Wait until you get onto service head fuses protecting incoming supplies to your home... scary. An 80A or 100A house fuse might well have an 80kA breaking capacity at a power factor of 0.15 for some of the top names. Breaking the current to a resistive load is one thing, its quite another when the load might be inductive. They have to break cleanly and not sustain an arc that would continue the connectivity.
And all that scales back down to the smaller stuff we use 🙂
And all that scales back down to the smaller stuff we use 🙂
As in one and a half ohms of ESR in the capacitor. A brand new Nichicon 470 uF/450V will give you that. Enough to kill your brand new Klein screwdriver and make you see spots for a while.
Seen that happen before. Tool companies don't cover that damage! lol!
Try this in a Conrad Johnson Premier One!
Try this in a Conrad Johnson Premier One!
What exactly do you mean with T fuses?
If you look at best performance, what types of fuses would be best to use for the voltage rails after the capacitors? Fuse holders add contact resistance. So I doubt a normal 5x20 glas fuse is best in this respect. SMD fuses would be better but need to be soldered when they have to be replaced.
Impedance in the rails is not the bogeyman to worry about. The element itself has higher resistance - and it is variable. You've got the wires from the supply as well. PCB traces have higher resistance typically. So a fuse holder is a non-issue. A bypass cap after the fuse eliminates the concern, and the high gain of the overall amp also makes it a non-issue.
'T' fuses are simply time delay or slow-acting fuses. These are best suited to amplifier rail protection because they will reliably allow much higher currents to flow through them for short periods of time, which is exactly what you want in an audio amplifier driving a highly dynamic impedance load like a speaker but will open quickly to limit damage if an overcurrent is sustained for any length of time. As noted by others, semiconductors usually fail before fuses do - the fuse is not there to protect the amplifier from failing, but to prevent possible fires and excessive damage to PCBs, wiring, etc. The graphic below plots the current-time characteristic of a range of 'T' fuses.
The series resistance of a 5 x 20 5 to 10A glass 'T' fuse and its associated PCB clips will not impact amplifier performance in any meaningful way - if it does, there is a serious problem with the amplifier.
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Yes, Träge or slow blow. Many things electrical originated either from Germany or France.
The opposite types are called F from Flink which means fast. This counts almost always for the well known 5 x 20 mm fuses.
In industrial fuses the naming is different: gL, gG, aM etc. These have more specific ranges for full range protection or short circuit protection.
The opposite types are called F from Flink which means fast. This counts almost always for the well known 5 x 20 mm fuses.
In industrial fuses the naming is different: gL, gG, aM etc. These have more specific ranges for full range protection or short circuit protection.
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I took some measurements to determine the resistance of some 5x20mm (T) glass fuses including the PCB fuse holder (that was not soldered in a PCB).The measurement current was 1A and 3A DC and I measured fuses of 3.15A, 4A, 5A, 6.3A and 10A. The differences between the 1 and 3A measurements are small, so measuring with 1A is most convenient. The measurements range from 24mOhm for 3.15A(T) to 16mOhm for 10A(T). The contact resistance of the fuse holder itself was about 5mOhm.
I also tried 2 pieces of a different type of fuse holder but this type gave much higher readings. Also it was not so consistent. Pushing the fuse or reinserting could lead to different readings as high as 45mOhm for 10A(T) fuse. Unfortunately, this was the most common type of fuse holder you come across. The model with the semi-circular clamps around the fuse.
Peter
I also tried 2 pieces of a different type of fuse holder but this type gave much higher readings. Also it was not so consistent. Pushing the fuse or reinserting could lead to different readings as high as 45mOhm for 10A(T) fuse. Unfortunately, this was the most common type of fuse holder you come across. The model with the semi-circular clamps around the fuse.
Peter
It is very difficult to do precise/reliable measurements of ultra low ohmic connections. You can certainly not do this with a DMM and normal test pins*. The contact resistance of the test pins and cables combined may be higher than the resistance one wants to measure 🙂 We do this with clamps or bolts/nuts at very low voltage at very high currents to have reliable test results. You can also do a safe assumption an A brand produced fuse holder to have been tested for its purpose. This unlike Aliexpress stuff. I have bought very nice looking stainless steel switches that had 40 Ohm resistance from Ali!
*Please don't forget Mr. Lorentz who has still a voice in this to this day (connect "semi-circular clamps" to mr. Lorentz).
Anyway I know enough of fuses to only use them to prevent catastrophe without having impact on performance one way or another so only at the primary side. This combined with real life requirements of only a few Watts output power and loudspeaker protection together is pretty safe. I have repaired expensive branded high power amplifiers that were not so kind to loudspeakers. Maybe 2 x 400W impresses some people but loudspeakers are scared when they hear this.
Expect thunder if you like to play with lightning.
*Please don't forget Mr. Lorentz who has still a voice in this to this day (connect "semi-circular clamps" to mr. Lorentz).
Anyway I know enough of fuses to only use them to prevent catastrophe without having impact on performance one way or another so only at the primary side. This combined with real life requirements of only a few Watts output power and loudspeaker protection together is pretty safe. I have repaired expensive branded high power amplifiers that were not so kind to loudspeakers. Maybe 2 x 400W impresses some people but loudspeakers are scared when they hear this.
Expect thunder if you like to play with lightning.
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I used a constant current source and took the voltage readings right at the terminals of the fuse holder and also at the endcaps of the fuse. Those maesurments can be trusted.
Not really JP.
We were discussing the impact of fuses and fuse holders on real amplifiers under common operating conditions.
I can see where low to no feedback designs might have more of a problem, but then they have so many other issues it's like crying about a pimple on a broken leg.
We were discussing the impact of fuses and fuse holders on real amplifiers under common operating conditions.
I can see where low to no feedback designs might have more of a problem, but then they have so many other issues it's like crying about a pimple on a broken leg.
Post #111 was a reaction on post #110. That low ohmic resistance is hard to determine exactly and fuse holders may behave not as expected when current flows hence the hint to Mr. Lorentz.
All I know is that the least fuses there are the better it generally is. Had a few amplifiers in the past that blew one of the rail voltages which did not work out very well in protecting anything so I never use those but I use very light power amplifiers as my hearing still is OK. They also only work when I want them to and when things go wrong I can switch them off. Even though DC protection may be there their maximum power is so low they are not able to put enormous currents through voice coils at all as that is not their task.
The finding of a crosspoint of simplicity, reliability, safety and highest performance is often granted with the KISS principle.
All I know is that the least fuses there are the better it generally is. Had a few amplifiers in the past that blew one of the rail voltages which did not work out very well in protecting anything so I never use those but I use very light power amplifiers as my hearing still is OK. They also only work when I want them to and when things go wrong I can switch them off. Even though DC protection may be there their maximum power is so low they are not able to put enormous currents through voice coils at all as that is not their task.
The finding of a crosspoint of simplicity, reliability, safety and highest performance is often granted with the KISS principle.
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That's fair JP. I use 4-wire and in tolerance meters for low resistance. That means the HP 3457A or Keysight 34465A meters. If you have a very accurate current source you can calculate the real resistance, a standard resistor can be used to determine the current accurately.
Fuses are to protect from wires catching fire, not really for circuit protection. They are for protecting life and property, not equipment.