Another amp wiring question.. Fuses!!!

Fri Feb 13, 2009 5:45 pm

im confused at to what size fuse i need in the power line for my system, my bass amp has 3x25a fuses in it so would this mean a total of 75a fuse up front? in theory at least as the nearest fuse size is 80a, what about if i add my other amp, as im planning to do soon which is 30a fused, would this be a total of 105a???

Cheers in advance

Fri Feb 13, 2009 5:58 pm

the fuse rating is only for protection, it does not mean the amp will consume the power of the fuse. a fuse is only to protect against short circuits as a short cuircuited DC battery generates a great deal of power and heat, more often then not resulting in a fire, a fuse is a weak point in the wiring that will burn through if the rated current is exceeded, once burnt through there is no electrcial path so no heat is generated in the wireing and no fires!

so yes it makes sense the bass amp has 3 of 25amp fuses (i assume they are in parallel so each fuse protects a differnent part of the amp but with out knowing what amp i cannot tell) i would bet money on you only need one 25Amp fuse for the single power supply lead, and this should be as close to the battery as possible, this way you protect the wiring too

and yes it makes sense the new amp has a 30amp fuse, again it should be an inline fuse as close as possible to the battery.

mrlee

Fri Feb 13, 2009 6:08 pm

mrLEE30 wrote:....the bass amp has 3 of 25amp fuses (i assume they are in parallel so each fuse protects a differnent part of the amp but with out knowing what amp i cannot tell) i would bet money on you only need one 25Amp fuse for the single power supply lead,
mrlee

But if each part of the amp is working at 25amps and there's three in parallel then that makes 75A in total needing to be supplied to the amp!? no....

Fri Feb 13, 2009 6:26 pm

ricey46 wrote:
mrLEE30 wrote:....the bass amp has 3 of 25amp fuses (i assume they are in parallel so each fuse protects a differnent part of the amp but with out knowing what amp i cannot tell) i would bet money on you only need one 25Amp fuse for the single power supply lead,
mrlee
But if each part of the amp is working at 25amps and there's three in parallel then that makes 75A in total needing to be supplied to the amp!? no....

That was my thinking, oh and mrLEE30, its a Magnat Phantom 1400w monoblock

Sat Feb 14, 2009 5:38 am

But if each part of the amp is working at 25amps and there's three in parallel then that makes 75A in total needing to be supplied to the amp!? no....

no it means each part of the amp requires a 25 amp fuse to protect it!! and as i said the fuse is not indicative of how much power is required to run the amp, if i put a 100A fuse in there it would not mean it requires 100A, it would only mean the fuse would not blow until 100A has passed through it. most amps have several fuses on the amp itself, this is what i assume you mean, as its quite a powerful amp it will likely be two smaller amps in series, so one fuse for each amp, then a third fuse for the control circuits. the total power consumption could be anywhere from nothing to 75amps. Secondly i am not a fan of only relying on the fuses for the amp, as this does not protect the wiring from battery to amp, you should have a fuse as close to the battery as possible, that way any break in the insulation will not short against the body and cause problems

but as i said without knowing the amp it is not possible to determine the actual power gain, this should be given on your design specifications included with the amp.

If the amp does indeed require 75A then you should have a slightly bigger fuse at the battery and yes if you plan to run a second amp from the same power supply of 30A then i would suggest 75+30+5% so about 110A, but now you will run into voltage drop problems unless you have very large guage wire (in this case 45mm2 which is roughly 8mm in diameter (and by this i mean the cable conductor not the whole cable)

mrlee

Sat Feb 14, 2009 11:13 am

Secondly i am not a fan of only relying on the fuses for the amp, as this does not protect the wiring from battery to amp, you should have a fuse as close to the battery as possible, that way any break in the insulation will not short against the body and cause problems

Its this fuse im trying to calculate

the one up at the battery end lol

but now you will run into voltage drop problems unless you have very large guage wire (in this case 45mm2 which is roughly 8mm in diameter (and by this i mean the cable conductor not the whole cable)

My cable is this size lol

Sat Feb 14, 2009 1:02 pm

mrLEE30 wrote:
But if each part of the amp is working at 25amps and there's three in parallel then that makes 75A in total needing to be supplied to the amp!? no....
no it means each part of the amp requires a 25 amp fuse to protect it!! and as i said the fuse is not indicative of how much power is required to run the amp, if i put a 100A fuse in there it would not mean it requires 100A, it would only mean the fuse would not blow until 100A has passed through it.

mrlee

Yeah that's what usually happens it's the same as all fuses they won't blow till their design current has been breached, and deppending on by how much and for how longand what type, it may take a while to blow. They're all like that.

By by my thinking if there are three circuits being supplied by the same source in Parallel taking 25A each and requiring that if going to be used at full potential then the supply must be prottected by at least a 75A fuse.

Go for a 75A or above or nip into Halfrauds or any other Audio place, they'll confirm this.

Sat Feb 14, 2009 1:17 pm

nip into Halfrauds

Dont be silly, wouldn't trust them with a light bulb let alone my system

Sat Feb 14, 2009 1:33 pm

secondtimelucky wrote:
nip into Halfrauds
Dont be silly, wouldn't trust them with a light bulb let alone my system

Just said that cause my mate works in my local one and he's sound and knows his stuff

Sat Feb 14, 2009 4:16 pm

Halford know nothing about car audio! , they always try to sell you there own brand (rip speed) over other's. Fusion is a good company they made some nice gear once a upon a time ago...

Go with a 80A fuse for now , then up it to 110A fuse, Add a Second Battery in the boot or upgrade the Stock with a deep cyle battery.

Sun Feb 15, 2009 12:12 am

Good good, cheers sati.

All this just for a pair of 6" subs lol

Mon Feb 23, 2009 8:54 pm

Where do you guys earth your amps?

thanks.

Tue Feb 24, 2009 1:54 am

i did mine to rear seat rest as there was a quite few holes to pick from , just sand down to bare metal and bolt it up nice and tight.

Tue Feb 24, 2009 1:56 am

what 6" subs need 80a of juice let alone 30amps?

Tue Feb 24, 2009 10:18 am

sati wrote:what 6" subs need 80a of juice let alone 30amps?

well, theyre JVC ones from a home system, anyone remember the 'giga-tube' stereo, with bandpass subs??

this one: http://cgi.ebay.co.uk/JVC-giga-tube-ste ... 240%3A1318

Well im using the subs off a 1400w Magnat Phantom amp

and they're taking it all in they're stride so far