Battery Drain

[OrangeCrush]

Originally Posted by vanderwielen

Nope, the fridge/freezer will draw 75w when the compressor is on with a duty cycle of 33% when the ambient is 70. I suspect you don't have an AI and are simply parroting others via previous posts.

No I don't have an AI. Yes I was parroting others who have measured actual average daily usage of a compressor fridge at 50-60 amps per day. I should have stated it more completely and called it 50-60 amp-hours of battery capacity per day. Lets use your numbers and go through the math. 75W/12V = 6.25 amp-hours which comes out to 24*6.25 = 150 amp-hours per day. Assuming a 33% duty cycle you have an average daily usage of 150/3 = 50 amps-hours per day. Over 3 days time that would be 3/4 of a 200 amp-hour battery bank.

[uncle_bob]

Originally Posted by richard5933

Since this happens after your third night of camping without shore power, I'm going to agree with the others that said there is a problem with the settings on your generator's auto-on feature. My guess is that you're not fully charging the batteries - just barely getting enough in them to make it through the first & second night. By the third night you hit the breaking point and use the reserve capacity.

It's also worth checking to find out if your solar is actually charging the batteries at all during these events. You should be able to monitor the amount of charge going into your batteries during the day when the generator is not running. I'm guessing that either the charge parameters are set wrong or the solar system is not charging for some other reason. If it were, then you'd have enough charge to make it through the night easily with only a 45-watt load.

Or, your actual load is much higher than 45w. Perhaps not everything on the house side of the system is actually going through your shunt? How many ground wires do you have on your house battery negative connection?

Hi

On the X, the 712 is a stock item. They wire it correctly. The grounds all go through the shunt.

The shunt may or may not be programmed correctly ( = it could be at the default settings ).

CPAP demand varies all over the place, just like the fridge. If the CPAP is running through the inverter (sounds like it is) that makes things even crazier for estimating numbers. As noted above, getting a DC/DC converter to deliver (most likely) 24V to run the CPAP is a really good idea.

The big load is still the fridge. Mainly because it runs 24 hours a day.

The solar is 200W as far as the house bank is concerned. If you *ever* see half that, you are doing great with all the junk that shades is.

Bob

[uncle_bob]

Originally Posted by OrangeCrush

No I don't have an AI. Yes I was parroting others who have measured actual average daily usage of a compressor fridge at 50-60 amps per day. I should have stated it more completely and called it 50-60 amp-hours of battery capacity per day. Lets use your numbers and go through the math. 75W/12V = 6.25 amp-hours which comes out to 24*6.25 = 150 amp-hours per day. Assuming a 33% duty cycle you have an average daily usage of 150/3 = 50 amps-hours per day. Over 3 days time that would be 3/4 of a 200 amp-hour battery bank.

Hi

Again, the OP is running an X. The fridge in that specific AS pulls just over 10A at the "100%" point. Shove 120W into your math and things just get worse.

Bob

[Rocinante]

If that fridge runs on both AC and DC power, it might be wise to unplug the fridge from the AC outlet so it always runs on DC. That’s more efficient than inverting from DC to AC and then converting that back again to DC at the fridge. The Norcold fridge in our 2016 works this way, and we yanked the AC plug for that very reason. Now it runs only on DC power.

[OrangeCrush]

Originally Posted by uncle_bob

Hi

Again, the OP is running an X. The fridge in that specific AS pulls just over 10A at the "100%" point. Shove 120W into your math and things just get worse.

Bob

Thanks Bob, yes that is significantly worse. I was just trying to illustrate that 75W at 33% is the same as 50 Ah per day. I think your numbers sum up the real daily draw pretty good though I think in all fairness we should be using a little higher voltage for lithium.

[Johncapp]

I can confirm that 50 to 70 amp hours per day is about right for a 12 volt fridge raider. Ours is 10 ft.³ ,works beautifully , but we did have to go to 300 amp hour of lithium batteries. We can boondock for many days with that reserve.

[uncle_bob]

Originally Posted by Rocinante

If that fridge runs on both AC and DC power, it might be wise to unplug the fridge from the AC outlet so it always runs on DC. That’s more efficient than inverting from DC to AC and then converting that back again to DC at the fridge. The Norcold fridge in our 2016 works this way, and we yanked the AC plug for that very reason. Now it runs only on DC power.

Hi

The compressor fridges they use in the X aren't to bad this way. Their effecendy on AC is very close to what it is on DC.

The *big* gotcha is the inverter. It is never a good idea to run the inverter to power something off batteries if that same item could go direct to the battery. Add another ~ 20% to the numbers if you go battery to inverter back to dc in the device.

Bob

Bob

[uncle_bob]

Originally Posted by OrangeCrush

......though I think in all fairness we should be using a little higher voltage for lithium.

Hi

..... which makes the example post even longer and gets into even more confusion using WH and KWH vs AH. Tracking battery voltage change as the battery dies ...yikes ... lots of tables and the like.

Bob

[Wazbro]

Originally Posted by OrangeCrush

Thanks Bob, yes that is significantly worse. I was just trying to illustrate that 75W at 33% is the same as 50 Ah per day. I think your numbers sum up the real daily draw pretty good though I think in all fairness we should be using a little higher voltage for lithium.

I believe using 12 volts, while less accurate, is better since it would give you a small margin for reserve to help compensate for other battery drains you might not have thought of. Remember the goal is to not run the batteries dead, not to be completely accurate as to why they went dead.