Powering 12v fridge from battery back

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Hatch

797 posts

Ultimate Geek

#280234 3-Dec-2020 12:15

Hi all trying to work out if a portable fridge can be powered for 6-8 hours overnight from a portable battery. Also want 240v for charging/running laptop.

Finding hard to work out power draw of the fridge and output of the battery to match up.

I have the equivalent of this:

https://www.rvworldstore.co.nz/mycoolman-36l-fridge-freezer-36l-12-24-230v

Technical Specs

Dimensions (mm): 652L 412W 428H
Weight: 18Kg
Volume: 36L
Voltage: DC12/24V, AC 100-230V, 50-60hz
Nominal Rated Current: 12V-3.40A, 24V-1.70A, 240V-0.30A

Looking at something like this:

https://www.jaycar.co.nz/multi-function-42-000mah-portable-power-centre/p/MB3748?gclid=EAIaIQobChMI7MXQsaqw7QIVmFVgCh2cngVQEAQYAyABEgKue_D_BwE

• It is a 100W 240V Inverter (modified sine wave)

• It provides 12VDC to 3 separate points. 9-12V at up to 15A. Ideal for a low voltage lighting system.

Battery Watt Hour Rating (Required for Lithium Batteries)

155Wh

Obviously something like this may be more suited. but outside of my budget:

https://www.torpedo7.co.nz/products/G7BAPN822/title/goal-zero-yeti-400-agm-intl-220v---silver-zero-green-black

12V car port (output): 12V, up to 10A (120W max)
AC inverter US (output, 60Hz, pure sine wave): 110V, 2.6A (300W continuous, 600W surge max)

Would appreciate any help in working this out. Kind regards.

wellygary

8312 posts

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#2615516 3-Dec-2020 12:21

The killer for fridges is the peak starting load when the compressor kicks in,

12V @15A gives you 180W, its probably enough, but you wont know until you try it.

Ge0rge

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#2615895 3-Dec-2020 21:08

I have this fridge, from the same crowd:

https://www.rvworldstore.co.nz/dometic-waeco-cfx-50-fridge

Annoyingly, yours doesn't have the following information that mine does have :

Energy Consumption 12 V DC (Internal @ 4 C, Ambient @ 32 C) 1.10 Ah/h

However as yours is an almost similar size, I would be happy using the same data.

155wh/12v = 12.91Ah so you're looking at around 11 hours of runtime, based purely on capacity.

Personally, I have a deep cycle truck battery that I hook mine up to when I'm camping - it'll last four days at least (longest I've used it for at a time, and it was still going fine).

Hatch

797 posts

Ultimate Geek

#2615903 3-Dec-2020 21:50

wellygary:
The killer for fridges is the peak starting load when the compressor kicks in,

12V @15A gives you 180W, its probably enough, but you wont know until you try it.

Ah yes thank you, something about cold cranking rings a bell. The fridge runs fine off a car 12v port from an old Subaru Forester but I’m not quite sure how much it is drawing from the car. I’m starting to think the battery pack won’t enough power.

Hatch

797 posts

Ultimate Geek

#2615905 3-Dec-2020 21:54

Ge0rge: I have this fridge, from the same crowd:

https://www.rvworldstore.co.nz/dometic-waeco-cfx-50-fridge

Annoyingly, yours doesn't have the following information that mine does have :

Energy Consumption 12 V DC (Internal @ 4 C, Ambient @ 32 C) 1.10 Ah/h

However as yours is an almost similar size, I would be happy using the same data.

155wh/12v = 12.91Ah so you're looking at around 11 hours of runtime, based purely on capacity.

Personally, I have a deep cycle truck battery that I hook mine up to when I'm camping - it'll last four days at least (longest I've used it for at a time, and it was still going fine).

Those domestic/waeco units look really nice!
Probably they are also more efficient than other brands such a mine too.
Thanks for checking the capacity, on paper it looks fine but not sure it has enough grunt to get the fridge cranking, although the fridge does have a low power mode. Probably I should look for something with more grunt and capacity, but those goal zero yeti models are quite pricey.

richms

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#2615917 3-Dec-2020 23:02

Those cheap powerbank things do not output proper 12v, they are just a 3S pack, so 12.6v charge voltage and it drops from there to about 8.something at cutoff. If a fridge uses a peltier junction cooler, they are pretty ineffective as voltage drops.

Richard rich.ms

Scott3

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#2615927 3-Dec-2020 23:22

richms:

Those cheap powerbank things do not output proper 12v, they are just a 3S pack, so 12.6v charge voltage and it drops from there to about 8.something at cutoff. If a fridge uses a peltier junction cooler, they are pretty ineffective as voltage drops.

The linked one is a compressor fridge.

