TheBeastie Posted July 6, 2010 Share Posted July 6, 2010 I have now had my voltmeter fitted for a couple of months and wonder if anyone can advise its behaviour. When normal running with no load it shows a tad over 13 volts - but definitely not 13.5v. With headlights on it goes to about 12v. On Sunday towing radio mast home after being blown off site so headlights, radio, wipers flat out, heater flat out (desperately trying to warm up/dry out) it was showing under 12v. When I switch on but do not start it is showing me about 11v. I have got two new Odyssey PC1200 batteries with an X-Charge splitter. I am beginning to wonder if this is telling me that my alternator needs to be replaced/upgraded but would welcome advice. Thanks for any input Malcy Quote Link to comment Share on other sites More sharing options...
zim Posted July 6, 2010 Share Posted July 6, 2010 Stick a voltmeter onto your battery and see what the actual voltage is. Has the voltmeter got a decent earth ? Where are you getting the feed for your voltmeter ? From the low voltages you're describing, i'd say a feed from in the dash somewhere - radio, cig lighter ??? Thus, try running a decent wire from a decent source (battery, starter motor, alternator, positive post on the bulkhead etc) VDO are a good make so the results should be pretty accurate. G Quote Link to comment Share on other sites More sharing options...
western Posted July 6, 2010 Share Posted July 6, 2010 what amps is your alternator ? mines a 100amp & I have the same voltmeters feed via a split charge to 2 PC1700's just done this for you as a comparison engine running at idle, no lights, 12.9v engine running at idle, side & dip headlights on 12.6v engine running at 1500rpm side & dip headlights on 12.8v engine running at idle, no lights 13.5v give the batteries a good charge soon as you get the chance. Quote Link to comment Share on other sites More sharing options...
Puffernutter Posted July 6, 2010 Share Posted July 6, 2010 what amps is your alternator ? mines a 100amp & I have the same voltmeters feed via a split charge to 2 PC1700'S Charging should be between 13.8 and 14.2 volts. It either means that your voltmeter is not connected in the right place, has a poor connection or the alternator charging circuit needs looking at. I would suggest: 1. Putting a voltmeter/multimeter directly across the battery and see what the volts are on idle and fast idle; then 2. Put a voltmeter/multimeter on the brown wires at the alternator (there shouldn't be any diference as one alternator brown wire goes to the battery. If there is a difference, check the body earths. If there isn't a difference and the voltages are still low, probably new alternator time! Cheers Peter Quote Link to comment Share on other sites More sharing options...
TheBeastie Posted July 6, 2010 Author Share Posted July 6, 2010 Thanks guys for that. Gives me some sensible courses of action to follow. Hopefully by a process of elimination I may be able to narrow things down. The feed is the original one but I may well run a new dedicated wire and will also double check the earth. Western's chart for comparison voltages is useful. I think my alternator is original but will see if I can find some markings to give me a clue as to amp output. At least I now have a plan of action. Will try and report back as I progress. Quote Link to comment Share on other sites More sharing options...
western Posted July 6, 2010 Share Posted July 6, 2010 if your alt. is factory original it'll either be a 45amp or a 65amp, my original was a 65, the standard voltmeter feed is off one of the White Ignition controlled wires behind the inst pack. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted July 9, 2010 Share Posted July 9, 2010 If you wire a voltmeter directly to the battery, will it flatten the battery if left for a while ? Mo Quote Link to comment Share on other sites More sharing options...
Puffernutter Posted July 9, 2010 Share Posted July 9, 2010 A very long while.... Cheers Peter Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted July 9, 2010 Share Posted July 9, 2010 It draws a current, so in theory yes. Whether that current is such that it wouldn't really make any difference bearing in mind other parasitic drains such as radios etc, I do not know Quote Link to comment Share on other sites More sharing options...
Puffernutter Posted July 9, 2010 Share Posted July 9, 2010 Assuming a 10kohm internal resistance for the voltmeter and a 25Amp/hour battery (on the low side for a LR) it would take about 2 years to run the battery down! So, not really a problem But to reduce the risk of short ciruits and live cables, I would attach it to a switched source! Cheers Peter Quote Link to comment Share on other sites More sharing options...
western Posted July 9, 2010 Share Posted July 9, 2010 If you wire a voltmeter directly to the battery, will it flatten the battery if left for a while ? Mo a 2nd voltmeter to monitor a 2nd battery can be fitted using a standard 30amp 4 pin relay connected like this, the note about the warning light only applies to non-td5 instrument fitted vehicles. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted July 9, 2010 Share Posted July 9, 2010 I think you're assuming a bit much about automotive gauges, you may be surprised by how much current the voltmeter will draw. OK, it's not loads, but it may be enough to run your battery down over medium periods of inactivity. Quote Link to comment Share on other sites More sharing options...
zim Posted July 10, 2010 Share Posted July 10, 2010 Get a voltmeter with a remote switching wire. i.e. when ignition on it's on. My brax is like this. G Quote Link to comment Share on other sites More sharing options...
