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The Transit conversion has a different electrical system than most RV's. Most RV's directly connect the house battery to the vehicle battery with a relay for charging. There are several reasons why this is not ideal:

  1. House battery is not charged with a 3 stage (bulk/absorb/float) charger that is programed to match the charge profile recommended by the battery manufacturer.
  2. Not advised to connect two different type /size/age/mfg. batteries together for charging.
  3. A low house battery "state of charge" can put a heavy draw on the alternator.
  4. Large quage cables required to connect the batteries from front of van to the back house battery. 12 volt requires 10 times the wire size compared to 120 volt.
  5. House 12 volt system must be grounded to chassis.

Instead of connecting the batteries together I have a second 1000 watt "vehicle" pure sine inverter powered by the Transit 12 volt system. This provides 120 volt AC power with engine running. I use the output for three purposes. "Shore power" for charging or heating shower water or powering a electric baseboard heater. The 300 watt solar panel is my primary method of charging the house battery. The "vehicle" inverter can supply "shore power" for charging as a backup in case weather conditions require its use. The water heating is done in a stainless steel non pressure tank using a 625 watt heating element. The air heating baseboard heater is a 750 watt electric heater located in the back of the van. The design always uses a quality 3 stage charger to charge the house battery with the proper charge profile by both the solar controller or the house Magnum charger.

Below is the block diagram of the Electrical System:

block diagram drawing ODJ127-08.jpg

The Electrical System design has 3 selector switches to direct the power for different uses.

  1. A selector to choose either real shore power or "shore power" from the vehicle inverter.
  2. A selector switch to select charging or water heating or air heating. Only one can be used. Selector switch prevents two being used at the same time.
  3. A selector switch to select water heating with 120 volt power from 3 different sources. Shore power or vehicle inverter "shore power" or from the house 1000 watt inverter powered by the house battery. Depending on weather conditions, sometimes I can use the house battery for water heating if I know the sun will be out and I will have excess power available from the solar panel. If weather conditions do not permit using the house battery, I can run the Transit engine for about 30 minutes to heat water or from shore power.

Below is the Electrical diagram for the conversion:


To load file into your Adobe Reader program right click the drawing and "save as" a document on your computer. Then select the file and open it into/with the Adobe PDF Reader.

The Magnum MMS1012 is a pure sine 1000 watt "house" inverter/charger/transfer switch. It is a combination of a inverter/charger/transfer switch in one unit. It has both the ME-BMK battery monitor and the ME-RC50 remote. The remote is used to program the Magnum and as a display to show the "state of charge" of the house battery. It also can display amps in/out and totals etc. I could care less about what is happening. I just want to know how much of the house battery capacity I have used. The transfer switch in the Magnum allows one set of duplex plugs powered by either shore power or vehicle inverter "shore power" or 120 volt power from the Magnum inverter. The transfer switch just transfers available shore power through the unit if it is available without the inverter being on. In my case the inverter is always off unless I need 120 volt house supplied by the Magnum house inverter. Idling the Magnum consumes too much power to be left on.

The 1000 watt Magnum with my 255 amp-hr battery will power a 600 watt microwave. The Proctor-Silex (K-Mart) microwave draws 1140 watts. That puts the inverter into its surge capacity but it works.

The house 12 volt system is not grounded to the vehicle chassis. Two wires to every load. Does not require grounding because the house battery is not directly connected to the vehicle battery for charging.

The shore power connectrion is just a 3 prong male plug hung below the driver's door on a aluminum angle. Out of sight when not in use. Out of the weather when connected to an extention cord. A 15 amp shore power connection is all that is required for a small conversion. It is also more convenient for my use because I connect to houses more often than to an RV park 30 amp receptical. I do carry a 30 amp plug to 3 prong 15 amp adapter. I avoid RV parks as much as possible and prefer to dry camp with a stealth van.


The house 12 volt system is located in the center of the van to limit wire lengths and where I had space available. The 8D AGM battery is located in front of the driver's side rear wheel well housing under the bench seat. The fuse, disconnect switch, shunt, positive busbar and negative busbar are located above the battery and below the seat top. The 1000 watt Magnum MMS1012 inverter/charger/transfer switch is located above the left wheel well housing. The longest # 2 AWG cable is about 17" long.

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Below is the Electrical diagram for the HOUSE 12 VOLT SYSTEM:


To load file into your Adobe Reader program right click the drawing and "save as" a document on your computer. Then select the file and open it into/with the Adobe PDF Reader.

