Freelander 1 Aux Power for Cool Box

Hi
I'm looking for a easy way to be able to power a small 8L 12v cool box when parked up.
A full split charge seems a bit over kill & solar is crazy expensive
I'm thinking about fitting a small battery, (maybe a motorbike battery) and connecting that up to a switched 12v supply in the boot (maybe tapping into the towbar elecs) via a diode so it charges when the car is running and then doesn't feed back when not running.
I know the std charge rate is approx. 14v for the car battery but it can charge a caravan battery via the twin elecs.
Would this work, any other suggestions?
Thanks.

Mr K said:

Would this work, any other suggestions?

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First off you need to know the current draw of the cool box. Most use a peltier heat pump, which will be rated at about 50 Watts, with another 5 Watts for the fan.

So you need a battery that is able to supply 55 Watt hours of energy for the time you need between charges.
Now a 100 AH car battery has about 550 Watt hours of energy storage before it needs charging, so this is about 11 hours of cooling before it's flat.

A motorbike battery will probably give you 2 maybe 3 hours before it's flat, so not much use.

The best way is with a lithium battery, but those are more expensive, but also have a much longer service life.

Thanks
The manual states 46 watts and 3.8A.
There's not a lot of room in the back of FL1 hence why I'm looking at small battery.

Mr K said:

Thanks
The manual states 46 watts and 3.8A.
There's not a lot of room in the back of FL1 hence why I'm looking at small battery.

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So how long do you want to power it for?

Buy a dual cool box, cool while you drive then cool on gas when stationary.

might be more money but will save extra batteries and/or wiring.

J

The cheapest way is fit a second battery and use that for your fridge connect + to + and - to - then both batteries stay as 12v both batteries charge when driving

Nodge68 said:

So how long do you want to power it for?

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A couple of hours will be fine.

Dbest43 said:

The cheapest way is fit a second battery and use that for your fridge connect + to + and - to - then both batteries stay as 12v both batteries charge when driving

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thanks but that would also drain both batteries when parked up.

Mr K said:

A couple of hours will be fine.

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It's easy to work out the battery size needed. Multiplying the AH of the box by the run time required, will give you the minimum capacity battery needed.
Add a solar panel of decent size and a charge controller, and you'll be able to charge the battery without running the engine.

I use a home made solar generator when camping. Its got more than enough power for tent lights, phone charging and running a cool box, all charged by solar panels.

Nodge68 said:

It's easy to work out the battery size needed. Multiplying the AH of the box by the run time required, will give you the minimum capacity battery needed.
Add a solar panel of decent size and a charge controller, and you'll be able to charge the battery without running the engine.

I use a home made solar generator when camping. Its got more than enough power for tent lights, phone charging and running a cool box, all charged by solar panels.

Click to expand...

thanks.
How do I find the AH of the box? the manual only states 46 watts and 3.8A.
Do I multiply 3.8 x 60 = 228AH? So I for 2 hours I wuld need a 456AH battery? (seems very high)
So a battery rated at 2Ah (25Wh) would be useless??

This website states I need a 3.83AH battery (I'm rubbish at elecs) so is the 3.8A that's stated in the manual the AH?

Just put an on/off switch in-between batteries if you think your going to use that much power back in the day we had lots of vans with auxiliary batteries with this configuration

Mr K said:

thanks.
How do I find the AH of the box? the manual only states 46 watts and 3.8A.
Do I multiply 3.8 x 60 = 228AH? So I for 2 hours I wuld need a 456AH battery? (seems very high)
So a battery rated at 2Ah (25Wh) would be useless??

This website states I need a 3.83AH battery (I'm rubbish at elecs) so is the 3.8A that's stated in the manual the AH?

Battery Capacity Calculator

Battery capacity calculator converts between amp-hours and watt-hours.

www.omnicalculator.com

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If it's 3.8 A, then it'll use 3.8 AH of electricity. So a 38 AH battery will give you 10 hours of running.

A 2AH battery would give about 30 minutes run time.

This should work, https://uk.rs-online.com/web/p/lead...KCIN22eEijw_iQV-x2xoCmMgQAvD_BwE&gclsrc=aw.ds

Mr K said:

This should work, https://uk.rs-online.com/web/p/lead-acid-batteries/6142475?cm_mmc=UK-PPC-DS3A-_-google-_-DSA_UK_EN_Batteries+&+Chargers_Index-_-Lead+Acid+Batteries|+Products-_-DYNAMIC+SEARCH+ADS&matchtype=&dsa-1592138853539&cq_src=google_ads&cq_cmp=15904458410&cq_term=&cq_plac=&cq_net=g&cq_plt=gp&gclid=CjwKCAjwx_eiBhBGEiwA15gLN8IbiRKpwP1h5DrFBaV8x2G4Js32Xsen8o1KCIN22eEijw_iQV-x2xoCmMgQAvD_BwE&gclsrc=aw.ds

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This would give a longer life, and comes with a charger.