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[Dave DND]

Due to the number of bad installations we see on a regular basis, we have started to show them in the hope that others may learn how not to do it !

Worth a look if you have a few minutes spare

http://www.dndservices.co.uk/htmls/flash_htmls/blackmuseum.htm

[zippo]

and i thought i was a plonka where electrics are concerned

[Marks DTM Calib]

LOL..........I love the ones on fuses.

I have preached until I am blue in the face about fuses and how

They must NOT exceed the rating of the cables after the fuse.

They must not exceed the maximum capability of the supply, and this also has to allow for any supply cables as well (particularly relevant if adding fuses to fuse boxes).

They must be as close as possible to the point of branch (i.e. the battery terminal or other wire that is being tapped into noting of course the above!)

They do NOT protect the equipment from damage....they are there to protect the supply from damage and to prevent fire risks in the supply cabling.

An additional point to note, once you get close to the 100A figure, fuses are not ideal and circuit breakers should be used. This is particularly relevant with car audio installs where you dont have many volts to play with.

[Dave DND]

Aahhh !  Cable ratings !!!

Will nobody ever listen to us !

Too many people (including those on this forum) do not appreciate that an incorrectly rated cable can be just as problematic as it can be dangerous.

Too many want to cut corners with cheap or thin cable and end up with either voltage drop over a long length, serious overheating or RF interference.

Professional audio costs money - and the installation accessories, if fitted correctly can cost nearly as much as the equipment itself.

Good point about the circuit breakers - they are preferred once the current gets into three figures as they often trip a lot faster than it takes for a solid bar fuse to burn out.

 

[Marks DTM Calib]

Aahhh !  Cable ratings !!!

Will nobody ever listen to us !

Too many people (including those on this forum) do not appreciate that an incorrectly rated cable can be just as problematic as it can be dangerous.

Too many want to cut corners with cheap or thin cable and end up with either voltage drop over a long length, serious overheating or RF interference.

Professional audio costs money - and the installation accessories, if fitted correctly can cost nearly as much as the equipment itself.

Good point about the circuit breakers - they are preferred once the current gets into three figures as they often trip a lot faster than it takes for a solid bar fuse to burn out.

 

More importantly, the volt drop across a (good) circuit breaker is much less than that of the equivalent fuse plus they are not prone to ageing through current in-rush (which all fuses are and hence why when thy get old they sometime fail for no apparant reason).

Fuses and CB's used to an area I specialised in many moons ago......I actulay did a paper for the IEE on the subject.

[TheBoy]

Yup, fit fuses as near to supply (or where you are teeing, if teeing into existing cable) as possibly, and ensure the cables are up to the job.

Such bodges annoy me (as Tunnie found out with his invertor fitting to his Senny).  Forgetting about the serious fire risks, surely your car is (probably the 2nd most valuable thing you'll own) worth more?

I know some people, hopefully not any on this forum, who think the expense is of cabling and protection up is not necessary, and would rather spend the extra on a bigger chavier amp. These people are very foolish.

Still, let these idiots burn - evolution is all about survival of the fittest

Harsh?

[TheBoy]

Fuses and CB's used to an area I specialised in many moons ago......I actulay did a paper for the IEE on the subject.

I did an A level study on fuses and breakers.  Fuses vary quite a lot, and (unless old) blow at significantly higher currents...

[Jay w]

Dave,

can i pick your brain? Just want to make sure that off the back of what you have show here my install is OK

Alpine MRV-F407/4 amp, rated at 120W per channel (running 4 channels)

I was recommended to use 8 guage with a 50 amp fuse, fuse is right by the power source (battery)

Never had a problem with it, just want to be safe  

[Dave DND]

50 Amp fuse by the battery is fine.

Although not an exact calculation, the general rule of thumb we use when installing is to add up all of the fuses on the amplifiers, and go for the next preferred value up. For instance if your amp has 2x20A fuses, that would make a total load of 40A, and the next preferred value up would be 50A. This means that everything can run flat out without an excessive main fuse. keeping the main fuse as close to the power source (battery) is critical for protection, and that cannot be stressed enough.

If only running the amp at low levels, then 8 gauge cable is ok (ish) although I would have preferred to see a heftier 4 gauge cable there.

At near 500 Watts, the Alpine amp is a good and powerfull choice, especially being a 4 channel, and it would be good to have an adequate power supply should you wish to use the full potential of it.

With the 8 gauge cable, the demand on power will be more than the cable can supply and over the 6 meters or so between the amp and the battery you will suffer from some voltage drop. You may find that if you crank the amp up, that it starts to cut out or distort at high volumes - at first it will appear that the amp is simply tripping out, but the switch mode power supply inside can only take that for so long before it goes bang. Distortion on a high quality amp is a very bad thing, and can always be solved!

For anyone else reading here, to understand and check for voltage drop, if you have a digital voltmeter, check the voltage at the battery, and check the voltage across the power terminals of the amp when running. It should be EXACTLY the same, but if you have even the slightest of differences, the gauge of the cable is most likely to be the cause of it, and needs to be increased in size.

[Craig_R]

120 watt amp on 4 channels will draw 40 amps

120 * 4 div by 12 = 40 amps

AWG 8 should be ok but depends on the lenth of the cable also I went for AWG 6 with a lower rating fuse to make double double sure it was fine



forgot to say may amp does not pull as many amps as yours so i can get away with a low fuse mine is only 80 x 4 so pulls 26 odd amps

[Jay w]

cheers for that chaps.

Mine does trip out from time to time with high volume, so time to replace the 8 gauge with 6 then

[Marks DTM Calib]

The fact it trips out is actualy the sign of poor design.....but its done to a price and its only car audio so far from Hifi.

If the DC-DC was an average design then it would tolerate the volt drop without affecting output until the max supply current is reached at which point it should lower the secondary supply.

This would result in distortion which is detectable by the ear and which generaly would cause people to turn the wick down......might occasionaly pop a tweeter but, many simple wind the things up until they distort anyway!

The rule of thumb on cable is that it should be rated to AT LEAST that of the main supply fuse.....as this is the current it needs to withstand under fault conditions.

And be wary of those tables, they assume cable with reasonable ventilation which given the routing on many cars, does not happen.

And dont frget to give your amps the maximum chance of cooling by ensuring the heatsink fins are vertical.

[Dave DND]

And if you walk into an audio store to buy 6 gauge, you will come out with 4 gauge !

Its not a common size amongst us car audio suppliers, as none of the accessories or connectors are made for 6 gauge at all !!

Common sizes supported with off the shelf connectors are

8, 4, 2, and zero gauge (lower the number, heavier the cable)

Others are available, but certainly not economic.

[Andy B]

Due to the number of bad installations we see on a regular basis, we have started to show them in the hope that others may learn how not to do it !

Worth a look if you have a few minutes spare

http://www.dndservices.co.uk/htmls/flash_htmls/blackmuseum.htm

You've got to give them marks for ingenuity!
At least they keep you in work.      

[Dave DND]

and its only car audio so far from Hifi.

be carefull with that statement my friend . . . .

I have a reputation to uphold here.

Some of my claims to fame would pitch my car stereo, and most of my customers ones against even the most expensive home systems.

We are well known for the records and trophies we have won for both audio quality and sheer volume - the party trick of one of my customers is to see how far he can fire his windscreen over the front of his car - around eight feet is easily achieved. And if quality is your thing, we were the first company in the world to achieve a pure flat frequency response in a vehicle - only a handfull of people have managed it since in the RTA competition world.

I accept that most car audio is a long way from what you may call HiFi,

But when you make your living designing and installing systems upwards of £10K each  . . . . .    8-)