Simple electrical question

Dmarcian · 06-09-2021, 02:43 AM

2020 VJ - I will be leaving on a trip next week and will spend some time off grid. Can I run the compressor fridge with the inverter turned off? Will my solar panels charge the batteries with my inverter turned off? Thanks!

DavidM · 06-09-2021, 05:33 AM

Yes, your solar panels will charge the batteries. But are the panels big enough to keep up with the fridge load? And what other DC loads are on at the same time. And how big are your batteries. Lot's of questions need answers to answer your question.

David

Dmarcian · 06-09-2021, 07:03 AM

Thanks David. Lithium’s. Pretty sure my fridge runs with the inverter off. Just want to reduce battery draw as much as possible. So if my solar, 200 watts, charges the batteries when the inverter is off then I should leave it off during the day when I am out.

DavidM · 06-09-2021, 07:33 AM

On average, depending on where you are and the time of year, a 200 watt panel will put out about 50 amp hours in a 24 hour period. That may not keep up with the compressor fridge and all other loads in that period.

David

Morich · 06-09-2021, 07:43 AM

The reason this becomes such a complex question is that things are often rated at one point when we expect them to do far different in actual use. solar panels that are rated at 200 watt are rarely going to put out that much! A frig that is rated to use a certain amount will rarely use that amount due to all kinds of factors like how often we open the door, heat in the Rv and how full the frig! If the frig is full when we open the door ,far less hot air rushes in to be cooled when we do shut the door. If we happen to have a bad habit of leaving the door open while we move things back and for the, it takes longer to cool.
So the estimates start out real loose and only experience over time tells what it really gets us and even that will vary with where we park and what the weather is on simple stuff like if it is cloudy!
I predict there will be a flood of new RV users selling RV in a few years as they find out what those estimates really work out to be!

Dmarcian · 06-09-2021, 08:08 AM

Agreed. I just want to be able to leave for long stretches. I want to minimize the load as much as possible because the fridge is such an energy hog. Turing off the inverter might not make much of a difference but it should help some anyway.

Ontario Don · 06-09-2021, 08:15 AM

Hi - I can also confirm that the fridges on the new Views run on 12 volts, and do not need the inverter to be on. I'd recommend that the inverter be left off for serious dry camping, as it pulls about 2.5 amps while idling, and will also idle the microwave and induction cooktop needlessly.

The microwave on inverter power will pull about 150 amps when in use, so even for a short burst of thawing and heating, our experience is that it will use up 5 or 6 % SOC on the lithium batteries. Again, not recommended for really serious dry camping.

Our 200 amps of solar is not enough to self-sustain the fridge and other loads, but it does help a bit. The good news is that with the lithium installed you will have several days of battery capacity. If you plan on not using anything the inverter gives you, and just go with the basics and fundamentals of old fashion dry camping, the new View is pretty awesome with lithium batteries. We had to dry camp a whole bunch in the early spring, and even with the furnace heater running, we were fine and had lots of margin for more than a couple of days. And, of course, if you really want to, and your environment can put up with it, you've got an option to run the Onan to keep the batteries topped up.

Have a great trip!

Cheers,

Dmarcian · 06-09-2021, 08:48 AM

Good info. Thanks Ontario Don.

**creativepart** · 06-09-2021, 09:45 AM

Really, all but the most basic camping usage and current RV construction will require a user to run a generator a few hours a day.

We find it necessary to run the generator during the morning and evening just to keep the batteries adequately charged. Now, we have a Class A with an AC powered residential fridge so we must use the inverter. But we also have 400 amp hours of (AGM) batteries.

Morning meal prep - coffee maker, microwave or toaster oven use far too much of our battery bank so, we don't use the batteries for that. We just start the generator and leave it running 45 mins or so. Same for evening meal prep - microwave, toaster oven etc are big current hogs and we run the generator in the evening usually for 1 1/2 hours to not only support those appliances but also to give the batteries a better state of charge for overnight.

Every RV is different and every RVer is different. But I think most will find that even with solar power helping during the daylight hours some generator running will be necessary even though most of us want to do that as little as possible.

Marine359 · 06-09-2021, 10:27 AM

Quote:

Originally Posted by Dmarcian

Agreed. I just want to be able to leave for long stretches. I want to minimize the load as much as possible because the fridge is such an energy hog. Turing off the inverter might not make much of a difference but it should help some anyway.

Guessing you have the Dometic 10cf 12v compressor fridge. That’s the fridge we have. If so, it will draw 25ah per day @65F ambient when pre-chilled, and with thermal mass inside. Expect up to 30ah draw in warmer climate, and if you open the door a lot.

When boondocking, turn your inverter off, preferably by disconnecting, as many inverters continue to use power in standby. We have been able to go for 3 days without using generator. We expect to be able to go 5 days now that we have a 110w portable solar panel. Then we’ll consider adding another panel to the roof. Hopefully, we’ll never have to use our generator again.

DavidM · 06-09-2021, 11:18 AM

Marine359:

I am really surprised by your low DC usage for the fridge. That fridge probably draws 5A while running, so 25 Ahs a day means it only runs 5 hours or about 20%. That is low. I would expect double that in moderate climates.

How are you measuring this daily current draw?

