Adding a Second Battery

Yes, my wife is right:  It is all about chili lights.  When camping amongst the behemoth RVs and 5th wheel trailers, we note that they frequently have lights hanging from their awnings.  If you are hooked up to "shore power", then you too can string lights on your van and add to the ambience of the campground (Just in case fresh air, tall trees, green foliage, camaraderie and the smell of campfires don't quite float your boat).

But what if you are not hooked up to shore power?  What if you are just totally roughing it?  Then you need some sort of battery-based energy source that can also produce alternating current (AC) to power these cheery little strings of lights.  Adding a second battery and a DC-to-AC converter, or inverter, can accomplish this.  But, doing this for the sake of powering chili lights yields other benefits as well.  For example you can re-connect your radio, satellite receiver and interior lights to the second battery.  Now, if you are up late drinking wine, listening to your Arlo Guthrie and/or Joan Baez collection and retire unexpectedly early (as in you pass out) with your favorite tunes going full on, the second battery will be exhausted - not the primary battery. 

Batteries that can perform the role described above need to be deep cycle batteries.  This means they can be drained all the way down, then recharged many times.  Normal batteries don't like that, and will become ex-batteries after some small number of complete rundowns. 

The second, or auxiliary, battery fits into a compartment behind the driver's seat. There is a space limitation and the most popular deep cycle battery, the Optima Yellow Top, needs to lay on its side if you want to be able to close the compartment cover.   Some folks stand it upright and remove the steel lid.  Of those, at least one has fabricated a very nice replacement cover.

For the AC power source, an inverter can be mounted in one of several places and receive 12 volt DC power from the auxiliary battery.  I chose to mount mine under the rear seat of the Westy, next to the engine's ECU (computer).  The AC output of the inverter powers the extra outlets shown in the above photo. 

The pic below shows the inverter and the battery "trickle charger" that was added.  Click it for a better view of what's under my seat.  The shiny aluminum stuff in some of the pics is FatMat sound deadening material that was applied at the same time the battery was added.  The devices are mounted to the driver's side of the rear heater box.   I need to add "temporarily" mounted, as I don't know the final configuration.  The inverter is now only velcro'd and may be a little precarious for my liking.  We'll see how it hangs.

The12 volt DC input to the 400 watt inverter is connected to the battery up front.  I used 8 gauge wire, which is sufficient to carry all the current the inverter can draw.  The wire runs out of the battery box through a grommet and under the van.  I would rather route it on the inside, but did not want to remove cabinets or run it under the carpet.  At the battery I installed a 40 amp circuit breaker in case the 8 gauge wire gets shorted.

Mounted next to the inverter is the trickle charger, connected to the "shore power" AC input after the Westy's circuit breaker.  Whenever the van is plugged into AC, either at home or at a campsite, the trickle charger will recharge the auxiliary battery.  It's called a trickle charger because it supplies a limited amount of DC current (1.5 amps).

This photo also shows the jumpers and plug that are used to check for engine codes (van's motor is from a Subaru SVX). 

 

Preparing for the Auxiliary Battery: 

The Optima Yellow Top will fit the compartment nicely, but only if you can get it in there.  Turning it onto its side the "top" terminals prevent the battery from laying flat.  Some have cut the top terminals off, but things like that tend to void warranties, so others of us modify the battery compartment to make it fit.  I laid the battery down (plastic protectors on the top terminals please) and marked the spots where they hit.  Then I used a saber saw and Dremel tool to cut notches for the terminals. 

This is some way hard steel.  Took a long time and did not come out pretty.  I guess some of the guys/gals cut out a large section but to me this seemed the simplest  (C4 anyone?).

 

 

 

At right shows test fitting the battery.  The thing is really heavy and you don't want to be lifting it in and out too many times.  I did commit the cardinal sin of not putting a strap of plastic web material under it to lift it back out.

In this pic I had taken the steel compartment cover off, thinking it would not close after the battery was installed.  I wound up re-installing it.  But it may be a good idea to remove it temporarily for the installation anyway, just to get it out of the way. 

I did not use the terminal lugs shown here, but rather two lower profile hex-head bolts cut to the proper length.   I cut the negative bolt to be a bit longer in hopes that the steel lid would hit it, rather than the hot terminal, if the insulation on the lid ever came off.

 

Battery "Isolator" or Battery "Separator":

The second battery is there to run our conveniences while camping, but must be recharged when we are driving the van.  So it must be connected to the engine's alternator to receive the recharging voltage.  But, if the batteries are connected permanently, then two things would happen:

Thing 1:  When the auxiliary battery was run down, the main battery would be depleted also.

Thing 2:  When starting the van, if the two batteries were connected by a less-than-jumper-cable-size wire, then smoke and flame would occur when the starter started demanding hundreds of amps from the connected power sources.

So we need something that connects the batteries when the alternator is producing a battery-charging voltage, and disconnects the batteries when it is not.  The device that I used is called a "Battery Separator" or "Battery Isolator".  Semantics could keep us up all night, but what is important is that a device exists that can keep the two batteries separated (or one battery isolated) while not driving, but join them together when driving. 

I used the Sure Power Model 1315 battery separator.  It has features beyond simply keeping the auxiliary battery isolated while stopped.  It can be used to help the main battery start the van if the main battery is dead.  I did not implement this feature because I carry jumper cables and will utilize the second battery if needed.

In this application the 1315 uses three connectors.  One goes to the main battery, so it can measure the charging voltage and connect the batteries when charging is occurring.  The second goes to the auxiliary battery to receive the charging voltage.  The third connection is to ground

In the pic above you'll see that the 1315 device is mounted to the battery compartment lid.  This seems to be rather handy, since there is not a lot of room to mount it any other way, short of cramming it down into the space beside the battery.  Sure Power technical support assured me there is not a problem with mounting the device in an inverted position.  Anybody mounting the device in this position should make sure the wires' insulation is pushed well inside the insulated part of the fork or ring lug connectors.  This helps keep the copper from flexing so much when the cover is closed.

Notes on the Sure Power 1315: 

In a Subaru engine conversion the "I am Charging" signal is not strong enough to energize the relay and the blue wire is disconnected.  If this is not done the charging signal is not strong enough to turn off the alternator warning light on the dash.

The photo at right shows the device as seen from the driver's side door.  The braided grounding strap is insulated by a section of shrink tubing, just as added safety in case a hot wire is dropped.  The 40 amp breaker is also inside shrink tube because its very large copper solder terminals are not insulated.

The back of the driver's seat has layers of duct tape to keep the wrench from shorting to the van when turning the positive terminal.  Also the inside of the lid has layers of duct tape, but really should have some thicker plastic or rubber glued on instead.

 

 

 

 

 

 

Well, there's the finished product.  Chili light power source hidden all neat-like.  I think the steel lid can go down a little bit more, but that's for a later tidy-up project.

 

 

 

 

 

                                       

 

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