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  1. #1
    Join Date
    Dec 2002
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    Gloucestershire
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    5,308

    Default Solar panel "spare power" for fridge

    I have one of these;-
    https://www.ebay.co.uk/itm/Solar-Pan...e154%7Ciid%3A2

    As usual, the instructions are in Chinglish.

    Although I have set "PV Off" to 13.6 volts, I have found battery volts at over 15 after a period of bright sunlight. That is concerning and I now switch off when leaving the ship.

    I have just fired up the fridge after many years waiting for action. It seems fine. I thought maybe I could use the pv "load" output to drive the fridge. It didn't work. I don't understand the symptoms. With 20v from the panel (two in parallel), the fridge motor stays inactive and there is no current drawn. The panels can produce over 5 amps into the batteries.

    Am I risking the compressor by feeding it 20V? Should I introduce a small battery to load the panel? What battery should I choose bearing in mind it will be totally drained from time to time?

    The compressor does not activate immediately, it takes a few seconds to fire up (as in the instructions).
    I'd rather be naked
    www.mastaclimba.com

  2. #2
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,438

    Default Re: Solar panel "spare power" for fridge

    It looks to me like it is a street light controller that will switch a light on automatically after dark for some preselected time period.
    Unless it can be set to have the load terminals energised for 24rs with only the low voltage disconnect feature active it is probably not suitable for controlling your fridge.

    Dont risk powering your fridge from 20volts ... I burnt out an Autohelm many years ago by accidentally powering it from an unregulated outboard engine power output

    I cannot make head nor tail of the instructions either

  3. #3
    Join Date
    Dec 2012
    Location
    Gone cruising
    Posts
    2,326

    Default Re: Solar panel "spare power" for fridge

    Those are some very dodgy voltages from the regulator.

    At 20V your 12V fridge controller has gone into over-voltage protection, which is why the fridge isn't running:

    BD35/50/80F/250GH/100CN: 12V DC systems: 10.4V cut-out (or 9.6V with optional setting) - 17V max.
    Get a better regulator before it fries something that isn't as smart as the fridge controller in protecting itself

  4. #4
    Join Date
    May 2007
    Posts
    37,288

    Default Re: Solar panel "spare power" for fridge

    I love the bit in the ebay description where it slags off some expensive competitor for having an inductor in the circuit.
    This suggests it's a crude controller.

    As Vic says, these things are made for controlling things like signs and streetlights. As are many of the more expensive options.
    It's possible that the 15V you are seeing is an absorption voltage and the controller always gives 'n' hours of absorption before reverting to the 'PV off' float voltage. That would be roughly what you'd want in a streetlight controller.
    It's possible that it's leakage, if the current flowing is very low.
    Or it could be broken. Some of these things blow up if you run them with no battery. There are warnings in the destructions about connecting the battery first? Well second actually, it seems to be saying connect load, battery, panels in that order.

    A big issue with these things is that there are some variants on the market which look the same. I had two old ones with different circuits in the same plastic case. Others I've heard about have the same circuit, but different software/firmware in them.

    Another potential issue is that the fridge has a switch mode controller in it, which is loading the solar controller with a very spiky waveform. You could try loading it with a dumb passive load like a headlamp bulb and see if it behaves any better.

  5. #5
    Join Date
    Dec 2002
    Location
    Gloucestershire
    Posts
    5,308

    Default Re: Solar panel "spare power" for fridge

    I have now found some more complete information on the fridge compressor. It is happy to run off 12 or 24 volts. It senses the input voltage and will switch off when that drops to 12.2 volts. (I assume there is some hysteresis in the detection circuit to avoid cycling). It will also switch off if the voltage reaches 17.2. It will switch on at 22.2V. It will try to fire up at around 1 minute intervals.

    My inclination now is to fit a small capacity sealed battery to supply the fridge permanently connected to the pv charger. It is not obvious why the "load" output needs to be used as the other three batteries on board are all charged from the same source via diodes. When the "sun goes down" the battery will power the fridge until it reduces to 12.2.

    I continue to be baffled by the Chinese determination not to use proper translators for their products. I gave up on the instructions when trying to understand the timing of the "load" function during the hours of darkness.

    It would be nice to return to the boat to find a cold beer waiting and no important flat batteries in consequence!
    I'd rather be naked
    www.mastaclimba.com

  6. #6
    Join Date
    Dec 2002
    Location
    Gloucestershire
    Posts
    5,308

    Default Re: Solar panel "spare power" for fridge

    Update. The addition of a dedicated battery has worked well. We have enjoyed bright skies for the last few days so perhaps it is not representative.

    The "12.2" volt reference was incorrect. The fridge shuts down at an input voltage of 10.4.

    I think this will result in destruction of the battery. Correct?
    I'd rather be naked
    www.mastaclimba.com

  7. #7
    Join Date
    May 2007
    Posts
    37,288

    Default Re: Solar panel "spare power" for fridge

    Quote Originally Posted by Graham_Wright View Post
    Update. The addition of a dedicated battery has worked well. We have enjoyed bright skies for the last few days so perhaps it is not representative.

    The "12.2" volt reference was incorrect. The fridge shuts down at an input voltage of 10.4.

    I think this will result in destruction of the battery. Correct?

    Depends on the size of the battery. A smaller battery will drop to 10.4 at a higher state of charge than a bigger one, for a given current drawn by the fridge. You also have to allow for voltage drop in the cables, fuse etc., as it's sensed at the fridge not the battery.
    I don't think relying on this undervoltage 'protection' on a regular basis would be good practice though!

  8. #8
    Join Date
    Dec 2002
    Location
    Gloucestershire
    Posts
    5,308

    Default Re: Solar panel "spare power" for fridge

    Quote Originally Posted by lw395 View Post
    Depends on the size of the battery. A smaller battery will drop to 10.4 at a higher state of charge than a bigger one, for a given current drawn by the fridge. You also have to allow for voltage drop in the cables, fuse etc., as it's sensed at the fridge not the battery.
    I don't think relying on this undervoltage 'protection' on a regular basis would be good practice though!
    But is 10.4 the death knell for a lead acid battery?

    I have ordered a voltage sensing device in which I can tweak the reference voltage. I thought 11.9.was the recommended for battery life.
    I'd rather be naked
    www.mastaclimba.com

  9. #9
    Join Date
    Mar 2005
    Location
    East Sussex.
    Posts
    21,251

    Default Re: Solar panel "spare power" for fridge

    Surely the other issue with the fridge not starting without the battery in circuit is that the compressor start current is greater than the run current, so there may have been enough current available from the solar panels to run the fridge, but not enough to start it.
    Working on immortality - One day at a time.

  10. #10
    Join Date
    May 2007
    Posts
    37,288

    Default Re: Solar panel "spare power" for fridge

    Quote Originally Posted by Graham_Wright View Post
    But is 10.4 the death knell for a lead acid battery?

    I have ordered a voltage sensing device in which I can tweak the reference voltage. I thought 11.9.was the recommended for battery life.
    There is no magic number where damage starts.

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