A Question For The Leccy Experts

Discussion in 'Motorhome Chat' started by Yorick, Jan 6, 2015.

  1. Yorick

    Yorick Funster

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    I sent a question to Dometic and got a reply. Just wondering if they are making sense ?

    To fill in the gaps, my fridge was hard wired to the vehicle battery until recently when my leccy mate wired it up to the leisure batteries and added a solar panel.

    Waddya reckon ?

    "
    Dear Sir/madam
    I am currently having problems with one of your fridges. I am not sure of the model so I am sending a picture.
    It’s worked OK for 3 years on 240v but it seems to have a fault on 12v.
    To explain. I have two 110 amp hour leisure batteries in my camper.
    And I have a 150w solar panel fitted as well. I am holidaying in Lanzarote so obviously get 10 hours good sunshine every day.
    The fridge is quoted as 100 watts in the manual.
    But when I put the fridge on, it flattens everything in about 5 or 6 hours.
    My electrical knowledge is minimal, but I have been told that the fridge should be drawing about 8 amps per hour (100w divided by 12v)
    This should mean that my 2 leisure batteries should be able to supply power for about 18 hours. I let them charge for 3 days in the sun and the meters in the camper both showed them as fully charged.
    And even without the leisure batteries, the 150w solar panel should be able to power just a 100w fridge, with the brilliant sunshine over here.
    And ideas or tips would be gratefully received
    "
    ===============================================

    their reply...

    "
    Hello Craig,
    Happy new year.

    Thank you for your email to Dometic UK.

    I will try to help in the best way I can how ever emails like this can be difficult to explain as normally the user is unable to understand the problem.

    OK here goes....

    Please remember firstly your 110 amp battery can not supply 110 amps. Lead acid battery's can only supply 60-40 % of the total amps stated before becoming to discharged to function.

    So with your fridge consuming 100 watts at 12v, this equates to 8.3 amps being consumed every hour out of your battery, times this by say 6 hours (the time it takes to flatten a battery), this would mean the fridge has consumed 50 amps from your battery, so would mean that your have reached the 60-40% make mentioned above.

    Please also note, battery's only have a life expectancy of around 2 years (If the voltage is not pulled below 12.1v at any point)- the issue hear is that everyone likes to think there battery's are maintained at this level but the reality of it is that most of the time the user does not know the level, or notice when the fail in voltage occurs.

    OK now to explain the solar panel...

    Your solar panel will also be adding power to the battery over this time, but solar panels are not 100% efficient. So the efficiency of your solar panel will also have an effect on the charge. Ie; An 150 watt solar panel providing 12v can produce 12.5 amps. However, if the solar panel is only 85% efficient, this means you would then loss 15% from the 12.5 amps produced. many of the cheaper models of panel don't even reach anywhere near the stated output of the panel due to impurity's in the cells and out components.

    When using a panel to run a deveice, most solar manufactures state the panel must be 2x- 3x larger than the applience being opperated. We are not solar experts, and further questions regarding solar use must be taken up with your manufacture.

    So with having read your email I would have assumed the fault is not with the product but the set up.

    Please also note, because the set up has worked for three years, this does not mean the set up was running correctly, and then lead to a fault over time.

    I hope we have been helpful?

    You can use our website to locate an engineer to visist you for a check over of the product. www.Dometicapproved.co.uk.



    Customer Services
    Dometic UK Limited
    Dometic House
    The Brewery
    Blandford
    DT11 9LS


    "


    Thanks in advance of any replies
     
  2. WillH

    WillH Funster

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    Why not use the 240v?
     
  3. Yorick

    Yorick Funster

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    Coz I'm wild camping in Lanzarote :)
     
  4. WillH

    WillH Funster

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    Use gas then. I know a bit about fridges, and electrics and running an absorption fridge off 12v without the engine running is not really feasible. The reply from Dometic is credible, and polite. I have yet to see a van that was meant to run the fridge off 12v without the alternator input, besides, the 12v heating element is not really sufficient to cool or freeze fresh food placed in the fridge, only enough to maintain it's temperature. It probably states that in the manual if you've bothered to read it.
     
  5. davanne

    davanne Funster

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    I thought fridges could only run on 12v when travelling ....when stationary on either 240 or gas
     
  6. Yorick

    Yorick Funster

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    Thanks for nice reply, until last bit ;)

    The manual is at home and I am short of gas, but will use gas next time and bring 2 bottles .
     
