How to auto switch to 12v Fridge Operation during driving

[Seamus]

Here's one for ya... I want rig up our 3way fridge to automatically switch to 12v during driving. We use mains hookup on sites to run the fridge, the gas option at startup is so temperamental & can take forever to ignite sometimes so we've almost given up trying.

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I saw this auction on eBay for an all singing all dancing (supposedly split charge relay that powers the fridge when driving but don't really want to get rid of my unit, I wondered if there is a doo-able workaround to automatically power the fridge with 12v once the engines running?

[billybigspud]

just do exactly the same as a normal split charge set up. Dont use one of them unimtelligent things and just use a relay. dont know the wattage of the fridge but just divide it by 12 and it will give you the amps. Make sure it is all rated correctly and volt drop allowed for.

[bigherb]

Perhaps if you said what your split charger set up is then we can help you as it may already have a take off for the fridge.

[MidLifeCrisis]

I had a similar thought about an auto-switch - but I think that the issue (if your fridge is like mine) is that there is a switch on the front of the fridge that you use to select either operation via 240v or operation via 12v.
This is the switch that you always forget to switch to the correct position.

Being forgetful (and lazy) - I would like the fridge to automatically run off 240v if it is available, then on 12v if 240v is not available (assuming that the 12v is only available with engine running via the usual relay setup)

This would prevent the situation where you are on 240v in the campsite, disconnect the 240v and merrily drive away - only to realise hours later that the fridge is still switched to 240v and has been slowly warming up ......

That split charge relay do-dad will very nicely supply 12v to your fridge when the engine is running but it won't be able to help you if your fridge is still set to 240v !!!

I think that there must be a solution using relays that are triggered by the presence of 240v or 12v but can't quite get my head around it (as it would also need to allow for you potentially wanting to run off gas even though 240v is available, and possibly even if 12v is available) ...... it would also mean messing with the wiring of the fridge !?!?

Best thinking caps on!!

[ajsimmo]

I wondered if there is a doo-able workaround to automatically power the fridge with 12v once the engines running?

Easy solution for this is a standard 4 pin relay. Pin 30 to starter battery +ve, pin 87 to fridge 12V feed. Relay is switched by connecting pin 85 to blue alternator charge light wire (find behind dash and connect properly - NOT scotchlocked!) and pin 86 to earth.

This setup can be further refined by putting a switch in the trigger wire to the relay so you can choose whether to have the fridge on when running, and/or a tell-tale light wired to pin 87 so you know when it's on and working. Don't forget to fit inline fuses (definitely one in the fridge feed, near the relay), and make sure cable is capable of carrying the current for the fridge.

[Seamus]

I wondered if there is a doo-able workaround to automatically power the fridge with 12v once the engines running?

Easy solution for this is a standard 4 pin relay. Pin 30 to starter battery +ve, pin 87 to fridge 12V feed. Relay is switched by connecting pin 85 to blue alternator charge light wire (find behind dash and connect properly - NOT scotchlocked!) and pin 86 to earth.

This setup can be further refined by putting a switch in the trigger wire to the relay so you can choose whether to have the fridge on when running, and/or a tell-tale light wired to pin 87 so you know when it's on and working. Don't forget to fit inline fuses (definitely one in the fridge feed, near the relay), and make sure cable is capable of carrying the current for the fridge.

that's very helpful indeed (if a little daunting) but I like the sound of that setup. I have a few relays in the spares box of various numbers so will get to it. Thanks again