kyidletime wrote:I looked at the diagram that you sent again, and saw all of the recommended fuses but only saw one that showed a 2 amp rating. What rating should the other three be?
Well, the way it works is that you are fusing according to the wire size. That's because these fuses are protecting the wire (thus if the wire is compromised, they will blow to do that). You fuse according to the "ampacity rating" of the wire. To find that you need to know a few things about your wire:
1) What size is it (say, 6AWG on your new wire)
2) Does it or does it not run through an engine space (what they really want to know is will it be in a hot space)?
3) What is the temperature rating of the wire (will be marked on wire). 105ºC is typical for marine/good wire, but you may also see 90ºC depending on what you bought. I've found 105ºC on pretty much all the Chinook original wire (but always check).
4) Is the wire running "alone" or is it bundled with other wires? If bundled, how many other wires is it bundled with?
BTW, for this the length of the wire doesn't matter. That affects voltage drop but not the ampacity of the wire.
So since your #6 wire is likely running alone (not bundled), we can look at the ampacity chart for single wires. Here it is:
And here is the bundled one for bundles of up to wires. The wire is de-rated more for larger bundles (different chart).
Okay, so back to your #6 wire. I don't know what the temperature rating is (should be printed on wire insulation) but let's say it's 90ºC. And the wire is not bundled but IS running through an engine space. So we look on the chart and follow over and see the number 82.0. That means you can safely fuse this wire to up to 82 amps (there are some cases where you can fuse to a certain percentage over rating, sometimes 50%).
But your #6 wire is leading from the house bank to the house DC load center, and also (I presume) from the charger in the load center back to the battery. The charger can put out 45 amps, and you are probably not going to be drawing more than 45 amps on the load center. For this wire I would probably choose something like a 60 amp fuse. Since there is some leeway, I might go with a slightly different size if, say, I already had a bunch of "some other acceptable size" fuses in another location so then I would need fewer different size fuses as spares. Nice to keep the number of spares needed down to a dull roar.
Now, what if you, say, ran #6 wire (or were thinking about it) for the 7622 leads? Then you look at the ampacity chart and see that 82 amps, but you realize that your starter can draw 150 amps, and your alternator might put out more than 82 amps at some point in time. The 7622 wires will need to handle both of these things, since it carries alternator power to the house battery, and may carry house battery power to the starter if you self jump start. Well, that tells you you need to use larger wire so that you can fuse it safely (not to mention voltage drop).
That's why I was saying that once you have your wire lengths figured out for the 7622, shoot me a PM as I may have some left over pieces of larger wire and could make them up for you. But let's say you use 105ºC rated wire for this, and that it (of course) is in an engine space, and that it is not bundled. Let's say you don't want to invoke any "exceptions," but instead want to fuse within the allowable limits listed. So back we go to the chart.... If your starter is similar to the one for the V-10 (don't know for sure) then it can draw around 150 amps. So let's see what size wire we need to use to be able to fuse to say, 200 amps, for starters (heh).
Okay, looking at chart, 105ºC wire, engine room, non-bundled, 200 amp fuse.... we see that leads to #1 wire, showing 208.3 amps. Well, #1 wire is not the most common size (and I don't have any pieces lying around!), and we did already "round up" from 150 amps to 200, and we know we can actually fuse a certain percentage over rating if we choose to. So let's look at #2 wire.... follow across, and see that is rated to 178.5. I would consider that good as far as fusing goes, and would be comfortable fusing it to 200 amps. In fact, my buddy's rig that we re-wired, he did use #2 wire for this run, and did fuse it to 200 amps.
One little potential gotcha to look for: Most Fords/RV's use a chassis ground for the negative (which of course is huge and beefy), BUT they often use little short leads to connect to the chassis, and if one of those is teeny tiny there goes your fusing scheme (I replaced a couple of mine with larger wire - not too bad to do).
Okay, but then you might also like to look at voltage drop, just to see what you have. That requires the wire size be known (or proposed), the amp draw that will occur (or be sent down the line), and the length of the wire (key!). Again there is a certain fudge factor you have to put in, and here is why: Usually you count the "round trip" of the wire in DC. Well that would be simple if you had a red #2 wire going out (positive) and a black or yellow coming back (negative). Add those two lengths together and there is your round trip length. But you have a "# infinity" wire (more or less) coming back on the chassis, so there is a bit of a fudge. Since I'm nearly always trying for low voltage drop, I *do* count the round trip as if it were the same size as the positive wire, but in reality you get a bit of a freebie on the chassis ground return.
Probably easier if we run a real example, so maybe you could come back with a rough idea of the length of wire(s) you'll be putting in for the 7622?
