HymerVan Posted April 21, 2012 Share Posted April 21, 2012 My new van has an LED condition indicator for the leisure battery (230ah) but not a voltmeter and no facility to give and indication for the vehicle battery. I like to monitor voltages when wild camping or in the winter when the vehicle is standing. If I measure the voltage by plugging my digital multimeter into the vehicle/leisure 12v sockets will the reading be representative of the condition of the battery ? Link to comment Share on other sites More sharing options...
crinklystarfish Posted April 21, 2012 Share Posted April 21, 2012 Probably not. The time to take voltages is when the battery has neither been charged, nor drawn from, for 24 hrs or so - impossible in wildcamping conditions. Also, most late model 'vans require the ignition to be switched on to activate the starter batt powered cig lighter sockets. With the ignition on, there are draws on the system. The readings just might be close enough as makes no difference from a leisure batt powered socket but that would also depend on whether there are any relays activated and the length / gauge of wire from the batt to the socket. I personally don't bother with any monitoring equipment at all. It's not really, in reality, massively useful. That said, if you really want to pursue it, something like a BM1 or similar 'smart' monitor is the best way to go. Link to comment Share on other sites More sharing options...
Robinhood Posted April 21, 2012 Share Posted April 21, 2012 HymerVan - 2012-04-21 9:03 AM My new van has an LED condition indicator for the leisure battery (230ah) but not a voltmeter and no facility to give and indication for the vehicle battery. I like to monitor voltages when wild camping or in the winter when the vehicle is standing. If I measure the voltage by plugging my digital multimeter into the vehicle/leisure 12v sockets will the reading be representative of the condition of the battery ? ....it will be representative, but probably not a correct reading, allowing for any voltage drop in the wiring. Also, if the ignition needs to be turned on for the vehicle-battery attached socket(s) to be live, then there is likely to be additional current draw (in the vehicles electronic systems) which would affect the reading. I can only assume that your batteries are relatively inaccessible, otherwise a meter across the terminals would be best. At least for the "leisure" side, it would be possible to "calibrate" your expectations. Take a reading (once only) directly across the leisure battery terminals, then choose your socket, and read again there. You will then know what value to add (the difference - if any) to future readings correct for the voltage drop to that socket. (If you really can't get to the leisure battery terminals, then fully charge the battery by hook-up or driving; leave off-charge and off-load for 24 hours; then assume a battery value of 12.75 volts, and measure at the chosen socket for any difference - unless you have a duff battery already, that should probably be close enough). As for the vehicle battery, inaccessible ones usually have a positive "jump-start" post somewhere under the bonnet, normally protected by an insulation cap. It is relatively easy, if you have one, to put a meter between here and earth to get a true measure of vehicle battery voltage. (To see if you have one, check your vehicle manual for jump-start instructions - my Transit has a "post" next to the underbonnet fuse box). Link to comment Share on other sites More sharing options...
Guest Tracker Posted April 21, 2012 Share Posted April 21, 2012 HymerVan - 2012-04-21 9:03 AM If I measure the voltage by plugging my digital multimeter into the vehicle/leisure 12v sockets will the reading be representative of the condition of the battery ? You used to be able to get a volt meter attached to a cigarette lighter plug which you could leave plugged in for ongoing monitoring? All any voltmeter does is tell you the voltage at the point of connection and the voltage at an outlet is probably more representative of the voltage available than when read at the battery terminals. The most you can expect from a voltmeter is advance warning of when the voltage starts to fall and you need to charge the batteries. Once you get used to them the led lights will probably give you the same information and in many ways could well be more reliable and easier to use than a voltmeter? What does the manual say about leds and voltages? Link to comment Share on other sites More sharing options...
dikyenfo Posted April 21, 2012 Share Posted April 21, 2012 Often a more useful reading is when using various 12V items and seeing the amount of voltage drop at point of supply which can indicate undersize wiring or resistive fuse carriers / switch contacts etc. I have checked many fridges on 12 volts and found that wiring and fuse carriers have caused very ineffecient fridges which is easily cured and some need 12 amps to fully keep cold. Link to comment Share on other sites More sharing options...
Guest Peter James Posted April 21, 2012 Share Posted April 21, 2012 I find no voltage drop through the wiring when just measuring with a meter, and everything on that circuit switched off, because the meter draws hardly any current. Its only when you try to draw a significant amount of current through the wiring that the voltage drops. Link to comment Share on other sites More sharing options...
Guest Tracker Posted April 21, 2012 Share Posted April 21, 2012 Peter James - 2012-04-21 10:57 AM . Its only when you try to draw a significant amount of current through the wiring that the voltage drops. It would do! I'm no expert but perhaps this will help? Liken it to the battery being the water supply and when you open a tap the water pressure immediately falls as does the available voltage supply from a battery. The greater the power demand the lower the retained voltage - it's normal - but it does explain why a tv or heater suddenly stops working and yet the battery voltage off load seems OK when you check it. Link to comment Share on other sites More sharing options...
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