Equipt 101: Troubleshooting Dual Battery Systems

Video Transcript

Intro

Hi, I'm Paul with Equipt Expedition Outfitters. We get a lot of questions about the maintenance and troubleshooting of the National Luna dual battery system. I think I can answer some of those questions for you. Let's take a look.

Overview

So what we have here is my Toyota Land Cruiser 200 series. It's a basic setup of the National Luna dual battery system. What we have here is the main battery on the passenger side, the auxiliary battery mounted over here on the driver's side, and then the back corner over there mounted vertically is the National Luna intelligent solenoid. The National Luna intelligent solenoid is an automated switch. It doesn't do anything to the voltage that is provided to it from the alternator. It doesn't change the current, the amperage, the voltage, any of those items. What it does is it monitors the voltage available and it connects and isolates the two batteries under the hood based on that voltage system.

Some of the things that we're finding is that people are saying that the National Luna system is killing their batteries. It's very difficult for that to happen because the National Luna intelligent solenoid runs on milliamps. It really doesn't do anything other than monitor the voltage available to it. So for it to kill a battery would take several weeks before you would find any effect whatsoever.

Now on the contrary, plugged into the intelligence solenoid is the National Luna dual battery controller. On the controller that's mounted in the cab of the vehicle, there is a set of lights on top of that controller. Those lights do take some power, so if you're going to store your vehicle for a given amount of time, it's best to turn off those lights. You can do that by holding down the left button on the controller for five seconds; it'll turn the lights off, or you can disconnect that controller.

Sometimes we have problems with the National Luna solenoid communicating incorrectly. Let's talk for a second about the connections of the wires that we have going on here, and this will help make sense of the answers here. What we are trying to do is to create a loop of wire so that we can monitor it with a switch. We have a positive lead that goes from the main battery to the left-hand side of the solenoid. From the right-hand solenoid, we have a positive lead that comes around to the auxiliary battery, and then we have a negative wire that goes between the two batteries. What we've created is a loop; we've bonded, we've put these batteries in parallel, and the intelligent solenoid is the switch. It either closes the contact to charge the batteries together or opens that contact to isolate those batteries.

There's a little black wire that comes off of that solenoid over there, and you connect that to the negative lead of the auxiliary battery. That is like the power cord for your computer. What that does is that completes the circuit of power for the circuit board and the firmware to do its job. A lot of cases, what has happened is we've either changed out a battery or we've done something where we've added a connector or whatever to the system, and the firmware in there gets its signals crossed and it's not exactly sure what to do. The easiest thing you can do is to go to the negative battery, take that little black wire off of the circuit board there, and take that off. That is, in essence, like booting up your desktop computer again. By disconnecting it, powers it down; by reconnecting it, it restarts that firmware on that circuit board and clears a lot of the problems out.

What you should see when you put that wire back on is the top light on that intelligent solenoid over there, where it says 'timer active,' is going to flash once. Now, if you can get that to flash once, what that means is that it's back up in business and it's ready to do its job. That's goal one on troubleshooting the system. If that does not flash once, what that means is that we have something incongruous in the loop of wire, our parallel loop of wire. This could be several things: one, it could be a loose connection; two, it could be a bad fuse.

There are several different ways to wire these systems up. You can wire them up without fuses. If you're planning on using a winch, it's best to leave the fuses out of inline because of the amperage draw that these two will have under a winching situation. So if you leave the fuses out, then what you want to do is you want to test the voltage coming off of, first of all, the main battery to the left-hand side of the solenoid. You check the voltage at the battery and you check the voltage at the left side of the solenoid. That voltage should be the same. If it is not, then something is going on between the main battery and the solenoid.

Secondly, check the other side, the right-hand side of the solenoid to the auxiliary battery. The voltages should be very close to the same, within a tenth of a volt of being the same. If they're not, if you're getting a voltage at the battery but not at the solenoid, chances are you have a loose connection or your fuse has gone bad. National Luna's inline fuses are very interesting. They're a fuse called a mega fuse, and it's an inline fuse that you can't really tell whether it's blown or not. It's a two-tab fuse that you put in inline with a lug on one side, lug on the other, a fuse in the middle. The only way to test those fuses is to take them physically out of there and flex them in your fingers between your thumb and your forefinger. If there's flex in there, then the fuse is blown. If it's solid, the fuse is okay.

So if you do use inline fuses, that's one thing you really want to check is to make sure that your fuses are in place. If you're still getting a different voltage between these two, it's obvious that there is a disconnect in the wire system. One thing you want to make very certain that you do not do is to put anything in that loop other than the wire that's in place. There's no extra switches in place, no extra cut-offs, any of those things, because the intelligent solenoid has sensitive material in there that it's trying to read the exact voltages for isolation and connection, and that can be thrown off whether you're using a body ground, which is not a good idea, or you're putting a switch or you're connecting wires in for other pieces of equipment on your engine. It's not a good idea. That needs to be a solid loop independent of any other electrical control to make that.

Sometimes what happens on the dual battery controller under the hood is that it shows up some very odd lights. You end up with top lights running, middle lights out, some oddball things happening. One thing that we found out is that in the instructions for the National Luna system, you are to install the red positive lines first and then add the negative lines second. The goal there being is that there wouldn't be any chance of an arc happening off of the main wires to the intelligent solenoid. If you hook up the negative wires first and then add the positive leads after, there is a chance of an arc fault at the battery connection, which goes straight into the intelligent solenoid circuit board and through the cable into the cab of the truck to the controller. It fries the circuit board on the controller, and that's not good at all.

So whenever you're working on any battery system under the hood, always remember: negative leads off first, negative leads on last, and that will take care of that arc fault concern with any battery connections underneath the hood.

I'm Paul May. I appreciate your time. Thanks for listening.