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Old 09-21-2021, 09:01 PM   #1
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Brand: Thor Motor Coach
Model: Quantum 24CR
State: Florida
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Solar / fridge

There are many threads on here about how long you can run your fridge off solar and battery. I decided to do a short experiment today. All of this is just my experience today and I’ve tried to give as many details as I could think of.

1030AM I unplugged shore power. Battery fully charged.
1130 I left to do errands
115 I arrived home but did not plug back in
3 PM checked battery level. Full
4 PM checked battery level. 13.4
445pm checked battery level. 12.6

Battery was fully charged at 1030AM. I will try to remember to check later but don’t want to fry my battery so will plug in before bed.

Outside temperature was approximately 90°. Coach sat in full sun until 3 PM then in shade from a tree. Starting at 4pm afternoon storm clouds started rolling in, very overcast, no shadows, no rain. All windows were closed, blinds were down, curtain was up dividing cab from house. No vents were open or running, no AC was running. Fridge was the only electrical draw other than parasitic. Refrigerator is empty. Temperature inside coach pretty darn hot.

I made two stops and turned coach off but I don’t have the length of time of those stops. I traveled 12 miles total in town traffic.

I have standard equipment 12v inverter fridge (which I LOVE) 10 amp Go Power solar controller, hundred watt solar panel on roof, one wet cell standard battery, Mercedes sprinter.

I leave fridge on all the time because I use coach like a large SUV and for grocery shopping. In Florida you need to get groceries home quickly. There was a news blurb the other night 15 minutes or less to avoid possible spoiling and contamination.

I have no real knowledge other than working use of solar and battery use. In the future I am definitely going with lithium and more solar but until my needs change for my current use I’m going to live with it as it is.

If there’s anyone out there who knows how to redo the solar and convert to Lithium and would like to park in a beautiful Florida town for a week and upgrade my coach let me know lol

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Old 09-22-2021, 11:49 AM   #2
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Update

At 930p I remembered to check battery. It had been dark for about 1.5 hours. An off and on drizzle so I didn’t take time to connect shore power. Instead I turned off fridge. Battery was 12.3

At 615a I went out to check. Battery was at 12.2. Turned on fridge dropped to 12.1

745a. Checked again and solar charging and battery still at 12.1. Think sunrise started around 645a
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Old 09-22-2021, 12:08 PM   #3
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Your experimental results are very confusing. I can't make head nor tails of it. But some observations:

Voltage is a very imperfect, maybe useless in some respects indicator of state of charge. Apparently your solar panels kicked up the voltage from "full" to 13.4V from 3:00 to 4:00. Then 45 minutes later it dropped to 12.6. What conclusions can you draw from this. Almost nothing as the solar panels were affecting the battery voltage.

Note that when you turned the fridge back on in the morning that the voltage immediately dropped from 12.2 to 12.1. Did the state of charge drop then? No, the fridge load caused the battery voltage to drop.

My point is if you are going to use battery voltage as a broad measure of state of charge, you have to let the batteries rest for at least an hour with no load or charging. Otherwise the load or charge effect totally distorts the voltage and makes it unusable as an indication of state of charge.

David
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Old 09-22-2021, 01:11 PM   #4
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Unhappy

I know, sigh. My mind works in mysterious ways. Or maybe it’s just exhaustion. I have read too many posts on here where OP was told they didn’t give enough information for people to give opinions. So I overdosed on details. But I somehow left off my actual question. If I replaced battery with one 100 amp lithium would I be able to keep other equipment and be able to run fridge all night. Or do I have to add more solar to fully charge battery. And if I can’t judge voltage without resting at what point do I need to turn off load so I won’t ruin battery?

