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Hellroaring Technologies, inc.

Polson, Montana  -  USA

Our Camper/Trailer Applications Page 

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Battery Isolator / Combiner Models:

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Application Notes for:

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High output Motorhomes

Popular Auxiliary battery Isolation

Trailer, Slide-in Camper mounted isolation

Tow Vehicle Backup system


Camper / Trailer Application Notes

rvpark.jpg (19800 bytes)When it comes to RV or trailer camping, the usage on your battery differs substantially from that of your vehicle primary starting battery.   When you set up for camp, you need lights, power for your water pump, maybe a fan, radio, or TV etc...   You operate these during times when the engine is not running.    During this time, your RV battery slowly empties its charge.   With your trailer or RV battery connected to your charging system, your starting battery will share the current to your loads.   The problem is, your starting battery was never designed to perform in this manner and, as a result, will fail early in its expected life.   The other problem is a little more serious.   You may be enjoying your stay so much that you stay put for a while.   Eventually you may run out of battery charge, leaving you stranded without starting power!   

People have utilized many different ways to save your starting battery from this annoying situation.   They have used diode isolators, relays with switches, relays wired to ignition circuits or accessory circuits, high current switches, or automatic  mechanical combiners.   Each of these methods have their own advantages and disadvantages.   Some are more complex than others.    Now, you have the choice of using a system with more advantages than ever before!    The Hellroaring BIC-75150A and BIC-75300A Battery Isolator/Combiners are the best solution on the market today.  

RV Starting Battery Isolation

For motorhome types with high output alternators and large house loads while operating, consider the RV starting battery isolation technique as a simple solution to multiple use batteries.  With this setup, a high output alternator can supply maximum charge current to large house battery banks.  All batteries receive proper alternator voltage from an internally sensed alternator due to the very low ON resistance of the BIC-75150A (less than 0.008 ohms).  Since there is no diode drop, the starting battery stays fully charged.  Electrical loads on either battery will not draw from the other.  If you choose this method, we recommend that you contact our technical support staff for assistance.

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Basic Auxiliary Battery & Trailer Application

For most applications, (i.e. slide-in camper, trailer, RV's with required continuous loads under 50 amps on the auxiliary side during engine operation, etc...) consider the basic deep cycle application.   Your primary objective is to prevent your  starting battery from draining while you consume power from your house (deep cycle) battery.   (Don't be fooled by low cost battery disconnect devices as a solution.  If you try to use these, your starting battery will get deep cycled and will result in early failure.)    You also want your house battery to obtain full charge as quickly as practical while operating your vehicle.   With the BIC-75150A installed as shown below, you will obtain those two objectives!   The BIC-75150A has very little resistance (less than 0.008 ohms) when ON during charging and it automatically isolates the two batteries when charge voltageBIC_small_photo.JPG (11235 bytes) stops, even if your alternator fails.   If desired, you will have the ability to combine the batteries manually for a starting boost (the main battery must still supply substantial cranking current).   It has no mechanical moving parts to degrade or wear out!  For those on a budget and who want the simplest installation, the BIC-75150A basic Auxiliary setup makes an excellent choice for full charging without the voltage drop or bulky physical size associated with diode isolators!  Works great for alternators sensed at the alternator output (internal sense.) 

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Trailer / Camper mounted battery isolation

With a Hellroaring BIC-75150A, you can install it in the camper itself. There is no need to alter the tow vehicle electrical system. Since the BIC-75150A is basically a DC Solid State Relay with integrated control electronics designed for dual battery systems, you do not have to run any wires from this isolator to the main battery!   Because it never receives all of the alternator output, it does not require ratings based on the alternator, like a diode isolator does. Rather, the BIC rating need only be higher than the maximum continuous current expected in the camper charge line.  And then, you normally protect it and the wiring by installing an in-line fuse or circuit breaker.    With common 10 AWG tow vehicle charge wire, this would be no more than 40 amps because this is the highest continuous rating for that wire.   This is well within the BIC-75150A continuous capability of 75 amps.  If you used 8 AWG, this would be 60 amps.  For those applications where even more continuous current is required, the BIC's can be wired in parallel for double or more capability. 

