Charging whilst driving

Discussion in 'Motorhome Chat' started by Vlad The Impaler, Aug 17, 2012.

  1. Vlad The Impaler

    Vlad The Impaler Funster

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    Just drove from Rutland to Loch Lomond driving approx 7hrs,had fridge on 12v DVD on socket in cab 7hrs.Just parked up checked battery level and it's showing three quarters full.Batteries showed full before leaving,after all that driving Surley they should be full now? What's going on?
     
  2. FULL TIMER

    FULL TIMER Read Only Funster

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    Don't think it would be the fridge causing the problem as after 7 hours I think the fridge would have taken around 70 amps in that time and should NOT be powered via the habitation battery anyway, The split charger should power the fridge and charge habitation battery via vehicle battery / alternator while engine is running, are you sure your 12v socket used for dvd isn't wired to the habitation battery? sounds as though the split charger has packed up (or fuse blown) and you have been drawing current from your habitation battery via the 12v socket if it is wired to habitation battery. only way I could explain it.
     
    Last edited: Aug 17, 2012
  3. Reallyretired

    Reallyretired Funster

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    Unless you have a special battery to battery charger, which you won't have as standard then the actual charge going to the leisure batteries is actually quite small when driving. However they shouldn't be discharging so something is wrong. Check the fuses on both sides of the split charge relay(s).
    I once had a van that when the fuse between the vehicle battery and the split charge relay blew, the fridge was running off the leisure battery, flattening it in short order. This was because that particular van had only a single relay serving both fridge and leisure battery, most have two.
     
  4. jonandshell

    jonandshell Funster

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    Not sure about the age of your Autotrail, but I wired a battery-to-battery charging system into a 2003 Cheyanne the other week.

    It had seperate fridge and split charge relays, both located under the bonnet.

    The original wiring was horrifying though. The cable running the length of the van from split charge relay to the leisure battery at the back was only 2.5 sq mm. The voltage drop would be horrendous!

    I wouldn't be surprised if there is nothing 'wrong' with your van except the original inadequate wiring.:Angry:
     
  5. Pigwam

    Pigwam Read Only Funster

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    Sorry have i missed something here?

    Unless I'm very much mistaken, the battery gauge is a volt meter not a battery capacity meter, so how do you know what capacity the battery has left in it.

    When just taken off charge the meter should read nearly 13 volts and when on load it would properly drop to around 12.5v, a battery in good condition and a large capacity may not drop off for a while, the battery would be considered flat at around 10.5v, but its very difficult to judge what capacity is in a battery from just looking at a volt meter.

    I also thought that the electrical systems in motorhomes wont allow the fridge to work off the leisure battery only, in the 2 motorhomes I've had when travelling you select the vehicle battery, once the engine is running and over 13v a relay kicks in and powers the fridge so as not to flatten the leisure battery, but maybe not all manufacturers make them the same way.
     
  6. jonandshell

    jonandshell Funster

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    Not so!

    An open circuit voltage of 12V is 50% discharged and effectively flat (for a standard leisure battery). You shouldn't discharge these battery types below 50% discharge.

    Just because your electrical panel switches off at 10.5V doesn't mean it's OK to discharge your battery that low.

    You will damage the battery!

    I'll just add that, with everything switched off, a voltage check of a battery is a reliable assessment of remaining capacity.


    For more accuracy, you need to get your hydrometer out!
     
    Last edited: Aug 18, 2012
  7. Vlad The Impaler

    Vlad The Impaler Funster

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    Doesn't say anything on my gauge about volts! It's a dual battery and water tank gauge.Pretty new to this but just assumed half on water means half full of water. Therefore is it not safe yo assume the same for battery?
    Or are u trying to say it means half full of volts? :Eeek::Eeek::Eeek:
     
  8. jonandshell

    jonandshell Funster

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    Gauges and readouts on motorhome panels should be taken with a pinch of salt.

    Trust the water by all means, but for your batteries, invest in a digital multimeter!

    Check your battery health by switching all your electrics off and then measuring the battery voltage between pos and neg.

    12.7 volts is charged, 12 volts (for a standard leisure battery) is recharging time.

