A/C off of 20 amp service?
Has anyone ever heard of a single a/c unit not being able to start and run on a 20amp shore power circuit? We bought a new coach and the dealer says don't run a/c unless connected to a 30 amp servic...
Forum Discussion
Autoformers are very useful devices as they can boost low pedestal voltage. However they cannot replace the lost power due to low pedestal voltage. Let’s take an example of 105V at the pedestal which limits the power to 2100W input to the autoformer running 98% efficiency yields autoformer output of 17.2A at 120V. Here’s the math:
105V*20A=2100W*98%/120V=17.2A
So using a autoformer to boost the voltage reduces the watts and amps available for the rig.
In addition the recommended sustained load on a plug is 80% not 100%. And certainly an A/C especially in hot weather represents a sustained load. So now the amps available are down to 13.7A.
105V*20A*80%=1680W*98%/120V=13.7A
Certainly 17.2A or 13.7A is adequate to run some A/Cs. My last rig had a 15K BTU Dometic A/C that drew 14A for the compressor plus 1.5A for the fan or 15.5A. So I would have been hard pressed to run the A/C on a 20A 120V circuit considering that there are other rig loads. However a autoformer is a more useful device on 30A in this situation. In my 12 years of using 50A power I’ve had exactly one CG with low voltage on 50A which limits my justification for a 50A autoformer.
There is no panacea with free power using a autoformer but they are a useful tool.
105V*20A=2100W*98%/120V=17.2A
So using a autoformer to boost the voltage reduces the watts and amps available for the rig.
In addition the recommended sustained load on a plug is 80% not 100%. And certainly an A/C especially in hot weather represents a sustained load. So now the amps available are down to 13.7A.
105V*20A*80%=1680W*98%/120V=13.7A
Certainly 17.2A or 13.7A is adequate to run some A/Cs. My last rig had a 15K BTU Dometic A/C that drew 14A for the compressor plus 1.5A for the fan or 15.5A. So I would have been hard pressed to run the A/C on a 20A 120V circuit considering that there are other rig loads. However a autoformer is a more useful device on 30A in this situation. In my 12 years of using 50A power I’ve had exactly one CG with low voltage on 50A which limits my justification for a 50A autoformer.
There is no panacea with free power using a autoformer but they are a useful tool.
