RE: Whole House Audio

["Phil Harris" <phillip.harris1@xxxxxxx>]

Exactly what I had ... a second 120Amp alternator mounted on the AC pump
brackets charging seperate batteries in the boot.

Phil

> -----Original Message-----
> From: James Hoye [mailto:james.hoye@xxxxxxx]
> Sent: 20 June 2001 22:22
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] Whole House Audio
>
>
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> ---------------------------------------------------------------
> > Unfortunately running an amp from 12v is pretty inefficient ...
> I used to
> > have an Orion 2100HCCA that we tested once at 1,280w RMS bridged
> > into a 2ohm
> > load without clipping and at that it was drawing slightly less
> > that 220Amps
> > at 13.8v.
>
> <really_sad_mode>
> Given that R=pl/A and the resistivity (p) for copper is 1.7E-8 (at 20
deg
> C), 1 metre of 35mm^2 copper cable is going to have a resistance of
> approximately 1.7E-8 x 1 / 0.000035 or 0.000486 ohms/metre
>
> The heating effect of a cable is I^2R, so 220^2 x 0.000486 =
> 23w/metre.  For
> a boot mounted amp. with 4m of power cable each way you're going to be
> losing nearly 200w in the supply cable alone!
>
> Of course with that sort of current draw you'd go for a split-charging
> system with additional batteries in the boot, thus keeping the
distance
> between the batteries and amps minimal.
> </really_sad_mode>
>
> Sorry - just reviving my A level physics (with textbook - can't
> remember the
> all formulae from that long ago).
>
> James H
>
>
>
>
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