    Beware 'surface' voltage. This is the higher voltage observed when the batteries have just come off charge. It soon goes when a load is applied and doesn't reflect the true battery state. Many people out there believe 13 odd volts is a fully charged battery. It's not, it's just the 'surface' voltage.

    So, bearing in mind the inaccuracy of Mh panel battery displays, you probably haven't got a problem to start with and have wasted everyone's time!!!! LOL:Laughing:

    We have learnt on our van that one yellow light left on our panel means time to recharge, but this was only learned by testing periodically with a multimeter.

    Hope this helps,:thumb:

    -Jon
     
  9. Gromett

    Gromett Funster

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    My guess would be you have a solar panel?

    If so the solar charge voltage shown at the battery may be 13.8V and this would read as the battery being full on most dumb motorhome battery meters.
    This would be the case even if the battery was half empty at 12.5V (aprox)
    The solar charge voltage tricks the vans dumb meter into reading full.

    Now when you are presumably in the shade or cloudy the solar charger is not pumping so much in so you are getting a closer to the truth reading.

    Just my guess?
     
  10. Terry

    Terry Funster

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    It could be I have to missed something :BigGrin: but did you not say did etc from cab? If this is the case then it should not say have to taken anything from your l/b :BigGrin: You need to check if you need have to a relay and it is working :thumb:
    Terry
     
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  11. spannermanwigan

    spannermanwigan Read Only Funster

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    Heres a photo of my van currently on hook up batteries fully charged in driveway,
    the upper scale of the gauge shows voltage and is only a guide,if your in the green
    as shown here your charged, the needle will never go to the end of the green.
    I dont get concerned about the state of my batteries unless it drops to the bottom of the yellow, never stayed in one place long enough for that to happen yet. Batteries soon charge with a couple of hours driving.

    As it also doubles as the water tank gauge, the lower scale reads the water level,
    when used for this purpose you will get a higher reading when tank is full. CIMG5106.jpg
    Hope this is helpful.
    :thumb:
    regards
    Steve
     
  12. Pigwam

    Pigwam Read Only Funster

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    I was trying to keep the reply short and had made some assumptions.

    I had thought from previous posts that the MH had new batteries fitted and I had assumed that they were SVLA otherwise I would of recomended a hydrometer, as for 12v being concidered flat you would need to check the technical spec of the battery.

    However I do understand why you have quoted 12v as being flat, as a rule 11v is normally considered the end of its useful life, I hadn't thought of the systems in the MH when I wrote the above.

    If the battery is made to the UK ISO spec 80% discharge is considered flat while if its made to the US ISO spec 60% discharge is considered flat, a lot of cheaper battery manufacturers tend to use the US spec as the batteries are cheaper to make.

    The reason I quoted 10.5v was simply at this point of discharge it is concidered an average maxium depth of discharge under load to achieve the full capacity of a battery without damaging the battery.

    We test thousands of batteries every year with very good test equipment, which normally discharges the batteries at 20a to 25a down to 9.51v the equipment will display the state of the battery and when finished produce a print out of the results if required.

    I think I've bored everyone now.

    The most important thing is when you get home always put your battery on charge (in the morning will do) and never leave it in a semi discharged state for a long period also make sure you have not left anything on.
     
  13. jonandshell

    jonandshell Funster

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    Hi Pigwam

    It's a good point you make about batteries reaching lower voltages whilst UNDER LOAD because I had excluded that fact from my post.
    Lead acid batteries are a complex subject. It is a shame that most motorhomes do not have adequate systems in place to get the most from, and correctly maintain, your van's primary power source.:Angry:
    I suppose it's all down to economics. One can fit several replacement batteries over a period of time and still not spend the money one has to invest to fit decent battery charging and management systems onboard.
    We have a traction battery bank and a Sterling Battery to Battery Charger which I fitted in our van. We demand a lot from our batteries and get exceptional off-grid endurance from our 12v system as a result. We discharge down to a max of 80% (11.66v) as is allowable with this battery type.
    Then again, we have become born-again skiers recently and the ability to go for 4 days without charging, in temperatures of between -10 to -20, with the blown air heating running 24/7 makes for a warm and cosy, stress-free holiday.:thumb:
    What sort of trade are you in, by the way? I hail from the electric forklift word, if that explains my OCD approach to all things lead-acid!:Smile:
     
