This discussion began on another comment thread. Maybe one of the moderators will move the posts pertaining to this discussion. TIA
I have questions regarding the efficacy of running the 3-way using an inverter to use the 120v option (like shore power) vs the 12v battery option, which we already know will suck up the battery bank. While I completely understand if the 2 settings work similarly, the math won't work on either setting, but that's not necessarily the case. The two settings might work differently and so using the 120v setting might actually work. Once I have my new battery and inverter setup I will be able to test it to see if there's any better function on the shore power 120v setting.
MOD NOTE: Relevant comments from the Tongue Box discussion have been transferred here.
Comments
On shore power (AC mode), a 3-way refrigerator draws approximately 2.7 amps. That 2.7 amps will work out to almost 30 amps when using an inverter to convert 12V to 120V. It will eat through your battery pretty fast.
edit:
I pulled the 2.7 amps from a quick search. Looks like it could possibly be more like 1.5 amps. Still, at 15 amps or more, it's a heavy load.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
By contrast, our 12V compressor fridge consumes 25Ah to 35Ah in a typical 24 hour period. Even with our 310W of rooftop solar and a 400W suitcase, I would never consider trying to power a 3-way absorption refrigerator on 120V electric with an inverter.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
2.7 amps at 120V is not the same as using a 12V source with an inverter to produce 120V. It's the wattage that you have to take into account. You'll draw at least 27 amps per hour while the compressor is running. That doesn't include the inefficiencies of the inverter.
Watts = Amps x Volts
2.7 amps x 120V = 324W
324W / 12V = 27 amps
edit to add:
If Watt's Law didn't apply, we'd all be running our air conditioners while dry camping.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
The problem may simply be not using the correct terminology. An inverter is simply an electronic device that converts direct current (DC) to alternating current (AC). It's not the same as a inverter generator (or any other generator) or a power station. Many owners use an inverter to power 120V devices and appliances using only their onboard 12V battery power. When someone says "inverter", that is what they should be referring to.
After reading past posts, it sounds like you are talking about a power station, not an inverter?
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
My 2-way Isotherm refrigerator uses about 42 watts when running on the mid-range setting (#4). This equates to 3.5 amps when running off of a 12 volt battery
(42 watts / 12 volts = 3.5 amps). So, for every hour it is running, it is consuming 3.5 'amp/hours' of battery capacity.
If I was running on 120 volt shore power, the amperage would be much less
(42 watts / 120 volts = 0.35 amps). But I'm still continuously consuming 42 watts of energy. It's just at a lower current...so my wires and fusing could be smaller.
If I'm pulling the power from my battery and then running it through an inverter, I'm still pulling the same amount of capacity out of my battery (plus an additional 10+% to cover the inefficiency of the inverter). The amperage between the inverter and the refrigerator is low, but the amperage between the battery and the inverter is still around 3.5 (or 3.85).
So, if the primary power source is a battery, using an inverter will drain that battery about 10% quicker than if operating directly on 12 VDC.
Let me know if this makes sense.
That makes a lot of sense. Keep in mind that your 2-way has a 12V compressor, so even when run on 120V there is a conversion to 12V taking place. However the energy consumption (wattage) of the compressor used is the same.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
Compared to a 2-way, which uses a 12V compressor, so does not have the duel heating elements, there would be no advantage to using it's 120V connection and an inverter. In fact it would consume more power from the battery setup.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
edit to say my mistake @Grumpy_G
"Increasing the voltage applied to a heating element will increase the current draw, assuming the resistance of the heating element remains constant."
Forgot about Ohm's Law ...
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
2013 Toyota Highlander 3.5L V6
2018 T@B 320 CS-S; Alde 3020; 4 cyl 2020 Subaru Outback Onyx XT
I noticed that too, but this is copied straight from the Norcold service manual. That doesn't mean it is correct. The manual also states
@Horigan I'm not interested in switching out the 3-way atm since I like the propane option, but... I'm interested in how the 12v compares to the 120v with the new inverter I'll be installing. Since I know the 12v is horrid on energy consumption, well, the 120v might be as well, but wo a full blown test... it's all a guess, imo.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
Been out of school for too long. Was thinking wattage was the constant with a heating element, but you reminded me that it's resistance.
2020 nuCamp T@B 320S * Jeep Wrangler
(47,171 towing miles through the end of 2024)
Thanks!
To run a 3-way on electricity, heat must be produced. NorCold uses a resistance heater for this purpose. Resistance heaters work better on 120v then 12v. That's why we pre-cool our 3-way on shore power before a trip. We've used one for 6 years and recommenced placing a thermometer inside a 3-way to enable more accurate adjustments. Math isn't needed, but cooling a 3-way before traveling on the 12v setting and frequent adjustment will keep you food cold,