I appreciate you replying, I’ve always thought your reply’s were helpful, non judgemental and informative. I can almost picture you scratching your head in confusion. Lol. Thank you. I envy those with analytical minds. Mine doesn’t work that way. If you’ve ever watched Kathleen Madigan I totally understand her skit about her brother explaining the deficit….
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Old 09-22-2021, 01:45 PM   #5
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Quote:
Originally Posted by Flwestcoast View Post
I know, sigh. My mind works in mysterious ways. Or maybe it’s just exhaustion. I have read too many posts on here where OP was told they didn’t give enough information for people to give opinions. So I overdosed on details. But I somehow left off my actual question. If I replaced battery with one 100 amp lithium would I be able to keep other equipment and be able to run fridge all night. Or do I have to add more solar to fully charge battery. And if I can’t judge voltage without resting at what point do I need to turn off load so I won’t ruin battery?

I appreciate you replying, I’ve always thought your reply’s were helpful, non judgemental and informative. I can almost picture you scratching your head in confusion. Lol. Thank you. I envy those with analytical minds. Mine doesn’t work that way. If you’ve ever watched Kathleen Madigan I totally understand her skit about her brother explaining the deficit….
To really answer your question about running the fridge and other loads all night you need to do real world measurements over several days. Same with the question about recharging.

For $18 you cam get this meter which will measure up to 100 amps in either direction and keep track of accumulated Watt-Hours into/out of your battery:



https://www.amazon.com/gp/product/B094RHQKMB/

Start your test with a full battery and see what happens to your existing battery status as the days go by. You should be able to see if you are running at a surplus or deficit of stored energy and what that surplus of deficit is.
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Old 09-22-2021, 02:57 PM   #6
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Ted is certainly correct about using a shunt based battery monitor to answer your question.

I presume your question is will your existing battery run the fridge during the non sunlight period for 24 hrs. I can answer that one right now, no. The better question is how much battery capacity and how much additional solar will it take to keep your fridge running for 1,2,3....days.

But if you tell us the exact make and model of your refrigerator, I can make a decent guess.

David
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Old 09-22-2021, 04:22 PM   #7
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Ted,
Thank you for your reply��
I have the shunt in my Amazon cart, how simple is this to wire to battery. I have an irrational fear of auto batteries, again, irrational…

David,
Here is data sheet showing all equipment including fridge. Is this what you needed? Thank you again!


I am really hoping as the fridge has its own inverter I will be able to do a simple battery swap until ready/need more power throughout coach. My controller does have lithium setting.

Monica
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Old 09-22-2021, 04:37 PM   #8
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Originally Posted by Flwestcoast View Post
Ted,
Thank you for your reply��
I have the shunt in my Amazon cart, how simple is this to wire to battery. I have an irrational fear of auto batteries, again, irrational…

David,
Here is data sheet showing all equipment including fridge. Is this what you needed? Thank you again!


I am really hoping as the fridge has its own inverter I will be able to do a simple battery swap until ready/need more power throughout coach. My controller does have lithium setting.

Monica
Spec sheet says it's a 12V fridge. No inverter necessary as it runs directly off the house batteries.
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Old 09-22-2021, 04:46 PM   #9
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Originally Posted by Flwestcoast View Post
Ted,
Thank you for your reply��
I have the shunt in my Amazon cart, how simple is this to wire to battery. I have an irrational fear of auto batteries, again, irrational…

David,
Here is data sheet showing all equipment including fridge. Is this what you needed? Thank you again!


I am really hoping as the fridge has its own inverter I will be able to do a simple battery swap until ready/need more power throughout coach. My controller does have lithium setting.

Monica
The wiring is pretty straight forward. The current part of the meter goes between the negative post(s) of the batteries and the lead to the frame (ground). You can use the house batteries as the power source for both voltage measurement as well as meter power so you only need on of the small plug-in leads.
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Old 09-22-2021, 05:35 PM   #10
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taylorbob1: Can that internal shunt handle the starting current of the generator which I would guess approaches 100 amps?

Also with that monitor you have to run the negative battery cable back and forth to wherever you mount the display. This will require big #2 cable.

Here is a more comprehensive battery monitor that I have used that is easy to install: the 500A shunt mounts near the negative battery terminal then a cable carrying the shunt voltage and the + and - power wires goes to the remote indicator. See https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

David
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Old 09-22-2021, 05:49 PM   #11
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OK, I see it is an 8 or 10 cu ft 12V Norcold fridge and you have no inverter, nor any absolute need for one as the fridge runs directly from 12V.

