adding a house battery and inverter etc.. to a bus conversion

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wnyma771

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Apr 20, 2010
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I recently bought a 1991 Ford E350 7.3l diesel 25 passenger bus that im converting to an rv. I have a decent knowledge of regular 12v car systems, however adding house batteries and inverters is a little foreign to me. I read up on some other forums and how to's but i still dont know exactly what i need and how to accomplish it.

Basically i want to run a 1000w home stereo system/dvd player and 32 inch lcd television. I have been told it is not good to parallel your house batteries with your starting/chasis batteries. However I would like for my alternator to charge my house battery as the stereo and tv will draw the battery down quickly. How can this be accomplished? could i parallel my chasis batteries to my house battery if i used an isolator? Could i hook up my house battery directly to my alternator? Is there some other charging option besides running a generator or line power? I realize i would need a generator or line power while the engine is not running.

Obviously i would need an inverter hooked up to my house battery, and probably a large one. Is a pure sine inverter necessary for optimal performance? I am aware of the cost issue.

Is there anywhere i can look for diagrams that explain how house battery, inverter, generator, line power could be installed. This is a side project and as im sure you all know its an expensive one so im trying to do it all myself with no professional assistance ($). Any help would be greatly appreciated.
 
There are several articles in our forum library that might help; Click the Library button above and look in Electrical power systems and hookups and Batteries and DC (12V) stuff.

 
Yes, you need an isolator between the engine batteries and the house batteries.  Many RVs use a device called a BIRD, a Bi-Directional Relay Delay, with a large solenoid to actually switch the power. It enables the alternator to charge the house batteries and shore power to charge the engine batteries.

Intelletec makes a variety of devices like this - see:

http://intellitec.com/pdfs/BATTERY_web/5300366.000.pdf
http://intellitec.com/pdfs/BATTERY_web/isol.htm

Intelletec makes a number of products you may find useful in your conversion. See the entire list here:
http://intellitec.com/products.htm
 
Some electronics don't function well on modified sine wave (MSW) while others work just fine. Mostly it is cheap "wall wart" power supplies that have a problem - computers and audio systems usually work fine because they have excellent power filtering and control built in.

The inverter size is driven by the total power demand. Usually a stereo and tv don't need that much input wattage (check the UL label to find out), so 1000W should be plenty. But if you also want to run a coffee maker or microwave once in awhile, you better go for at least 1500W. Equally important is the size of the battery bank.  A 1000W inverter draws nearly 100A @ 12v, so a single battery cannot cope for more than a minute or two. Even two batteries isn't enough, so you better think in terms of 4 or more, depending on the length of time and the average power draw.

You also need to insure that the inverter NEVER attempts to power the outlets while shore power or generator power is present. Nasty things will occur if that ever happens, even for a second. That means you need an automatic transfer switch or some foolproof manual of changing from shore/generator to inverter.  Elegant inverter/chargers typically have a transfer switch built in but are expensive, while basic inverters do not but are quite cheap.  We can discuss wiring alternatives for this when you are ready.
 
There is a positive cable coming from the chasis battery to a soenoid that is activated when the key is turned on. The solenoid is then hooked to a fuse panel to run the radio, interior lights etc... Would this be an isolator or a BIRD?
 
No, that is just a relay to control the power to those devices.  It's necessary as the ignition switch isn't able to handle the current draws of all the 12VDC devices connected through the relay.

An isolator is to allow charging of multiple battery banks from the same charging source without a permanent connection between the banks.  It connects the chassis and house battery banks to a charging source, like the alternator or the RV built in charger.
 
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