Blue Sea Systems Dual Battery System and Automatic Charging Relay

The Dual Battery install for me was done in no fewer than 3 distinct phases. It was originally not even my intent to create such a setup; I was initially just trying to upgrade the stock battery in exchange for one which could capably handle the load of the winch. So think of this as less of a ‘how-to’ manual and more of a discourse of what to expect/anticipate and proactive measures that can be taken to avoid some of the pitfalls I encountered. Ultimately I’m satisfied with the setup. I need to complete final wiring of the winch itself (funny how that has been neglected when that was the initial impetus). I think I’ll have the opportunity to use it on this trip, but hopefully it is to pull someone else out of a jam and not me.  It is presently mounted and the wires are roughed in. My departure date and some of the other preparations quite literally came down to the wire. I’m writing this after having logged nearly 1,000 miles on the road today after a little over of 3 hours of sleep the night prior (again, wrapping up things). I took frequent breaks to compensate and at no time drove a stretch exceeding 3-4 hours consecutively. The additional mileage beyond my projections means that I get to sleep in and will be continuing on with nearly a full 8 hours respite. I digress. Here’s how the dual battery went down.

This first progress photo is all of the parts I anticipated needing and procured. 

The bulk of it was obtained from West Marine, a boating enthusiast supply merchant and there happens to be a location not far from me. I was first turned on to the Westin Automotive system which is marketed specifically for automotive applications. However, at the time I finally set out to do it, the product had suddenly become unavailable through most venues, and those that did still offer the item, did so at rates that seemed to be marked up on a daily basis. Some supply chain anomaly was in play. I also had concerns over the gauge of wiring utilized in the packaging. Although it meant a significant cost premium to use the Blue Sea System setup (which does not include any wiring), the ability to select the gauge of wiring based on the anticipated amperage draws was a major selling point.

My setup design changed. Initially I had intended to mount the controls (switch and relay) under the hood and have the backup (or ‘house’ per the manufacturer diagram) staged remotely in the toolbox. This proved problematic as the most viable locations for me were also the least accessible. And I wanted the install to be serviceable in the event a fuse was blown or additional loads needed to be added.

So although I had only purchased enough wiring for the initial concept, with relatively modest modifications, I was able to relocate all of the switching and relay components to the rear tool box and only use one conduit run beneath the chassis. For the bends, I used Liquid-Tite flexible conduit. To cut down on weight, I used EMT in lieu of rigid conduit which is considerably heavier than the former. My reasoning was that the nerf bar and body afford some modest protection of the EMT tubing. And if I’m striking obstacles that high (and now with a 2” lift) I’ve got more expensive problems on my hand than shorting out the backup battery (which is fused; my thought is that the fuse would blow prior to anything igniting).

The diagram provided with whatever system used will prove to be relatively straightforward. I’ll skip the minutia of the individual connections. Here are the problems I encountered, which are more illustrative. And perhaps you will devise better means of mitigating.

1: The pole positions of the stock battery and the Yellow Top are reversed.

What I ended up doing to extend the leads was not pretty. The ground extender wasn’t so bad. For the hot lead, I had a lot of trouble with doing anything to the harness. I couldn’t separate the holding nut&bolt. They appeared to have been bonded with JB Weld or Locktite. Which was great from the standpoint of resisting vibration, but bad for my purposes. Also, the difference in the height of batteries (the 34 D I used is about 2” shorter) meant that the harness would not rest on top of the battery even if the pole positions hadn’t been switched. Perhaps select a Yellow Top with the same arrangement if available. 

2: Pay attention to the components of the secondary battery harness. The top ‘bar’ was no bar at all for the first one I picked up.

I just had to go get another. Loss of like 5 bucks, a little time, and gas money.

3: This wasn’t a problem, but maybe a good detail. Consider how you want to mount the components if you are going with an exterior tool box arrangement.

 I didn’t want screws poking out of the bottom of my toolbox and I also thought some sort of insulating/non-conductor ought to be the base of the equipment going in there. Some spare 2x10 was sacrificed. I pre-drilled the holes from within the box down through the bottom. Then to secure the wood base, I screwed the screws from beneath up into the wood. So all that is exposed is the screw heads. But I anticipated needing to unscrew and rescrew the switch into place several times to add or remove items, and I didn’t want the location holes in the wood to be stripped over time. So I tack welded some weld nuts onto the back of an electrical cover plate and created this pedestal to be mounted to the wood with an offset. The offset allows the excess length of the screws which mount the switch to the plate to pass through and not immediately make contact with the wood. At least one good thing I thought of.

4: Consider ‘future’ provisions.

In construction, even if only one pantry is being built, we often have direction to stub out an additional tap or two in case there are other utility needs in a space or if the space gets reconfigured at a later juncture. So why I neglected this on my own project is beyond me. Probably because the conductors fully occupied the conduit and I could barely pull them through. (Helpful tip from the Home Depot electrical pro; save your money on buying the expensive pulling liquid and just use liquid soap to lubricate the feeder wire. Your run is going to be comparably short compared to what an electrician contends with. So when I revisited my work to install a roof cargo basket, I had to drill a second, 1” hole (which I didn’t want to do) to provide another point of entry for the conductors. But this time I got smart and used a T-shaped junction box with the outlet capped for now. If I want to power something else, I just will uncap the unused outlet and use the same path to enter into the toolbox from the side without needing to drill a third hole. 

5: An inverter might be a good thing to add to your setup and design for its inclusion from the beginning.

