13.8 DC regulated Supply




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  1. #1
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    Default 13.8 DC regulated Supply

    I have a 13.8v, 3amp- 5 amp surges, regulated power supply, which i contemplate using in my new caravan build. Running the 12v in the caravan off this supply, when 220v is available. A relay to do automatic switching between battery or power supply.
    The fridge, Dometic CF40, automatically switches between 220/12v. It will then only be the lights running off the power supply.
    LED lights to be fitted.
    Power supply too light?
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    Default Re: 13.8 DC regulated Supply

    Pieter, have you actually tried running the fridge off this PSU? My humble opinion is it will not do the job. A fridge draws 4A when running and at least double that (if not more) on start up. The power supply you have is more than likely not designed for running more than 3 amps and probably not continuously at that rate either. The maximum surge rate is 5 amp, which is probably too low to start the fridge compressor.

    As far as your lights go, as longs as total current consumption is not more than 3 amps, the PSU might be suitable for this only.


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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by Pieterk View Post
    I have a 13.8v, 3amp- 5 amp surges, regulated power supply, which i contemplate using in my new caravan build. Running the 12v in the caravan off this supply, when 220v is available. A relay to do automatic switching between battery or power supply.
    The fridge, Dometic CF40, automatically switches between 220/12v. It will then only be the lights running off the power supply.
    LED lights to be fitted.
    Power supply too light?
    Here's my tip.

    Don't use a switch between battery or power supply.

    Simply leave the PSU connected to the battery. The PSU will supply the average total energy consumption, and the battery will pick up the slack between fridge cycles.
    Last edited by Fluffy; 2018/05/12 at 09:30 PM.
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    Default Re: 13.8 DC regulated Supply

    [QUOTE=Family_Dog;3892355]Pieter, have you actually tried running the fridge off this PSU? My humble opinion is it will not do the job. A fridge draws 4A when running and at least double that (if not more) on start up. The power supply you have is more than likely not designed for running more than 3 amps and probably not continuously at that rate either. The maximum surge rate is 5 amp, which is probably too low to start the fridge compressor.

    As far as your lights go, as longs as total current consumption is not more than 3 amps, the PSU might be suitable for this only.


    -F_D[/QUOTE

    Thanx Family dog.
    I suspected the PSU would be too light for the fridge. The Fridge automatically switches between 220/12v. Thus. The fridge will not be running off the PSU at all.
    I will have to fit a battery charger for the charging of the battery, which of course negates the PSU. Unless one can use the PSU for a battery charger?
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    Default Re: 13.8 DC regulated Supply

    [QUOTE=Pieterk;3892358]
    Quote Originally Posted by Family_Dog View Post
    Pieter, have you actually tried running the fridge off this PSU? My humble opinion is it will not do the job. A fridge draws 4A when running and at least double that (if not more) on start up. The power supply you have is more than likely not designed for running more than 3 amps and probably not continuously at that rate either. The maximum surge rate is 5 amp, which is probably too low to start the fridge compressor.

    As far as your lights go, as longs as total current consumption is not more than 3 amps, the PSU might be suitable for this only.


    -F_D[/QUOTE

    Thanx Family dog.
    I suspected the PSU would be too light for the fridge. The Fridge automatically switches between 220/12v. Thus. The fridge will not be running off the PSU at all.
    I will have to fit a battery charger for the charging of the battery, which of course negates the PSU. Unless one can use the PSU for a battery charger?
    Yes. The PSU will be too light for the fridge on peak demand. But on average a fridge wont draw more than the energy the PSU can supply if the battery tales up the slack.
    Cheers

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    Default Re: 13.8 DC regulated Supply

    Thanx Family dog.
    I suspected the PSU would be too light for the fridge. The Fridge automatically switches between 220/12v. Thus. The fridge will not be running off the PSU at all.
    I will have to fit a battery charger for the charging of the battery, which of course negates the PSU. Unless one can use the PSU for a battery charger?
    The battery charger will not be ideal for charging the battery either, batteries like a raw pulsating DC voltage applied for charging, not a perfectly regulated DC as would be supplied by the regulated PSU. Should the battery state of charge be low, the PSU will try charge at the maximum rate, most likely destroying itself in the process.

    Typically, these power supplies are designed to supply 3A for a limited time but allowing for a 5A occasional surge, they are not designed to provide a constant voltage of 13.8v at 3A at a continuous rate.


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  7. #7
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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by Family_Dog View Post
    The battery charger will not be ideal for charging the battery either, batteries like a raw pulsating DC voltage applied for charging, not a perfectly regulated DC as would be supplied by the regulated PSU. Should the battery state of charge be low, the PSU will try charge at the maximum rate, most likely destroying itself in the process.

    Typically, these power supplies are designed to supply 3A for a limited time but allowing for a 5A occasional surge, they are not designed to provide a constant voltage of 13.8v at 3A at a continuous rate.


    -F_D
    mmmm, we need to discuss this sometime. The very last thing a battery needs is pulsating DC. Ripple from a raw pulsating PSU will kill a battery.

    The only exception is the very initial "wake me up" stages that the Intelligent Chargers do. After that. its a death wish.

    All batteries have very stringent ripple specs during the charge phase, and especially the float phase.
    Cheers

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    Default Re: 13.8 DC regulated Supply

    Here is the maths:

    Volt x Current = Watts
    13.8V x 3A = 41.4W

    Now start subtracting your loads from that, e.g. Light bulb watts. Stop before you reach 0. Typically a MR16 downlighter is between 3 and 6 watt each.

