This is all great info & I thank all who have contributed b/c I love learning.
Checked the specs on my amp and looked at the power lead, which is pretty lean, probably 16g or so (nowhere close to 12). Specs say voltage range is 11 to 16 & current consumption is 15a. So if I understand correctly, my goal for best performance should be to wire it to the fuse block in a way that delivers 15a at the amp end of the power wire. Is that right?
Also, given the bottleneck effect, does it do any good to use a 12g wire from the fuse block if the amp power wire it will connect to is a higher gauge, assuming 12g is not needed to deliver 15a at the necessary run length?
You are not delivering 15 amps per say... but the device can draw up to 15 amps max. 15 amps is it's "max load" or worst case scenario.
The amp draw will vary depending on how hard you push the device. Louder you play the music, the more amperage it will consume.
It would be safe to assume during normal operating volumes, it's going to be well below 15 amps.
The 11 to 16 volts is the allowable input range for that amp. Pretty typical for an automotive accessory.
To try and answer your question, you really don't NEED to run larger than 16awg unless you have a really long run before you get to the amp, but larger never hurts. I would probably use a conservative 14 awg and call it a day. There is such a thing as over-engineering it and the law of diminishing returns.
Ohms law might be some good fundamental reading if you were so inclined.
Power calculations...
amps x volts = watts
15a x 11 volts = 165 watts
15a x 12 volts = 180 watts
15a x 16 volts = 260 watts
That amp at its theoretical peak maximum power delivery is 260 watts... and it only happens at 16 volts. Anything below that, the amp isn't going to be as efficient and won't delivery as much power.
This is why I made my argument for minimizing voltage drop.
Alternately, if you try and draw 260 watts with only 11 volts, the amp is going to try and draw 23.6 amps, and in turn will pop a fuse to protect itself because it can't handle that thermal envelope.
Play around with these wire size calculators, and voltage drop calculators.
Circuit Wizard - Blue Sea Systems
And here is a quick voltage drop calc for your amp at "max load"
Voltage Drop Calculator
With 14 volts and 16 AWG wire, 10 feet of cable, and 15 amps worth of current moving though it. The amp would see 13.4 volts at its input. That is a 4.25% loss across the run.
Just shortening the same cable to 3 feet, gives you 13.82 volts at the amps input, a 1.29% voltage drop.
If you wanted the same 1-2% voltage drop with a 10 foot run, you would need to use 12awg wire.
Acceptable voltage drop really depends on what you are trying to achieve and could be anywhere between 3% to 10% depending on the application.
Use the calculator and play with the amperage and you will get an idea of a real world line loss because that amp isn't going to be running 15 amps. This is also why I measure my electrical equipment and not just take the max wattage of a spec sheet. Helps me design for the real world...
Example: The below is a measurement from a e-bay "240 watt light bar" which only uses 150 watts in the real world. and before someone asks... Increasing the voltage doesn't make it brighter, it just reduces the amp load. Still uses 150 watts...
Hope that helps.
