Couple of points you're missing:
With low voltage circuits, voltage drop becomes more of an issue (Vd is the
same, regardless of circuit voltage, thus it becomes an increasing
percentage and more of a problem with 12V than 120V). Also, there's no
such thing as 'magic wire' -- some 'published ampacities' of
high-temperature wire are shockingly high, however one must read the 'fine
print' and realize what the operating (not ambient) temperature and
commensurate Vd would be at those currents. Thirdly, draws of most audio
systems are ragged (not continuous) in nature, thus a transient condition
might want to be 'handled' by a larger fuse, but not generally a great idea
for continuous loads.
There too, the battery (i.e., a larger one) can act like a capacitor in
handling transient loads, but for the emergency power application it should
make little difference since the system will be 'running' off of the DC-DC
converter. As always, Prius should be in 'ready' mode before using the
Bottom line: Use adequate wire size for the continuous load, and proper
fusing (ditto) to avoid problems. No magic here.
Pete (Wire guy)
P.S. 40A is a bit much for #10 wire... it will get rather warm when you go
over 30A continuous load.
P.P.S. The 10A limit of the outlet is NOT set by the wire - the contact
system in the basic design will toast the plug/jack if you exceed that
rating for any amount of time. Did lab work on that, and it's the
On Mon, Nov 12, 2012 at 11:38 PM, Dan <hyattdj@...> wrote:
>> Yes you are correct, but there is some critical information.
> The amperage the circuit can draw is dependant on the source, the gauge of
> the wire, the length of the wire, and the limits of the components.
> For instance, on my jeep, I had a 6' run of 10 or 12 gauge wire from the
> battery to an overhead fuse block. I think we calculated we could draw 40
> amps of 12v, or 360 watts of power.
> I am trying to figure out how the fuse blocks on the cars can be rated at
> so many amps max capacity with 10 gauge wires.
> The big problem with the power ports is that they still use 18 guage wire,
> designed for 5 second duty cycles. You use a 5minute or 1 hour duty cycle
> and you can (I have) burn the wire.
> A much debated limit for the Prius is the OE 12v battery, by the factory
> manual, is woefully low on reserve capacity. While the Optima will have
> lots of reserve capacity for your deep draws.
> Radio operators also have a tendacy to use anderson connectors, which have
> excellant capacity and often have thier own wire to the main block.
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