bassace Posted April 18, 2009 Share Posted April 18, 2009 After a 'near miss' when our keyboard amp blew a fuse last week I've bought spares for all my amps. The ratings range from 6.3A for the Clarus down to 2.5A for the MB150. Some are fast blow and some slow blow. Anyone know the significance of this? And no sexual innuendo........please! Quote Link to comment Share on other sites More sharing options...
SteveO Posted April 18, 2009 Share Posted April 18, 2009 (edited) [quote name='bassace' post='466366' date='Apr 18 2009, 09:30 PM']After a 'near miss' when our keyboard amp blew a fuse last week I've bought spares for all my amps. The ratings range from 6.3A for the Clarus down to 2.5A for the MB150. Some are fast blow and some slow blow. Anyone know the significance of this? And no sexual innuendo........please![/quote] They do 'what it says on the tin'. Basically some equipment sometimes needs to draw extra current, it's usually the fans when you turn on. A slow-blow fuse will allow momentary operation at a higher than normal current whereas a fast-blow fuse won't. So a fast-blow fuse of the correct rating may blow whenever you turn the amp on even though there may not be a problem. Putting a slow blow fuse in everything is not the answer though as this potentially may allow a momentary high current into the equipment which may fry whatever it is that the fuse is there to protect A general rule of thumb is Fans = slow blow, although this is by no means universal. Edit: If you're ever unsure I'd advise always using a fast blow fuse first. If it pops at turn-on then try a slow blow, but be cautious. Edited April 18, 2009 by SteveO Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted April 18, 2009 Share Posted April 18, 2009 [quote name='SteveO' post='466371' date='Apr 18 2009, 03:42 PM']They do 'what it says on the tin'. Basically some equipment sometimes needs to draw extra current, it's usually the fans when you turn on.[/quote] The high draw is from the power supply caps, which will draw a lot of current when charging at turn-on. Extremely high value caps can appear as virtual dead-shorts for a few milliseconds, and even moderate values will draw far more current when charging than the amp does at full output. Quote Link to comment Share on other sites More sharing options...
SteveO Posted April 19, 2009 Share Posted April 19, 2009 [quote name='Bill Fitzmaurice' post='466408' date='Apr 18 2009, 11:09 PM']The high draw is from the power supply caps, which will draw a lot of current when charging at turn-on. Extremely high value caps can appear as virtual dead-shorts for a few milliseconds, and even moderate values will draw far more current when charging than the amp does at full output.[/quote] Thanks Bill, I wasn't aware of this, I thought it was just the fan motors that drew high current at startup. Does this mean that most things will need slow blow fuses? i.e. anything with a transformer in the box? Quote Link to comment Share on other sites More sharing options...
bassace Posted April 21, 2009 Author Share Posted April 21, 2009 Thanks for the helpful relies, guys. Fans or caps, it's the startup current that determines the fuse. Quote Link to comment Share on other sites More sharing options...
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