Thanks for your help I need to power a CPAP breathing machine for sleep apnea as well I would like to power a small 1000 watt microwave and a fan that is about It I am located in the Great Lakes basin in Ontario Canada I have to large deep cycle marine batteries. I haven't purchased a charger and or inverter yet. Be interested in your thoughts.
Fans such as Hella, Caframo & cheap truckers fans can be run on 12V DC. They draw multiples less current than a home fan run through an inverter.
Many CPAP's can also be run on DC but you may need to get a bit creative. If not a small pure sine inverter dedicated to only the CPAP would be the most efficient..
Inverting is inefficient and with two small batteries keeping your devices running off DC will use far less energy.
We have an Emerson 700W microwave. It draws a measured 1190W at 119V!
1190W at 11.5V = 103.5A X 1.20 (for approx inverter inefficiency) = 124.2A
This equates to a 70% increase in consumed wattage than most would ever assume. Apply the same 70% increase in consumed wattage, with a 1000W microwave vs. a 700W, and you are burning approx 1700W!!
1700W at 11.5V = 148A X 1.20 (for approx inverter inefficiency) = 178A
124A for a 700W Microwave!!!
178A for a 1000W Microwave!!!
If the battery voltage sags to 10.7V you are now at approx 133A just on a 700W "rated" microwave.....
Battery temperature, battery type and the Peukerts constant will also dictate how long the bank can support a 100+A load before dropping out the inverter on low voltage at 10.5V or so....
Keep in mind that even a 3% voltage drop equates to the inverter dropping out at a terminal voltage of approx 10.8V and the wire voltage drop does not include terminals, fuses, terminations or switches... This means an inverter sized for a wire drop of 3% could in actuality drop out at 11V or more as installed.....
With short term microwave use most
good sized flooded deep cycle house banks can easily survive this load for the duration the microwave is run, if they are healthy. If they are sulfated and not healthy, or not large enough, you'll know it pretty quickly.
I would suggest learning to use the stove/oven, if equipped, and looking to DC solutions for the rest.....