Re: Wiring an amp

On
>In rec.audio.car on Fri, 19 Aug 2005 01:19:45 -0500 "Sean"
><anonymous@xxxxxxxxxxx> posted:
>
>>On
>>>I have a Kenwood KFCW-300S Sub that I am connecting to a SPLX SPLA350 Amp
>>>using an Autoleads PC4-20 wiring kit.
>>>
>>>The wiring kit comes with a 15, 20 and 30 Amp Fuse, should I use the 30, 20
>>>or 10 Amp fuse for the amp live from the car battery?
>>>
>>>
>>>
>>
>>Look up the current draw the amp pulls from the battery (it should be in the
>>manual), and put in a fuse that's closest, but not above, that amount.
>
>I think you mean closest but not *below* that amount.
>
>If the amp draws 17 amps and he puts in a 15 amp fuse, it will blow
>every time.

The draw listed in the manual is it's maximum draw, and I definitely don't
want my amp drawing more than it's designed to handle. My amp draws a maximum
of 60 amps, and the closest i could find and a little under was 55 amps. I
haven't replaced this same fuse for 3 years now.
>
>Another thing you could do, Chris, is start with the smallest fuse,
>prepared to see it blow. If it does, move up to the next bigger.
>Etc. You can do this when the wires are connected but not in place,
>or after the wires are in place unless you think you messed up already
>:) (I don't like to waste things, but I don't think there are any
>low-supply materials used in fuses. ??)
>
>I don't know details about amps, but it seems they must draw more
>current when one is playing something loud. So either test with
>something loud, or keep the next size bigger fuse around for the day
>you go real loud and blow this one. (It's a car. I carry a bunch of
>fuses of various physical and electrical sizes so that I'll always
>have a spare for any circuit. The fuse box of my car even came with a
>place for storing spare fuses. Actually, I don't have the big fuses
>that are used under the hood, but none has ever blown.)
>
>Maybe one shouldn't, but temporarily I would use a bigger or even much
>bigger fuse than I should. It won't make a difference until there is
>a short in that circuit. Even then, a fuse that is 5 or 10 amps too
>big will probably blow before there is added damage to the circuit.
>If the fuse is 20 amps too big****, what I think will happen is that
>from the short (inside the amp, for example, or where the wire to the
>amp rubs or cuts against a metal part of the car) back towards the
>fuse until it reaches wire that is heavy enough to carry the full load
>of that fuse (say 30 amp wire if you used a 30 amp fuse) the wire
>itself acts as a fuse, and might blow in one spot, but more likely
>will heat the insulation which can drip off the wire. You may be
>stuck replacing that entire length of wire, from the short back to the
>heavy duty wire.
>
>Other people here know a lot better than I how extensive the damage
>can be, and how much trouble it can be to replace it.
>
>****but there was no real short that caused the first fuse too blow.
>Either the amp was too big for the fuse, or perhaps you stuck a
>screwdriver in a light socket and let the shaft touch a ground.
>That's a temporary short, but when you remove the screwdriver it's
>gone.
>
>Another thing you could do is put in a big enough fuse and run the
>current through an ammeter to see what it really is. The ammeters I
>have are part of multimeters, and I think the highest they go is 10
>amps. Sounds like "not enough" and you will or may damage the ammeter
>I guess if you go higher.
>
>(I suppose you could connect two or three in parallel and add the
>readings, but how would you make sure the current spread out so that
>no meter got more than 10 amps. A bad connection anywhere would mess
>this up, and even if all the connections were good, how would one know
>what would happen? Don't try this.)
>
>I built a shunt a long time ago, when someone gave me some low but
>measurable resistance wire. So I could run the current through that,
>and measure the voltage drop across it. (That's what an ammeter
>vasically is, except the low-resistance wire is part of the meter, and
>the scale is already calibrated in amps, and not volts) But I've never
>noticed this wire for sale since then. And I've only used the thing 2
>or 3 times in all these years. My first suggestion is probably better
>than my others, or Sean's with the modification.
>
>Meirman

.

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