fuse calculation?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Chip Amps Amplifiers based on integrated circuits

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 14th March 2013, 05:42 PM #1 lost eden   diyAudio Member   Join Date: Sep 2009 fuse calculation? I have a pair of LM3886 monoblocks in a single enclosure with a single mains inlet. I know that the mains inlet should really be fused, but how do I work out what is a suitable value? Each amp has a 120VA toroid & 2x 8300uF filter caps, so the total inrush will be for 2x 120VA toroids & 32,800uF of caps. I'm guessing that even if I push them to their full power (which I never will) the current draw from the mains will likely be less than 1A but obviously the inrush when I turn them on will be a lot more. Would something like a 1.5A timed fuse be enough? Is there a proper way to calculate what I should use?
 14th March 2013, 06:21 PM #2 Mark Johnson   diyAudio Member   Join Date: May 2011 Location: Silicon Valley If Vmains = 230VAC is applied to the primary of a 120 VA transformer, the max permitted primary current is 0.522 amps RMS. So you'd probably use an 0.6 ampere, time delay / slow blow fuse in each primary circuit. FYI, I just bought a Triad Magnetics transformer, 80 VA, whose datasheet says: Output voltage: 18.0V @ 4.4A Recommended fuse** 250V @ 5A, Littelfuse p/n 313 5.0 HXP, slow blow ** Fuse must be used on secondary as conditions of acceptability for UL Class2/3 operation The manufacturer's datasheet of the fuse, shows plots of current-versus-time-to-blow, which can help you decide whether your inrush current might blow the fuse during the first two cycles (40 milliseconds) of the 50 HZ mains wave: http://www.mouser.com/ds/2/240/313P_315P-60249.pdf Last edited by Mark Johnson; 14th March 2013 at 06:28 PM.
 15th March 2013, 01:12 PM #3 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders fuse each transformer separately. Use a T500mA in the primary of each transformer. Close rated fuse = VA / Vac = 120/240 = ½ __________________ regards Andrew T.
lost eden
diyAudio Member

Join Date: Sep 2009
Quote:
 Originally Posted by AndrewT fuse each transformer separately. Use a T500mA in the primary of each transformer. Close rated fuse = VA / Vac = 120/240 = ½
1x fuse per primary seems like the best approach. Now to decide whether I can be bothered to dismantle the amp enough that I can drill & mount panel fuse holders or whether I just splice in-line holders...

 15th March 2013, 02:33 PM #5 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Now that you have decided to adopt close rated fusing, you will need a soft start. __________________ regards Andrew T.
lost eden
diyAudio Member

Join Date: Sep 2009
Quote:
 Originally Posted by AndrewT Now that you have decided to adopt close rated fusing, you will need a soft start.
Oh. Can you explain a bit? Soft start circuits would probably double the number of components in the amp!

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post bigcatdairy Multi-Way 1 15th August 2011 06:14 PM rawadia Car Audio 21 2nd August 2008 11:39 AM artquake Power Supplies 23 24th June 2008 10:41 AM digital desire Solid State 10 3rd December 2006 09:07 PM riotubes Parts 5 27th August 2006 04:10 AM

 New To Site? Need Help?

All times are GMT. The time now is 10:26 PM.