    Yeah, mentioning the fridge just confuses everybody, since it will not go anywhere near your PSU.
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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by RogueFrontier View Post
    Here is the maths:

    Volt x Current = Watts
    13.8V x 3A = 41.4W

    Now start subtracting your loads from that, e.g. Light bulb watts. Stop before you reach 0. Typically a MR16 downlighter is between 3 and 6 watt each.

    Yeah, mentioning the fridge just confuses everybody, since it will not go anywhere near your PSU.
    You left out the most important parameter.

    TIME.
    Cheers

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    The nice thing about going the extra mile - the road is never congested.

  10. #10
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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by Family_Dog View Post
    Pieter, have you actually tried running the fridge off this PSU? My humble opinion is it will not do the job. A fridge draws 4A when running and at least double that (if not more) on start up. The power supply you have is more than likely not designed for running more than 3 amps and probably not continuously at that rate either. The maximum surge rate is 5 amp, which is probably too low to start the fridge compressor.

    As far as your lights go, as longs as total current consumption is not more than 3 amps, the PSU might be suitable for this only.


    -F_D
    The PSU will ONLY be used when the caravan is plugged into 220V mains. The fridge will run off the mains and the battery will get charged from his fancy CTek battery charger.

    This is purely just to drive 12V-only appliances while he has 220V available. Pieter could always just use an old transformer and a bridge regulator. This might just be the way he has to go if he wants to run the built-in car radio and subs in the caravan...
    Last edited by RogueFrontier; 2018/05/12 at 10:23 PM.
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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by Fluffy View Post
    Here's my tip.

    Don't use a switch between battery or power supply.

    Simply leave the PSU connected to the battery. The PSU will supply the average total energy consumption, and the battery will pick up the slack between fridge cycles.
    +1

  12. #12
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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by Pieterk View Post
    I have a 13.8v, 3amp- 5 amp surges, regulated power supply, which i contemplate using in my new caravan build. Running the 12v in the caravan off this supply, when 220v is available. A relay to do automatic switching between battery or power supply.
    The fridge, Dometic CF40, automatically switches between 220/12v. It will then only be the lights running off the power supply.
    LED lights to be fitted.
    Power supply too light?
    I recommend you get a bigger one that also has adjustable voltage and connect it directly to your battery - not really expensive, but you need to be the brain of the setup.....

    In my Man-Cave I have various 12V appliances permanently connected to a battery also connected to a 200W Meanwell power supply set to 13.8V

    The power supply easily tops up the battery to full when the fridge is not running and the battery deals with any startup surges

    Now and then I crank up the voltage to 14.2V for a while to ensure the battery gets a full charge (I monitor this with a HcDP Battery monitor )

    http://www.mantech.co.za/ProductInfo.aspx?Item=372M0437

    http://www.hcdpelectronics.co.za/ind...&product_id=60

    ..................

    OR - you can install this, connect it permanently to your battery and forget about the hassles:
    (This charger will not mind if there are other sources/chargers on the system)
    (On special - hurry)

    http://www.4x4direct.co.za/home-char...er-12v-6a.html

    ...................

    OR - stick with your idea, but connect it directly to your battery
    (of course the unknown here is what would happen to your power supply when some other source you might have tries to provide 14.4V to the battery?)

    .................

    OR - if you already have a 220V charger on the system that can provide your energy needs fully, do not add other stuff...
    Last edited by Dungbeetle; 2018/05/13 at 07:47 AM.
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  13. #13
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    Default Re: 13.8 DC regulated Supply

    Thank you to all the inputs.
    It seems i have opened a interesting topic.
    The little bit of electronics knowledge that i have, makes me dangerous, and i enjoy releasing the special smoke from electronic components.
    I know there is still a bit of difference of opinion, and it seems that the overall concept would then be:
    Connect the power supply direct to the battery and run all the components off the battery. That is unless there is a battery charger connected to the battery.
    I am going to try this and see how long the PSU lasts. This output from the PSU is not enough to charge the battery fully? Or am i missing something
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  14. #14
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    Default Re: 13.8 DC regulated Supply

    Correct
    If the PSU cannot be set to 14.2V it wont charge the battery fully + at that max 3 Amp rate it will take forever to charge the battery.
    (Assuming you do not have another charger in the system)

    To easily murder a battery - "modulate" at a low state of charge for periods without fully being charged.

    So your greatest risk here is that you will loose an expensive battery by using a "small" PSU.
    Last edited by Dungbeetle; 2018/05/14 at 06:53 AM. Reason: added "3" before "Amp"
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    Default Re: 13.8 DC regulated Supply

    Quote Originally Posted by Pieterk View Post
    This output from the PSU is not enough to charge the battery fully? Or am i missing something
    Typically the PSU will have a charging circuit very specific to the battery it houses. The charging current will be set accordingly for this battery, as will the float voltage. So while you may connect a larger battery it will take longer to charge and it is possible that the output voltage may not be able to overcome the back emf of the battery to facilitate full charge. As Fluffy said it is all about time (duration), you may not have the time required for you battery to recover via the charging cycle.

    For me all revolves around the battery, this is the only continuous source of power (when charged). Off this you can run lighting and refrigeration. If your charging rate is poor then you will require a greater battery capacity. If you have a decent high capacity charger then you can get away with less capacity, one can later add the option of solar so that you can run even without 220V.

    So being in the design stage you have choices to make that may impact on your later.

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