Wanted the 8D battery inside to limit the cable lengths and eliminate the holes in the floor. Bought the 255 amp-hr 8D instead of multiple batteries to keep the wiring simpler and to make it easier to install. The 8D is oversize for my application. The oversize battery may be the reason I can power a 600 watt microwave.

The Magnum inverter/charger/transfer switch also makes the system simpler. I can power the charger either from shore power or "shore power" from my second vehicle powered inverter. The 1000 watts will also just power the 600 watt microwave. Microwave draws 1140 watts which puts inverter into the surge capacity of the Magnum. Once ran the same combination for 10 minutes in the Sprinter conversion. I like the transfer switch function. If 120 volt shore power is available, then the Magnum just passes the power through the unit to the duplex plugs without the inverter turned on. One set of daisy chained 120 volt duplex plugs are connected to the Magnum. They are either powered by shore power or from the Magnum when it is turned on. The house electrical cabinet is located at bottom of the refrigerator wall. It has the 12 position DC fuse block, the Morningstar solar controller, the battery conditioner and the shunt controller on the panel. The 12 volt house battery power is connected to a Blue Sea # 5026 twelve position fuse block. DC loads on the left side of van are powered from the 12 position fuse block. A second Blue Sea # 5025 six position fuse block is located on right side of van under the sink and powered from the 12 position fuse block. The DC loads on that side of the van are powered from the the 6 position fuse block.

The house 12 volt system is not grounded to the chassis. Two wires to every load. The system would work if it was removed from the van and set on the driveway. The reason it does not need to be grounded to the chassis is I do not directly charge from the vehicle alternator. There are three methods of charging the house battery. The primary method is the 300 watt solar panel. If that does not provide enough power, I can use the Magnum charger function. The charger can be powered by shore power or "shore power" from the vehicle powered second inverter. All charging is done with a quality 3 stage charger that is programmed to match the charge profile suggested for the 8D battery. The house battery is never directly connected to the vehicle battery. My experience with the Sprinter's 205 watt solar panel was I did not need to use the second inverter's "shore power" for charging. The "shore power" is a backup in case of extended grey days. Last year of Sprinter conversion never required the use of the backup charger.

All wiring in the van is done with "SO" cords instead of wires in a conduit. The cords are much easier to run and can make sharper turns. No wiring buried in the walls. All cords are run behind or inside the cabinets. The only wire that is buried is the cord to the Maxxair fan in the ceiling. There are three cords that run across the van in the floor to get power to the right side of van. Two for AC and one for DC. The DC powers the six position fuse block, one AC cord powers the electric heater and the second AC cord powers the duplex plugs on that side of the van.


The vehicle powered inverter is a pure sine 1000 watt Samlex SA-1000K-112 with a S-R8 remote control. It is installed behind the driver seat on the shower enclosure wall. The inverter is powered by the three Ford 60 amp CCP terminals that are on the back of the seat pedistal. Have three # 6 AWG cables from the Transit CCP 3/16" studs to a four stud Blue Sea # 2307 positive bus bar with 1/4" studs. A # 2 AWG cable is bolted to the fourth stud and goes to a FB-a fuse holder with 3/8" studs that holds a 150 amp class T fuse. A # 2 AWG cable goes from the fuse holder to a Blue Sea # 6006 on/off battery switch that has 3/8" studs. From the switch to the inverter positive post there is a # 2 AWG cable with 5/16" connector. The inverter negative cable with 5/16" connector goes to an existing 3/8" diameter hole on the emergency brake bracket. Negative cable goes down to the floor from inverter, across the floor behind driver seat and then under the Ford emergency brake plastic cover. Had to modify the cover for cable entry.

The cables were made by the local Interstate battery store. First step is to measure the diameter of all the studs and determine if a straight or 90 degree cable end is required. Second step is to use a string to measure the distance from one stud to the other stud. Then I cut a cotton rope to that length and double checked that it was the correct length. Next I put a red or black tape on each rope to denote color wanted. Added a piece of tape on rope to specify the wire size. At each end of the rope I put a tape to denote the size of the connector and if it is a straight fitting or a 90 degree fitting. Take the ropes to Interstate and they make the cables. All the cables were made correctly. Only problem I had was the three cables from the CCP could not have 90 degree connectors that I wanted on the bus bar end. Had to add an angle to remount the bus bar to turn it 90 degrees. A picture shows what the ropes look like with the tags.

