SuperScoobySpeed

Hi,

Hope someone can shed light on a slight problem I have recently had.

I have had fitted for a couple of months a 1300 watt 5 channel SPL amplifier. Ok it's not the best amp in the world , but I hoped it would do what i wanted it to do.

On Friday, one of the fuses that I had fitted had blown, for a moment I thought my headunit had gone, but on closer inspection found that a fuse had blown.

I have 4awg power cable running from battery in the boot up to the amp. I have 2 inline fuses fitted, one 6" away from battery -- 60amp, and the other just before the amp itself -- 20 amp. The amp itself has it's own blade fuses, 2x 20 amp.
The earth cable is also 4awg and runs to a new hole that I had drilled and also sanded down for good clean connection. The earth point is around 6" away from the amp.

It was the 20 amp fuse that I had installed that blew.

It is one of those large gold ones that fit in to the fuse distribution blocks that you can get (Think made by Shark). The fuse had blown and what looks like the glue that holds the gold top on to the glass had melted. So it must have got quite hot.

I'm happy that I have plenty of fuse protection to protect my amps and things. But just want to know why it has blown.

I used a 20 amp fuse because the amp uses these too.
I'm thinking that I'm using too small a fuse. But why does the amp have 20 amp fuses.
It does have 2, would x2 combine to make 40 amp ??

I don't want to increase the size of the fuse just yet incase I do some real damage.

Any help is much apprecaited.



SuperScoobySpeed

ru'

The purpose of fuses is to (generally) protect the wiring, not the equipment (as is comonly believed).

As long as you have the power cable go directly to the amp (i.e. not split into smaller cables etc.) then it will be protected by the 60 amp fuse by the battery.

Seeing as the amp has two 20A fuses, it's not suprising the single 20A one blew.

You're right; 2 x 20A is 40A. I don't know the specs of your "1300 Watt" amp, but I'd guess there's no way it's 1300 Watts rms.

If you want to estimate the current needed by your amp, get the Watts in rms and divide by 12 (W/V=A). Then divide by 0.8, which allows for the amplifier being 80% efficient.

The resulting number will be the maximum current draw, which you'd hope to be 40A or less.

So (without knowing all the ins and outs of your install, but based on your good description) I'd suggest ditching the in-line 20A fuse altogether!

chiark

1300W = 118A at 12V, and that's assuming 100% efficiency. Allow for 75% efficiency and you're into needing 160A of juice. That's not likely to be forthcoming

If your amp is ever going to make anything near its rating, it'll need a 100A fuse. You'll also be advised to run larger than 4AWG!

There's no point in having 2 fuses - you need one as close to the battery as humanly possible, and definitely before the wire passes through the firewall, and that's it.

ru's advice is excellent... Basically, ditch the 20a fuse

muddy

good advice there

SuperScoobySpeed

Thanks guys, your advice is excellent.

The amp is of a 5 channel type. So basically 4 channels of 200watt and 1 channel of 500 watt. Don't know the full specs sorry. It's an SPL one as previously described.

Like you said I doubt very much that it will deliver it's full potential of a full 1300watts, it's probably only half that!!!!

Larger than 4awg would be massive!!! (You would see it under the carpet )

I'm assuming that it could be classed as 5 seperate amps even though they are in the same box (Would I be right in saying this)

I put the second fuse in for peace of mind, looks like I have been over cautious.

SO, did it blow because it was too small???

I will ditch the second fuse then.

Will the amp be ok then with it's own fuse protection???
Anyway, thanks again for your help, you have eased my mind greatly.


SuperScoobySpeed

ru'

"Like you said I doubt very much that it will deliver it's full potential of a full 1300watts, it's probably only half that!!!!"

There are different ways to measure power; rms is the only one worth mentioning, but others like 'peak' and 'peak music power' etc. look good in the showroom.

Assuming it really does take 40 Amps (2 x 20A fuses) then that's 480 Watts rms. Assuming 80% efficiency, that means the amps putting out around 380 Watts rms at most.

Don't feel bad, 'cos (assuming the 'speakers can take it) to sound twice as loud the amp would have to put out 3,800 Watts rms...

"I'm assuming that it could be classed as 5 seperate amps even though they are in the same box (Would I be right in saying this)"

Yes.

"I put the second fuse in for peace of mind, looks like I have been over cautious."

Yep.

"SO, did it blow because it was too small???"

Yup.

"I will ditch the second fuse then."

Fine (although if you really want to stay over-cautious, replace it with a 40 Amp one!).

"Will the amp be ok then with it's own fuse protection???"

Yeah, as ok as it will ever be.

SuperScoobySpeed

Ru'

You are a star, thank you very much for your help.

I will leave the fuse block in place and replace the old fuse with a 40 amp fuse and see how it goes. It should be ok as you have explained. It's easier for me put a fuse in then completely remove the fuse block. Means a 5 minute job to put a fuse in or a 2-5 hour job re routing cables etc etc etc.

Regarding the power output side, not really that concerned what kind of power it is really pushing out, as long as it drivers the speakers better than the headunit alone.

Thanks again.

Superscoobyspeed.

ru'

Glad to be of some assistance.