Running a 12V fridge from MG4 LV Battery

Blacksmith

Blacksmith

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I am looking to run a 12V car fridge full time in my MG4 77. Is it better to use the onboard 12V battery or add a second 12V lithium battery to do the job?
The fridge draws about 3-4 amps when running.

My concerns are running the onboard 12V battery down too low, that the car won't start, or having the fridge without power for extended periods (if it cuts off on low battery).

I think there is enough space in the front next to the onboard 12V battery to fit a 60AHr Lithium battery as well, and use a voltage sensing relay (for a dual battery ICE setup) from the Onboard 12V battery to keep it topped up.

Any advice or input is welcome.
 
In theory the car will top up the 12V battery using the HV battery, so this will work.

In practice, however, the cheap 12V battery SAIC use has low capacity and isn't deep cycle and there seem to be bugs some people have in this top-up system that lead to a flat 12V battery.

We won't know until someone tries it and all you need is a jumper battery if your 12V does go flat - so if you are willing to risk that, by all means try and share here so we can hear how you get on.

Perhaps there are other members who have already tried this?
 
I have concerns about the SAIC 12V battery being able to run a fridge for a few days while the car isn't in use, so that is why I think an extra battery just for the fridge, rather than swapping out the SAIC battery is a better way to go. I can have more control over its charging voltage, and have fewer concerns about the SAIC battery running low.
If the SAIC battery does go flat it is easy to jump it from the 2nd battery.
 
A bit of a long shot but could you use a Noco boost and kill 2 birds with one stone ? It would depend very much on what percentage of the time the fridge actually runs for and whether it needs to automatically charge, and it turns out your budget too.

Hmph - It looks like the newer boost x models have power delivery on USBC so a £15 12V adapter thing can get you 12V at 3A. Also it's the same port for charging so no go on both counts.

I knew they had a version which has simple 12V out up to 15A, but it turns out you need the GB70 for that which is £200. I also don't know if you can charge whilst delivering 12V. The battery is 56 Wh so probably too small. Handy to have if your other car is a 6L diesel though ?

I'm guessing all the smaller ones for cars would be all that's needed to start an EV, even if only partly charged.
 
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My new 30L 12V fridge consumed an average of 250Wh over a 4 day test run. This works out at around 20Ah at 12V. I doubt the 12V battery in the MG4 is much more than 20Ah capacity and not deep cycle. Consequently your battery will run flat within a day unless the car charges it from the traction battery. AFAIK the charging only happens when the car is in use or being charged. Ergo it's not IMO practical to run the fridge from the 12V battery.
 
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MozFromOz said:
My new 30L 12v fridge consumed an average of 250WH over a 4 day test run. This works out at around 20Ah at 12v. I doubt the 12v battery in the MG4 is much more than 20AH capacity and not deep cycle. Consequently your battery will run flat within a day unless the car charges it from the traction battery. AFAIK the charging only happens when the car is in use or being charged. Ergo it's not IMO practical to run the fridge from the 12v battery.
Click to expand...
The car should charge the 12V battery whenever needed, not simply when the car is on or being charged.

There do seem to have been some bugs with this - which is why a few people have had a flat 12V battery every so often. So it may depend which updates the car has.

I've not heard anyone actually try adding a high load device and see what happens when the car is left alone. It would be a useful experiment.
 
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I don't know much about the 12V charging in my essence yet. Only had it for a month. My Nissan Leaf only charges the 12V when the car is on or when plugged in and charging. I guess the only way to know is to put a logger on the 12V battery and see what the voltage does.
 
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I've had 14.5V showing on the app for the 12V battery when the car has been sat on my drive, not connected to the charger and has been locked for some time.
On some of the first cars there seems to be a software glitch that stops the main battery charging the 12V battery if the car is off.
 
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Did anyone found a fridge that could work? I am planning a roadtrip and would love to get ideas and experiences. We don't need anything big, maybe even find something compact for between the front and the back seats?
 
MozFromOz said:
My new 30L 12V fridge consumed an average of 250Wh over a 4 day test run. This works out at around 20Ah at 12V.
Click to expand...
That doesn't sound right. That's an average of 250Wh / 96h = 2.6W or about 0.22A at 12V. 20A at 12V for 96h is some 23kWh. You would need a 20 * 96 = 1920Ah battery. Neither of those makes sense.
 
Fridges running on 12V are very power hungry devices. Most caravans and motorhomes use 3 way fridges 240v AC / 12V DC / Gas. The 12V is only configured to operate when the ICE is running for very good reason! Some high quality cool boxes are a little better with their good insulation but generally they still use power hungry Peltier pumps to provide the cooling. If you're going to use the onboard 12V I would suggest you only do that while the vehicle is in operation and even then when it's not under high loads such as heated seats, HRW, lighting etc. If youre going to use LiFEP04 battery, make sure it's protected from over discharge which will give it a premature end of life.
 
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My advice is go for the biggest deep cycle battery you can afford, but have solar charge it, or wind.
 
External panels, charge controller and a big capacity battery.
Until the regen on the car is significantly high, then charging a second battery off a MG4 will just shorten the range, by how much, not sure, but it'll take more away from the 12V battery leading to recharge it more. My option for camping ended up being a big cool box full of ice. Just changed it out every 2 days. Cost 3 bags of ice per 2 days. It's an Igloo brand.
 
Sorry to go back on topic, but if i want to run a fridge for 3 days from an industry standard 12V plug, the suggestion is: this is not possible unless i do crazy mods on the car?

Would the main reason be that EVs can't use the 12V sockets for more than a phone?

Or, do i just need to buy a new higher quality and bigger in KW battery?

Or is there something like an EV fridge that has it's own battery? Still using a single stupid 12V connector and zero mods required.
 
The 12V socket on the MG4 is only rated to 120W. If you can find a 12V fridge that will accept that maximum input power then it should be OK.

Not sure I'd want to drive the 12V port at 120W constantly though, nor would I want to do so when the car wasn't in the READY state. But maybe that's just me. ?‍♂️
 
siteguru said:
The 12V socket on the MG4 is only rated to 120W. If you can find a 12V fridge that will accept that maximum input power then it should be OK.

Not sure I'd want to drive the 12V port at 120W constantly though, nor would I want to do so when the car wasn't in the READY state. But maybe that's just me. ?‍♂️
Click to expand...
The job I'm doing for a few weeks has the accessory sockets on a Tesla Model Y feeding 135w each into some I.T. equipment in the boot. 6 weeks into the job I have had to hardwire both circuits due to the plugs and sockets burning up, they could not stand the constant 10 amps. On one of the cars the rear nearside of the boot actually caught fire and had to be extinguished. I think your assessment and opinion is a very wise practice.
 
I have a 240v/12v Engel fridge that we use in our campervan. I added a leisure battery to run the fridge, lights, etc when camping. A 60Ah deep cycle battery will last almost an entire weekend, but I also have a 80w solar panel that is used to top up the leisure battery. I would definitely recommend fitting a second battery with relay for the fridge.
 

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