The opportunity when off-grid is that there are several options for dealing with a limited supply of electricity. There are 12V and 120V needs.

My Sprinter Class C motorhome has a diesel engine. The onboard generator (Onan) runs on propane. The diesel version was unreliable and was discontinued. Therefore, when off-grid, the refrigerator, furnace, range and generator all run on propane. Running out of propane (40 lbs / 9 gal) would be a problem. The generator (120V AC) will run for about 20 hours at 50% load. Using the A/C requires 120V AC and using it for very long is not practical.

Propane Generator

Option one is to install an propane adapter and use a 20 lb supplimental propane tank. These tanks are easy to transport and easy to exchange. The onboard propane tank is permanently mounted hand has a 40 lb capacity. Transporting 20 lb tanks in the basement storage requires ventilation and is a safety concern.

“Suitcase” Generator(s)

Option two is to use “suitcase” inverter generators that use gasoline. A 2000 watt generator will run all appliances except the A/C and can charge the house batteries. A second 2000 watt generator can be run in parallel and will supply enough power to run A/C. A single 3600 watt generator will also work. Carrying gasoline cans in the basement storage is also a safety concern.

Solar / Engine Charging

Option three is to charge the house batteries using a DC to DC charger. This charger uses both solar power (future plan) and engine power to charge the house batteries. If propane is low, it’s a cloudy day and there’s no suitcase generator, this is a good fallback. Here’s a list of resources for implementation:

Renogy DC TO DC Charger Install
DIY Sprinter Camper Van Electrical Install
Install Steps
How To Install Solar Panels On Your Van Conversion

Sprinter notice:

For further study: House Battery Charging from Alternator

Charge Time

I have two 100 Ah LiFePO4 batteries for 200Ah total. Charging at 20A from empty to full would take 10 hours. Charging at 60A would take 3 hours and 20 mintues. While my house charger is rated at 60A, shore power is only 30A. Charging time should therefore be 6 hours and 40 minutes. The 2000 watt inverter generator should generate about 10A. It would take 20 hours for a full charge cycle at this rate. The generator should run as much as 10 hours with a light load. The low voltage cutoff is 8.8V.

My Sprinter alternator is rated at 220A. The maximum LiFePO4 battery charge rate is 100A. There is a Renogy 50A DC to DC charger that should charge my batteries in 4 hours.

LiFePO4 Voltage/Capacity Chart

LiTime LiFePO4 Chart

I want to provide cheap remote surveillance for my motorhome that is in a storage facility. I think a wifi camera and mobile hotspot is the answer. I found a hidden T-Mobile 30gb hotspot plan for $10/month and a T-Mobile Franklin T9 mobile hotspot device for $20. I have a spare Blink Mini indoor camera. Both devices use minimal 12V power. So far, so good.

The problem is that the hotspot shuts down after a few days to save the battery. With the battery removed, the hotspot shuts down after a few days because it “charged too long”. Power cycling the hotspot fails because the power button must be manually pressed to restart the hotspot. Using a timer to charge only part of the day may work but that requires 120v. I want to use power from the 12v RV house batteries without using an inverter. This should extend how long the house batteries last.

It’s time to hack. Rooting and unlocking the T9 is a start. I hope hacking it yields a solution to my problem.