I N V E R T E R S   3 0 1

By David Parsons       

In my first article, Inverters 101, I went over the terminology commonly used when discussing inverters.   In the second article, Inverters 201, we discussed the settings normally used with your Magnum Remote, and posted the recommended settings.  In a few cases, my recommendation is somewhat different than that published by Fleetwood.  In each case my reasoning was explained as best as I could.  I hope everyone has digested all this information, but if you still have any questions or confusion, please do not hesitate to send an email for further clarification.  All feedback is appreciated, and it will help me formulate an answer that can be understood by all.  OR – find out why my reasoning or explanation was faulty.

 

OPERATION:  Operation of your inverter/charger is quite strait forward.  Turn both on and forget it.  Mine stays on, mostly untouched, 24/7/365.  The only adjustment needed is if you plug into LESS THAN 30 amp power.  In this case the SHORE setting must be changed to match the incoming power supply.  Don’t forget to put it back to 30 A when going back to normal 30 or 50 A power.  For extended dry camping, you might need to change your BATTERY AMP HOURS setting in the setup menu.  This was discussed in INVERTERS 201, so will not repeat here. 

 

Another important concept we all must understand is the technical differences between 50 amp and 30 amp power.  This can be very important in understanding how an inverter, and related systems, works.  On our 50 amp power input, there are 4 wires; namely 2 hot wires, called L1 and L2, neutral (white) and ground (green).  The ground wire is sometimes a bare copper wire.  Note that both neutral and ground are at 0 volts.  But they are for entirely different purposes.  The green ground wire is for safety reasons, and should never carry any current (amps).  The white neutral is the current carrying return line for the current coming in on the hot leg(s).  Because the green ground is not directly involved in loads or current carrying functions, it is usually left out of the discussion.  But its safety function is very important.  Don’t ever operate without a proper ground.

 

On 50 amp circuits, with 2 hot lines, (L1 & L2), each line is capable of handling 50 amps, for a total of 100 amps available to use in the coach.  L1 and L2 are 180 degrees out of phase, which causes a couple interesting effects.  With a voltmeter, you will measure 120 VAC from either L1 or L2 to neutral.  This is what feeds your  120 volt circuits on the coach.  If you measure directly from L1 to L2, you will get 240 Volts, although we do not directly use 240 V anywhere on the coach.  The control circuits do use that feature to automatically determine if the coach is plugged into 240V / 50 A power, or 120 V / 30 amp power.  The other interesting fact is that the neutral leg will only carry the difference of the current that is coming in on legs L1 and L2.  For example, if you are pulling 30 amps on line 1, and 25 amps on line 2, 25 amps will be travelling back and forth (alternating current) between L1 and L2, and only 5 amps will be on the neutral leg.  Going to extremes, if you are using 50 amps on L1 and 50 amps on L2, you can see how it is all circulating back and forth on L1 and L2, and no current is flowing in the neutral leg.  If you use 50 amps on L1 and 0 amps on L2,   there will be 50 amps on the neutral leg.  Thus it can be seen that when buying new wire, even though you have a 100 amp capacity, all wires must be sized for 50 amps. 

 

On a shore 30 amp circuit there are three wires;  a hot wire (black), a neutral wire (white), and a ground (green, or bare).  If you use a (30A / 50A) pigtail/adaptor to plug into 30 amp power, that pigtail will connect both L1 and L2 together, and to the hot line from the pedestal.   Thus on the coach, your L1 and L2 lines will each read 120 V to neutral, but if you test from L1 to L2, your reading will be 0.  This is how the coach automatically knows you have 30 amp power, or less.  But the coach now has no way of knowing if it is a rating lower than 30 A.  If so, you must set that in manually on the Intellitec EMS load meter.  Note that electrically speaking, there is no way to tell the difference between 30 A, 20 A, or 15 A.  They all have the same 3 wires.  It is a matter of circuit breakers and wire sizing.  The physical plug may also be different.

 

Sorry about the electrical lesson above, but understanding those differences will be necessary to understanding how our inverters are set up, and operate. 

 

If you are plugged into 50 A power, it would seem that with 100 amps available, there is nothing to worry about.  Wrong!!!  The weak link is the inverter itself.  On your main panel is a 30 amp circuit breaker feeding the inverter.  Remember that when plugged in, the inverter is actually charging the house batteries.  All other inverter loads will be passed through the inverter directly to the inverter sub-panel and to its loads.  And if the total of all that exceeds 30 amps, you will surely trip a circuit breaker.  And it is usually the hard to find one on the inverter.  So let’s take a detailed look at what is powered from, or through, the inverter. 

