Rob Y Posted March 16, 2015 Report Share Posted March 16, 2015 Hi Everyone, I was out for a drive in the TR6 the other day on a beautiful Spring afternoon - . I noticed the volts on the meter varied from around 13 to 11 without any obvious changes in the car - I mean without putting the fan on or the windscreen wipers etc. Is this normal? I have only had the car for around 6 months so still learning about it, and its the first car I have had that has even had a voltmeter so I have no idea what is "normal". I don't know how old the battery is, if this makes any difference, but she always starts ok with no apparent problems as far as the battery is concerned. any comments would be appreciated. Thanks Rob. Quote Link to post Share on other sites
RogerH Posted March 16, 2015 Report Share Posted March 16, 2015 Hi Rob, I would have thought that the first place to look would be all the connections between battery/Alternator/gauge. Battery to body earth, Chassis to engine earth Give everything a good clean. And while your about it fit an earth cable from the battery direct to the engine It could be possible that the Alt diodes are suffering with heat, but the TR6 Alt is well exposed. Roger Quote Link to post Share on other sites
Spit_2.5PI Posted March 16, 2015 Report Share Posted March 16, 2015 It could be possible that the Alt diodes are suffering with heat, but the TR6 Alt is well exposed. ... or just vibration. The alternator on my old Dolly would do this - random hi-lo-hi voltage. Lifting the bonnet and wiggling the connector on the back of the alternator would bring it back to life. Eventually took alternator to a Lucas service centre (remember them?) who popped it on their jig and diagnosed faulty diode pack -fairly simple job to swap pack if you're confident with a soldering iron. Richard Quote Link to post Share on other sites
john.r.davies Posted March 16, 2015 Report Share Posted March 16, 2015 Rob, Do you have an alternator or a dynamo? The second will have. somewhere on the loom from it towrads the battery,a "Control Box, with lots of connections and three coils inside. The function of this is to stop the battery being overcharged, by it being disconnected from the dynamo when it has been fully charged. In fact, that happens intermittently, so your volt meter, seeing the violts at the battery terminals, sees 13V (dynamo) then 11V (slightly discharged battery) and back again. See: http://www.mgb-stuff.org.uk/controlbox.htm Could be poor connections elsewhere though. If you have an alternator, the equivalent circuit is inside the alt. Still could be the cause, in the same way, but an alt. will charge up the battery far quicker, so unlikely to cause this intermittent change. JOhn Quote Link to post Share on other sites
Rob Y Posted March 16, 2015 Author Report Share Posted March 16, 2015 Thanks for the comments. I think it's an alternator, I will double check though. I was hoping everyone was going to say it was normal, and not really a problem at all. I will check and clean connections etc and see if this makes a difference next time I go out. The charging light isn't coming on so I guess this means it is charging at least. Cheers, Rob. Quote Link to post Share on other sites
peejay4A Posted March 16, 2015 Report Share Posted March 16, 2015 It's probably not charging at 11 volts. Does the charging light come on with the engine stopped and ignition on? Quote Link to post Share on other sites
RobH Posted March 16, 2015 Report Share Posted March 16, 2015 Before suspecting complicated things like a duff alternator etc, its worth checking that the meter itself is reading OK. Try connecting a known good voltmeter first to see if its telling you porkies. Rob Quote Link to post Share on other sites
Rob Y Posted March 17, 2015 Author Report Share Posted March 17, 2015 Thanks again for replies. I have checked and it is definitely an alternator - Lucas type. Problem with using a voltmeter to check is that the problem only seems to happen while I am driving so checking this way is not easy. It may be related to vibration/going down bumpy roads but that is hard to correlate. Charging light does come on when engine off but ignition off, but I hadn't checked this before so its always good to do this. I will clean the connections and also check the drive belt tightness - it looks a bit slack although I haven't measured it and it doesn't sound as if it is slipping, but while I am checking things in this area probably worth doing. It's funny as I say that on other cars - including my modern one, there is no Voltmeter and if I couldn't see this varying, I would be unaware of any issue, battery seems to be charging ok, but now I have seen it I need to fix it! Cheers Rob Quote Link to post Share on other sites
peejay4A Posted March 17, 2015 Report Share Posted March 17, 2015 You could "calibrate" the voltmeter against your multimeter with the engine off and with it running. That would give you a little confidence that the meter isn't telling porkies. With the engine running you should see around 14v across the battery terminals (13.8 to 14.2 ish). Quote Link to post Share on other sites
RogerH Posted March 17, 2015 Report Share Posted March 17, 2015 Hi Rob, ammeters were fitted in the 'old' days to give the driver an idea that the battery was being charged. When Alternators become popular/common a voltmeter was considered a better choice. In this new age of computors etc the ECU monitors what is going. If the battery stopped charging or the Alt had a problem your dash board would light up with signs you never knew you had. Roger Quote Link to post Share on other sites
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