JonM Posted October 8, 2009 Posted October 8, 2009 I don't know if the charging meter on my 1992 200Tdi Defender is an amp meter or a voltage meter. Anyway, for the last 4 years it has been reading 3mm to the + side. Recently however, it has been erratic, sometimes 3mm + ve, sometimes on the centre line, sometimes on the - ve side. I had the alternator and battery checked and they are fine. Anyone had this problem? Maybe the gauge is dodgy or the wiring is flaky?? Thanks. Quote
Mo Murphy Posted October 8, 2009 Posted October 8, 2009 Jon, can you stick a photo of it up so that we can see what gauge you have ? Mo Quote
BogMonster Posted October 8, 2009 Posted October 8, 2009 It's almost certainly a voltmeter, so you can put a digital meter on the battery when it is playing up and see what is going on. I haven't seen a factory ammeter in anything newer than a S3 but a lot of vehicles had voltmeters fitted, on the farm we have two late 80s 90/110 and both had voltmeters as standard. Ammeters usually have some numbers on the scale otherwise they are a bit of a waste of time. Quote
Aragorn Posted October 8, 2009 Posted October 8, 2009 How would a volt meter be able to show negative? Sounds more like a charge (ie ammeter) to me given his description of 0 in the middle and + / - either side of that. It showing negative would suggest that the alternator is no longer providing charge TO the battery, but if as you say the alternator and battery check out then its likely to be a faulty guage or wiring i would think... Might be an idea to keep a multimeter handy and when it starts showing negative have a quick check of the voltages present at the fuse box and battery to see if the voltage suggests the alternator is charging (ie 14v) or that everything is running off the battery (12v) Quote
FridgeFreezer Posted October 8, 2009 Posted October 8, 2009 How would a volt meter be able to show negative? It depends on the scale really, it may assume that a certain centre point is "normal" so anything below that would be bad. I agree though, sounds more like an ammeter. Quote
BogMonster Posted October 9, 2009 Posted October 9, 2009 OK this is the one I am talking about - is this the same as yours Jon? best pic I could find on Google but they were fitted in loads of vehicles. Having driven several vehicles with one of these in over a number of years I am quite sure it is a voltmeter and not an ammeter despite the appearance. On startup in any of ours, it tends to initially hover somewhere around the white line in the middle and in normal driving after a short time it will rise to a point about half way between the centre line and the red on the right hand side, which is exactly what you would expect a voltmeter to do (battery voltage rises a bit initially and then up to about 14.4 continuous after the engine has been running for a while - bear in mind it is only a poxy 45A alternator on older vehicles) and exactly the opposite of what you would expect an ammeter to do (which would be a high reading after startup, tailing off to zero as the battery voltage rises to the regulated voltage and charging current drops back). Although they don't have any figures on them it is a useful tool as once you know what is "normal" any deviation is quickly spotted unlike modern vehicles where unless you notice the lights are a bit dim, the first you know of an alternator problem is usually when it won't start in the morning... Quote
JonM Posted October 9, 2009 Author Posted October 9, 2009 Yes, this is the gauge on my 200Tdi. When we checked the voltage at the battery with the engine running it would rise to 13.8 volts, while the "meter" would go to about the centre line. Sounds to me like wiring, don't see why the gauge should become erratic. I'll check the voltage on the back of the gauge. More later. Quote
Aragorn Posted October 9, 2009 Posted October 9, 2009 In that case i'll agree, it does look like a voltmeter. I'd give the voltage a check at the guage like you suggest and see what you find. Quote
BogMonster Posted October 9, 2009 Posted October 9, 2009 Yes, this is the gauge on my 200Tdi. When we checked the voltage at the battery with the engine running it would rise to 13.8 volts, while the "meter" would go to about the centre line. Sounds to me like wiring, don't see why the gauge should become erratic. I'll check the voltage on the back of the gauge. More later. It should really be a bit higher than that - the gauge may be telling the truth. I would do a few tests with a meter on the battery and putting major loads on and off and varying engine revs - i.e. main beam, heated rear window, heater fan all on full and then off again. You may find the alternator is working but a little tired - hence the voltage varies with load and so does the gauge. The older alternators aren't that great at keeping up with demand even when they are working properly, especially the 45A ones. Quote
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