Charge a second battery from a cigarette lighter socket

[steve-r]

I thought this was an easy one but I can't find the answer anywhere. My van is all set up with power solar etc and great. However I want to use my mobile fridge in another car. I have a portable leisure battery I can use for the fridge when parked but how can I charge the battery from a cigarette lighter socket while driving?

 

[roadtripper]

Is it a compressor fridge or a peltier electric coolbox? Both are going to draw significant power, but coolboxes will draw quite a lot more.

The reason I ask is it's almost certain you will not be able to replace the charge in a few hours of driving that the fridge will take out running all day without a high current fixed charging arrangement.

 

[sparkzer]

Can you expand upon what portable leisure battery you have? Jackerys and the light generally have an option to change from cigarette lighter socket?

 

[steve-r]

I have a leisure battery which is not connected to anything so 'portable'. It is a battery only with no extra electrics. The fridge is an engel which is very power economical but I will check wattage tomorrow. But really my question is how to charge a 12 volt car battery from a cigarette lighter socket while driving. If if runs out then so be it, but I just want to maximise the battery when possible.

 

[sparkzer]

Ah, ok...some sort of DC-DC charge controller will be your best option to limit the current being pulled out your cigarette lighter socket, however I'm not sure something exists on the market. If you just connected the battery directly to the socket, it could well draw far more than the socket can deliver and as such it will blow fuses in the car as they typically can only delivery up to about 10A, where as your flat leisure battery could draw significantly more than this.

Depending on your fridge how much current it draws etc and what you are planning on putting in it, you could just power it directly from the cigarette lighter socket, then leave it unplugged at night. Its obviously going to get warmer over night, but if you don't open it etc it may maintain temp to an acceptable level. I actually do this with my van in winter, I like you have solar, which in summer give me plenty of power but in winter if i leave the fridge on 24/7 after a few days the leisure battery voltage starts to drop so I turn my fridge off at night. I guess you could conduct a test in your van as to how 'warm' your fridge gets if not turned on over night.

 

[steve-r]

Thanks Sparkzer. I use it for long day out sporting events. I plug the fridge directly into socket during travel but once on site I no longer have car power so I use the portable leisure battery. Then the fridge gets opened and used all day. Maybe my best solution would be a mobile portable solar panel to keep the battery topped up. I would fit a better permanent solution but I keep using different cars!

 

[roadtripper]

If it's for a single day then maybe approach it differently - you can treat a good block of ice as a thermal battery.

A couple of large ice packs should keep a well insulated fridge or coolbox good for a day, and if you can run it in the vehicle even better. We do the same with our electric coolbox to move frozen food between home and our apartment when going on holiday.

If the ice packs take up too much room a trick we've used for events before is to freeze cartons of fruit juice - a useful kilo of ice to keep things chilled and then a really refreshing chilled drink as you are packing up.

 

[cgtmiles]

If it's for a single day then maybe approach it differently - you can treat a good block of ice as a thermal battery.

A couple of large ice packs should keep a well insulated fridge or coolbox good for a day, and if you can run it in the vehicle even better. We do the same with our electric coolbox to move frozen food between home and our apartment when going on holiday.

If the ice packs take up too much room a trick we've used for events before is to freeze cartons of fruit juice - a useful kilo of ice to keep things chilled and then a really refreshing chilled drink as you are packing up.

We do the same for extra storage when going away in the van. Cool box connected either to mains if hooked up or 12v when travelling but we store it most of the time in the awning so just have ice packs on rotation from the van fridge. Does the job nicely to add a bit more booze cooling and allow for at least some food to be taken!

 

[roadtripper]

Just to note that I came across this item on Amazon for this use case:

https://www.amazon.co.uk/dp/B09R28SL75

To be clear this isn't a recommendation but it does look like some lower current portable DC-DC chargers might be around, I think possibly for charging mobility scooters, e-bikes and similar. The use of a 3-pin XLR connection for the batery-to-be-charged end gives me nightmares as a some time lighting and sound tech, but there you go...

 

[roadtripper]

A further note that I came across the DC-DC battery maintainer from a reasonably well known brand. The charge rate is only 2A but that might still be useful.

Optimate DC-DC 12V 2A Battery Charger & Optimiser TM-500

The OptiMate DC-DC - 12V 2A Battery Charger & Optimiser OptiMate DC to DC, recovers, charges & maintains a 12V lead-acid or lithium battery from another 12V battery or DC supply. OptiMate DC to DC brings you the advanced OptiMate features to places where there is no access to an AC Mains Power...

www.tayna.co.uk