Is it a good idea to fuse secondaries?

ransom peek · 15th May 2006, 02:03 AM

Building a briangt chipamp with a 330v a toroid, posts in this forum advise a fuse on the primaries at something above the toroid rating, above the normal inrush current.

So a 4 amp fuse on a 330va toriod protects above 120v x 4 amp = 480 va.

Shouldnt there be protection for normal usage at or below the toroid rating, perhaps in the secondaries?

25 volt dc x 6 amps = 150 va. With 2 secondaries, each with a 6 amp fuse, total wattage allowed would be 300 watts on a 330 va toroid.

Is this a good idea?

xplod1236 · 15th May 2006, 02:21 AM

The inrush current is caused by the ps caps charging. So the inrush current will be present on both the primary and the secondary.

billdinva · 15th May 2006, 02:22 AM

put a fast blow fuse on each rail downstream to the filter caps.
Until you have the power supply debugged, put a slow blow fuse on each rail between the bridge and the filter caps. The fast blow fuses will help protect when you short your speaker wires. The slow blow fuses will protect from faults in the filter circuit.

AndrewT · 15th May 2006, 06:41 AM

Hi,

Quote:

inrush current is caused by the ps caps charging

balderdash.
Inrush current, for a toroid, is trying to establish the magnetic flux in the iron core.
Once the magnetic circuit is up and running, taking one to three cycles of the mains, then the caps can charge, but at a much smaller charging current.

So the recommendation for a T (delay) rated mains fuse and F (fast) rated secondary fuses AFTER the smoothing capacitors.

ransom peek · 15th May 2006, 04:38 PM

Seems to be some disagreements here, I'm siding with Andrew T's recommendation.

I have the 2 briangt 3875 amp boards in hand. and am trying to figure out where to wire the fuses in the circuit, and what amperage fast blow to use.

I am using an avel landsberg 330 mah 25v x 2 toroid.

Any advice?

Bazukaz · 15th May 2006, 05:21 PM

Quote:

Originally posted by AndrewT
Hi, balderdash.
Inrush current, for a toroid, is trying to establish the magnetic flux in the iron core.
Once the magnetic circuit is up and running, taking one to three cycles of the mains, then the caps can charge, but at a much smaller charging current.

So the recommendation for a T (delay) rated mains fuse and F (fast) rated secondary fuses AFTER the smoothing capacitors.

Hi,
As far as i know , it is important to keep both resistance and reactance low between supply caps and amplifier.For example, National recommends to use as short supply leads as possible.
Fuse can be not reliable here - oxidising contacts, etc.
To prevent it from accidentaly blowing due to current peaks , we would have to use higher amperage fuse. But then , what is the use of it ?

These are just my thoughts , i may be wrong.

Regards,
Lukas.

cpemma · 15th May 2006, 08:02 PM

Both my NAD and Rotel amps have pairs of fuses factory-fitted between secondaries & rectifier. 3A for the 25Wpc NAD (plus 1A on the preamp section's separate secondary), 5A on the 30Wpc Rotel.

ransom peek · 15th May 2006, 11:54 PM

Has anyone inserted fuses between the secondaries and the rectifier board? Is this the way to go?

hitsware · 16th May 2006, 12:56 AM

put a slo-blo in series with the primary of the pwr xfmr
a fast-blo in series with the speaker ........ enough allready

lndm · 16th May 2006, 01:03 AM

With some amps that have twin rail fuses, there can be the concern that if one rail fuse blows, the output may slam toward the other rail and your speaker may get a taste of DC.

So, any arrangement where all rails blow with one fuse sounds good to me.

15th May 2006, 02:03 AM	#1
ransom peek diyAudio Member Join Date: Nov 2003 Location: fort collins co	Is it a good idea to fuse secondaries? Building a briangt chipamp with a 330v a toroid, posts in this forum advise a fuse on the primaries at something above the toroid rating, above the normal inrush current. So a 4 amp fuse on a 330va toriod protects above 120v x 4 amp = 480 va. Shouldnt there be protection for normal usage at or below the toroid rating, perhaps in the secondaries? 25 volt dc x 6 amps = 150 va. With 2 secondaries, each with a 6 amp fuse, total wattage allowed would be 300 watts on a 330 va toroid. Is this a good idea?

15th May 2006, 04:38 PM	#5
ransom peek diyAudio Member Join Date: Nov 2003 Location: fort collins co	Where to place the fast blow fuses? Seems to be some disagreements here, I'm siding with Andrew T's recommendation. I have the 2 briangt 3875 amp boards in hand. and am trying to figure out where to wire the fuses in the circuit, and what amperage fast blow to use. I am using an avel landsberg 330 mah 25v x 2 toroid. Any advice?

15th May 2006, 11:54 PM	#8
ransom peek diyAudio Member Join Date: Nov 2003 Location: fort collins co	Should fuses be inserted between secondaries and rectifier pcb? Has anyone inserted fuses between the secondaries and the rectifier board? Is this the way to go?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Is this a good idea?	Nolantor19	Multi-Way	3	12th August 2009 12:36 AM
Is this a good idea?	AC439	Multi-Way	0	30th December 2008 07:48 PM
One transformer with 4 secondaries or two transformers with dual secondaries	Baka	Chip Amps	5	28th November 2008 06:39 AM
Seems a good Diy idea !!	sivan_and	Everything Else	1	12th November 2006 07:44 AM
is this a good idea???	dmh	Solid State	16	24th February 2005 03:47 AM


	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

15th May 2006, 02:21 AM	#2
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	The inrush current is caused by the ps caps charging. So the inrush current will be present on both the primary and the secondary.

15th May 2006, 02:22 AM	#3
billdinva diyAudio Member Join Date: Mar 2006 Location: Virginia	put a fast blow fuse on each rail downstream to the filter caps. Until you have the power supply debugged, put a slow blow fuse on each rail between the bridge and the filter caps. The fast blow fuses will help protect when you short your speaker wires. The slow blow fuses will protect from faults in the filter circuit.

15th May 2006, 08:02 PM	#7
cpemma diyAudio Member Join Date: Jul 2003 Location: S Yorkshire OK	Both my NAD and Rotel amps have pairs of fuses factory-fitted between secondaries & rectifier. 3A for the 25Wpc NAD (plus 1A on the preamp section's separate secondary), 5A on the 30Wpc Rotel.

16th May 2006, 12:56 AM	#9
hitsware diyAudio Member Join Date: Mar 2002	put a slo-blo in series with the primary of the pwr xfmr a fast-blo in series with the speaker ........ enough allready

16th May 2006, 01:03 AM	#10
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	With some amps that have twin rail fuses, there can be the concern that if one rail fuse blows, the output may slam toward the other rail and your speaker may get a taste of DC. So, any arrangement where all rails blow with one fuse sounds good to me.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read