Fridge Run-times / Small Dual Battery Build

[jhguth]

I think you might be misunderstanding what I was trying to say...

100% duty cycle meaning the battery will have enough capacity to run the fridge continuously for that duration, not that it will

In real world use, it will be closer to 50% duty cycle depending on loading and ambient temp.

If it can run 12 hours 100%, it can run 24 hours 50% duty cycle.

This is also a "24 volt" battery... meaning you need half the Ah to do the same job of a 12 volt battery, and the fridge runs more efficiently at 24 volts by about 15%.

I don't have to worry about voltage drop of the rear 12v outlet because it's not running the fridge, only charging the batteries using a 12 to 24v DC to DC charger.

And I am actually on the opposite end of unsure about wiring... I have two other trucks with dual batteries setups. One of them being a 4th Gen which is my off-road truck and where the fridge has usually sits.

I just felt like doing something different in the 5th Gen just for fun, consider the last video proof of concept.

Real world is nowhere near 50% duty cycle unless you're running your fridge empty or something, mine runs less than 15 mins/hr with interior temps over 100F.

And even if you're running a DC-DC charger you probably dont want to use the rear plug, it's only rated for 120W which would make it tough to replenish your second battery unless you're driving a whole lot or have a solar helping out.

 

[Titanpat57]

I did a bunch of testing and at this point I think I am going to go small... as small as possible to run 1/2 day 100% duty cycle.

I want this to be 100% plug and play to run only off the existing outlets already in the cargo area.

This is where I am at so far... I might even consider building it into a drawer system or something.

Why not load the fridge with food and beverage and get a real world cycle of what's going on......running an empty fridge, even as a test, is pretty much useless. Although I do like where your're going...I think you're going to need about three times that amount of batteries to maintain a fridge under somewhat "normal" conditions.

 

[Bumbo]

Why not load the fridge with food and beverage and get a real world cycle of what's going on......running an empty fridge, even as a test, is pretty much useless. Although I do like where your're going...I think you're going to need about three times that amount of batteries to maintain a fridge under somewhat "normal" conditions.

Absolutely... I agree 100%

I had a busy night just trying to get one board finished... and I was a bit eager to test.

I wanted to do was a startup load test to what types of currents are being pulled at 24 volts to see if this is even feasible, and it sure is. Most people who have issues with the fridge starting is because of voltage drop over small lines or too low of voltage. Running at 24 volts only help both those things so I really wanted to see if it turned the compressor over on a single board.

Future test will include a 24 hour cycle while sitting in a hot car with food and drink to see a true representation of actual consumption over the course of a day.

I have 20 boards to play with, but I will probably use 8 total.

Probably something like this, laying out flat in a enclosure so the fridge can sit on it. I could fit more but I need room for other hardware like the 12 to 24v charger and other bits and bobs.

 

[Bumbo]

Real world is nowhere near 50% duty cycle unless you're running your fridge empty or something, mine runs less than 15 mins/hr with interior temps over 100F.

And even if you're running a DC-DC charger you probably dont want to use the rear plug, it's only rated for 120W which would make it tough to replenish your second battery unless you're driving a whole lot or have a solar helping out.

What you are saying only works in my favor...

Lets do the math:
15/60 = 25% duty cycle

Fridge uses about 40-50 watts when the compressor is running, call it 50 watts.

So every hour it uses about 12.5 watt hours per hour @ 25% duty cycle.

The battery I am using for the actual build are 2900mah Panasonic 18650 cells x 7 cells = 75 watt hours PER board.

75/12.5 = 6 hours.

Personally I think its higher than 25% duty cycle because that's almost too good to be true. Lets just call it 50% for some fudge factor, and that gives us about 3 hours of actual run-time on a single board.

I won't get excited until I do more testing, but I think we are on the right track here.

 

[jhguth]

so i checked a random day to give you some data to use; it was really hot here thursday (114 degree recorded interior temp in my vehicle, 91-93 degrees outside temps during this time) and my fridge was pretty empty. Fridge is set at 35 degrees, I'm using a Dometic CFX-40.

I parked at 8:37. Fridge Ran:
9:09-9:17 (8)
9:57-10:07 (10)
10:43-10:53 (10)
11:27-11:37 (10)
12:09-12:19 (10)
12:51-13:01 (10)
13:35-13:43 (8)
14:19-14:27 (8)
15:03-15:15 (12)
15:47 engine started to go to meeting

One downside of this monitor is that i can't export anything to excel, i have to scroll through with my finger. I think my sampling rate is 1/min (Edit: actually i noticed all of those times are odd numbers, so i bet the sampling rate is every 2 minutes)

So 86/430 minutes or a 20% duty cycle. I have a basic cheap battery monitor and check tthe trend data occasionally and the cycling thursday is consistent with other summer daytime trending i've checked.