David

Marine359 · 06-09-2021, 11:30 AM

Nope,
Fridge is surprisingly efficient. The old Norcold compressor was a hog, I’m told. I tested this fridge twice with my Victron bm. Inverter disconnected. In practical use while camping, on my last trip, it really doesn’t use much. Because we boondock more often than not, I really was considering early on, after we bought the MM, of swapping it out for an absorption fridge. But we’re doing just fine with the compressor. We do carry ice in the freezer, and swap out bags into the fridge. We also try to keep freezer and fridge full, and only open doors quickly. We can sit for 30 min or more without the compressor kicking on. Dometic did a good job with this product. I think we were one of the first to get a WBGO build with this fridge as standard equip. I think the fridge was released by Dometic in Aug last year. I have my test data in a prior post on the Micro Mini thread.

Marine359 · 06-09-2021, 11:39 AM

Quote:

Originally Posted by DavidM

How are you measuring this daily current draw?
David

Restating here:
Two tests run over a 2 day period. Each test started with 100% SOC.
Inverter disconnect switched off. SP disconnected.
All other DC loads off, but not switched off at panel, so there was still small loads from alarms and sensors.

Two bags of ice in freezer. Fridge empty.
Victron reported 25amps consumed in first 24hr period.
Recharged to 100% SOC for second test. Started second test about 3 hrs later.
Victron reported 26amps consumed in second 24hr period.

Morich · 06-09-2021, 11:39 AM

One of the things not mentioned yet is the battery temp as a cold batteries will give less service than ones which are kept warm.
One of the problems with sizing battery groups for industrial use is that we often lose the heat in the building when we lose the power and have to go to battery backup. Cold batteries give less amp hours, making the need for having generators there sooner really important as then you can get both power to heat as well as to the equipment that you can't run on the generator.
One of the big points being ignored on the talks about how to prevent another winter electrical disaster in Texas is the need for real generators on site, not some theoretical idea that you can go rent one when you need it! They have already opted out of requiring the gas production groups to have backup power, so if they can't continue to provide the gas they can't ship it to power the power plants!

mricet1005 · 06-09-2021, 02:32 PM

Quote:

Originally Posted by Dmarcian

Thanks David. Lithium’s. Pretty sure my fridge runs with the inverter off. Just want to reduce battery draw as much as possible. So if my solar, 200 watts, charges the batteries when the inverter is off then I should leave it off during the day when I am out.

I have factory Lithium (250 ah). With full battery at dusk, going overnight using fridge, lights, TV, few minutes of microwave, CPAP, etc. my SOC at morning is around 70% (based on battery BMS app). I do put fridge into night mode when going to sleep. So you can go at least 24 hours. 200W solar is not enough to refill usage and charge batteries to full. I recently upgraded to 510W solar and hope that will allow 2-3 days boondocking without generator if I get decent sun. But haven’t tested yet.

To answer other question, yes fridge is 12V and doesn’t need inverter. You should be okay.

Marine359 · 06-09-2021, 02:46 PM

Quote:

Originally Posted by mricet1005

I have factory Lithium (250 ah). With full battery at dusk, going overnight using fridge, lights, TV, few minutes of microwave, CPAP, etc. my SOC at morning is around 70% (based on battery BMS app)

Hmmm. We manage to get by on 40ah per night. Curious if you’re using humidifier on your cpap. Huge difference 5amps vs 1amp. I bypass humidifier when boondocking. And, are you running cpap on 120v? If so, you must have your inverter on all night. I switched to 12vdc adapter and now can turn off my inverter at night. That saves about 5ah.

mricet1005 · 06-09-2021, 03:01 PM

Quote:

Originally Posted by Marine359

Hmmm. We manage to get by on 40ah per night. Curious if you’re using humidifier on your cpap. Huge difference 5amps vs 1amp. I bypass humidifier when boondocking. And, are you running cpap on 120v? If so, you must have your inverter on all night. I switched to 12vdc adapter and now can turn off my inverter at night. That saves about 5ah.

No humidifier on CPAP powered directly to 12v. Sometimes I use less power. No attempt to conserve. Use Microwave for 3-5 minutes, hours of TV. I’m sure I could use less but don’t feel I need to. System performs great. My data was during cold weather and fan on propane furnace was running too overnight.

Marine359 · 06-09-2021, 04:32 PM

If you were using furnace, and tv, and some inverter, your total consumption makes sense. I don’t want to conserve, or should I say, I don’t want to think about it. If I can do 3 days, I’m happy.
Happy Camping!

Elkman · 06-18-2021, 01:19 PM

With lead acid batteries and 250Ah in total it is safe to draw them down to 50% SOC and so you have 125Ah at most for the fridge. With the refrigerator set for a temp of 38 degrees and the freezer at +15 degrees and no opening of the doors at all and with outside temperatures in the 50's the two lead acid batteries would be a 50% SOC after two days and that was with the two factory installed 100W solar panels operating.

With normal use the generator is going to need to be run but the RV can be left for hours and the fridge temp will be maintained and food inside will be lost. One big advantage of the lithium phosphate batteries is that they recharge 3 times as fast as the lead acid (flooded or AGM) and so make better use of daylight solar panel output and 70% less generator run time to get them back to 100% SOC.

Dmarcian · 06-19-2021, 07:39 AM

Update - 5 days into my trip. On the few times we have been not hooked up over nite the batteries were drawn down by about 25percent with only the fridge running and the inverter turned off. Everything working perfectly except my Mercedes motor no longer charges the batteries while driving during the day. Yes, I switched the inverter back on while driving. The motor used to charge them, not exactly sure when it stopped doing so. Not too big of a deal because solar keeps them well maintained during the day. But I do need to run the generator a bit at night to fully charge them for the overnight hours. They charge fine with the generator and shore power. Any ideas?