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D a v i d   P a r s o n s            

 

 

 

 

 

 

 

 

This article is written to go over the basic terminology and operation of our inverters.  But first let me say that although I have installed & operated inverters in other equipment for many years, this is my first American Coach (2006 Tradition).  It has a Magnum 2500 watt inverter, which is still being used on newer coaches.  Older coaches may have different brands of equipment, but the basic terminology and operation will be the very similar. 

 

“Inverter” is how we usually refer to this piece of equipment, but it is actually an inverter/charger.  It can either invert or charge, but never both at the same time.

 

Following is a list of terms and their definition.  We all must understand what these terms are, or mean, before we can get into how they relate and operate.

 

Inverter:  Inverting power is taking 12 VDC from the batteries and making 120 VAC for use in limited services (via the inverter sub-panel) in the Coach, when there is no shore or generator power available.

 

Charger:  This is nothing more than a simple battery charger that takes 120 VAC from the shore or generator, and converts it to 12 VDC to charge the batteries.  It was usually called a “converter” in years past.  A battery charger from Wal Mart or an auto store does the same thing. 

 

Current or Amps:  It is interesting to note that when inverting (dry camping) it takes 10 amps of current from the batteries to make 1 amp of electricity for house use.  You will pull over 150 amps from the batteries to run the microwave.  A huge load you don’t want to do very often.

Going the other way, 1 amp of 120 v electricity will produce 10 amps of battery charging current. 

As you can see there is a 10:1 ratio difference between AC and DC current.  So when discussing amps or current, you must be sure you and everyone clearly understand whether it is AC or DC.  Above amperage conversions are disregarding efficiency.  Output will always be slightly less.

 

Pass Through:  When on shore or generator power, and in the charging mode (no inverting) the unit will simply pass 120 VAC through the unit to the inverter sub-panel. 

 

3 Stage:  Our chargers are actually much better than the older converters in that they charge the batteries faster, then taper off to no charge to prevent overcharging the batteries.  This is done in 3 stages:

1.        Bulk charge.  This first stage pours the charging current to the batteries.  Could be 100 amps or so depending on the units rating and settings.  Battery voltage will run up to about 14.3 V during this stage.  The time for this stage will depend on the battery state and condition , but is usually in the minutes, or even seconds.

 

2.       Absorption charge.  This 2^nd stage will maintain the battery voltage at, but not exceeding, the high value, so the batteries can be charged at maximum rate.  As the batteries get recharged, the charging current will taper off so as to not go over the 14.3 V maximum battery voltage.  The time for this stage again depends on the battery state and condition and controller settings, but can be an hour or 2 or more.

               

3.       Float charge.  This final and long term charging state drops the battery voltage to about 13.4 volts, and will supply only enough power to match what you are taking out of the batteries with 12 VDC loads on the coach.  Thus the charging current normally runs from 0 to 10 amps or a little more, depending on how many lights you have on.  I recommend leaving this on forever.

 

Sine wave:  Until the last few years, all inverters produced what is called a “modified sine wave”.  Those inverters could not produce a smoothly changing sine wave.  It was a boxy shape, sometimes called a square wave, to produce alternating current.  Worked fine for most applications.  But as many found out, heating element units such as a coffee pot or an electric blanket did not like this at all and frequently suffered an early demise.  Newer inverters now produce a “pure sine wave”.  This duplicates a normal sine wave, and is greatly preferred. 

 

Inverter Sub-Panel:  On your main power panel, one of the circuits is to feed the inverter/charger.  It is usually a 30 amp breaker.  When on shore or generator power, this breaker feeds 120 VAC to the charger  side  of  the  inverter  to  charge the batteries.  And, through relays in the inverter, also feeds 120 VAC power directly through the inverter to the inverter sub-panel.  On older coaches this sub-panel may be under the bed as part of an inverter upgrade.  On newer coaches it is part of the main panel, usually having 4 breakers on one side of the panel.  It is important to note that these sub-panel breakers feed the microwave and virtually every 120 VAC outlet on your coach, including the TV and entertainment systems. 

 

Shore power:  Note above where I refer to incoming power as “Shore or Generator Power”.  For most discussions about equipment relative to 120 VAC, the equipment does not care, or even know where the 120 VAC is coming from.  So switching from one to the other as a troubleshooting technique is of little value.  Notable exceptions are where they come into the coach at the ESP system, or a suspected shore power problem.

 

Magnum Energy Inverter/Charger and Remote Control.  This is the heart of the Inverter/Charger.  Learning all the proper settings, adjustments, and operation of the controls will be discussed in the next article. 

 

BCC:  Battery Control Center, manufactured by Intellitec.  This is a small metal box mounted near the inverter and batteries.  The electronics in it control the charging of the “other” bank of batteries.  When plugged into shore power (or generator) the inverter/charger will charge the house batteries; and through the BCC, charge the engine (Chassis) batteries.  When the engine is running, its alternator will charge the engine batteries, and through the BCC, charge the house batteries.  Although there are several fuses inside the BCC, there are no operator adjustments, and the BCC is rarely opened. 

 

                Big Boy Relay:  This is the heavy duty relay inside the BCC that physically connects the 2 battery                 banks together.  Sometimes called the  isolator, aux start, or combiner relay, or possibly            other     local names.  Mfg is Big Boy, so I prefer that name.

 

EMS:  Energy Management System, also manufactured by Intellitec.  This system consists of your main electrical panel, with the above mentioned inverter sub-panel, and the Smart EMS Load Meter display.  Although it is not directly involved with the inverter & charging systems, its function of energy management and load shedding is closely related.  How they work together, and their relationships will be discussed in a later article.

 

ESP:  Electrical System Protection.  As I did refer to the ESP above, I did want to say it is the box where the shore power and generator power cables come together, and sometimes called the transfer switch.  It controls the use, or non-use, of power and has a VAC meter mounted on the side of the bed, or in the display at the front of the coach.  It is not involved with the inverter or charging systems, and will not be discussed further. 

 

Above is the first in a series of articles I hope to write in a how to, or Q&A series.  Next month I will get into the set-up of the Magnum Remote Control and the everyday operation of your Magnum Inverter/Charger.  If you have any questions or comments or corrections or suggestions, please send me an email.  Or knock on my door at San Antonio, or Marksville, or even Madisonville.

 

Dave Parsons

DavidTish@aol.com