Voltage geek query - is it time to replace the leisure battery?

Discussion in 'Tech/Mech General' started by magicsurfbus, Apr 13, 2012.

  1. magicsurfbus

    magicsurfbus Funster

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    After another foreign trip plagued by control panel battery monitoring problems and a fridge that refuses to work on 12v I bought myself a brand new multimeter this morning (despite B&Q's best efforts trying to flog a duff batch of said items) and have been round my van testing everything. My leisure battery is a four year old Carbon Fibre 110Ah, hardwired via a charge controller to an 85W solar panel. It has discharged a couple of times in the extremely cold winters of 2010, which I realise is not a good thing.

    Here's what I found, bearing in mind we've driven 1800 miles in the last couple of weeks and returned less than two days ago, and the van hasn't been driven any distance for about 24 hours. The control panel shows both batteries to be topped up.

    With solar panel working in April sunshine, leisure battery terminals read 13.5v
    With solar panel covered (and all devices off), leisure battery terminals read 12.7v

    With solar panel covered, engine running, (and a reading of 14.5v at the engine battery terminals) leisure battery terminals read 12.68v

    With solar panel covered, engine running and the 130W fridge switched to 12v, the fridge relay clicks on and off every few seconds and the leisure battery voltage jumps between 12.27v and 12.46v with each click of the relay. 12v Socket voltage in the living compartment drops just below 12v while the fridge is on.

    With a full load on the engine battery (lights on full beam, heater and fan on full, wipers on constant) the voltage at the engine battery terminals reads 13.9v, which suggests the alternator is doing its stuff.

    This would suggest to me that the solar panel (when on) is masking the fact that the leisure battery is no longer holding sufficient charge for the fridge to run properly on 12v - or am I missing something here?

    As always, your thoughts, observations, advice and insults are most welcome.
     
  2. hilldweller

    hilldweller Funster Life Member

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    That 12.7V suggests a fully charged battery, of course half the plate area could be past it making it 10Ah not 110Ah.

    But last hope, make sure the terminals on the battery are clean and tight.

    Fridge is an odd/complex load.

    Can you load it with a known resistive load, say a headlamp bulb. Panel covered, I assume 12.7V, add load and log the volts every hour for 5 hours. That will give the active capacity ( for that low load ).

    Nice bit of measuring there !
     
  3. magicsurfbus

    magicsurfbus Funster

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    hilldweller: Thanks. Surely with the engine running and the fridge on I should be seeing at least 12v at the living compartment's 12v socket? We've not had any trouble running devices like DVD players, laptops, phone rechargers etc with the fridge on in the past. At present we can't even get the fridge to run. As an alternative we tried running a 12v coolbox whilst travelling and it was struggling with that too.

    It's partly complicated by a further issue. The control panel is giving all sorts of screwy readings for the engine battery. In a matter of minutes (engine off, no load on the engine battery) it can display anything from four green lights (full voltage) to one flashing red (low voltage) and back again, for no obvious reason. I'm beginning to wonder if the switch between the engine battery and the leisure battery is sticking in the on position, or if there's a fault in the control panel's relay/circuit board. This might be affecting when/if the control panel feeds current from the alternator to the leisure battery. One symptom has been repeated on/off clicking in the relay box behind the driver's seat when the engine is running.

    This issue has been driving us scatty - I'm trying to work out if it's time for a new control panel circuit board or if there's a simpler, cheaper solution to the problem.
     
  4. Gromett

    Gromett Funster

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    That is a comprehensive set of tests :BigGrin:

    It does sound like the battery is fully charged. However you would need to leave it without input for a while. Ie cover the solar panel, disconnect EHU and leave engine off for a few hours then test the voltage.

    Voltage will only give an indication of charge it is not fool proof.

    I would also suspect the 12V side of the fridge.
     
  5. Terry

    Terry Funster

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    Hi I am deffo no sparky but the relay clicking on and off sounds iffy to me.Once it clicks on with engine running you should be getting all the power to run fridge on 12v (bear in mind fridge should only run on 12v while engine is running)from the alternator - Is the wiring up to the job ie thick enough.It should not be on/off all the time-either faulty fridge /12v side or faulty relay-I would start by checking/getting a new relay (about 10 quid)for either single or twin -single will work either fridge or L/batt twin will do both :thumb:
    terry
     
  6. bungle.bear

    bungle.bear Read Only Funster

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    With the engine running the leisure and engine battery should have the same voltage as they will be joined together.

    Have you checked the spilt charge fuse?

    regards Anthony
     
  7. magicsurfbus

    magicsurfbus Funster

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    Having rooted around on the Control Panel manufacturer's support page, they make a similar point, so thanks for that suggestion bb. It's a bit of a chicken and egg problem - is a faulty fridge pulling too many volts from the alternator and confusing the control panel, or is a faulty control panel failing to support the fridge? Next step I think may be to check all the connectors in the control panel to see if there's any obvious breaks, loose wires or blown fuses.
     
  8. pappajohn

    pappajohn Funster Life Member

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    my first thoughts, after a hard days work and little sleep last night, would also be a faulty 12v split relay or a knackered battery.

    12.7v is fully charged but may just be a surface charge so leave untouched, with no load or charge, for an hour or two and check voltage again.

    surface charge is a bit like painting over unprepared gloss paint......it looks good at first but it aint stuck to the old paint so will soon fall off.

    the charge current needs to 'soak' into the battery to be of any use.

    i used to use an old car battery to power a 12v workshop lamp.....couple of days charge = 12.6v....connect the 50w lamp and within a couple of minutes the voltage was around 10.5v
     
  9. bungle.bear

    bungle.bear Read Only Funster

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    It does not matter if it is fully charged or dead flat. you should see alot more voltage than 12.7V at the leisure battery with the engine running, The voltages should be near identical.

    It is unlikley to be anything other than the engine alternator is not charging the leisure battery or the other equipment would not work with the hook up lead connected and the battery charger keeping the battery fully charged.

    Regards Anthony
     
  10. magicsurfbus

    magicsurfbus Funster

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    Having just been rootling around in my engine bay to refresh the mouse bait boxes I was reminded of something that may be relevant here. After my new engine battery was fitted I noticed a disconnected cable with a very distinctive plug on one end hanging loose. There is no visible socket for this plug within reach of the cable, unless it's somewhere behind the battery. The plug seems very clean on the end, ie devoid of 7 years' engine grime so is it possible that this socketless item is linked to my power distribution board's apparent problem with monitoring and distributing the correct voltage in the system, or is this loose cable simply a redundant component?

    It has two thin wires going in at the back, one yellow, one red. I've attached a photograph - click the thumbnail for the larger version. If anyone can identify its purpose (or lack of purpose) that will help narrow things down a bit further.
     

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  11. Stu V

    Stu V Read Only Funster

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    Hydrometer

    The only way to find out if a battery is serviceable is to buy a Hydrometer, suck up the electrolyte from the six cells in turn (assuming there's fluid in the cell) and check the float is showing green, should one or more cell show in the red 'Get a new battery'. :Doh:
     
  12. pappajohn

    pappajohn Funster Life Member

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    Not if the split charge relay is cabbaged !
     
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