12v Power form ignition to tub

[Mark R]

Hi Guys

I need power to the tub for our small 3way fridge and want it to turn on/off with the ignition as it is just to keep cold while travelling.

Can anyone tell me where to find a suitable power source to run the cable? From a search it seems a cable run from somewhere in the fuse box near the battery will work but I am not sure specifically where to connect to. It will need to be at least 10Amps and I will wire in a fuse as well.

I have no need for a dual battery set up or anything fancy, just a cigarette lighter plug in the tub to plug the fridge into. I already have lights in the canopy but not sure these cables can handle the power from the fridge.

Thanks

Mark.

 

[bods]

In all honesty, a 3 way will be hopeless on 12v if it is turning on and off all the time. You really need to hook an inverter up and power it with 240v so it does a decent job of keeping things cool... they will also draw a hell of a lot of power, especially on 12v as they don't have any thermostat control, so if that is a concern it may be worth taking a gas bottle and running it off that when you are stopped to keep it cool...

If none of that worries you, then you will need decent sized cable to minimise voltage drop between the engine bay and tub. The fridge might only draw 10a, but with almost 6 metres of cable needed to reach from the battery to the tub, you need something big enough that will give the full amount of power to the fridge. 6mm (50a) cable may be a bit big for you have in mind at the moment, but it would be worth running something around that size in case you decide you want more power in the tub at a later stage and have to run more wiring. That way too, if you decide the fridge isn't running the way you want it to on 12v, you will have enough capacity in the wiring to handle fitting an inverter to run it off 240v instead...

 

[Mark R]

Thanks Bods

We only use it to carry cold stuff from home to the camp ground, typically no more than a 3 hour drive. We leave it on 240V overnight at home to get cold, load up with cold items from the home fridge, unload at the other end and either plug it into 240V or connect the LPG.

I hear ya on the cable size and have 6mm in the garage already. I also have an inverter that I can use ( good idea, thanks!!) and if I go this route I will still need a source for the 12V power that switches off with the ignition and will wire in an Anderson plug instead of a cigarette lighter. Might have to wire in a relay as well, but again will need a 12v ignition source.

Any ideas on where I can find a suitable connection to an ignition controlled 12v source with the capacity to run the fridge?

 

[leo d40]

I needed an ignition source for the redarc unit I put in the tub, took it from the fuse box behind the battery. Used a test light to see what came on with the ignition then used a splice connector to tap into the wire, it's only 15 amp wire but it does the job from what I need. I run 6 B&S cable from the main battery to the redarc in the tub

http://www.redarc.com.au/images/uploads/files/wire_gauge_worksheet.pdf

 

[Old.Tony]

Bods is spot on the money. I do that in my caravan too - let me explain.

3-way fridges work by heating an ammonia+water mix which causes the ammonia to boil and in doing so it becomes a gas which expands, goes through a heat exchanger, eventually drawing heat from the inside of the fridge and the ammonia reforms in the back of the unit where it's heated again. That's a basic look at it - but the key thing to note is that ANY power source is used to HEAT it.

On gas and 240V, the amount of heat is regulated by using a thermostat. This thermostat is NOT used in the 12V circuit, yet both the 12V and 240V circuit use similar amount of watts of electrical power.

This means that to get the best out of your fridge, whack an inverter on the end of the 12V power line and run the fridge on 240V instead. It will actually cool things down faster and stop using power when it doesn't need to.

Now, organising the power - your original question - is easy. It comes from the battery to a 40A thermal breaker (or fuse) into a 80A relay and then to a HEAVY GAUGE cable (both positive and negative, don't need to fuse negative) and run that heavy cable down to the tub.

The relay has to be wired a certain way. You CAN earth it (pin 86) inside the cabin via a switch - since the coil is low power, a thin wire is fine - this allows you to turn on and off the power to the rear from a switch inside the cabin. Pin 85 runs into the power distribution box behind the battery to a point that is live when the ignition is on. Then connect pin 30 to the thermal breaker mentioned before and pin 87 goes to the cable running towards the rear. If you don't want the switch inside, earth pin 86 anywhere in the engine bay (you can use battery negative if you wish).

THAT is the only safe way to send power to the rear of the car.

 

[jonney]

how about the Techni-Ice cooler, 5 to 16 days with a block of ice.

 

[bods]

Thanks Bods

We only use it to carry cold stuff from home to the camp ground, typically no more than a 3 hour drive. We leave it on 240V overnight at home to get cold, load up with cold items from the home fridge, unload at the other end and either plug it into 240V or connect the LPG.

I hear ya on the cable size and have 6mm in the garage already. I also have an inverter that I can use ( good idea, thanks!!) and if I go this route I will still need a source for the 12V power that switches off with the ignition and will wire in an Anderson plug instead of a cigarette lighter. Might have to wire in a relay as well, but again will need a 12v ignition source.

Any ideas on where I can find a suitable connection to an ignition controlled 12v source with the capacity to run the fridge?

As old tony has mentioned, you can wire it to switch on automatically when you turn the ignition on. You have a couple of options. You could use one of the smart dual battery solenoids that will wait until the alternator starts charging before it lets power through, you would simply connect the aux battery side of the isolator to the input for the fuse or circuit breaker that is protecting the wire running to the tub. The advantage with this is it will continue to run for a short time after the engine is shut off, until the battery charge drops below the cut off level and then the isolator will cut the power to the tub.

You could also use one of the basic dual battery solenoids that is powered from an ignition "on" source. Normally rated to around 100a and most auto shops will keep them on the shelf. Something like this http://www.ebay.com.au/itm/like/291...901706361414&chn=ps&lpid=107&ops=true&viphx=1 it will do a good enough job for what you need. As the others have mentioned about the ignition switched power under the bonnet. I don't have a d40, so can't help you there... with these type of isolators, you simply hook one side directly to the positive terminal of your battery and then the fuse on the output side and power to the tub...

 

[Old.Tony]

Thinking of isolators ... I just bought one of these (all gone now, but others available) for my caravan. I have a solar panel that charges the van's battery, but because the van is over 2T, it has a breakaway brake system which has its own separate battery. The system wasn't thought out too well - because the battery is only charged when connected to the tow vehicle.

I'm connecting the VSR to the van's battery and then connecting its output to the breakaway battery (which does have an "aux" power input but it was never hooked up to anything).

The theory is that the solar panel will charge the house battery and keep its voltage around 14.1V+ while charging. The VSR will come on, allowing the breakaway battery to charge, until the solar panel is not producing enough power - it then disconnects the breakaway battery until the sun's up again and the main battery has been charged enough.

A similar thing could be used in the car. Notice that the VSR is 140A - more than enough.

 

[Mark R]

Thanks Guys!!

We are not planning to go touring, just tow the boat to the lake camp for a few days and head home. So I don't want to go to great expense but I have been educated here.

The VSR sounds like the go, with a second battery. Then my 240V inverter connected at the end to plug the fridge into. Also gives me a power point for our movie's..... We often connect the lap top and projector up on the tailgate, and use the white walls of the gazebo as a screen and stream the sound through the car stereo. Outdoor cinema, done! We check out the Go Pro videos of the day on the water - wipeouts and all! Also watched "The Castle" at Bonnie Doon camp site last summer!!!