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  #21  
Old 14-10-2016, 01:16 PM
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Quote:
Originally Posted by happy john View Post
Hi DVR, I'd use the term "no brainer" to refer to the morons that run their 3 way on gas as they travel and fuel up, due to the fact their fridge has been poorly installed and wired this is the path they use.

You'd have more chances being trapped in a burning car with a fire started by 12 volt than electrocuted by a 600watt invertor in the tub. The 3 way is on the way out now, due to the reduction in price of solar and soon Lithium compressor is the way to go.

No more sordid milk or hot beer to worry about too. Have you a link to these electrocution claims?, I've never heard of it.

Cheers
Hi John, Just google "3 way fridge on inverter" this and others will come up
http://www.exploroz.com/Forum/Topic/...e_driving.aspx

This is just one of the pages I found. The dangers are discussed through out the replies (as well as good 12V solutions) but the final reply sums it all up the best.

And your right, not running on gas while traveling is a no brainer.
Also.
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  #22  
Old 14-10-2016, 08:57 PM
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Part of what he talks about is concrete but there's also reliance on what-ifs.

His spec for cabling is also grossly inadequate. "6mm solar" ? No chance. Not over the distances we're talking. I use 21mm2 cable. It's fused. It's active when the ignition is on ONLY. It's connected by screw-in connectors (not ciggy lighter, he's dead right about their reliability). The only thing connected is the fridge and my inverter sits immediately beneath my fridge, no extension cable required.

I take the issue about an accident seriously though. I can't predict when that sort of thing will happen, so my little relay circuit is going to be upgraded - I'm going to build a circuit that will stop working when the vehicle goes off more than a certain amount from level (indicating a roll-over) or when a certain amount of impact is detected. Sound safe enough?

Note that the biggest difference between 12V and 240V operation is the bypassing of the thermostat under 12V. Even if they claim the heating elements draw the same amount of watts (see below), over an extended period this is not the case: without a thermostat, the 12V operation continues mercilessly, whereas once the thermostat determines that the fridge has cooled sufficiently, the 240V operation - and thus the draw from the car - ceases.

Given the efficiency of the insulation in the fridge (and I know this for a fact, because I have an ammeter sitting on top of my brake controller in the cabin that monitors the power going to my fridge) the inverter actually draws power for a very small amount of time while driving.

12V heating elements: in a word, they're rubbish. A 150W element might draw 150W (about 12A) but it seems to produce vastly less heat than a similar 150W element under a higher voltage. They can't be the same element, either. The heat produced by a heating element using DC power can be calculated by the formula V2/R = watts. This means that under 12V, you need a fairly low resistance element to produce similar heat to that used by 240V. In numbers, for a heater producing 150W: 12V requires 12 * 12 / R = 150 or 144/150 = R = 0.96Ohms.

Fundamentally, it works the same for AC current although the values are averages based on the RMS values of the power. 240V requires 240*240/R = 150 or 57600/150 = R = 384Ohms.

I still prefer the 240V method, but I am switching over to 12V operation for the time being. Because my fridge isn't an AES model there's little point in having the circuit disable the 240V side and enable the 12V side, but I'll build that in anyway. My next fridge though will be a compressor fridge so it doesn't really matter, and the inverter will be tossed.
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  #23  
Old 15-10-2016, 07:19 AM
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The 3 way seems to present a problem to qualified Auto Electricians, sadly most are unable to wire a fridge in a van properly. I followed a elderly gent into a servo and told him he had no lights on the van.

On inspection the trailer plug was a molten mess, the sparky used 5mm wire through the aux of the plug to a fridge that consumed 22 amps. The poor bloke had to have the tug and van towed back home on their first trip in a 60k van.

Tony, I have seen folk use the extra protection you spoke about in the event of an accident via one of these.http://www.rvpartsexpress.com.au/rv-...ge-switch.html
You just need to modify the time delay circuit by ajusting a trimpot, and have it inline from your power supply to the inverter.

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