd have to use two in series for each rail because of 90V rail voltage, thus needing a 4 way circuit breaker for each channel.

I've never seen those circuit breakers inside amplifiers. Almost everyone has them in the house electricity instead.

Do you think it is a good idea to put circuit breakers inside an amplifier?
Maybe it's crazy, stupid or even innovative?

Thanks,
Lee
Attached Images
File Type: jpeg LS-Schalter_2polig.jpeg (6.6 KB, 119 views)
File Type: jpeg LS-Schalter_2polig_Siemens.jpeg (26.4 KB, 117 views)
  Reply With Quote
Old 23rd January 2011, 08:50 PM   #2
llwhtt is offline llwhtt  United States
diyAudio Member
 
Join Date: Jun 2008
Location: SoCal
IIRC the old Mark Levinson ML-2 used a three-way CB. One section handled the mains, and a section for each rail. The multi-input protection circuit would crow bar the two unregulated rails and trip the CB. You can find schematics for the ML-2 but I don't think the circuit breakers are shown on what's available.

Craig
  Reply With Quote
Old 23rd January 2011, 09:13 PM   #3
atx is offline atx  Austria
diyAudio Member
 
Join Date: Dec 2010
Location: Wien
Quote:
Originally Posted by Lee Knatta View Post
Hi all

I'm building a powerful Sym-A-Sym like amp at the moment and break my head about profer fusing of the amp.

I used LT spice to simulate what would happen if one of the rail fuses tripped and was shocked to see that the absence of the positive rail makes the output go to the negative rail. This is not a nice behavior. After an overload condition I could have serious DC at the output.

They are designed for AC mainly but can switch some DC, too.

Thanks,
Lee
I believe it is a good idea. The use of magnetic-thermal breaker is common use in industrial DC panels. Most of those breakers would work just well with 90 V DC. Just take care :
1) Use a real bi-polar one, i.e. having the magnetic and thermal protection built in on both sides. Get one with In= rated fuses.
2) take one with a high interruption current. This parameter has nothing to do with the nominal current (normally written as In, and that means the thermal overload threshold) , is normally marked in KA and that means the maximum short-cicuit current that the contacts can safely interrupt.Note that on case of short circuit the magnetic protection (that is faster) will take place, but at a value that is several times In.
A 6KA (6000 A)swich should be robust enough to safely habdle the bigger arcs generated by DC. A 10KA, better.
3)choose a "B" intervention curve that should comonly available in Germany and has a faster intervention than C and D.

ATX
  Reply With Quote
Old 23rd January 2011, 10:46 PM   #4
ontoaba is offline ontoaba  Indonesia
diyAudio Member
 
ontoaba's Avatar
 
Join Date: Nov 2009
Location: Kudus, Malang, Dieng
Hi, how about make it also for overvoltage protection. I am using them for my amplifiers.
  Reply With Quote
Old 24th January 2011, 01:00 AM   #5
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
TBH you could do something easier. Connect only the drivers and output transistors to the fuse. Connect the VAS and LTP stages via 100 ohm resistors. If you want safety, make them 100 ohm fusible resistors. If you have a failure then it is likely to be drivers or outputs. If you now lose a rail, you will simply get a distorted signal instead of DC.

This should even be readily possible on the Symasym design - from memory it connects those small signal stages via resistors anyway.
  Reply With Quote
Old 30th January 2011, 06:41 PM   #6
diyAudio Member
 
Join Date: Apr 2010
Location: Germany
Thanks to all who replied. This helped me a lot.

I thought about all this for some days now, gathered more information and came to some conclusions:

The circuit breakers might be a good idea because they have a much higher current interruption capability than the 5x20mm fuses used in most amps. For most amps the 5x20mm fuses should be sufficient.

In my case a 8A 5x20 with M characteristic could interrupt 300A, a standard CB can do 10kA (didn't find the 6kA anywhere).

Rating and de-rating of the circuit breakers is a bit difficult but could be very rewarding.
Downside is that they are expensive and I ran out of money a bit.

Thanks Jaycee for pointing me on what I've totally overseen. I already split rails for frontend and output stage but didn't in simulation. With split rails the catastrophic hangup shouldn't occur.

I'll let you know whether the CBs made it into the final amp.

So far,
Thanks,
Lee
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Where to place amp: Inside a common cab or inside speakers? goldyrathore Chip Amps 3 3rd September 2010 12:39 PM
Fuse housing melting but fuse not blowing, ppi amp rawadia Car Audio 21 2nd August 2008 10:39 AM
amp rating for fuse and fuse holder? riotubes Parts 5 27th August 2006 03:10 AM
Is it a good idea to fuse secondaries? ransom peek Chip Amps 14 17th May 2006 01:49 AM
Adding second bridge to integrated amp, good idea? KevinLee Solid State 1 24th November 2003 12:11 AM


New To Site? Need Help?

All times are GMT. The time now is 01:36 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2