UKH

How long could you use a 21L 12V cooler box in a car with a decent battery without risking flattening the battery if the vehicle was stationary? Would a shortish journey every 2/3 days do the trick? 

Thanks. 

Not long. In fact i've flattened mine overnight and had to call AA out to the campsite. I left it plugged in accidentally and am very wary now. I think some have an automatic cutoff to save your battery but while ever its off its not doing its job (obviously).

What Tom V said.  Also, many modern vehicles de-power the auxiliary socket when the vehicle is switched off.

They're for keeping your food cold on a long drive.

Not very long at all if you had it plugged in all the time. A thermoelectric coolbox draws about 4A continuously so a typical starter battery would be dead if you left it on overnight. A short drive every 2/3 days wouldn't be sufficient. Even a 120Ah leisure battery in a van/caravan would only last max 15 hours (as only about 50% of the capacity is usable) 

A 12v compressor coolbox has much lower power consumption once cold so you could conceivably leave it on for a day but they start at about £200 for a 20L version. Still not recommended to run things off a starter battery continuously as they're not meant for that.

Don't chance it. I did and regretted it. Had a 12v cool box connected to my yeti and 'forgot' about it overnight (vehicle was supposed to cut aux power below a certain level to preserve the battery power but obvs didn't) came back to car following morning and battery was dead. 

Thanks to all for helpful replies. I will adjust my meal planning accordingly. 

I'm guessing as you are in a car you are(or might) be using campsites. If so, on many campsites you can(or certainly could in the past) put freezer blocks in the campsite freezer.

These, with a well insulated cool box, could keep stuff cold for a good while.

Dave

I often car camp using a small, insulated cool bag/box thing. If I put two or three frozen meals (homemade chilli or Bolognese mince in those plastic boxes takeaways come in) they act as cooling and thaw over a day or two. Milk and other perishable stuff stays cool and lasts fine for days. I keep the thing covered under sleeping bag and other stuff. Seems to work even when the sun is full on the car.

Really good question. I’ve often thought of buying one of these but after reading the replies I’ll give it a miss.

I second this. Rotating sets of freezer blocks, morning and evening, have kept the cool-box tolerably cool for me in the past. I wouldn't leave my steak tartare in there during a hot day though.

Edit: the better the insulation of your cool-box, the better -- obviously. I use a polystyrene box. 

As others have said, a coolbox is very inefficient.  They burn through about 4a per hour.  A car starter battery is about 70-90ah and it isnt a case of being able to use those full 70ah, more like 35-40a.  You would be lucky to get a night out of one.  

Instead, do what i did when i used to camp.  Fill as big a water bottle as you can fit and freeze it.  Put it in coolbox with rest of your gear.  I have seen me get 2-3 days out of a coolbox this way with pretty good results

A dislike? For a reply with my own advice (hopefully of use) to a request for help. There are indeed some saddos about on here.

Yes we have had good success camping in Italy with a religious routine of changing ice packs twice daily. You can add extra insulation to your coolbox wrapping in a blanket or under spare clothing.

I've flattened the battery in my (new at the time) subaru too much to start the engine by running a TE coolbox for an afternoon.  The other thing is that TE coolboxes don't actually have the ability to cool things down, they can only keep cold stuff cold.  You're better off rotating cool blocks or 2litre bottles of water in the campsite freezer, I've been doing this very successfully on scout camps for 20 years. Write your name on them so you know they're yours. Coolblocks are simply water with stuff in to stop them growing algae and bottles of water work just as well.  If you use salty water in your bottles you'll get the melting point down to -2 or so. I've found the best thing to do is create a 'cold core' of bottles/coolblocks in the centre of the coolbox with the food arranged outside it, that way energy always comes out of the food instead of the sides of the box.

TE coolboxes are often pretty poor designs - having the TEC in the lid severely limits the amount of thermal insulation it can provide, and the TEC achieves little.

