DC Electrical Knowledge

Berkshire DC Electrical System

Or more correctly the DC Electrical Systems, as in two: House and Chassis. (Forest River and Freightliner respectively) and only in one place do they meet.

Chassis 12VDC Electrical System

Not unlike your car the 12VDC chassis system generates 12VDC with the alternator mounted on the engine. It stores power in the Chassis Battery Bank, located in an outside compartment near the engine. There’s a cutoff switch, and then a supply of 12VDC to the engine computers, and a variety of chassis lights (headlights, tail lights) the radio when driving, the wipers, dash A/C system and a few other things. There’s power modules and control boxes all over the chassis. There’s a fuse box in the outside compartment under the drivers window. The Chassis Battery Bank is generally two 12V sealed, maintenance free batteries. And that is about it…..little or no maintenance as long as everything works. One common problem around the 2017-2019 model years has been with the Rear Power Distribution Module…. I replaced mine.

House 12VDC Electrical System

The house system is more involved. It powers all the house lights, awnings, furnace, water pump, radio when not driving, the Inverter when no Generator or Shore power is available and selected on, and a few other things.

Energy is stored in the House Bank. An in depth description of the house bank is part of my “Battery Monitoring Kit” writeup, and there are maintenance tips HERE. The house bank is charged by the alternator when driving, or by the I/C when Generator or Shore power are available and the charger is selected on. This is, once again, controlled by the Magnum RC50 remote control panel.

And now things can go one of two ways:

On the pre-mid 2017 (depending on model) coaches the 12VDC goes to fuse panels located in the outside compartment under the drivers window, and then to the various users, with regular switches controlling their operation.

And on the new(er) coaches it goes to the Precision Plex system, which is the brand name for the Multiplex System that controls the 12VDC house system. Whereas the old system is a source (battery), switch and say a lightbulb, on a multiplex system the switch is on a computer network and sends a signal to the “brain” which then in turn sends electricity to the light bulb. There’s a variety of reasons for this design, but one of the major ones is that, just like your car, you can now program a host of features into the system. And, you can control the system not just from switches but also through digital interfaces like the touch pad mounted on the wall, or an app on your smart phone. Sensors collect data for display for, say, tank quantities. A/C controls, awnings and slides are now controlled through the system. The brain and various modules are usually located under the bed with fuses for the individual circuits. At this point this is as far as I will go into the system.

Much of managing the House Battery Bank is done through the Magnum RC50 remote control. At the risk of sounding like a broken record I  HIGHLY recommend reading the manual for this.

The (Smart) Battery Isolation Manager

On my coach it’s the black square “box’ above the house bank. Newer coaches have a different looking device, it does the same thing.

Screen Shot 2017-07-13 at 7.22.07 PM

Above I said that there is only ONE place where the two 12VDC Systems (Chassis and House) meet, and this is it. (Actually not quite true, but true enough for now). The Battery Isolation Manager (BIM) is a relay that connects the two battery banks. It monitors voltages in both banks, and based on that information it closes the relay and connects the two. It does this as follows:

  • Driving, after the Chassis bank (which was used for starting the engine) has been replenished the alternator also charges the House Bank.
  • Parked with engine off the BIM isolates the two banks, so you cannot accidentally drain the Chassis Battery overnight and not be able to start your engine in the morning.
  • But, if there is Shore or Generator power available and the Battery Charger has charged the House Bank, the BIM will close occasionally to keep the Chassis Bank topped off.
  • You can force the BIM closed with the Emergency Start Switch on the dash board. If, somehow the Chassis Bank got low you can tie in the House Bank to help start the engine. Or, if the House Bank is low, you can tie in the Chassis Bank to help start the Generator. (It starts off the House Bank)

Anytime the BIM has closed to combine the two banks you’ll see an occasional flash in the Emergency Start Switch.

So that’s the basics on the DC systems. Again, please read the Magnum RC50 remote manual. The remote is critical in managing these systems.

I will update these pages as topics come up.