Batteries, Battery Monitor, Communications & Electronics, Computer, Electricity, Solar Panels, Technical 
14 Comments Knowledge is Power
A grey stretch commences…
I want to thank everyone who has commented about charging house batteries with a truck or the RV itself. I encourage everyone to read through the comments on my last few points. I will address a few things here.
Airmon provided a good charging strategy (more on that below) and asked: “Did you set your linkPRO up with the capacity of your batteries and the float voltage charge profile from your solar controller?
Answer: Yes.
Croft suggested a battery cut off switch to separate the alternator from the batteries so that I can get more charge to the house batteries. I will research this further.
Dave chimed in to say that it’s easy to get a battery to 80%, but the last 20% takes hours. This goes with what Airmon said, that I should only use the truck to charge if I’m below 80%, get to 80%, and then let my solar do the work. He also said to attach the jumper cables before the shunt and fuse, but not directly to the battery posts. Dave, huh? I understand the theory, but the only thing before my shunt and fuse are the battery posts.
Finally, Alan said that folks who use their motorhome engine to ‘top off’ their batteries do get a little charge, but it will never truly charge the batteries to full capacity.
This morning is very overcast and I have barely 2A coming in. I did start the day with my batteries in much better shape than they have been in a week (12.4V versus 12.1V!). I finally rehardwired the little solar panel in and that’s giving me an extra amp. So I’m fine for power today… if I don’t charge my computers. That’s where I’m a little stuck. I ran the truck for more than two hours this morning (!) and got a full charge out of the PC and only 75% out of the Mac. The PC wins, right? Ha. That full charge out of the PC gives me at most 2 hours of run time while the 75% on the Mac gives me 3.5 hours. I have to scrap the library idea as it is closed on Mondays! 
I really, really need the Mac today, so I may sacrifice some amp hours in the middle part of the day. And hey, it looks like it might be clearing a tiny bit! And I’m now at 2.5A!
Now that I really understand how the battery monitor works (and that it is working properly), I feel very empowered. I know that even though it is grey out there right now, as long as I don’t charge my laptops, I will end the day with more charge than I started with. That means that I can face tomorrow without fear of a dead battery. It also means that if I ever get to 4A coming in, I can charge the computer during that time, quit when the incoming amps go back down below 4, and still end the day ahead.
But that still leaves me the computer charging problem. I just can’t seem to get out of it. Running my truck for hours to charge a laptop is very inefficient! I am nowhere near due for a new computer, but the Macbook Air’s seven hours of run time on a single charge is starting to look pretty good. My 17″ Macbook Pro is four years old now, but there’s no reason it couldn’t serve me well for many more years. The hard drive on it is good, I’ve maxed out the RAM, and it has a new battery. So I’m back to finding a better way of powering it.
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Head to Starbucks and plug your computer in while having a cuppa.
That’s my usual strategy, but the nearest Starbucks is over an hour away.
McDonalds don’t always have power outlets. The newer ones tend to, but Port Lavaca has an older one, so I’m doubtful. I haven’t gone in yet to check.
Just to clarify, I meant that the jumper cables should be on the house side of the shunt and fuse. This way the charging current is captured by the shunt and supplied to the monitor.
Dave Sand
So attached to the shunt and fuse posts?
In reality, the positive side is not important, but the negative side with the shunt directly impacts the accuracy of the battery monitor.
battery bank negative connection >>> shunt >>> house wiring (includes DC distribution panel, inverter, solar controller, RV converter, connection from engine for charging while driving and any other power source such as jumper cables).
Dave Sand
Dave, I think my battery bank is wired wrong!
What I have is a 1-gauge cable from the negative post to the shunt. On that same shunt post I have all the negative cables. On the other shunt post, I have 1-gauge cable going up to my inverter.
Same thing on the positive side. 1-gauge cable from the positive post to the fuse and all positive connections on the same post. Other fuse post has the positive cable going to the inverter.
If I read you correctly. The first 1-gauge cable should be going to a post all by itself and everything else should be on the same posts, including the cables to the inverter?!
It does sound like you’re wired wrong, though from what you describe, you would only see loads from your inverter displayed on the monitor. You would not see any other loads or charging, and it sounds like you have seen positive charging loads when the solar panels are active.
Does your monitor show a load for lights in the RV that changes as you turn more on or off?
When I spoke to Xantrex about my own LinkPRO installation, they said that it was also important that the positive side be connected directly to the battery bank, though my question was more about which side of my battery disconnect the positive side should be on.
Xantrex said: Direct to the battery. According to them, disconnecting the LinkPRO when storing the RV could cause it to lose settings.
I second Dave’s point that the only thing that should be connected to the battery terminal side of the shunt is the cable going to the battery. Everything else, all system grounds, all negative cables running to devices, should be on the other side of the shunt.
If you mentally trace a line from any device, following the negative cables back to the battery, that path should go through the shunt.
All the readings on my monitor make sense. I do see the amps go up and down according to what I’m using. I will move the main power cables over to the other post and the put the inverter cables with the other stuff and see if that makes any difference. Thanks!
Dave is right: your shunt is wired incorrectly.
EVERYTHING–not just the inverter–has to go through the shunt, or your battery monitor can’t do its job. That means the only cable going to the battery side of the shunt should be the jumper, and all the other cables must go to the other side of the shunt.
About the laptop charging issue: seems to that it would be a lot less expensive (and a lot more beneficial) to add another solar panel or two than to buy a laptop that uses less power.
Okay, rewiring is in order for tomorrow. And, yet, the readings I’m getting on the monitor make 100% sense…
As for buying a new panel versus buying a new computer, I agree. But the point is, if I end up replacing my computer, I’m going to have to factor in battery life. It never occurred to me I’d have so much trouble with a laptop while boondocking.
airmon is correct about wiring the positive wire for the LinkPRO directly to the battery bank instead of through the fuse. If the monitor is disconnected from the battery bank for any reason it will need to be re-configured. This implies that it will be another parasite drain. Although very small, but they do add up.
Dave Sand
Guess, I’m a moron but not an idiot apparently. I just went to rewire everything this morning, and, *sheepish grin*, everything was wired correctly!
You are like me, our only imperfection is self-doubt!
*Snort*
Really, what I’m seeing with the battery bank is that my theory was flawless. Where I failed was in the technical execution, especially in making good connections. So I really do think that I would be better off hiring a pro to do future upgrades, but I would reduce the cost of that by doing all the thinking and math and laying out myself.