v8bertha Posted February 1, 2012 Share Posted February 1, 2012 Any alternator geeks out there? I've got one of these National Luna battery monitors mounted on the dash of the 110 On the way home from work this afternoon I was keeping an eye on it and noticed that the reading was fluctuating between 12.6v and 13.6v regardless of whether I has lights/heaters/stereo on. A couple of times the 14.4v led lit up momentarily. Considering my split charge doesn't start split charging until 13.7v, I'm left with a second battery that is now completely flat meaning the heated seats won't work !!! My question is this... is it normal for alternator output voltage to fluctuate or should it be a steady? A cold bum in the mornings is not nice, hence an urgent need to solve this problem! Cheers Dan Quote Link to comment Share on other sites More sharing options...
western Posted February 1, 2012 Share Posted February 1, 2012 depending on how old the Alt is might be sticky or worn brushes or a poorly regulator pack. Quote Link to comment Share on other sites More sharing options...
fozsug Posted February 2, 2012 Share Posted February 2, 2012 Sounds like regulator pack cruising home it should be easily putting out 13.7 vlts Quote Link to comment Share on other sites More sharing options...
Sip Posted February 2, 2012 Share Posted February 2, 2012 I had one of those monitors and it was giving false readings. When I connected both sides of the monitor to the same battery, I got two different volt readings. Might be worth putting a meter on the batteries to check the monitor. Quote Link to comment Share on other sites More sharing options...
zim Posted February 2, 2012 Share Posted February 2, 2012 As said above, chances are that the alt needs it's brushes looking at them is pretty easy If you're ok with a spanner. Or... Your voltage regulator might be plying up, but generally when this happens it'll overcharge. The other possibility is a duff battery. But think you'd have had starting problems by now. You may end up just having to clean them up as well as replace the back bearing. Howcome you have the split relay at 13.7? How've you done this. Quote Link to comment Share on other sites More sharing options...
nickwilliams Posted February 2, 2012 Share Posted February 2, 2012 It will also depend on where you are reading the voltage - if the measurement is taken directly off the battery terminals it will be a lot more stable than if it is being taken from some convenient point behind the dash board. Nick. Quote Link to comment Share on other sites More sharing options...
v8bertha Posted February 3, 2012 Author Share Posted February 3, 2012 Thanks all... I think I'll look at cleaning/replacing the brush pack first as these are fairly cheap and easy to do. As suggested by Sip, I'm inclined to agree that these things aren't overly accurate and are only there to provide an indication, rather than an exact measurement. Zim... It's a VSR. I'm pretty certain it kicks in at 13.7v, but it's quite possible I'm mistaken! Oh, and not sure if I should admit to this, but making sure the connection is done up, rather than rattling about on the battery terminal helps!! Cheers all Quote Link to comment Share on other sites More sharing options...
zim Posted February 3, 2012 Share Posted February 3, 2012 VSR. Ok..... Is it a coincadence that you're dropping from 13.6 to 12.x. Are you sure it isn't your vsr that's affecting things ? Try making your split relay switch with just a normal live feed whilst running and then see if you're getting voltage fluctuations. If the above is causing your problem, it'll start off at a low voltage whilst the extra battery charges up. Your second battery is possibly flat and can't take charge because when the circuit opens the voltage drops and thus switches off the relay. Gordon Edit : A quick google came up with this http://bepmarine.com/home-mainmenu-8/product-269/125-amp-voltage-sensitive-relay-vsr- The Voltage Sensitive Relay (VSR) allows two batteries to be charged at the same time. When the engine is started and the start battery reaches 13.7 volts, the VSR engages, allowing two battery banks (start and house) to be charged simultaneously. When the voltage drops below 12.8 volts (eg the engine is stopped), the VSR disengages, separating the batteries. Those voltages mentioned above are the same as what your fluctuations are going to and from. From reading this for diagnosis, i'd definately say just join the two batteries in parrallel without any relay and see what happens. Quote Link to comment Share on other sites More sharing options...
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