For me, it was, surprise, an afterthought. When I first ‘finished’ it, I didn’t have any loads connected to either contact point on the switch. I wanted the direct connection of the alternator to the start battery to not be compromised. That was important to me for winching operations. I anticipate that 90% of the time, I’ll either want to pull myself up and over something (or through something) and the balance of the time, I may just have to chicken out, tuck my tail between my legs and drag myself out of the mess I had gotten myself into. But the point is that most of the winching will be done from the front and that’s where the alternator is. When I got around to building my own cargo basket, naturally I wanted to put lights on it. And those lights need power. Great. I can actually use the switch to control a load and not just as a means of combining the batteries in an emergency. That function is KEY, but I hope not to frequently be doing that. Controlling the house loads via the switch is good. My dilemma, though, was that I didn’t want to contend with trying to hardwire everything into the switch for items I might only occasionally use. And then there are things like tools and perhaps TVs, etc that I’d want to use for camping or tailgating. Enter: the inverter. So if you are doing a dual battery, you probably ought to consider having that hooked up to your switch so you can have plug-in loads and hopefully reduce your dependency on hard-wiring loads to the switch.

6: The light box (see the very first pic of the overall setup)

It was a great idea and the top mounting plate looks very professional, in my humble opinion of my handiwork. Problem was that I did not initially count on the depth needed to accommodate the switches and the thick #4 gauge pigtail wire I used to connect the hots from the lights to the switch. The #4 is the big space hog in the box. And it didn’t help that I used switches with slide-on connectors that enter from the back/bottom of the switches as opposed to the side. I had already painstaking made all the connections and didn’t want to undo them and have some go on not as tightly/securely as before. So I had the brilliant idea of trying to weld on the spacer box that I made with everything connected. Do not do this. I nearly burned up all of my work! A few of the tacks held in lieu of a full weld. If I find a reason to modify it, I’ll go back, disconnect everything, fully weld the boxes and reinstall. I just really thought I could stuff everything in there like you sometimes have to do with real light switches, but the connections were a bit too temperamental and I didn’t feel confident in handling them that roughly. At least with a receptacle, you’ve got good mechanical attachment via the set screws. All of these were essentially friction fittings.

7: Wiring pathways

I did a reasonably good job of routing the wires within the toolbox. I could have done better. Replacing the battery in my setup will not be the easiest. I’ve had to take the battery in and out maybe 6-7 times either because it was being replaced (I used the stock battery for a while) or because something fell behind it. Every time it was a chore because you have to lift straight up, and then tilt to clear the edge of the box and the lid and the wiring. And the wiring invariably either gets hung up on the battery or blocks it from seating. You may have more success with cable management. I do think they are at least bundled well and sit in place neatly. And hopefully the action of swapping it out isn’t done with any greater frequency than once every 3-5 years. Maybe longer since it is only a support battery and doesn’t have the same demands as the primary starting battery.

How do I know it works?

I used a multi-meter to check the initial charge on the house battery. I connected some loads to it and let it get drained down while I worked on other things. I checked again and the voltage had dropped. I started the engine and let it run. The voltage was back up.

What about back-up recovery?

Well, I didn’t want to unnecessarily drain down my first yellow top which was doing the primary starting at this point. (My experiment was back when I had the stock battery as the house. I didn’t care much about that leaky thing).  So what I did…and this was a terrible idea I think for my electrical system, was to remove the positive cable lead from the starting battery. I thought there’s no better simulation of a depleted battery than to have no battery whatsoever in play. I flipped the switch to combine. The little LED initially did not illuminate to confirm they were linked. I was convinced I had miswired something. Anyway, I went ahead and tried to crank the engine, not expecting much, and surprising it turned over and was ‘running’. But this is why I say, don’t ever do this. My gauges were quivering. All of them.  I revved the engine and the tachometer just quivered, albeit more feverishly when revved. I think the issue was that the alternator was not able to kick in to take over the electrical lifting of actually running the truck, and so the second battery was trying to do all of that alone. I’m clearly not an electrical expert, but I feel pretty confident about sharing what I found to NOT have been a great idea. So assuming your primary battery is just drained, and not missing, using the Combine feature will furnish the needed reserve power to provide ignition and all of your needed electrical connections will be in place. 

Here are just some general progress photos that may help clarify how certain connections/transitions worked out for me:

Roughing in feed to the box

Basic assembly of transition from Liquid-Tite to EMT

Pulling conductors through conduit run

This was phase 2. While I was waiting for the lift package attempt to get started, I had the notion to start making a light rack. I wedged the light control box I fabbed up in between the switch and the relay.

Underside of chassis looking up at the flexible Liquid-Tite transitioning to the EMT

This is an important little junction. I have the one feed from the positive post of the starting battery run to this terminal post. From there, I split off two leads; one goes to the relay and one to the switch. It saved on having to provide a second 20' run of conductor. I felt this was ok as the relay is only ever 'sensing' charge on a battery, not really being the source of a heavy draw. So they share the long path and branch off of this node/junction.

 Update 7/21/12
Just wanted to confirm that we ran a heavy duty hammer drill off of the inverter setup connected to this bad boy at work this past week. The mason's had already demobilized and didn't have their generator on site. I needed them to install some reinforcement on our revised mockup wall. Wheeled the truck over to the mockup, popped the toolbox lid, plugged the hammer drill in and let her rip. This might be one of my favorite features of the truck right now. I get regular use out of it.