Monday, April 8, 2013

Installing The House Battery The Correct Way!

Everybody knows the advantage of having a separate "house" battery when living in a van, RV, or even a car.  You can use your accessories with wild abandon, and when the screen of your DVD player goes blank you can still start the car and move on.

For now, my power needs are rather simple.  I hooked up two batteries as "house" batteries but decided the space taken by the second battery was invaluable, so I opted for a simple one battery system.

There are a number of misconceptions that often cause the DIY installer to go a bit overboard when hooking up extra batteries to their vehicle.  Most common is the concern that they need to replace their original equipment alternator with one of larger output.

This is totally inaccurate, because the amount of power that is being used while driving (excluding charging the house battery) really hasn't changed.  Upgrading the alternator will allow the battery to recharge faster, but is that really all that important?  Who cares if recharging the house battery takes 30 minutes or 1 hour if you're driving the vehicle while doing it?

The next often miscalculated installation mistake is the size of the cable running between the house battery and the original starting battery.  There is no need to install anything heavier than 10 gauge wiring going from the house battery, through the continuous duty relay, on to the starting battery.

Sure your starting battery is equipped with much heavier cable, possibly a 2 gauge or even larger.  The reason is, it's operating the starter.  The starter is the heaviest drawing item in the whole vehicle.  Your house battery will never draw that amount, unless you install a bypass switch to allow the vehicle to start using the house battery.  Not something that's needed if your starting battery is in good condition.

Using 10 gauge automotive wire, protected with a 40 amp auto-resetting automotive circuit breaker, is the appropriate way to supply recharging power to your second battery.  In fact, this is the way it will be installed if you take your vehicle to a certified RV dealership and ask them to install it for you.

For my needs, a smaller wattage inverter is more than adequate.  The only appliance I foresee using is my laptop computer.  For this, I purchased a 450 watt model from Sears for about $75.  One nice feature is it can be used simply by plugging into a standard 12VDC outlet... A cigar lighter, which is commonly fused for 20 Amps.

I have no need to run heavier cables from the second battery to this inverter, though if I chose to use my 1,500 watt inverter it would be a different matter.  If I was planning on installing a microwave oven, the larger inverter would be required, as well heavier cables between the inverter and the house battery.  For that reason it's recommended you install the inverter as close to the house battery as possible.  Long cables means voltage drop, and electronics don't do well running on low voltage.

Here again, let me restate that no matter what you're running off as large an inverter as you want, this in no way affects what size wiring needs to be installed between the starting battery and the house battery.  10 gauge wiring is the correct way to do it.  The only time the starting battery and the house battery are connected together is when the engine is running.  At that point you're only recharging the house battery.

Earlier I mentioned the continuous duty relay.  It's purpose is to connect your house battery to the starting battery when the engine is running, only for the purpose of recharging your house battery.

Because I used 10 gauge wiring I do not want to run  a microwave, or any other heavy drawing equipment, while the engine is running.  The charging wire is protected by a 40 amp circuit breaker so no damage can result, but there is no point repeatedly going beyond what it is designed to do.

The continuous duty relay is only activated when the ignition is turned on, so for the most part it is only energized when the engine is running.

On my particular vehicle, the Dodge Caravan, I am supplied with two 12 VDC power outlets down near the floor between the front seats.

The continuous duty relay requires very little power to turning on and off (energizing the electromagnetic coil within).

It was a simple matter to hook up a power plug to the relay and plug it into the port that is only energized when the key is on.

No digging around in the fuse panel looking for a source of power, I simply plugged it in.  Now everything about my house battery is automatic.

I can run my computer, or the 12 VDC portable fan I will be using for ventilation.  All done without damaging my new Dodge Caravan.


Mark Keeler said...


Could you provide a simple schematic for your house battery? What kind of battery did you use? I have a place on my Ford Club wagon that is set up to mount a second battery on the frame. I want to install a Fantastic Fan on the roof and run it off the house battery.

I like the looks of your Dodge! Looks like you are getting 30 MPG! My big Ford can sometimes hit 20 mpg.

Mark Keeler said...

Do you have schematics for your house battery? something real simple for dummies. I want to install a house battery on my Ford Club wagon to run our Macbooks, cell phone chargers, and other small thing. I also want to install a Fantastic Fan and run it off the house battery.

Curtis Carper said...

Mark, I'll put together a simple drawing and make a blog post out of it. Thanks for asking!

Meg said...

Is there a link to the simple drawing or post about the house battery? We are just about at that point to install one into our 07 chevy express.

Curtis Carper said...

Here's a link to the diagram for hooking up you batteries: