Ton Bouw wrote: >> Assuming that the rated current for a product is 1.0A, and assuming that the fuse rating is determined at 1.5A, then a rating of the power adapter of anything over 1.0A would seem to be sufficient for operation and protection. However if the rating of the power adapter does not exceed 1.5A, the fuse would probably never blow. Is this acceptable? Is there a rule of thumb for the rating of a fuse and for a power adapter? <<
With an external power supply that does all the things you say, the fuse may be redundant. It may never blow -- if your equipment is used with that power supply. However... Does the fuse protect the user from electrical shock? Is your equipment connected to the mains safety ground? Could a failure place mains power on the fuse (which will then blow)? And aside from THAT, might your equipment ever be used with a different power supply? Might you not have a responsibility to protect those who do use a different power supply? Might you not wish to protect the equipment anyway, to keep users from cursing you and never buying from you again? (grin) A discussion not long ago asked about rating fuses for elevated temperatures. Will your equipment ever be get hot? That fuse might not carry the rated amount when hot. Assuming the fuse does not blow and the current is limited, is it possible that something in your equipment might with the limited current available still get hot enough to catch fire? This is a common oversight when current-limited power is assumed. I've had a board (removed from its cabinet) with limited power applied catch fire in my hand! Also, you would do well to examine the reliability of the external power supply you use. it may fail early if always run at rated maximum output. Cheers, Cortland This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