I've wondered before about a custom coolbox design that places the ice core inside an insulated sub-compartment within the chiller.  Both inner and outer faces of the insulated sub-compartment would have aluminium cladding, and bimetallic strips would form thermal contractors that only engage when the outer food storage part is warmer than say 3°C.  By regulating the outer box temperature, the cool store in the inner sub compartment lasts far longer, compared to it trying to crash the food down to -18°C and so drawing far more heat in through the outer walls.  This system would then be compatible with "super-ice" from -80°C freezers to provide longer lasting passive cold.  Combined with a vacuum panel and aerogel sandwich construction it would be quite the passive fridge.  If I couldn't get the bimetallic contractors to work, it could have a microprocessor powered contractor system that would need very little power - which itself could come from a small TEC through which heat enters the super-ice core from the food compartment.

As I've been working away from home for the last 18months and the hotels have not been doing food I needed a way of storing food and keeping it cool.

Picked up Dometic WCI33 cool box (passive, no electrics) using a few freezer packs and bottles of frozen water it stays cool for the week. Bottles are usually only half defrosted after 5 days even during the summer and left in the car. 

We have the small 13l Dometic - very pleased with it. Worth saying that size is everything, the bigger the coolbox the longer it'll stay cold. 

Not long:

Typical starter battery capacity 70Ah (but don't use move than 1/2 or you'll shag the battery, you need a leisure deep discharge rated battery for running down regularly that but they're generally not good for stating cars).

Typical cooler current draw ~5A

Typical time it runs 35/5 = 7 hours before trouble, my experience is trouble occurs faster!

Compressor fridges (very expensive) rather than the cheap thermoelectric ones are much more efficient. You might get 2 days from a compressor fridge with a big leisure battery in holiday conditions. Obviously you'll get as long as you want in very cold conditions!

You can actually pick up compressor cool boxes a lot cheaper now. I bought a 25 litre one for about £200 towards the end of last year. Pretty decent, digital control and will even go to -18C, which came in handy when I was defrosting the freezer.

Where? I might want one...

Alpicool brand, available on Amazon

https://www.amazon.co.uk/stores/page/E574CBC1-D0C9-4409-A924-6800623EC7E4

Annoyingly the prices do seem to have increased by 20% since last time I checked but they're still half the price of the Dometic equivalents.

We used to have a dual powered one, 12Velectric & gas bottle.

Just put it outside the car/van when parked up (and out the wind) and run it on the gas.

Hi....Ordinary vehicle batteries are not intended to be essentially released in typical use. Running them down radically abbreviates the battery life.

You need to confine release conceivably 20% at most from full, on the off chance that you would prefer not to harm the battery. That lone gives several hours use.

Preferably you would have a different "recreation battery", which are intended for profound release cyclic use. That interfaces with the vehicle through a split charge hand-off, so it charges when the vehicle is running yet doesn't permit any channel from the typical vehicle battery.

No they don't. They might burn through 4Ah per hour, also known as 4A.

In any case, a cold box will stay appreciably cold for a day or two if you don't keep opening it and keep it full of cold food. A drive every couple of days to bring the temperature back down would keep food for a while.

apologies if I have phrased it incorrectly.  So 4Ah per hour.  Sums still stand and a car battery will not cope with running a 12v cool box without some other tactics similar to what you suggest which tbh falls into a similar suggestion to my own to get 2/3 days out of one.  But as long as you have made your point eh 😀

4pt milk bottle good for this.

Yep.  I tend to take a 2 pint which i use and a frozen one which generally defrosts over a period of a couple of days and gives me nice fresh milk for my breakfast.

I have to be careful though in case tlouth7 questions my use of semi or full fat milk.  He may decide i have misslead you in some way.......

Way round this is to buy a cheap bag of ice and put in the box. Keeps everything cool while it's turned off.

I've run and installed every possible type of fridge over the years, mostly in boats in the Med and for my own use in Europe. A well installed (10cm insulation) compressor fridge with 2 big solar panels and 110Ah batts copes pretty well but normally it's more effective to run an engine driven compressor.

12v Peltier systems are worthless in normal European summers, I have two one of which is an original Ford extra for my Galaxy and it achieves  no better results turned on or off. Like many I use a coolbox with pre-cooled contents, 6 deep-frozen bottles of water and after the third or fourth day buy bags of ice to keep my beer cool.