Inverters

I have a chescold 40ltr fridge which is a great unit - biggest problem is it gets too cold. But when travelling we run it from a second battery using the 12 volt connection on the fridge. Would we be better off running it through a 350 watt Waeco inverter and using the 240 volt plug from the fridge. I'm not electrically minded but just wondered if the fridge might run more efficiently using the 240 volt plug - given the reviews indicate it is a better unit on gas and 240 volts.
Peter
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Reply By: Member - Rosco from way back - Saturday, May 03, 2014 at 11:24

Saturday, May 03, 2014 at 11:24
G'day Peter

3 way fridges such as yours have a 12V and 240V heating element, both of which do a similar job. From my recollection of one we had a few years back, the 12V system bypassed the thermostat so it ran full chat all the time which could be your problem, notwithstanding that it's a tad unusual as they are notoriously woeful on 12V. I think, but I'm not sure, that the 240V utilises the thermostat so you could give it a try, however it's a fairly inefficient way to do so, considering the losses in the inverter and the safety issues to consider with 240V. Remember the old adage ........... "One flash and you're ash".

Another suggestion would be to wire in a relay as a switch for the 12V wiring, accessible from the driver's seat. Then you could simply turn the fridge off for a while to keep it from getting too cold.
AnswerID: 531729

Reply By: Member - John and Val - Saturday, May 03, 2014 at 11:27

Saturday, May 03, 2014 at 11:27
Peter,

It's a 3 way absorption fridge which works off heat - great on gas, or can run off 240 volts using a big electric element. On 12V though there is another electric element to provide heat, enough to keep things cold but no more than that since electric heating is very demanding of electricity. This 12V element will draw about 12-15 amps continuously, which will 50% discharge a 100 Ah battery (typical size in a van) in a few hours. A battery simply cannot deliver the power that you need for serious cooling in a three way fridge.

Would it help to run the 12V through an inverter to get 240V for the much bigger 240V heating element? No way! The energy is still being drawn from the battery, but now the load will be much bigger due to the higher demand of the 240V element (plus inefficiency in the inverter). While your battery might have managed 4 hours at 12V, it probably wouldn't manage 1 hour on the inverter.

Sorry - fact of life with 3 way fridges - they need lots of heat to keep them cold! Great on gas. Not a job for a battery, but can do a half-hearted job on 12V if drawing from the alternator while travelling.

Cheers

John

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AnswerID: 531730

Follow Up By: Member - John and Val - Saturday, May 03, 2014 at 11:30

Saturday, May 03, 2014 at 11:30
Sorry Rosco - we were composing together and you got there first. Quite agree about the safety issue too.

Cheers

John
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FollowupID: 814809

Follow Up By: Peter56 - Saturday, May 03, 2014 at 11:57

Saturday, May 03, 2014 at 11:57
I had not thought of the safety issue - I run a small inverter to charge mobiles etc in the cab using the 240 volt plug. Is that a problem as well?
May be I should do a course in electronics - I had been told using the inverter was fine.
Peter
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FollowupID: 814811

Follow Up By: garrycol - Saturday, May 03, 2014 at 12:50

Saturday, May 03, 2014 at 12:50
If you run an inverter while the car is running and have an accident - there is a chance, albiet remote, that you, rescuers can get zapped if it is still connected to power.

I believe that rescuers have received shocks from these in the past.

Just not a good safety practice.
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FollowupID: 814813

Follow Up By: Member - Rosco from way back - Saturday, May 03, 2014 at 13:14

Saturday, May 03, 2014 at 13:14
No worries cobber ........... Great minds and all that :o)
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FollowupID: 814814

Follow Up By: The Bantam - Sunday, May 04, 2014 at 10:15

Sunday, May 04, 2014 at 10:15
pretty well every device that comes with a 240v charging adaptor can be charged direct from 12 volts using an appropriate adaptor.

So there is no need to have a 240V supply for this purpose.

cheers
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FollowupID: 814891

Reply By: auzinomad - Saturday, May 03, 2014 at 14:43

Saturday, May 03, 2014 at 14:43
A quick trip to your local Fridgy and get a freezer thermostat with a medium tail.
Drill a SMALL hole just big enough to get the tail into the fridge and down to the bottom of it , insert tail and seal !

Then wire the 12v supply thru the thermostat and by trial and error get the best setting that suits you.

I did a similar thing to the Caravan fridge for 12v supply, after all no need to run the fridge's 12v supply if it's already cold enough.

Saved on power draw leaving more for the van battery as well.


Ron
AnswerID: 531740

Reply By: Batt's - Saturday, May 03, 2014 at 22:01

Saturday, May 03, 2014 at 22:01
Tried running mine off an inverter when travelling yrs ago it made no difference still ran like crap especially in hilly areas that's why I bought an Evakool compressor fridge which gives you better control of your temps and doesn't freeze things in the fridge in cold weather when your camping.
AnswerID: 531779

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