Aragorn Posted July 10, 2010 Share Posted July 10, 2010 i'd start by testing the battery with a good multimeter and see what you've got coming out of it. You should be seeing 12.5+v with the engine off and the battery fully charged, and somewhere around 14v with the engine running. (14.1 is optimal, but between 13.8 and 14.4 is ok) If your not getting 14v at the battery with the engine running, and assuming the alternator is working, then you need to be looking at the cables between the alternator and the battery. I had an old astra that only managed 13.5v at the battery with the engine running, but if you stuck the meter between the B+ post on the alternator, and the alternator casing itself, you'd get 14.1v. I attached a large earthstrap between the alternator case and the engine block to replace the standard puny item and the battery voltage came up to 14v. If the battery/charging circuit is healthy, then you need to look at upgrading some of your wiring to the dash area. As above check all the earth first, and if in doubt simply run a decent sized cable to a good earthing point. You can then probe various parts of the circuitry to see where the voltage drop is occuring. I recently did this on our A4 after noticing the headlights were only getting 12.9v when on. I initially thaught it was simply voltage drop along the cabling, and planned to fit thicker wire, however it became apparent after some playing that the problem was caused by a box in the dash designed to detect bulb failures. It had 13.9v going in and only 12.9v going out. I can only imagine it draws the circuit thru a resistor, and uses the voltage drop to calculate the current being consumed. Quote Link to comment Share on other sites More sharing options...
TheBeastie Posted July 18, 2010 Author Share Posted July 18, 2010 Hi guys. Finally got to some testing. With engine off I am getting about 12.7 off the main battery. It did not seem to make too much difference between slow idle and fast idle (but perhaps I was impatient). The voltage steadily climbed to about 14.1V. In both cases it looks like the new dash voltmeter is reading a good 1v low so I am guessing it is time to have another look at the state of the dash wiring and run some new cables to it. At the end of the day I now know I am not looking at critical - I was running radio all day yesterday on RAYNET with full 25W on 2m Tx off second battery without any issue and the split charge got everything back up to full charge very quickly, so the fundamental charging system is working. So, unless someone points out something to the contrary, it is a job I will tackle on a quiet day (Ho Hum) Thanks for all the advice. Quote Link to comment Share on other sites More sharing options...
Ian J Posted January 11, 2011 Share Posted January 11, 2011 Hi everyone, Apologies for bringing up an old thread, but a Google search brought me here! I am in the process of installing a second battery in my Defender via a simple split charge relay. I had planned to fit dual voltmeters in my MUD dash console, one for each battery. Then it occurred to me that as soon as the engine is running, both voltmeters will show the output from the alternator. Correct? Is there any advantage to having a voltmeter on each battery? Presumably with the ignition on but the engine not running I will be able to see the voltage of each? To complete the picture, my plan was to hook each battery up to its voltmeter via a relay each, triggered with the ignition turning on. Thanks in advance, Ian. Quote Link to comment Share on other sites More sharing options...
western Posted January 11, 2011 Share Posted January 11, 2011 wire your 2nd voltmeter as per my diagram above & it'll also switch off when the ign is off, works for me. for the start battery connect it's voltmeter to a ign controlled WHITE wire, that's how LR did it on pre Td5 vehicles & again it'll switch the voltmeter off when ign is off. Quote Link to comment Share on other sites More sharing options...
Ian J Posted January 12, 2011 Share Posted January 12, 2011 Hi, Thanks for the prompt reply. I was less concerned with turning the voltmeters on and off with the ignition as I have that covered. But I wanted to make sure that I understood what the behaviour of the two meters would be. i.e. Ignition off - both voltmeters off Ignition on / engine not running - each voltmeter displays voltage of its respective battery Ignition on / engine running - both voltmeters display the charging voltage from alternator (that is, both will read the same value) Correct? Ian. Quote Link to comment Share on other sites More sharing options...
western Posted January 12, 2011 Share Posted January 12, 2011 Ignition on / engine running - both voltmeters display the charging voltage from alternator (that is, both will read the same value) depends on which battery needs the most charge, better off charging via a split charge relay, rather than direct from alternator. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.