Questions on 12 volt power use

[Javi]

I'm still researching DC power needs for my unique camping style.

Currently the only draw on the inverter is the fridge, my question is what is the DC draw of the posted fridge.

[JRTJH]

115 VAC @ 3 Amps = 345 watts

345 watts @ 12.6 VDC = 27.3809 Amps

The refrigerator label says, "Defrosting Input 320 watts", which is 25 watts less than the "calculated wattage indicated by 115 VAC@3 amps"...

The refrigerator maximum draw would be 27.4 Amps on the inverter input from the battery plus the intrinsic loss from the inverter operation (fans, LED indicators, electrical conversion losses, etc) and the voltage drop from the length/gauge of the battery cables.

[pasayten]

Yes, maximum draw would be about 27,4 amps... But that is only during defrost mode and everything must be sized to account for that... Energy guide annual use is about 600K watta per year... 1650 watts/day or about 70 watts/hr... So using JRTJH's math...

70 watt / 12.6 vdc = 5.6 amps avg draw

Are you thinking solar power to charfe batteries? Probably 200-300 watts of panels... Gas generator? Lots of options...

Need to generate 1650 watts/day or 5.6amps x 24hrs = 133 amphr for avg 24hr day of running... Consider that in figuring battery capacity to get thru dark hours or cloudy days... probably a 100amphr lithium battery for the refrigerator may do it... maybe two for safety and bad weather... All these are rough numbers... :-).

[Javi]

Originally Posted by pasayten

Yes, maximum draw would be about 27,4 amps... But that is only during defrost mode and everything must be sized to account for that... Energy guide annual use is about 600K watta per year... 1650 watts/day or about 70 watts/hr... So using JRTJH's math...

70 watt / 12.6 vdc = 5.6 amps avg draw

Are you thinking solar power to charfe batteries? Probably 200-300 watts of panels... Gas generator? Lots of options...

Need to generate 1650 watts/day or 5.6amps x 24hrs = 133 amphr for avg 24hr day of running... Consider that in figuring battery capacity to get thru dark hours or cloudy days... probably a 100amphr lithium battery for the refrigerator may do it... maybe two for safety and bad weather... All these are rough numbers... :-).

Let me preface this with these facts as they now stand.

1. The DW and I will never intentionally boondock or dry camp.

2. I’m old, with two bad knees and eight discs bad in my back; so, I’m NEVER going to climb up on the roof of my 5th wheel.

3. The only reason I’m considering Lifepro4 batteries is for the convenience, charging profile and relative costs. Basically, I like the idea of plug & play.

4. I don’t want to fool with suitcases, generators or solar panels. Yes if I were twenty-five years younger I’d probably have twelve billion watts of solar panes and be able to run everything on even a cloudy day. But that ship sailed a long time back.

Now, I want enough battery that I don’t have to worry about traveling ten hours to get to a campsite in the Texas heat and finding all my ice melted.
Or, (this has happened at least twice to us); the park’s power goes out late in the evening and won’t get repaired until tomorrow. I don’t want to have to hook-up and get ready to leave just in case.

Bottom line, I don’t mind spending two or three thousand dollars to get the convenience and piece of mind that when I get a rare day off from the office I can enjoy myself petting Max (the Golden) and sipping fifteen to twenty year old bourbon and watching the few sunsets I have left..

Outside of the fridge, LED lights WIFI Gateway, furnace and the DW’s CPAP there is not much drawing from the batteries. And The inverter is only powering the fridge and the CPAP..

So… how many batteries to get us through an eight hour drive, or through say twenty-four to forty-eight hours without charging.

[JRTJH]

Javi,

IMO, you're asking an "impossible to answer" question.

Just considering the CPAP power requirement, depending on the settings and the type of CPAP, the input amperage @12 volts could vary anywhere from less than 0.5 amps to well over 7 amps. Take a look at this document: https://document.resmed.com/document...de_glo_eng.pdf and it will give you some fairly objective facts concerning CPAP machines from RESMED. I'm pretty sure that other manufacturers have a similar document that outlines their machine use while on battery power....

Note, on page 4, the following: "Converter or Inverter?
We strongly recommend using DC-to-DC converters to power your ResMed device from a battery rather than DC-to-AC inverters. Let’s start with a couple questions to help identify which process steps to follow"

Most CPAP companies have a DC-to-DC converter that is significantly more efficient (battery saver) than using an inverter to change battery power to AC power and then back to battery power...

Another consideration is the humidity features on the CPAP. Heating that water tank to create the steam used to humidify the hose and then to heat the hose to keep the temperature constant uses a TREMENDOUS amount of battery power. If your DW is able to turn off the hose heat and the humidifier, you can get anywhere from 3 to 5 times the number of sleep cycles on a single battery charge....

So, when considering "what size battery bank do I need" type questions, just the CPAP type/model and what features are needed can cause you to double or triple the battery bank size. Then considering the refrigerator, how often it's opened, how hot the trailer is, whether the ice maker is being used or not are all factors that can "sneak you by with minimum use on a cool night with one battery or fully discharge 3 batteries overnight, just making ice and opening the door to fill the glasses....

Seems everything is a compromise, what are you willing to turn off and what are you not willing to do without "in a pinch, when the campground power goes out"....

[Javi]

Originally Posted by JRTJH

Javi,

IMO, you're asking an "impossible to answer" question.

Just considering the CPAP power requirement, depending on the settings and the type of CPAP, the input amperage @12 volts could vary anywhere from less than 0.5 amps to well over 7 amps. Take a look at this document: https://document.resmed.com/document...de_glo_eng.pdf and it will give you some fairly objective facts concerning CPAP machines from RESMED. I'm pretty sure that other manufacturers have a similar document that outlines their machine use while on battery power....

Note, on page 4, the following: "Converter or Inverter?
We strongly recommend using DC-to-DC converters to power your ResMed device from a battery rather than DCto-AC inverters. Let’s start with a couple questions to help identify which process steps to follow"

Most CPAPs have a DCC converter that is significantly more efficient (battery saver) than using an inverter to change battery power to AC power and then back to battery power...

Another consideration is the humidity features on the CPAP. Heating that water tank to create the steam used to humidify the hose and then to heat the hose to keep the temperature constant uses a TREMENDOUS amount of battery power. If your DW is able to turn off the hose heat and the humidifier, you can get anywhere from 3 to 5 times the number of sleep cycles on a single battery charge....

So, when considering "what size battery bank do I need" type questions, just the CPAP type/model and what features are needed can cause you to double or triple the battery bank size. Then considering the refrigerator, how often it's opened, how hot the trailer is, whether the ice maker is being used or not are all factors that can "sneak you by with minimum use on a cool night with one battery or fully discharge 3 batteries overnight, just making ice and opening the door to fill the glasses....

Seems everything is a compromise, what are you willing to turn off and what are you not willing to do without "in a pinch, when the campground power goes out"....

Not trying to be difficult and most of the questions you ask are totally subjective to the circumstance. For instance if it's a 110 degrees in the shade and the power is going to be out all for 12-48 hours... we're gone anyway

CPAP 3.12

And she can sleep without it one night if she has to..

Ice Maker off.. never turn it on until hooked up to water and power anyway.

DW needs ice for her sweet tea, but she does use a Yeti Mug

I can sip my bourbon neat

Inverter is 1000 watts WFCO

Generally speaking is all I'm really asking... 2 100 AH Battle Born, or 3 100 AH..

I didn't have a residential fridge or inverter in any of the other RV's we've had and we've never run out of power with only two series 27 Lead Acid batteries... got close once and had to pull out the jumper cables but that's it..