I originally was just going to send this to Ed, but thought there are some pretty smart cookies in our group that might be able to shed some light or their thoughts on what I've been thinking of doing:

In another thread we were discussing that it'd be a good idea to add a second charge cable from your alt (any of them) to the Pass side batt since the single one there now is only (8 gauge?).

I posted in that thread about why not add the second charge cable off the Alt to the Driver's side battery. I thought of why this might be good, and then why bad, and would be interested in what others less electrically challenged than I, thought about it:

The Good: sending charge level power (14V or so) right from the alt to + side of DS batt is where major other electricals are fed from (like FICM) so possibly give them a better source (higher volts there before feeding battery) on start-up/idle.

The Bad: The PCM controls the charging of the batts, right? or is that only if there are two Alts? If the former, it would falsely think batts are fully charged and shunt power.

Please go easy on me if these thoughts of mine just show my pure ignorance of the charging system on our trucks...

Thanks for any noodling on this. And Happy 4th of July to all! Be safe out there whatever your plans call for...

 

That's the "more is better" line of reasoning. There is (generally) no such thing as too big of a wire, however a wire can be too small. Add a wire to an existing circuit and you increase it's amperage carrying capability but it will have little effect on the voltage reading in your circuit -unless the existing wire is too small and acting like a resistor. Adding a wire either place you describe could be an improvement if you install a higher amp alternator. I feel confident the engineers who originally designed the circuit did the basic math necessary to determine the correct wire size for the factory components. On the other hand, adding the wire will have no negative effects if it's done properly.

 

Thanks Rusty I appreciate what you are saying and the engineers might very well have had a good reason not to put another wire to the 2nd batt. besides just being overkill.

Seems like we have ended up figuring out stuff on our trucks well after they left Ford's design hands, and heck even Ford figured some things out (where the design didn't work quite well enough) as the 6.0 stayed on with the vans. I'm thinking of the STC replacement, bluespring, turbo oil lines, degas level, etc.

Some of what had got me going on this was: all my battery failures have started with a dead/dying passenger side batt, the importance of voltage to the FICM, and Ford upped the standard Alternator to the HD 140 (optional on 6.0s) with the 6.4. Why?

So let me ask you this: do you see any harm or issue with running an extra + wire to the drivers side batt? And is the current one a 6 or 8 gauge?

I've found some interesting threads on other forums about methods to test if the wiring is adequate, simply by looking at Voltage differences between various points in the battery and charging system -- I may just do some of that before spending effort on running wires.

Thanks again...

 

I don't see a problem adding the wire to the driver side battery. There is such a thing as "load balancing" when there is more than one power supply in a circuit -and this circuit has three- but it is a pretty nuanced subject math wise. You're also right that the engineers didn't get everything right, the alt is barely adequate for the application and if the truck is in harsh conditions temperature wise it's not big enough. All the factory wiring is sized to the OEM components so if you go up in alt output, I agree that the wiring upgrade is a smart idea.

Ed (FICM.com) has posted a diagram with suggested routing/wire sizes. If you haven't seen it search "big three" and give that a look.

The voltage drop tests you've likely seen will test the conductivity of the wires and connections. It's a good test and often overlooked part of checking out the system.

I think the factory cables are something like 0ga on the battery cables and maybe 4 or 5ga on the Alt wire (just guessing).

Again, "bigger is better" isn't always wrong and there's value in peace of mind .

 

American Wire Gauge (AWG) Cable Conductor Size Chart / Table

 

1 single 0-2 gauge cable is more than enough for the charge cable. The choke point will always be the voltage regulator output stud on the alternator.

If anything needs to be increased in size it would be the starter cable.

Josh

 

I like this chart, due to the fact that it factors in the length of cable also.

http://assets.bluesea.com/files/reso...on_chartlg.jpg

http://circuitwizard.bluesea.com/

 

Thanks for the help guys!

 

I added a heavier wire (0-gauge) connecting the 2 batteries after corrosion caused the factory wire to get fried. This made a big difference when starting and maintaining charging levels (that factory connecting wire was already corroded when I bought the truck, so the improvement may have mostly been from repairing the problem and not the increase in size). I also added a 0 gauge charging cable and ground cable when I upsized the alternator.

I don't really think you need a separate charging cable to the drivers side if you have a good big cable connecting the 2 batteries. Make sure you have good positive terminals that can fit all the extra wires and a good crimper for making tight fittings for your wires. I like the Ancor Marine heat shrink tubing to cover the crimp too.