what fuse size for amp?

Hey guys,

I have an OLD SCHOOL Rockford Fosgate (1993 I believe) Punch 200 watt that is bridged.  I'm pushing (2) RF P1 12" woofers (4 ohm).  If my thinking is correct, it is pushing around 400 watts????  Some say that this amp is way underated too so who knows.....

It currently has a 40amp fuse (I didn't buy the amp new so I don't know what it should have).  Well, today I was playing a really heavy bass song with long notes and it blew the crap out of the fuse!!!!  lol

The speakers sounded awesome---no distortion that I could hear and didn't sound quite maxed either.  I don't usually listen to this type of music (Rap) or that loud, but wondering if I can run a 50 or 60 amp fuse or am I cooking this amp/speakers?  The speakers are rated at 150RMS cont / 300RMS max.  Just bought them, but I've been running this amp for years.

Thanks.

Do you have 2 8 ohm woofers, or are they 4 ohm drivers that you have paralelled to a 2 ohm mono load?    That amp will do around 700 watts into a 4 ohm mono load.  It will do a touch more into a 2 ohm mono load, but it will not hold up long.  Re-read the end of the last sentence. 

They are 4 ohm drivers.  Supposedly, the amp is good for 100 watts per channel.  So 2 channels x 100 watts = 200 watts.  When you bridge the amp to 2 ohms doesn't that double the output?  So 400 watts right?

What are you basing the 700 watt output off of ????  Are they that under-rated?  LOL, that would be awesome!A little more info, I've been running this amp for about 7 years (I don't run it at 100% too often) with some 12's from 1993 too.  Well one of them ripped (the outer ring which allows the speaker to move up and down)---it was missing about 6 inches of material---lol!  The material felt really dry rotted and being as they are 15+ years old, I'm assuming that is why it failed.  Maybe the power through them was a concern too??

http://www.rockfordfosgate.com/products/product_details.asp?cat_id=4&series_id=31&family_id=9&item_id=108270&locale=en_US&p_status

Yes, I believe they are (see the link below for more info).  I'm currently running a 40 amp fuse to the amp.  It has only blown once (about 6 years ago). 

That amp will not blow a 40 amp fuse unless it is run 2 Ohm mono.  There is no fuse mounted to those amplifiers.  The 700 watts is based on the Ohms Law formula of Power = E2/R.  When that amp was introduced we benched several.  A punch 150 would do 200 a channel into 2 ohms. 

You are running your amp into a 2 ohm mono load.  If you like the amp, connect it in stereo or wire the woofers in series.  If you do not like it, or if you want to have to get it repaired real soon, keep it bridged the way you have it.

That amp was rated at 100 per channel into 4 ohms.   2 ohm per channel is acceptable, 2 ohm mono is not.

I have a 40 amp fuse wired right off of the battery that feeds the amp and it has been bridged since I got the system (1999).  I didn't wire it that way, it was wired that way in a mustang that I bought.  I've just transferred parts of the system over to a couple of different cars over the years. 

If I don't run it at high high levels all of the time, will it hurt anything?  I guess I can go rip it out and re-wire it too. 

Please educate me here as I'm familar with basic electronics but not really too much with car audio.  If I understand this correctly, since I have (2) 4 ohm woofers wired in parallel that equals a 2 ohm load.  Now that I've taken that across a 2 channel amp and bridged the channels to one, I'm essentially running this amp at 1 ohm???  Is that right?

That would explain the insane power output---lol!  I get what you're saying about the amp and its life span --- thanks for pointing that out as I like the amp and don't really want to buy another.  My other question is about the speakers.  If they are rated at 300watts max/150 rms, what might happen to them?  Over extend the woofer?  I know little to nothing about this stuff. Thanks for the help.

Yes a 2 Ohm mono load is the same as a 1 Ohm stereo load.  Yes the amp running 2 Ohm mono will make it put out some insane power.  You said you have had it connected that way for years.  Aren't these woofers new?  Were your ald woofers 8 Ohm?

Following is a diagram of any bridgeable amplifier.  Notice the left negative and right positive terminals are both ground.  A  2 Ohm load on left and a 2 Ohm load on the right, will read 4 Ohms across the bridge terminals.

I just ckd them (thankfully I didn't throw them out---lol) and they are actually 6 ohms.  I didn't believe it and I ckd them 2 or 3 times and ckd the other woofer to be sure.  Definitely 6 ohms---never heard of that before--just 4 and 8ohm....

They say "Impact" on the sticker and have "Md 2" on the cone.  Ever heard of them?  I couldn't find anything on them when I googled it recently.

I will re-wire those speakers soon.  Thanks