Scott3

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#2615936 4-Dec-2020 00:20

Could go the cheaper and nastier route:

Near new 60Ah sealed Lead acid battery (15.8Kg) for $100.

https://www.trademe.co.nz/a/motors/car-parts-accessories/batteries-chargers/listing/2880144203

2x clips to cigarette lighter cords at $13 each:

https://www.jaycar.co.nz/cigarette-lighter-socket-to-battery-clips/p/PP2007

12V universial laptop adaptor: $25

www.trademe.co.nz/a/marketplace/electronics-photography/other-electronics/adaptors-chargers/listing/2887176333

Can charge the 12v Battery fairly quickly with jumper cables hooked up to a running car, or overnight with a 12v wall charger. I have both allready but if not, the warehouse sells jumper leads for $29 and a smart charger for $59 (or get a nice ctek one for $150)

60Ah works out to 720Wh at 12v. Can't fully discharge lead acid without hitting low voltage cut out's, but even if we only got 60% of that, it works out to 432Wh vs the 155Wh of the Li power bank. At 1.1A average draw, it shroud give 32 hours running.

If you are only looking to get through a couple of nights, a chilly bin and a few frozen 1.5L bottles might be a cheaper, easier bet.

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Hatch

797 posts

Ultimate Geek

#2616244 4-Dec-2020 10:36

Scott3:

Could go the cheaper and nastier route:

Near new 60Ah sealed Lead acid battery (15.8Kg) for $100.

https://www.trademe.co.nz/a/motors/car-parts-accessories/batteries-chargers/listing/2880144203

2x clips to cigarette lighter cords at $13 each:

https://www.jaycar.co.nz/cigarette-lighter-socket-to-battery-clips/p/PP2007

12V universial laptop adaptor: $25

www.trademe.co.nz/a/marketplace/electronics-photography/other-electronics/adaptors-chargers/listing/2887176333

Can charge the 12v Battery fairly quickly with jumper cables hooked up to a running car, or overnight with a 12v wall charger. I have both allready but if not, the warehouse sells jumper leads for $29 and a smart charger for $59 (or get a nice ctek one for $150)

60Ah works out to 720Wh at 12v. Can't fully discharge lead acid without hitting low voltage cut out's, but even if we only got 60% of that, it works out to 432Wh vs the 155Wh of the Li power bank. At 1.1A average draw, it shroud give 32 hours running.

If you are only looking to get through a couple of nights, a chilly bin and a few frozen 1.5L bottles might be a cheaper, easier bet.

Thanks @Scott3, yes looks like best bang for my buck. I have a couple of 12v batteries from the dinghy that I keep topped up but never use as they are too heavy for the tiny thing but came with it. I do have a basic citek charger for my motorbike battery. You're right about the chilly bin, but I'd prefer a longer term fix for all those crays I will be catching!

Scott3

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#2616277 4-Dec-2020 11:29

Hatch:

Thanks @Scott3, yes looks like best bang for my buck. I have a couple of 12v batteries from the dinghy that I keep topped up but never use as they are too heavy for the tiny thing but came with it. I do have a basic citek charger for my motorbike battery. You're right about the chilly bin, but I'd prefer a longer term fix for all those crays I will be catching!

Given you have some 12V batteries and the fridge, might as well run an experiment to see what run time they give. Assuming your charger does 12V, you have everything other than the $13 clip to cigarette lighter socket adapter to make this work.

I don't know your use case, but the 6-8 hour run time proposed is a pretty short term fix. If you use case is travel to campsite on day 1, pitch tents, go diving in the afternoon, sleep the night, then travel home (plugging fridge into boat or car) the next morning it might work, but a decent chilly bin and 4-6kg of ice could easily deal with that.

Note that Li power bank is going to be quite slow (like several hours) to charge with its 2A adapter.

In aussie SUV's kitted out for camping are common. They have a dual battery setups like a camper-van, With fat wiring etc. Will charge at 50+ amps with the engine running, so doesn't need that many running hours per day to keep up with the load of a compresser fridge. Could be a route you could look at if you wanted a longer term solution.

Otherwise something with solar to re-charge during the day. (common for the rangatoto island batches).

Or just go for an old style absorption fridge and a LPG bottle that should last for more than a week.

If it is just for crays, getting a decent chilly bin, and (depending on how remote you are going), swinging past a dairy for a $5 bag of ice every second day could be a cheap easy option.

Goal Zero Yeti range looks super sweet, but unless you use it on a daily or weekly basis, or can avoid purchasing a generator because of it, it would be hard to justify the cost (and they are sold out).

Senecio

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#2616284 4-Dec-2020 11:49

I have this Engel fridge for my camper. Running off an 80A/hr deep cycle lead acid battery I get about 3-4 days with low power LED lights and charging mobile phones.

https://www.burnsco.co.nz/shop/boating/galley-cabin-storage/coolers-chilly-bins/engel-mt35fp-32l-fridge/freezer?gclid=Cj0KCQiAtqL-BRC0ARIsAF4K3WH0Yp2c-Wkizy0MgoB_32c4XmxGhDSwMiXEYQu0ndZbfPJHRb01TDMaAnrIEALw_wcB

I haven't tried to run an inverter off it for any 240v appliances. If I did I'd expect a larger battery and/or supplemental solar would be required.