 

[Bumbo]

That's excellent feedback, so thanks for that. Things are starting to look positive with that data. Send me some info on your battery monitor, you have peaked my curiosity.

With regards to charging... ill agree that the 12v DC supply is a little light, but it's really just for supplemental capacity when the engine is on. I just want this thing to last at least a day as-is so I could even go without plugging it in all together.

Its pretty rare that I need more capacity but with some top off coming from the truck, ill be in great shape. I can always use the AC plug too, the fridge will run off AC while the full 120 watts goes to charging when the engine is running. Its easily controlled by just pushing the inverter ON button because the ARB fridge automatically transfers priority to AC.

 

[Titanpat57]

Absolutely... I agree 100%

I had a busy night just trying to get one board finished... and I was a bit eager to test.

I wanted to do was a startup load test to what types of currents are being pulled at 24 volts to see if this is even feasible, and it sure is. Most people who have issues with the fridge starting is because of voltage drop over small lines or too low of voltage. Running at 24 volts only help both those things so I really wanted to see if it turned the compressor over on a single board.

Future test will include a 24 hour cycle while sitting in a hot car with food and drink to see a true representation of actual consumption over the course of a day.

I have 20 boards to play with, but I will probably use 8 total.

Probably something like this, laying out flat in a enclosure so the fridge can sit on it. I could fit more but I need room for other hardware like the 12 to 24v charger and other bits and bobs.

Very interesting...sub'd!

 

[JSparky]

I decided to go with X2 Power 27F and a Renogy 100W solar suitcase. As long as I have decent light, I can run indefinitely. Worked great camping the last 2 1/2 days.

I accidentally drained my X2 to 6V. Took it to Batteries+ and they kept it overnight to charge and test. Came back and holds at 13.8, been using it steady the last two weeks with no faults. Pretty impressed with it so far.

 

[JSparky]

I’ve run an ARB fridge for over 4 years in 4x different vehicles, only one of which has a dual battery system. I did use an agm marine or dual cycle battery in each rig though.

For overnight trips I’d have absolute confidence in using a single battery. Keep an emergency jump starter for redundancy if camping alone.

 

[jhguth]

For just an occasional overnight camping trip the stock battery is fine, it's just not happy with the kind of cycling it would see with day to day use. Mine lasted about 6 months running my fridge 24-7 before it had reduced performance (it never didn't start the truck, but eventually it would only last a few hours before it would hit the low voltage shutoff on the fridge)

Sent from my SM-G930V using Tapatalk

 

[snuffleupagus]

Following...What cell chemistry are you planning on using there? Guessing some Li-ion flavor by the voltage. I've been toying around with doing a similar setup, but likely with 4 of the larger prismatic cells (20-60AH) in LiFePO4.

 

[Bumbo]

Following...What cell chemistry are you planning on using there? Guessing some Li-ion flavor by the voltage. I've been toying around with doing a similar setup, but likely with 4 of the larger prismatic cells (20-60AH) in LiFePO4.

I am using Li-ion... various sub chemistry in my inventory (ICR, INR, IMR) but they are all 3.6-3.7 nominal... its basically your typical run-of-the-mill 18650 flashlight battery.

If you have a good line on LiFePO4 cells then use them! Those are great, especially for 12 volt applications because the voltage matches perfectly for assuming your charging system doesn't exceed 14.4 volts, plus they last forever and can handle more abuse.

I have some small LiFePO4 cells, but I was saving them for something that needs the juice. I have a whole module full of these I bought off ebay.

EACH cell is capable of 70 amps of discharge power... heres the spec sheet.
https://www.buya123products.com/uploads/vipcase/844c1bd8bdd1190ebb364d572bc1e6e7.pdf

Not that I have plans on replacing my starter batter, but they are impressive. I just bought them for things that NEED 12v compatible voltages.

 

[Isais101]

I decided to go with X2 Power 27F and a Renogy 100W solar suitcase. As long as I have decent light, I can run indefinitely. Worked great camping the last 2 1/2 days.

What is this? Are these panels? What else do I need other thanks panels for solar power?

 

[Tuc4R]

What is this? Are these panels? What else do I need other thanks panels for solar power?

It’s a complete solar package. Panels and controller. I just plug the solar panels into my battery, and it keeps the battery topped off so I can run my fridge through the night with no problems. Also allows me to charge a smaller battery pack. First time using it, and I really like how efficient it is.