 

1)      Battery Charger

2)      Microwave

3)      Galley 120 V receptacles

4)      Coach left side 120 V receptacles

5)      Coach right side 120 V receptacles

6)      Central vacuum cleaner system 120 V receptacle

7)      Ice maker 120 V receptacle

8)      Water bay and other bay 120 V receptacles

9)      TV & entertainment 120 V receptacles

10)   Engine block heater 120 V receptacle

 

As you can see, when plugged into shore power, the inverter is feeding a lot of stuff, besides the battery charger.  It takes very little effort to exceed the 30 amp limit.  Some of the above, plus:  A coffee pot, a space heater, a hair dryer.  They all add up!  Assuming you have the SHORE set properly, the Magnum Remote Control will automatically cut back on the battery charging, but the other 9 items on the list above can easily exceed 30 amps.  It behooves you, the operator, to manage your power usage to avoid tripped circuit breaker(s).  If plugged into 30 amp power, OR LESS, it becomes even more important that you how these circuits work, and to manage power usage so as to avoid tripped circuit breakers. 

 

LOAD SHEDDING:  The Intellitec Smart Energy Management System  (EMS) is an excellent system, and does a wonderful job, but is very easy to defeat.  It is certainly NOT a complete answer to all your overload woes.  Note that it WILL NOT WORK at all when you are plugged into 50 amp service.  What does it do?  It will shed (shut off) selected equipment if it senses an impending overload when plugged into 30 amp service or less.  It will not allow the equipment to restart until the total load had dropped enough for the load to be restarted.  Read your EMS display panel to see what, and in what order equipment is shut down to reduce the load.  Then you must carefully consider what IS NOT on that list.  First off, the 10 inverter items listed above WILL NOT be cut off.  On my coach, the #1 air conditioner WILL NOT be cut off.  So you can see there is a good chance that even with everything on the EMS list shut off (shed) you can still exceed 30 amps, and trip circuit breaker(s).  It behooves you, the operator, to manage your power usage to avoid tripped circuit breaker(s).

 

LOOSE ENDS:  When making the Amp Hour setting in your Magnum Remote, I previously mentioned that you should use the house battery capacity only.  The reason is that you are probably only charging the house batteries.  The engine batteries are just floating along.  And the only time this might seem to be a factor is if you have been dry camping.  But think about this:  During the night you may have run the house batteries down to 50%, but the engine batteries were not in use.  They should still be nearly fully charged from yesterday.  But to me, this is a moot point, as I set my Amp-Hour setting to what I NEED, not what some EE in Decatur says, when he has no idea how I use the coach.

 

The above 50% is another factor I have mentioned a couple times, and would like to explain.  In the interest of battery long life, battery manufacturers usually recommend never allowing a battery to be exhausted below 50% capacity.   Capacity being AMP-HOURS.   A battery bank of 4 - Group 27 AGM  batteries will have a capacity of about 400 amp-hours.  Thus you should never pull more than 200 amp-hours out of the batteries before recharging.  But most of us have no way of measuring amp-hours used while dry camping.  Reading the 12V amps on your Magnum remote, and multiplying that by the hours in use will give you a very rough idea of amp-hours, but that is only what the inverter is using, and does not include the other 12V loads.  A better method is to read your house battery voltage.  When it drops to 12.0 V, it’s past time to recharge.  Even that number is iffy.  If you are using a higher than normal load, the voltage will drop faster, then recover when the load is removed.  Turn on the microwave for 30 seconds, and watch the battery voltage drop!

 

Another caveat I should mention is that all the above assumes you have good, properly installed, batteries.  Old or weak batteries and/or loose or corroded connections can cause all sorts of problems.  I cringe whenever I hear:  “My batteries are 10 years old and doing great.”  That is a catastrophe about to happen and probably at the worst possible time or location.  A 36 month battery is good for 3 years.  After that you are on borrowed time.

  

As always, if you have any questions, comments, corrections, or suggestions, please send me an email.  Or knock on my door at Marksville, or Montgomery, or Searcy, or Sevierville, or even Madisonville.

 

Dave Parsons

DavidTish@aol.com