The S-R8 remote is mounted on the base of the driver seat pedistal between the pedistal and the emergency brake handle. Raised seat 13/16" with spacers to access the existing holes in the seat pedistal. The S-R8 has a pushbutton to start/stop the inverter and also has a spade terminal that can turn on the inverter automatically when 12 volts DC is supplied to the terminal. One of the "user defined" dash switches is used to supply the 12 volt signal. The connector for the four dash switches is under the driver seat on 2015 Transits. Bought Ford part # WPT-1408 which is the male connector for the underseat female socket. The WPT-1408 connector has four wires supplied with the connector. I bought a 4 position Blue Sea part # 2504 terminal block and mounted the block under the emergency brake plastic cover behind the emergency brake. The four wires from the connector go out an existing slot on the back of seat pedistal and down to the terminal block. Put a rubber grommet around the four wires at the slot. Ford wires were the correct length to reach the terminal block. The terminal block is parallel to the dash switches and the wires were attached to the block in same order as the dash switches. Used the # 1 dash switch so used the terminal closest to the seat base. From the terminal block the wire goes to a "on delay" timer relay also mounted under the emergency brake cover but in front of the brake. Wanted to delay the start of the vehicle powered inverter so engine is running before inverter starts. Wanted to avoid a inverter electrical load on the batteries when engine is being started. Tried a Dayton # 2A562 time delay relay between the terminal block and the remote. That did not work because a solid state time delay has enough current leakage through the relay to trigger the Samlex remote "ROF" terminal. Had to change to a different time delay with mechanical contact points. The new relay that worked is a Dayton 21EP67. The manufacturer of the relay is Macromatic and their part # is THR-3816U.

When #1 "user defined" switch is on then there is a 30 second time delay before the inverter starts. If the #1 "user defined" switch is off then the inverter can be manually started/stopped with the remote pushbutton. If 12 volts is supplied to the "ROF" terminal then the start/stop remote button is inactive.

The cost of the vehicle powered inverter was:

Inverter and remote: $406.25

4 position terminal strip: $18.45

Class T fuse and holder: $45.07

Blue Sea battery switch: $24.81

Time delay relay: $53.65

Total cost about $650.

The vehicle powered inverter is used for three purposes when the Transit engine is running. A four position selector switch is used to direct the 120 volt AC power for house battery charging or to heat shower water or to heat air with a electric baseboard heater or off. When power is sent to the house 1000 watt Magnum MMS1012 inverter/charger/transfer switch, the duplex 120 volt AC receptacles in the van are also powered while you drive.

Using the vehicle powered Samlex inverter output to power the Magnum house inverter always charges your house battery with a three stage (bulk, absorb, float) charge profile that matches your battery design. That does not happen if you directly connect your house battery to the vehicle battery for charging. The Transit engine with the vehicle powered inverter eliminates the need to carry a generator.

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The selector switch panel is installed at the top of the shower enclosure wall behind the driver. The controls are read from the shower side of the wall. Water will not reach that area.

The items on the panel are:

1. Three position selector switch to select shore power or vehicle inverter power or off.

2. Four position selector switch to select charging or air heating or water heating or off.

3. A 15 amp double pole circuit breaker for shore power.

4. The Magnum ME-RC50 remote control for the Magnum house inverter.

5. A digital voltmeter to show the Transit battery voltage.

6. The male end of the pull out power cord for the water heater heating element.

The enclosure front panel can be removed for access. There also is a removable panel on the driver side of enclosure for access. All the power cords are tie wrapped to the outboard 80/20 vertical extrusion up to the panel. The water heater power cord pulls out from the panel across the shower and can be plugged into either a duplex outlet powered by shore power or a second duplex outlet powered by the house battery/inverter. Wanted to be sure to unplug the water heater before showering so bright orange cord reminds me to do that. There is also a indicator light to tell me when the water heater is heating water. When it goes out I know I have 6 gallons of shower water ready for use.

Shore power must be available or the engine must be running with vehicle powered inverter on to power water heater from the shore power outlet. The water heater can also be plugged into a duplex outlet powered by the house battery/inverter. The house inverter has to be turned on to power this duplex outlet. When weather permits and I have excess solar power, I can heat water from the house battery. Water heating can be done with the house battery without needing to run the engine. Water heating with the house battery uses about 10% of the 255 amp-hr battery capacity to heat 6 gallons.

Had two problems wiring this panel. Found out the Magnum house inverter does not actuate its transfer switch if the Magnum control panel is not connected. Second problem occured when I removed the two jumpers that were installed on the four position Blue Sea # 9010 selector switch. Found out they need to be left installed for the switch to function correctly.

Completed panel lets me select where the power comes from and to send the power to the Magnum inverter/charger/transfer switch or the air heater or the water heater. Due to the size of the 1000 watt vehicle powered inverter only one item can be used at the same time.

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© Dave Orton 2015   © Dave Orton 2016   © Dave Orton 2017      All Rights Reserved