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  7. NickNic

    NickNic Funster Life Member

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    What they are saying is basically right. 100W fridge = 8 and a bit amps

    Once a battery is down to 50% it's flat so you get 55ah from each one to play with so 110ah total if they are 100% charged when you start. So if you aren't using any other electric at all you would get about 13 hours max. Other use, lights, water pump, charging your phone etc will obviously reduce that.

    The solar panel won't be 100% efficient so probably isn't replacing charge at the rate you are using it.

    Also do you know if your batteries are taking and holding a full charge?

    Probably time to get the meter out and take some readings - battery voltage when "fully" charged, charging voltage when the solar is flat out, work out exactly what you are using. I'm sure someone clever will do the maths at that point.

    As I understand it with a 3 way fridge the 12v option is only to keep it ticking over when travelling. As WillH says it will be a lot more efficient on gas.
     
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  8. Yorick

    Yorick Funster

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    It's making sense now :)
     
  9. Yorick

    Yorick Funster

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    oops
     
  10. WillH

    WillH Funster

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    No problem Yorick. Two years ago we lost our 240v element on the first day in France, used gas for the whole tour and found that the fridge was a lot more efficient and we didn't use much gas day to day. When I eventually fitted a new element found myself still using the gas in very hot weather. It is a good idea to read the manuals, there is a lot of information in them and I speak as a retired engineer.
     
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  11. Wildman

    Wildman Read Only Funster

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    A compressor fridge is what you need if you want to run on 12v and have sufficient means to recharge. Irrespective of the amount of sun you are getting the suns angle is low in the sky during the winter you will be lucky to get 40% of the stated output from the solar. As already stated on an absorption fridge 12v will only maintain the temp it starts at. I think the mistake you are making is overestimating the amount of solar power you are getting. Good luck getting sorted. There must be means of topping up your gas.
     
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  12. TheBig1

    TheBig1 Funster Life Member

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    what the dometic rep said about the fridge and batteries is generally correct. no way would a 150watt solar panel keep pace with an absorption fridge running on 12v.

    dont forget that your 110amp battery is only going to provide max 50% power when it is brand new. they get weaker over time and if not maintained perfectly. theres only a limited number of recharge cycles in a lead acid battery, but the sellers rarely draw your attention to this
     
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  13. Dazzlin

    Dazzlin Funster Life Member

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    As all the above. I have 2 x 100w panels, 2 x 110ah agm batteries and a votronic solar controller with aes output.
    With the panels tilted at 45° and due south to max the exposure to the sun even when in North Africa they only keep the fridge going 50% of the time during daylight.
    But it is january!
    I am hoping it gets a little better as the seasons change or I may throw another panel up.
     
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  14. Jimbohorlicks

    Jimbohorlicks Funster

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  15. mjltigger

    mjltigger Funster

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    I don't know about the rest but a couple of people have commented on the 12v not being very efficient

    My can doesn't have the 12v connected to the fridge yet.. a spring job I think.. but my last MH and the caravan before both had 12v and would freeze the fridge contents. I'm sure things have changed but in both those fridges the 12v wasn't thermostatically controlled and ran constantly leading to frozen milk and butter in more than one occasion
     
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  16. Jaws

    Jaws Funster Life Member

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    Yorick, get your chum to wire the fridge to the cab battery via a relay that will only kick in when the motor is running. That is how they are supposed to be done mate..
    When off the grid, stick with gas.. They consume very little usually :)
    I have run our fridge for 4 weeks solid ( by accident ! I left it turned on when I parked it up December 2013 and did not discover the oops until I was packing up in early January to go to Spain
    It had used just a tad over 1/2 a bottle of gas
     
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  17. sadlonelygit

    sadlonelygit Read Only Funster

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    If you are low on gas, get a camping gas adaptor and plug it into your feed pipe and you can use the little cans of gas to get you out of the poo.
    As has been said, 12v is for travelling only. We use gas 100% as we have gaslow fitted. We came to this decision after running out in Spain.
     
  18. eddievanbitz

    eddievanbitz Trader - Funster

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    And we find that people tend to forget when they are doing their sums,me everything else that they use on 12 volt. Lights, heating, water pumps, charging devices, TV, computers etc.

    This all has a bearing.

    Let me know if you need a simple diagram to add a four pin relay to sort out the problem

    Eddie
     
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  19. Techno

    Techno Funster Life Member

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  20. Daz n Tina

    Daz n Tina Funster

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    When I done the electric's in my self build I used a w4 split relay which controlled the fridge and battery charging. It was very easy to install.
     
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