Dropping the Generator

Last time we used the generator was when we drove to Las Vegas in July 2017 and ran both Air Conditioners, we really not need this we can run one from the battery bank or from solar power during the day. Anything else in our RV can run from the 4000 Watt Inverter with the right scheduling of loads. The Generator is basically turning into a waste of weight and require yearly oil changes and monthly exercise.

When boondocking is the amount of fresh water we can carry out our limit. The 400+ pounds Onan 7500 Diesel generator can be replaced with an 80-gallon freshwater tank. So would it be possible to have different backup than the heavy Generator?

Just dropping the large Inverter for a ~2000 Watt mobile Generator is not solving the requirements. With the Magnum MS4024 that cannot run in Hybrid mode is the generator required to sustain the full load and charge at the same time. The 7500 Watt generator is enough to supply 5000 Watt for the coach and charge with 105 Ampere to 24 Volt, another 2500 Watt for the full capacity of the Onan Generator.

2000 Watt Gas Generator and Stand-Alone Battery Charger

The option is then to run one or more secondary chargers directly from the small 2000 Watt Generator to the Battery Bank. 50 Ampere @ 24 Volt charger can be purchased for ~$250, This can simply be controlled with a voltage controlled AC breaker. When only needing this for an emergency is the Charger only needed to bring the battery from low SoC to ~80% SoC. So just disconnecting when Battery Volt reaches 24 Volt is good enough for controlling this. The Gas Generator is also useful for other purposes to bring on Off-Roading trips.

Using a 50 Ampere charger with a 2000 Watt Gas Generator can charge the Battery Bank from 0% SoC to 80% SoC in 16 Hours (((80% * 21000 Watthour / 22 Volt) / 50 Ampere). This can also be done at the same time as the Solar is charging, basically making a double charge possible in 8 hours with 2 Generators.

DC to DC converter and using the Diesel Engine

The Engine already generates a lot of electricity with the Alternator and charge the 12 Volt Engine Batteries. So could the 8.3 Liter Diesel engine be used as emergency Generator?

This requires a DC to DC converter from 12 Volt to 24 Volt. A good brand that is also very configurable is the Sterling Converters. A 70 Ampere Input is around 1000 Watt. Charging 80% to the battery bank is going to be a very long process with 22 Hours to charge from 0% SoC to 80% SoC (((80% * 21000 Watthour / 22 Volt) / (70 Ampere / 2)).  Not a very efficient use of a large engine, but very rarely needed. This Sterling Converter cost ~$450 and really offer no additional use than backup charging.

Instead of using the Sterling Converter can a Solar Controller take the 12 Volt from the Engine Battery and charge the 24 Volt Tesla Battery Bank. Most Solar Controllers require the input to be higher than the Battery Bank. So going from 12 Volt to 24 Volt is maybe only possible with a few controllers.

Price of the options

A good quality 2000 Watt Generator is ~$1000 and the charger $250. The control is simple and less than $50. So using a small stand-alone generator is $1300, but also give a lot of other uses for the Generator.

With a Sterling Converter for $450 allow charging while driving, but this is really not needed. So the Converter is really insurance for the bad weather we can have. Based on the last 1.5 years history is nothing really requiring this option.

Both options offer the saving of yearly oil changes and 80 Gallon more Fresh Water for Boondocking expeditions.


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