In my experience that fridge will draw 75 or so amp hours daily. That will run your single battery down in a half a day if you mind the 50% discharge limitations.

If you want to dry camp with such a DC fridge, lithium batteries are essential. I would install a minimum of 200 amp hours which will carry you for 2-3 days without sun. Then supplement that capability with 300+ watts of solar panels. Scrap your 10A controller since it is too small for the additional panels and replace it with a Victron, Renogy or Epever MPPT controller of at least 40 amps capacity.

If you want to recharge your batteries using your generator, I would upgrade the charger from what you have which is a cheap WFCO 55A with an 80A Progressive Dynamics 9160ALV lithium specific charger. This will recharge the batteries much faster.

See, complex questions result in expensive answers ;-). And FWIW I think Thor and your dealer should be shot for selling you an RV with a DC fridge with only a single lead acid battery to power it.

David
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Old 09-22-2021, 05:59 PM   #12
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Originally Posted by DavidEM View Post
taylorbob1: Can that internal shunt handle the starting current of the generator which I would guess approaches 100 amps?

Also with that monitor you have to run the negative battery cable back and forth to wherever you mount the display.

Here is a more comprehensive battery monitor that I have used that is easy to install: the 500A shunt mounts near the negative battery terminal then a cable carrying the shunt voltage and the + and - power wires goes to the remote indicator. See https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

David
Dunno, much of this is above my pay grade.
That said, OP doesn’t have a 120V residential fridge, nor does he have a 120V/propane absorption fridge.

He’s got a new efficient 12V fridge.

Amp Draw: 12V/DC
Standard Mode - 8.3
Night mode - 6.2

Not sure what the numbers mean, but it’s much more efficient than running an inverter and powering a 120V compressor
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Old 09-22-2021, 06:01 PM   #13
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David,
Your link didn’t work. Would you mind posting pic of that one?

Taylorbob1
Ok, please help me understand. I thought the 12v fridge had an internal inverter that allowed it to work off battery. And that is why it works also off shore and genie. I thought I read that. That allowed Thor to use this fridge without putting a whole house inverter in. If it does not have an inverter and works directly off batteries does that mean it is ALWAYS running off batteries and never shore or genie? Those just recharge batteries and fridge works from battery? Do I have that right?
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Old 09-22-2021, 06:06 PM   #14
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Always running off batteries

So if boondocking, and at night…you can turn off the fridge to save power.
That is, if you are not plugged into shore power, or don’t run your chassis engine or generator or you do not have solar, your batteries will not re-charge.
Hence your fridge will eventually drain your house batteries.

Just be aware
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Old 09-22-2021, 06:11 PM   #15
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One more thing…
In theory your fridge is always draining your house batteries
But, your fridge is not always running
It only runs when the thermostat tells it to turn on to lower the temp inside the box

Meanwhile, if you’re plugged into shore power…your batteries are always being “topped-off”.

So your system is working fine

Just be aware that if you’ve got your fridge running while you’re at a park somewhere without plug-in power…
Your fridge will eventually drain your house batteries

On edit: I see you have solar, so that helps during the day when sun is out to charge & top off house batteries
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Old 09-22-2021, 06:15 PM   #16
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OK, I see it is an 8 or 10 cu ft 12V Norcold fridge and you have no inverter, nor any absolute need for one as the fridge runs directly from 12V.

In my experience that fridge will draw 75 or so amp hours daily. That will run your single battery down in a half a day if you mind the 50% discharge limitations.

If you want to dry camp with such a DC fridge, lithium batteries are essential. I would install a minimum of 200 amp hours which will carry you for 2-3 days without sun. Then supplement that capability with 300+ watts of solar panels. Scrap your 10A controller since it is too small for the additional panels and replace it with a Victron, Renogy or Epever MPPT controller of at least 40 amps capacity.

If you want to recharge your batteries using your generator, I would upgrade the charger from what you have which is a cheap WFCO 55A with an 80A Progressive Dynamics 9160ALV lithium specific charger. This will recharge the batteries much faster.

