I've pretty much completed the design of Blue's electrical system and am busy putting it together. I probably won't get all of it completed by our departure date of May 1, but I should have the essentials. In this blog, I'll describe the ac side of things.
I borrowed heavily from Dave Orten's design. He did a conversion on a Mercedes Sprinter which he used for awhile and then sold. He's now working on a new conversion using a Transit. I like many of his electrical ideas, which he has generously shared in his website and on the Ford Transit Forum.
Shore Power and Breaker
I kept a 30 amp electrical cord that was a spare on Nine of Cups that we'll use when shore power is available. I'll be buying a 30 amp to 15 amp adapter so that it can be used on a normal household circuit as well. Until we install an air conditioner or need to run a space heater, a 15 amp circuit should be adequate for our needs. The incoming shore power is routed through a double pole breaker. The double pole is necessary to open the downstream circuits in the event of an overload if the hot and neutral wires are reversed. The breaker, a Blue Sea 8077 also has power and reverse polarity indicators.
Alternator and Inverter
We will have an inverter powered by the Transit's oversized alternator. This is a Xantrex ProWatt 1000 watt sine wave inverter. A 1000 watt inverter is about the maximum I'd want to draw from the 200 amp inverter without a risk of overloading it. Also, the Transit has three 60 amp, user accessible circuits connected to a terminal block next to the driver's seat. By combining the three circuits, they provide enough current to power the 1000 watt inverter, making the installation easy. The three circuits will be connected together on one side of a 150 amp breaker, then connected to the inverter input. We also bought the remote for it, which can be controlled by an external 12vdc signal. By connecting it to one of the auxiliary switches on the dash, it will only run when the ignition is on and the auxiliary switch for it is turned on.
I'm not sure what happens if the incoming shore power is connected to the output circuitry of the inverter. It's probably not good if the inverter is shut down, and it certainly can't be good if the inverter is also running, which could very well occur if we were connected to shore power and decided to switch on the ignition. Much worse, a potentially deadly situation could occur if the inverter was powered on and one end of the shore cable was connected to Blue – energizing the male prongs on the other end of the cable. Thus, it's essential to isolate the two ac sources, and to accomplish this, I'll install a selector switch that has three positions: Shore Power, Inverter, and Off. The selector switch I've ordered is rated for 30 amps.
On Cups, we had meters that showed the incoming voltage and the amount of ac current we were consuming. I found these quite useful. I always knew at a glance whether we were getting close to a brown-out condition. I also knew whether we needed to juggle the electrical loads to avoid exceeding the 20 or 30 amp limit of our shore power - or the 12 amp limit of our onboard inverter. Should we run the heater at half power while the battery charger is running? Can we run the fridge, battery charger and both laptops at the same time? When using the Xantrex inverter on Blue, we'll be even tighter on our power budget than we were on Cups, since it's only rated for a continuous output of 900 watts or 7.5 amps. I've ordered the Paneltronic 9982304B, which combines the two meters on one panel.
AC Breaker Panel
I ordered a Paneltronic 9982305B with space for six circuit breakers as the main ac distribution panel. Initially, only two circuits will be used, one for the refrigerator and one for the Magnum inverter/charger. Three more of the circuits may eventually be used for a small water heater, an air conditioner and a microwave, if and when we ever get to them and still think they're important after a few forays with Blue. The sixth space is for future expansion, in case we think of something else – a pressure water system maybe.
Magnum Inverter, AC Transfer Switch and Charger
The Magnum MMS-1012 is a cool device. When it's turned off, it becomes a simple transfer switch that passes the ac on its input directly to its output. If it is turned on and there is ac present on its input, the ac is passed to its output as before, but it also becomes a 50 amp, three stage battery charger to recharge the house batteries. Finally, if it is on and incoming ac is lost, the Magnum switches to inverter mode and provides 1000 watts of pure sine wave ac. This part of the circuitry was originated by Dave Orten, and I really like it. I'll talk more about the battery charger and monitoring features, and why I decided on having two inverters in next week's blog.
The ac output from the Magnum must have overcurrent protection. I added a Blue Sea 7235, 15 amp double breaker.
Four GFCI protected outlets will be installed to provide power for laptops, tools, kitchen stuff, etc.
Next week, in part 2, I'll talk about the dc circuits, including the house batteries (which ones I chose and why) and the charging systems.