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How long can you safely run a 3way fridge on 12v without charging the battery ??
Hi, Domino, and welcome to MotorhomeFacts!
The 'standard' 2-way fridge won't run off habitation 12V. It is designed to run off either gas or mains electric. It will run off the engine 12V, but only when the engine is running - the fridge takes too much power. Also, the efficiency is much lower on 12V, so typically the fridge won't reduce its temperature off 12V - only maintain it.
Hope this helps.
Gerald
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How long can you safely run a 3way fridge on 12v without charging the battery ??
Hi, Domino, and welcome to MotorhomeFacts!
The 'standard' 2-way fridge won't run off habitation 12V. It is designed to run off either gas or mains electric. It will run off the engine 12V, but only when the engine is running - the fridge takes too much power. Also, the efficiency is much lower on 12V, so typically the fridge won't reduce its temperature off 12V - only maintain it.
Hope this helps.
Gerald
Oh yes it will!
If someone has wired the 3-way fridge to do so!
Trev
______________________________________________________________ OH! if your going away, donīt forget your motorhome!
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How long can you safely run a 3way fridge on 12v without charging the battery ??
Hi, Domino, and welcome to MotorhomeFacts!
The 'standard' 2-way fridge won't run off habitation 12V. It is designed to run off either gas or mains electric. It will run off the engine 12V, but only when the engine is running - the fridge takes too much power. Also, the efficiency is much lower on 12V, so typically the fridge won't reduce its temperature off 12V - only maintain it.
Hope this helps.
Gerald
Oh yes it will!
If someone has wired the 3-way fridge to do so!
Trev
OK going with what Trev suggests a typical 12V heater in a 2 or 3 way fridge is 100W that is about 8 Amps So dividing that into the Ahr of your battery gives the result in hours BUT that assumes nothing else is on AND you are going to run your battery down to flat. As its recommended not to take it below 50% and never below 10% this complicates things.
Remember though as Gerald says most systems are wired so that the 12V only works when engine running , and 100W is enough to maintain temperature but not to cool down or cater for you opening the fridge door.
Hope this helps
______________________________________________________________ Regards Frank
Get behind early - it gives you more time to catch up.
Denn wir haben nichts in die Welt gebracht; darum offenbar ist, wir werden auch nichts hinausbringen.
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Oh yes it will! If someone has wired the 3-way fridge to do so!
Sorry - of course, you're right. It will if wired so to do. But as Frank has pointed out, it's not at all ideal, and not the way it was intended to be run.
Gerald
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I am afraid in this case the "piece of string" is rather short than long...
A 3-way fridge is based on the absorber principle, which is bound by the laws of physics to be significantly less efficient than the compressor principle that your domestic fridge runs on. As Sallytraffic has already pointed out, a typical 100-litre absorber fridge draws about 100 watts in 12-v-mode, which means 8.3 amps. However, if you deplete your leisure battery down to 10%, then it will already have suffered permanent damage. Do this 4-5 times, and the battery is dead!
A lead battery should never be discharged to less than about 40% of its nominal charge. And, keep that in mind, the MH's alternator will normally not be able to charge it up more than about 85%. So, if you have a 110 Ah battery:
85% charge means 93.5 Ah, 40% charge means 44 Ah. Only the difference, so 49.5 Ah, is available for consumption! Means you can run the fridge just a little less than 6 hours, provided that no charge is used for any other purposes like lights, water pump etc.
So, better don't bother about re-wiring your fridge, but use the 3rd of the 3 ways of operation: Gas.
Best Regards,
Gerhard
______________________________________________________________ Never attribute to malice that which can be adequately explained by stupidity. (Finagle´s law)
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I am afraid in this case the "piece of string" is rather short than long...
A 3-way fridge is based on the absorber principle, which is bound by the laws of physics to be significantly less efficient than the compressor principle that your domestic fridge runs on. As Sallytraffic has already pointed out, a typical 100-litre absorber fridge draws about 100 watts in 12-v-mode, which means 8.3 amps. However, if you deplete your leisure battery down to 10%, then it will already have suffered permanent damage. Do this 4-5 times, and the battery is dead!
A lead battery should never be discharged to less than about 40% of its nominal charge. And, keep that in mind, the MH's alternator will normally not be able to charge it up more than about 85%. So, if you have a 110 Ah battery:
85% charge means 93.5 Ah, 40% charge means 44 Ah. Only the difference, so 49.5 Ah, is available for consumption! Means you can run the fridge just a little less than 6 hours, provided that no charge is used for any other purposes like lights, water pump etc.
So, better don't bother about re-wiring your fridge, but use the 3rd of the 3 ways of operation: Gas.
Best Regards,
Gerhard
Hi Gerhard
I only have one thing to challenge you on and that is the 85% charge from the alternator.
Up to very recently I thought that was true but DABurleigh pointed something out that I hadn't known so rather than change the topic on this thread I'll start another.
______________________________________________________________ Regards Frank
Get behind early - it gives you more time to catch up.
Denn wir haben nichts in die Welt gebracht; darum offenbar ist, wir werden auch nichts hinausbringen.
Plusnet, Safari 3.1, G5 PowerPC iMac running OSX 10.4.11, Eee 4GB running Linux EeePC 1.02.15 and an Eee900 running Linux EeePC 1.1.0.66, Salisbury UK
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