Boat versus RV Generator
Just curious of why our Onan generators in our boat and RV are designed to operate differently. In the 2006 boat (11KW) it operates at a constant RPM regardless of load but in the 2018 RV (8KW) it ru...
Forum Discussion
The difference between Marine and RV is largely about the cooling system.
- Dedicated boat generators will pull seawater to provide engine cooling and pump it overboard.
- RV generators will use air for cooling. Depending on the size and complexity, it could utilize liquid cooling with a radiator or it may be a simple air cooled engine (like the old VW bugs).
The RPM is unrelated to boat vs RV. AC power in N. America is standardized at 60hz frequency (in other parts of the world, they often use 50hz). There are two common ways to achieve this:
- The old school way and the way power companies do it, is to spin the generator at a speed that corresponds to 60hz and then adjust the throttle to keep it there. Often this is 1800rpm and the generator head will produce 2 cycles per rotation of the engine. 60hz is equal to 3600 cycles per minute and 1800rpm * 2 = 3600 cycles per min. The downside, particularly for small generators, is any sudden change in loading causes the generator to speed up or slow down until the throttle can adjust resulting in inconsistent power output. Another downside is even with a very light load, the generator has to keep feeding enough fuel to keep the RPM up at 1800rpm. Big power plant generators have so much momentum and the draw from thousands of houses averages out, it's not really an issue.
- The newer way for small generators is inverter based technology (newer being at least a couple decades in common use). The generator actually produces DC power which is immediately fed into an inverter, which converts it to 120v AC power. This has advantages for smaller generators. The electronics in the inverter can control the Hz very accurately. They can also eliminate the spikes and dips in voltage. This makes the power much nicer for sensitive electronics. Also, since the Hz is not dependent on RPM, when under light load, it can throttle way back to idle speed cutting fuel consumption.
- Dedicated boat generators will pull seawater to provide engine cooling and pump it overboard.
- RV generators will use air for cooling. Depending on the size and complexity, it could utilize liquid cooling with a radiator or it may be a simple air cooled engine (like the old VW bugs).
The RPM is unrelated to boat vs RV. AC power in N. America is standardized at 60hz frequency (in other parts of the world, they often use 50hz). There are two common ways to achieve this:
- The old school way and the way power companies do it, is to spin the generator at a speed that corresponds to 60hz and then adjust the throttle to keep it there. Often this is 1800rpm and the generator head will produce 2 cycles per rotation of the engine. 60hz is equal to 3600 cycles per minute and 1800rpm * 2 = 3600 cycles per min. The downside, particularly for small generators, is any sudden change in loading causes the generator to speed up or slow down until the throttle can adjust resulting in inconsistent power output. Another downside is even with a very light load, the generator has to keep feeding enough fuel to keep the RPM up at 1800rpm. Big power plant generators have so much momentum and the draw from thousands of houses averages out, it's not really an issue.
- The newer way for small generators is inverter based technology (newer being at least a couple decades in common use). The generator actually produces DC power which is immediately fed into an inverter, which converts it to 120v AC power. This has advantages for smaller generators. The electronics in the inverter can control the Hz very accurately. They can also eliminate the spikes and dips in voltage. This makes the power much nicer for sensitive electronics. Also, since the Hz is not dependent on RPM, when under light load, it can throttle way back to idle speed cutting fuel consumption.
