SkinnyBoy said:
Don't worry, the main fuse WILL blow.
The main fuse can be around 4 amps in your case.
Much smaller than if you put fuses on the secondaries.
And, when there's a problem, the primaries blow, the secondaries won't.
Because the primaries' wire are much thiner than those on the secondaries.
If you have a burned transformer, it's the primary.
If you put one fuse on the primary, you are protecting it all.
carlosfm said:
Don't worry, the main fuse WILL blow.
The main fuse can be around 4 amps in your case.
Much smaller than if you put fuses on the secondaries.
And, when there's a problem, the primaries blow, the secondaries won't.
Because the primaries' wire are much thiner than those on the secondaries.
If you have a burned transformer, it's the primary.
If you put one fuse on the primary, you are protecting it all.
4 amp fuse won't handle the inrush current of three 250VA transformers... if I have seperate fuses for each amp module, if theres something wrong with the chip or whatever, these will blow... even a 4 amp slow blow fuse probably wouldn't cut it.. I was thinking 8 amps... allow the transformers to give twice their rated power... but if there is a problem it should blow.... hmm..
I ah.. don't think mains voltage has anything to do with the inrush current required by toroidal transformers... (well, it does, but its still there) 4 amps is only 960watts..... not enough.... especially considering the inrush current.. the fuse is only there incase of failure... failure which will result in quite a low resistance, and quite abit of current flowing.... with just a fuse on the mains, I could have a near short (near enough) that would cause 960watts to flow through the circuit.... thats 125% of the transformers rated output.... it would fry, and the fuse would do nothing.... there needs to be some fusing on the secondary....
I have a 384VA toroid on my main GC.
Without the resistor, even a 4A fuse blowed up sometimes at
switch on.
And that was with only 1000uf caps.
If I put a bigger fuse on the primary, the amp could burn and the fuse would be intact.
Now I have a 2.5 fuse and no problems.
This is for toroids, they have much bigger inrush currents at power on than frame transformers.
Without the resistor, even a 4A fuse blowed up sometimes at
switch on.
And that was with only 1000uf caps.
If I put a bigger fuse on the primary, the amp could burn and the fuse would be intact.
Now I have a 2.5 fuse and no problems.
This is for toroids, they have much bigger inrush currents at power on than frame transformers.
GregGC said:
Always slow.
At power-on with a big toroid you can hear a little "bonc" noise (and vibration) and then it stays quiet.
This is for a period of around 1 second.
Enough to blow a slow-blow fuse from time to time.
A resitor cures this.
No noise at switch-on, no vibration, no blown fuse and you can use the right fuse you need (you don't have to put a big fuse just because of the switch-on).
I feel more protection this way.
caps across the power switch will also help. A high-voltage (1 KV) film or paper cap across the resistor should ensure the supply is not terribly loose and the inrush current will be limited. I have not personally tried the resistor, but it helps to absorb the bump from switch-on, again from frame transformer experience (no toroids in India, at least not in single units) to have a small 10 nF cap across the switch...
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