In the case of SR fuses, my perception has been that the rationale for going up one or two rating increments from stock has simply been that a number of users (at least 8, as I recall) have reported in the Red Fuse thread and other fuse-related threads that SR fuses having stock current ratings blew unnecessarily. While I can only recall one instance in which someone reported that an up-rated SR fuse blew unnecessarily.
That suggests, IMO, that the combinations of current and time which would cause an SR fuse to blow are more similar to those of a typical stock fuse having a somewhat lower current rating than they are to a stock fuse having the same current rating. Which is why I had said in the Red Fuse thread that IMO it makes sense to go up one or two ratings. Other opinions differed in some cases, as Nonoise pointed out earlier, and unfortunately there is room for differences of opinion because the detailed technical information that is provided by Littelfuse and Cooper Bussmann defining the blow characteristics of their fuses (nominal melting point in amperes squared x seconds, and graphs of maximum current vs. time) are not provided by SR and most or all other boutique manufacturers. With the warranty concern cited by Uberwaltz also being a consideration.
Regarding PS’s questions, I suspect from the wording of his posts as well as the rating of the fuse that he is referring to a DC rail fuse, rather than a mains fuse. Which means that inrush current at turn-on probably won’t be much of a concern, if any. However it sounds like he is considering going from a 1 amp stock fuse to a 1.25 amp HiFi Tuning fuse, and I have no idea whether the rationale I cited above for going up a rating or two in the case of SR fuses would be applicable to HFT fuses. On the other hand, though, intuitively it doesn’t sound like much of a difference to me, so IMO it is a reasonable course of action.
Regards,
-- Al
That suggests, IMO, that the combinations of current and time which would cause an SR fuse to blow are more similar to those of a typical stock fuse having a somewhat lower current rating than they are to a stock fuse having the same current rating. Which is why I had said in the Red Fuse thread that IMO it makes sense to go up one or two ratings. Other opinions differed in some cases, as Nonoise pointed out earlier, and unfortunately there is room for differences of opinion because the detailed technical information that is provided by Littelfuse and Cooper Bussmann defining the blow characteristics of their fuses (nominal melting point in amperes squared x seconds, and graphs of maximum current vs. time) are not provided by SR and most or all other boutique manufacturers. With the warranty concern cited by Uberwaltz also being a consideration.
Regarding PS’s questions, I suspect from the wording of his posts as well as the rating of the fuse that he is referring to a DC rail fuse, rather than a mains fuse. Which means that inrush current at turn-on probably won’t be much of a concern, if any. However it sounds like he is considering going from a 1 amp stock fuse to a 1.25 amp HiFi Tuning fuse, and I have no idea whether the rationale I cited above for going up a rating or two in the case of SR fuses would be applicable to HFT fuses. On the other hand, though, intuitively it doesn’t sound like much of a difference to me, so IMO it is a reasonable course of action.
Regards,
-- Al