    Last edited: Aug 19, 2012
  14. Pigwam

    Pigwam Read Only Funster

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    Hi Jonandshell

    The company I work for used to make electric vehicles which ranged from small tugs mostly used at airports to the Tractor unit on an articulated lorry, we have also made electric fire engines and i remember them making some odd ball forklift trucks.

    today we don't make anything and have gone into the mobility industry 100% although they had been involved with the NHS since 1954 when we were asked to repair electric Invalid Cars.

    before I started working for Ross (34 years ago) I used to design and build electronic speed controllers, battery chargers and battery test equipment for the model industry.

    and finally i have a bit of a battery fetish, i think you can tell that

    the one thing I have never understood is why do MH manufacturers skimp on the battery side, if they fitted decent Monobloc (traction) batteries the benefits are tremendous as you have found. :BigGrin:
     
  15. beerdrinker1

    beerdrinker1 Funster

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    Motorhome battery

    I have just been reading the thread from " Vlad the Invader" re the onboard battery,
    I have just been out for 10 days staying on sites with hook up, one night after returning from the pub, and making the bed up, I was aware of a very hot area around the battery together with an acrid smell, I thought "Hi Hi" something wrong here, checked all connections etc, could not find anything wrong, but on checking the gauge the reading from the battery was way up to about 13.5, as I couldn't do anything else at that time, and the battery was very hot to the touch I just opened the outside battery/ hook door and left it open,
    Despite my fears I didn't go up in flames during the night, and in the morning the battery had cooled to a point where it was just warm, which seemed normal,
    Could the battery be goosed or is it just another idiosyncrasy of Motorhome Fun !,
    A couple of days before when I didn't have a hookup available for one night, the battery lost its charge quite quick, and showed a reading of about 10, its this that leads me to believe the battery is possibly knackered, I dont have a tv or any other high drainage items apart from the fridge,
    Any advice would be most welcolme before I shell out a few more hard earned quid on a new battery. :thumb:
     
  16. JeanLuc

    JeanLuc Funster

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    The symptoms suggest that the battery is failing. A hot battery is a sign that one or more of its cells have failed. I suggest you do not recharge it again but get it checked / replaced pronto as charging a failing battery can cause it to gas. That may be the source of the acrid smell and one of the gases given off is likely to be hydrogen (no smell) which, as I'm sure you know, is highly explosive. I suggest you disconnect the negative terminal from the battery post and tape it securely away from the battery then get to a supplier for a new one.
     
  17. Pigwam

    Pigwam Read Only Funster

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    sounds like good advice to me.
     
  18. beerdrinker1

    beerdrinker1 Funster

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    Thanks Jean Luc,
    You confirmed my suspicions, I am just about to take the battery out,
    Any advice as to the maximum amperage battery I should replace it with, the duff battery ( 110amp ) was fitted as a second hand one by the dealer as a goodwill gesture ! ?, when I picked up the new MH in Oct last year, and has only been used for 3/4 weekends, each time on mains hookup, until this last trip when the fault manifested itself the day after one night on internal battery power,
    Plus, I remember reading in one of the forums that there is a specific voltage reading on a new battery that should be essential,
    Cheers,
    Ken :thumb:
     
  19. jonandshell

    jonandshell Funster

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    Hi Pigwam

    It's great to have another Funster who knows his arse from his SCRs and Mosfets!:thumb:
     
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  20. pappajohn

    pappajohn Funster Life Member

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    I have to agree.

    'at rest' voltage and 'under load' voltage are two completely different things.

    a perfect example is a car battery.

    check the voltage of a good battery with a digital multimeter.....say it's 12.7v

    now crank the engine (assuming it wont start) for just a few seconds with the meter still attached and the voltage may be as low as 9v while cranking as you will be drawing 400/500amps for that couple of seconds.

    stop cranking and the voltage will rise back to 12.7v
     
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