FEOA Forums banner

1 - 16 of 16 Posts

·
Super Moderator
Joined
·
8,139 Posts
i have never used one of those before. funny thing is every system i can calculate in it i have wired better then ti recommends. mainly i always go bigger then i feel is needed.


NEUMAN
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #3 ·
Yea you should always use bigger power and ground wires but I like for the fuse ratings and that it tells approximately how much current you will draw at max power.
 

·
Super Moderator
Joined
·
8,139 Posts
wbarnes570 said:
Yea you should always use bigger power and ground wires but I like for the fuse ratings and that it tells approximately how much current you will draw at max power.
that is nice no doubt. i commonly the same size as the fuse on the amp. that way it pops that fuse before the amp in alot of installs fuses liek that are easier then the amp fuse.

i book marked the site.

NEUMAN
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #5 ·
yea but what if you are running two or more amps off of one power wire with a distribution box, would u just add all the fuses together? Also what if the amp has more than one fuse, say two 25 amp fuses, would you use a 50 or a 25?
 

·
Super Moderator
Joined
·
8,139 Posts
from what i have heard and i could have been misinformed but....

if you have 3 - 30amp fuses it is 30 + 15 + 7.5 = 52.5 amps. so a 50 amp fuse in the dist block should be good enough.

so 2 - 25's would be 37.5 amps.

about 75% of the amps i have installed never had internal fuses. i used to use alot of older fosgate and kicker stuff. so i just looked in the owners manual as to which fuse was reccomended and put that in the dist block.


NEUMAN
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #7 ·
I have no idea if that would be accurate or not. But if you think about it, if you have 2 amps that each have a 25 amp fuse built in, that would mean that each amp could be capable of drawing 25 amps, any more and those fuses would blow, so if both amps are can pull 25 amps and you only have a 40 amp fuse on the power wire, you would keep blowing fuses. Then again I have no idea if I'm going in the right direction with this.
 

·
Super Moderator
Joined
·
8,139 Posts
wrong direction. im speaking of a single amp that has 3 fuses marked 30 amp. not 3 different amps with a 30 amp fuse each.

2 - 25 amps = 37.5 amps


3 - 40 amps = 70 amps


NEUMAN
 

·
Registered
Joined
·
7,043 Posts
Here's an excellent article about cascading and paralleling fuses vs. using a single large one. It gives some basic idea for derating due to impedance mismatch and such.

http://www.ecnmag.com/Dual-Fuses-Protec ... px?menuid=

One large fuse is always better, of course. But, 2x20 amp fuses will essentially be 40 amps, or 3x20 would be 60. So that 3x40 pictured above would work out to 120 amps on paper, although there's the 20% derating, so it works out to more like 3x32 amp fuses, or 96 amps. Whoever mentioned that paralleling fuses linearly causes the ampacity to half didn't know what they were talkinga bout.
 

·
Super Moderator
Joined
·
8,139 Posts
UnexplodedCow said:
Here's an excellent article about cascading and paralleling fuses vs. using a single large one. It gives some basic idea for derating due to impedance mismatch and such.

http://www.ecnmag.com/Dual-Fuses-Protec ... px?menuid=

One large fuse is always better, of course. But, 2x20 amp fuses will essentially be 40 amps, or 3x20 would be 60. So that 3x40 pictured above would work out to 120 amps on paper, although there's the 20% derating, so it works out to more like 3x32 amp fuses, or 96 amps. Whoever mentioned that paralleling fuses linearly causes the ampacity to half didn't know what they were talkinga bout.
or the fact it was 10 years ago when i didn't fully understand things like that and i confused me. LOL im not perfect. but i will tell you this i have never installed and amp with more then one fuse in it so i have never cared. but i am reading that link know caue i always like to learn.

this diagram would resemble what i was told best



NEUMAN
 

·
Super Moderator
Joined
·
8,139 Posts
if you read that link it tells you a 10 amp fuse is only good to 7.5 amps. it has a tolerance level that is figured. so that with the 20% degration on the second fuse that equals 45% close enough to 50% for the guy to be correct in his statement. please correct me if i am completely off track.


NEUMAN
 

·
Registered
Joined
·
7,043 Posts
It's being applied incorrectly, though. You'd have to derate all fuses by 45% for it to be correct.

Using your above example of 2x25 amp fuses wouldn't work out to be 37.5 amps...you have to assume both fuses only pass 75% of their rated current, and then derate another 20%, so they only pass 55% of their rating, so 2x25 amp fuses works out to 27.5 amps, because you don't know which fuse (if either) is incapable of passing enough current to cause an open.

Another example: 3x40 amps (like the picture) works out to be 40 x .55 x 3 = 66 amps. You can also add all three together and then multiply by .55 to acquire the derated ampacity. Using the linear 50% derating as you were told works out to 70 amps (40+20+10). It's close, but that 4 amps can mean the difference between blowing fuses or not. I also like the simplicity of just multiplying the overall load instead of always halving things.
 

·
Super Moderator
Joined
·
8,139 Posts
this is true! im going to side with the 25% 20%. but in the end not really care. because most good or high end amps run no built in fuses or a single. thus making you have to put in a dist block with fuses. not just for looks but for a solid purpose! most all systems i install if there is more then one amp is getting a fused dist block. no ghetto ground blocks to dist power.


NEUMAN
 

·
Super Moderator
Joined
·
8,139 Posts
UnexplodedCow said:
I tend to run individual lines for everything just because I like isolation on circuits. Still, nothing wrong with a solid distribution block (electrical manifold?).
when i had the 3 15's in the red car i ran a solid dist block for my speaker wires to the subs. one 8ga to teh dist block and 3 12ga's out. worked mint!

NEUMAN
 
1 - 16 of 16 Posts
Top