I have a 17 liter hot water
tank on my Dragonfly which can be heated from the engine's cooling
I also have rebuilt my refrigerator
with Aerogel insulation
and installed a keel
cooled Vitrifrigio compressor
As I have only one bank of batteries (200 ah worth of LiFePo4) but 320 watts worth of solar panels
, I have LOTS of spare electricity, and don't need to run the engine
is the only thing left wanting, so I decided to do an experiment
with my 1500 watt sine wave inverter
This time of year the weather
around the PNW is nasty and cloudy most of the time, but I decided to go ahead with the experiment
The water tank started out at 47 degrees fahrenheit, and the lithium phosphate 200 amp/hour battery
bank was 100%.
(See the thread on LiFePo4
for house bank)
temp sensor indicated 48 degrees at the start.
I hooked up the 1.5 kw sine wave inverter
to the 1 kw hot water tank and took measurements every 5 minutes.
As soon as I turned on the inverter, the floating batteries (13.8v) immediately went to 12.6 volts.
The discharge current
from the batteries averaged about 105 amps.
input was minimal as we had heavy overcast during the whole test.
Slowly over the space of one hour, the battery voltage dropped in a linear fashion from 12.6 to 12.3 volts while the discharge current
stayed constant at 105 amps.
The inverter supplied 117 VAC @ 9.5 amps AC as measured with my trusty Fluke 97 at the input to the tank through a cheesy six foot extension cord from the inverter to the tank.
At one hour and one minute, the thermostat on the tank shut off the heating
The battery monitor
indicated 105 amp hours used, my 200 ah battery bank was at 45% and the battery temp was at 65 f.
(LiFePo4 batteries can go to 20% before any damage takes place)
The inverter never missed a beat, the fan only ran at low speed the whole time, and the water temp (measured at the galley
faucet) was 157 f !
The battery voltage immediately jumped back to 12.6 when the tank thermostat turned off the load.
I figured doing this experiment with COLD water this time of year and no sun would be the absolute worst case scenario, so if it was doable now, it ought to be a piece of cake in the summer with longer days.
Kicking the hot water tank around noon, and then topping up the batteries during the rest of the day ought to keep the MPPT
in bulk mode most of the day instead of floating half the time. Make the sun work for its living!!
Hot showers, here we come. WOO HOO !!