Car audio electronics info

[lee]

found the site below and the site owner has put a LOT of work into trying to describe everything about the electronics involved with car audio. makes a good read if you are so inclined.

As an aside, SVX owners with the battery/alternator wire mod might consider taking a look at the discussion about fuses.

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

[Trevor]

Good one Lee, a truly excellent site and should have a link installed. A lot of the posts covering car audio show that many could learn a lot from it.

I have mentioned short circuit protection in regard to the alternator upgrade in a previous thread and your comment is well founded.

[mattski]

I have found a 60 amp fuse and holder at a local car stereo shop and am seriously considering installing it. Do you guys think that would work? Thanks in advance.

matt

[lee]

Originally posted by mattski
I have found a 60 amp fuse and holder at a local car stereo shop and am seriously considering installing it.

I'm not an engineer so.....

Are you talking about putting the fuse inline with the alternator mod wires? First, so we have a common point of view - you only need to protect the wire from alternator to battery - not the ground wires. If this wire is the one you're asking about, then 60 amps may be too low - depends - isn't that always the answer. The SVX alternator is rated at 85 amps (assuming stock) and most of the mods have talked about using 4 gauge wire. So I would suggest a fuse somewhere between 85 (alternator rating) and 125 amps (4 gauge max). Of course you could employ a fusible link at this rating if you can't find a suitable fuse.

What the fuse is doing in this loop is preventing a possible burn of your wiring loom, not component protection. So actually a 60 amp fuse would work, but then you're limiting the current draw to whatever it takes to blow the 60 amp fuse.

On shaky ground (pun intended - sorry) for me, but assuming you still have the stock alternator/battery wires, the combo of the old wire and the new (with 60 amp fuse) may allow full current flow. Somebody that understands electricity would have to answer this, not sure how current flows with parallel paths. I think if I ever did the mod, I would remove the original wire and put in a 4 gauge wire with suitable fusible link just to make it simpler to understand.

[Trevor]

If you have put in an extra cable and retained the original which is the sensible thing to do because there is no point in hacking about the original loom and the original will still carry some current. You must consider the two cables as resistors of very low value connected in parallel in order to calculate the current flow in each. I had a brief look at the site covered in this thread and I think you will find all the information you require there. However there is practical difficulty is in establishing the resistance of the two circuits with a useful degree of accuracy but you will be able to understand the principle involved.

I will stick my neck out and say that you should get away with a 60 Amp fuse assuming this a normal slow blow type. I doubt that the heavy cable will carry a high enough current for the period of time required to melt the fuse. Again l think there is reference to fuses in the site which should illustrate my reasoning. If I am wrong I will have cost you a few bucks but not a big deal as you can then fit a higher rating and your experiment will be worthwhlle posting to assist others.

You will get the best protection using a fuse of minimum rating and this is desirable as there will be two current paths to open each having a separate fuse link in the case of a short within the alternator which will be protected. It is accepted that an electrical fault within the alternator would be a rare occurence but a mechanical short as a result of a collision leading to an engine compartment fire is a distinct posibillity. What can happen in a crash is a major consideration in the design of electrical system protection in vehicles.