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      11-28-2009, 02:35 PM   #21
VP Electricity
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Drives: F34 xDrive
Join Date: Jan 2008
Location: portland oregon

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A bit more detail on how I am running my B+ and how I determined if it was sufficient:

Since the double-receptacle on the outside of the batt terminal is missing the fusible link output pins (see my link to the other thread), I am switching to a double and a single, and then linking the input side of my two 8-to-4 "reverse-distribution blocks". Thus I will have three 8AWG feeds from the positive battery terminal to my distribution block array.

So - is that enough? Follow along...

The article in Wikipedia on American Wire Gauge is interesting, and has a table with diameters and areas. When you double a diameter, you drop wire gauge by 6. When you double an area, you drop wire gauge by 3. So two 8AWG wires are only the same as a 5AWG wire.

Three 8AWG wires have roughly the same cross-sectional area as a single 3AWG wire. (This was not specifically addressed in the Wikipedia article, but was addressed in this helpful and more detailed table.)

Since I have three 12" lengths of 8AWG feeding my distribution block array, and this is analogous to a single 3AWG wire, this gives me about 110A capability (depending on length, but I am using the chart in the Wikipedia article as a reference here).

The DC650 is rated at 80A when all channels are loaded to 2 ohms, the DC500 is rated at 40A when it is loaded to 2 ohms, and the DC200 is rated at 26A when it is loaded to 2 ohms. That's 146A.

However, all these amps are loaded at 4 ohms, and the DC200 is playing a pair of 4", at very low levels, bandpassed, so it's almost not there at all.

My estimate of my 4-ohm current requirements is 100A with the, ah, current configuration, and so three 8AWG feeds, only 12" long, turns out to be a perfect bit of wire for my needs

This agrees with the Zapco DC manual which states that for an 85-105A load, with wire less than 4' long, you need a minimum of 6AWG. Since I have the equivalent of 3AWG, I am within these directives as well.

If I had all channels loaded at 2 ohms, though, i would be in their 125-150A column, which would require 2AWG, and I would be slightly under the required gauge (although there is an argument that for a 12" run, it's not really a dealbreaker).

Now if we could only find out the per-fusible-link rating of the BMW distribution block
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