See, complex questions result in expensive answers ;-). And FWIW I think Thor and your dealer should be shot for selling you an RV with a DC fridge with only a single lead acid battery to power it.

David
My worst fears confirmed. The madness of my query was that I knew the answer just hoped it would be different. I don’t feel comfortable doing all the changes and hoped I could sneak by with just changing out battery to lithium. I won’t be traveling much for now unless my moms health drastically improves. I have shore power at home, Genie is now working again, I just wanted to have at least a day leeway in case I don’t hook back up right away after using.

I agree on the single acid battery, I was very surprised there was not at least two. But this is the unit my mom said she liked and would not be afraid to ride in.♥️ And it was arriving the day after I called. Her happiness is number one.

I will keep your suggestions in case I have time and willpower to tackle the changes. I already decided there is room under bed for at least battery storage beside the water tank. I think😏. Couple questions. Can I exchange the 100 watt solar with a single 300 watt so I don’t have to mount more hardware on roof, or go with flexible? If no more solar for now and I put in the lithium’s, change to MPPT 40 controller Would that work combining with my shore power or genie recharge? I really just needs battery that will cover my fridge for 24 hours.

Thanks again.
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Old 09-22-2021, 06:23 PM   #17
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Originally Posted by taylorbob1 View Post
Always running off batteries

So if boondocking, and at night…you can turn off the fridge to save power.
That is, if you are not plugged into shore power, or don’t run your chassis engine or generator or you do not have solar, your batteries will not re-charge.
Hence your fridge will eventually drain your house batteries.

Just be aware
Darn it! I definitely had that wrong. I thought it switched when I plugged in.

My ultimate goal for now is if I am using and for some reason I don’t plug back in, moms needs more important, raining, exhausted, just plain forgot, the worthless wet cell won’t die on me. Hence the lithium upgrade desire. Like last night. I just turned off fridge because I forgot to check and by then it was raining and I was too tired to plug in.
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Old 09-22-2021, 06:27 PM   #18
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Yes, my recommended meter can handle the starting current for the generator - the generator is on a 100 amp breaker.

If you want to mount a meter away from the batteries then one with an external shunt is better like David recommended - his link DOES work.

Although the fridge in question is connected directly to the 12 VDC buss, (no connection to SP or Generator), it does have a single purpose internal inverter used to run the motor(s) which are 3 phase. Modern DC motors are actually 3 phase AC motors controlled by a DC powered Electronic Speed Controller; which is simply a 3 phase inverter.
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Old 09-22-2021, 06:39 PM   #19
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Yes, my recommended meter can handle the starting current for the generator - the generator is on a 100 amp breaker.

If you want to mount a meter away from the batteries then one with an external shunt is better like David recommended - his link DOES work.

Although the fridge in question is connected directly to the 12 VDC buss, (no connection to SP or Generator), it does have a single purpose internal inverter used to run the motor(s) which are 3 phase. Modern DC motors are actually 3 phase AC motors controlled by a DC powered Electronic Speed Controller; which is simply a 3 phase inverter.
If I do upgrades will first meter work? I can’t get Davids to link, blank page, could be operator error…

Now I am confused again on fridge. So it DOES have internal inverter? Best question for me to be clear is if I have NO house battery connected but I am hooked into shore power or genie running Will fridge work?��
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Old 09-22-2021, 07:00 PM   #20
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....cut....

I agree on the single acid battery, I was very surprised there was not at least two. But this is the unit my mom said she liked and would not be afraid to ride in.♥️ And it was arriving the day after I called. Her happiness is number one.

.....cut....

Lack of a second battery option may be largely due to weight concerns. Your motorhome is fairly large and with two slides which is considerable weight for the 11,030-pound Sprinter chassis.

If you switch from the Group 31 standard battery to 2 X 100 Amp-hour lithium batteries as suggested by others, that in itself won’t add much if any weight. Solar panels don’t weigh much either within reason. I am just suggesting you keep an eye on total motorhome weight as you consider upgrades.
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