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  1. #1

    Default Where does the electricity go?

    We have a motorhome that can be parked up for a month before going out on the road. We have a battery monitor and find it necessary to charge the battery every so often when the charge drops below 12v.

    What I am wondering is why should we have to charge the battery? Why does the battery discharge? It's not as though the battery is old - we just recently had a new one installed.

    We have had our motorhome for about eight years and charging the battery every so often has always been necessary right from the beginning.

    There is nothing on standby and the only thing we can see that is using power is the mileage display and that must be almost nothing. So where does the electricity go?
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  2. #2
    Senior Member 1101's Avatar
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    Default Re: Where does the electricity go?

    batteries self discharge . It happens. Could be worse with a crappy battery, even if new
    More likely something is draining the batt. You'll need to track down what .

    Whats the voltage after fully charged
    How long below it goes below 12v
    Did you check with a good multimeter on the batt itself ?
    With the current draw when everything is off ?

    1 or 2 batt's in the motorhome ?

  3. #3
    Awaiting Enlightenment R2x1's Avatar
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    Default Re: Where does the electricity go?

    The memory in the radio uses power ~ only a little, but always on, battery monitor likewise; any alarm fitted, varies between brands, but surprisingly hungry on cheap alarm systems, clock- just a trifle but eternal, the vehicle computer(s), and always the primitive old battery does a pretty good job at self-discharge(regardless of any connected loads). A month is not too bad, lots of cars won't manage that long. A small solar panel takes care of it, if it is chosen with sizing as a prime concern it wont need a regulator as the panel can't supply more than the battery can happily and harmlessly dissipate once it is fully charged. Economy solar panels may require an isolation diode to prevent it discharging the battery while the sun is on sabbatical.
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  4. #4
    Computer Technician wainuitech's Avatar
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    Default Re: Where does the electricity go?

    The Battery in my car discharged after 3 weeks of not being on during Lock down to the point of not wanting to start, how if did was more good luck that anything else. Once it got going it started recharging, but took it to the local mechanic and they threw it on charge over night to get it right up, (no cost) he did make the comment about discharging - If your car has a computer and most do that's using a tiny amount of power all the time to keep it going, not much and normally wouldn't even notice but leave it for a longer time and it will drain.
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  5. #5
    Senior Member piroska's Avatar
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    Default Re: Where does the electricity go?

    Quote Originally Posted by wainuitech View Post
    The Battery in my car discharged after 3 weeks of not being on during Lock down .
    My mums lasted until lockdown was over. She had a GPS in it, but that turned off earl on. It's a 2000 model Honda, nothing special in it, but it needed the jumper leads. I had taken it out once after 2 weeks, then it sat again. They do leak a bit. Household Batteries sitting in a drawer for ages go flat too, and nothing is using them at all.
    Ex-pctek

  6. #6
    pcsourcepoint
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    Default Re: Where does the electricity go?

    I have a few flat batteries that i'm testing to try restore during lock down. Often a cell goes weak/bad, i.e. forms lead sulfate. Hence reading of 10.4 or so volts. loses about 2.1 V. Many ways to try fix. Super charging (redissolve the lead sulfate, sometimes by adding Epsom salts) or more cumbersome spot weld/solder in good used cell of lead plates.

    You cold solar trickle charge to prevent a flat battery.About 30 dollars for a 4.5 W clip on solar pad charger. I test with multi meter, load tester and check for current draw (if battery becomes flat in car with a few days of non use) sometimes (see vid here for draw test)
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  7. #7
    Soaring like a chicken prefect's Avatar
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    Default Re: Where does the electricity go?

    First check with an ammeter you have no load going out with everything switched off. Its not unknown to get a discharge (reverse charge) through the solar panel at night if the solar controller is playing up. Easy to find put an ammeter in series with the outlet wire or buy a clamp contactless ammeter from aliexpress. Lead acid batteries self discharge just plug it in to your home 240VAC every 3 weeks or so. You should never let a start or even a house battery drop below 12.0 volts as it degrades them.
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    Soaring like a chicken prefect's Avatar
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    Default Re: Where does the electricity go?

    Quote Originally Posted by piroska View Post
    My mums lasted until lockdown was over. She had a GPS in it, but that turned off earl on. It's a 2000 model Honda, nothing special in it, but it needed the jumper leads. I had taken it out once after 2 weeks, then it sat again. They do leak a bit. Household Batteries sitting in a drawer for ages go flat too, and nothing is using them at all.
    Any car since the early 90s has a computer which has a standing draw also the clock draw a few milliamps. Its not rocket science with a car put an ammeter on amd measure the amps max should be 50 milliamps.
    Its amazing how Potatoes give us chips,fries and Vodka.

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  9. #9
    tweakedgeek tweak'e's Avatar
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    Default Re: Where does the electricity go?

    Quote Originally Posted by kahawai chaser View Post
    You cold solar trickle charge to prevent a flat battery.About 30 dollars for a 4.5 W clip on solar pad charger.
    i used to have a vehicle parked away from the house so tried a few things to keep battery charged.


    small "trickle charge" solar panel. they are often rated at a high voltage. eg its 4.5w but at 18volts. battery drags it down to 12v. so the real wattage rating is 3 watts.
    now factor in time exposed to decent light that gets the panel above battery voltage (otherwise no current flows). that is often only a few hours a day by the time you take into account rain days, cloud cover, shading etc.
    so its only say 5-10 watt/hrs per day. where as a mains powered trickle charger even a measly 1 watt charger is 24 watt/hrs per day. use a 5 watt trickle charger its 120 watt/hrs.
    sorry thats somewhat crude, but you get the idea. small solar panels are crap. i ended up using a 10w panel, even better when you use a regulator that can boost the voltage up in low light conditions.
    Tweak it till it breaks

  10. #10
    Senior Member piroska's Avatar
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    Default Re: Where does the electricity go?

    Why care? A drive charges it up. And if it starts to go flat quickly, often, it's new battery time.
    new batteries are fine if you drive once a week....my mum doesn't go out that much, only over lockdown she had that one issue.
    Ex-pctek

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