With this setup, you can connect your trailer to the tow vehicle and leave it connected for as long as you want.  The trailer loads will not drain your vehicle battery.   If your tow vehicle is already equipped with a towing package, you should have a charge wire available near the trailer hitch.  If you have sufficient alternator capability, you can increase your charge rates by upgrading the charge wire to 8 AWG, 6 AWG, or even 4 AWG. 

With the AC charger connected as in the diagram, you will charge your camper battery only.  If you connect it to terminal "A" instead, then you will charge the vehicle battery also.

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Tow Vehicle Backup Battery System

If you like to disconnect your trailer and drive around to enjoy the scenery, you will not have your trailer loads to worry about.   But, suppose that, while you are out and about, your alternator fails.   They always seems to fail at the most inopportune time.   You may not notice the problem until it is too late and your engine dies or will not start.   You may be parked 20 miles from nowhere, walk back to your vehicle after a nice afternoon fishing, and find your vehicle unable to crank.   It sure would be nice to have a spare battery at a time like this.   Then consider the Basic Backup Battery setup illustrated below.   With this setup you have an emergency backup battery that is always fully charged, even when you disconnect your trailer and your alternator quits.  

If you look closely at why you need an isolation system anyway, you will discover that it is for one primary reason.  That is; to have the ability to start and operate your engine when you have inadvertently drained your starting battery.     Most people only foresee the possibility that their house loads will drain the starting battery.   Because they aren't aware of other possibilities, their focus goes toward preventing that condition only.   We believe that you should not limit your security to only one of the possible ways to drain you starting battery.  When you spend time in the field, you should cover all likely possibilities, including alternator failure.   Those who connect relays to your ignition system obtain a false sense of security.  If their alternator unknowingly fails, their vehicle will continue to operate until both batteries are drained.    All the while they believed that their backup battery was being charged!    Our BIC units will protect a spare backup battery from discharge due to either draining your house/trailer battery, if your alternator quits, or even if your main battery effectively gets disconnected due to corrosion!

Consider this installation suggestion:

Suppose you install a super combination deep cycle/starting battery such as an Optima Yellow top as your starting battery (It is rated for deep cycle use, yet it has plenty of cranking power - 750 CCA.)   Then install, in your vehicle, a regular starting battery as a spare backup battery isolated with a Hellroaring BIC-75300A configured for high current.   With this setup, you don't need isolation tobic75300 -small.JPG (10033 bytes) your trailer or house battery.   You will always have a spare capable of cranking your engine!   If your house loads drain your starting (deep cycle) battery, you can, with the simple flip of a micro-switch, crank your gasoline engine  (You will need two units in parallel for a Diesel Engine.)  An added benefit to this system is that you will gain battery capacity by the amount of your main battery.    This will add life span to your batteries because you will not need to discharge either one as deeply than as with a single battery.   With this setup, you will need less circuit breakers, less hardware, less space, and will receive more security.

Sure, there are less expensive individual isolation products available.    But, none stack up to all the benefits that the BIC-75300A is capable of.   After considering all the parts and labor needed to perform the same functions, We believe this setup is one of the simplest, most convenient to use, most reliable, most economical and practical system available for Tow Vehicle applications.   

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Here is one very nice benefit from this setup.   If you use your tow vehicle in cold climates, then you can have double the cranking power when you need it the most as the temperature drops to below -10F.   There is no need to even get out of the vehicle nor open the hood!   Simply flip a micro-switch on the dashboard and you are on your way!   We believe that this is one of the very best setups available!

With this setup, we believe that you do not need isolation between the trailer battery and main battery for two reasons.  1) You will have the backup starting capability, and 2) The trailer battery usually is not connected all the time.  However, if you feel you must have isolation here in addition to having the backup capability, it is very simple to add a BIC-75150A between the alternator and trailer battery or in the trailer itself as described above.

If your application is extreme such that you want multiple and different isolated batteries/loads, you can add a BIC-75150A for each battery bank in addition to the BIC-75300A backup. 


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Last modified: 1/5/2008