Running time on compressor fridge

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mariner
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Running time on compressor fridge

Post by mariner »

Hi all. Got myself a Dometic CRX50 a while back and I'm trying to get to grips with it's run time. It's wired directly to the new leisure battery (smaller one under passenger seat) and unless on EHU to keeo topping up leisure has no other power source - will be fitting solar at a later date.

I've read that they can run for 2-3 days continuously off the leisure battery but I'm getting much less than this. Yesterday I charged up the leisure to 12.2 and set the fridge running overnight on level 3 of 4. Checked it this morning (14 hour later) and the fridge was flashing low voltage signs at me and the leisure battery was at 9.8!

Is this to be expected? I was hoping for a bit more run time - I have no idea at what point overnight it dropped below what the fridge requires but I'm guessing it was long before 14 hours!

Going to charge up the leisure and try again on the lowest temp level to see how much more time that eeks out but I reckon it'll still be well below the 48-72 hour mark.

Be interested to hear from anyone who has a similar set up and what you've found. Am I being too ambitious in my expectations?! Cheers. 
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Re: Running time on compressor fridge

Post by TONYT25T25 »

I would imagine it would require some sort of trickle charge to help in keeping the fridge operational, or an occasional run of the vehicle to recharge the leisure battery.  The solar panel will help, there is feedback on it on JK website regarding use with a solar panel.
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Re: Running time on compressor fridge

Post by Jim San »

Mine runs for days no problem ( I was even amazed it mananged it these last few days after being stood for so long and well past their best batteries).  It kicks in and the comp runs for a few minutes at a time.

Stab in the dark, but during your test run, have you got the fridge full of stuff (or at least half full)
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mariner
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Re: Running time on compressor fridge

Post by mariner »

Fridge was empty during test run, hadn’t really thought about this affecting it. Have run it on it’s lowest temp setting and voltage on leisure battery dropped from 12.2 to 11.8 in about 30 mins (empty again) before staying stable. Fridge seems happy pulling on 11.8.

Certainly not getting days out of it!
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Re: Running time on compressor fridge

Post by Oldiebut goodie »

You are not starting from a good position - at 12.2v the battery is only 60% charged. If you have a small battery as you say I would expect 4 or 5 hours running before the battery is too flat. ( Not good to run them under 50% of the rated capacity without ruining it if just a standard battery) Running it down to 9.8v may well have cooked it, you really need a low voltage disconnect device to protect the battery.

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mariner
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Re: Running time on compressor fridge

Post by mariner »

Have managed to get the LB up to 14+ volts with a proper charge from a battery charger. It's settled now at about 12.7 but that's without running anything. I tried to charge it using the 240v EHU but it wouldn't get past 12.2v and the Zig unit got very hot, as in couldn't hold your finger on the front plate hot! I've read elsewhere that this can be another sign of a knackered LB. I did replace the wiring from the Zig to the LB recently but made sure I used 6mm so should be okay there.

My question is what has killed the LB? It was new this year. The last post suggested I get a low voltage disconnect device for the fridge to protect the LB but I thought this was inbuilt to the fridge...I've contacted Dometic to check this.

Thanks for the help all - all signs point to a dead leisure battery but there's little point replacing it until I work out what's killed it (and why the Zig got so hot!) 
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Re: Running time on compressor fridge

Post by R0B »

I am pretty certain the Dometic has a built in low voltage cut out.
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Re: Running time on compressor fridge

Post by mariner »

R0B wrote: 11 Aug 2020, 12:33 I am pretty certain the Dometic has a built in low voltage cut out.

Cheers Rob, me too. Will post on here when I get confirmation either way from Dometic.
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Re: Running time on compressor fridge

Post by R0B »

Taken from here.This covers all crx models. https://www.waecofridges.co.uk/pdf/CRX80_Manual.pdf


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Re: Running time on compressor fridge

Post by Oldiebut goodie »

That is a pointless low voltage cutout! The battery is dead by that point, I would set it at 12v then you can reasonably keep the battery in good order.
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mariner
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Re: Running time on compressor fridge

Post by mariner »

Oldiebut goodie wrote: 11 Aug 2020, 14:23 That is a pointless low voltage cutout! The battery is dead by that point, I would set it at 12v then you can reasonably keep the battery in good order.

I’d agree and would explain why the leisure battery needed a bloody good charge to get going again. Will have to wait and see how permanent the damage may be but in all honesty don’t think I’ll run the fridge again until I’ve got the solar set up.
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Re: Running time on compressor fridge

Post by Oldiebut goodie »

For the sake of £5 I would add a low voltage disconnect - far cheaper than a new battery.
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Re: Running time on compressor fridge

Post by MidLifeCrisis »

Found the below stats for the fridge (or at least the Waeco equivalent which seems identical)
1.1 Ah/h at +25°C ambient temperature,
1.7 Ah/h at +32°C ambient temperature,
both at +5°C interior temperature and -18°C in the freezer compartment

And a youtube video of a chap testing it for real who saw average of 2.4Ah/hr over a one day test (which included the initial cooldown)

So, if you take your average leisure battery at 100Ah capacity and want to keep it at roughly 50% charged (which seems sensible) - then you are looking at less that 24hrs of life before the battery will be spent.

 
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Re: Running time on compressor fridge

Post by Mocki »

A three way is the way to go, cheaper in every way imho
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