GrahamB Posted June 6, 2021 Report Share Posted June 6, 2021 I do not understand your system. If the battery is capable of starting the engine, if you measure the voltage on the + battery terminal with the engine stopped you should get a steady 12 V or slightly more. This will drop to about 9 V as you crank the engine and rise to about 14 V with the engine running and the alternator operating. If the voltage does not rise above 12 V, the alternator is not functioning. As mentioned previously, the alternator has to be energised by a 12 V supply, via the dashboard ignition light which should be a standard filament bulb. The alternator should not be run without being connected to the battery. With the engine running, there should be a steady 12 V plus to the input to the ballast resistor. As suggested by Pete, if the ballast resistor is fed via the white/pink resistance wire ( K on the wiring diagram indicates pinK), you will get a fluctuating voltage, and hence unsteady reading, at the input to the resistor and very little current through the coil resulting in a weak spark Link to comment Share on other sites More sharing options...
PeteH Posted June 6, 2021 Report Share Posted June 6, 2021 Bear in mind that on Alternators the Regulator is most often built into the back of the device. They can fail, I am not 100% sure but part of the circuitry I think incorporates a series of Diodes?. Failure of any one of which could affect output?. (Correct me if I am wrong it is the best part of 50? year since I did Electronics theory) Pete Link to comment Share on other sites More sharing options...
Adrian Posted June 6, 2021 Author Report Share Posted June 6, 2021 I've been measuring the altermator output to the resistor and getting highly variable readings (with engine running). I'll check the charge to the battery tomorrow (the red charge light on the dash is working). Not sure if I can get an accurate check for A/C current >0.5v on the alternator as mine has 200 or 500 so not sure if it is low enough (I've read >0.5 A/C indicates diode failure). Definately no pink/white wire, on close inspection it is the standard white/yellow so its all pretty standard wiring and components. But definately not getting a constant 12V feed to the resistor. (maybe I didn't make it clear, but the later measurements are with the engine running). Cheers Adrian Link to comment Share on other sites More sharing options...
GrahamB Posted June 6, 2021 Report Share Posted June 6, 2021 Yes you are correct. The alternator produces an alternating current which passes through a diode pack to supply a direct current to the battery. In the Lucas alternators and others, the diode pack is in the back of the device immediately under the black plastic cover. I once had a Mk1 Fiesta to which I fitted a 4 branch exhaust which came close to the read of the alternator and the extra heat caused the diodes to fail on more than one occasion. Fortunately you could buy just the diode pack in order to repair the alternator. Link to comment Share on other sites More sharing options...
johny Posted June 7, 2021 Report Share Posted June 7, 2021 worn brushes on the alternator slip rings can give fluctuations due to making partial contact and sparking. Also good to confirm readings with another meter.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 7, 2021 Report Share Posted June 7, 2021 Just to hark back to the original post on fuel; I was trying to trim hedges recently and the hedge trimmer was fighting against me, refusing to rev and actually getting red hot. I thought it was the clutch or drive. Went on a help forum, someone suggested old fuel, so I emptied the tank and refuelled with fresh and it ran perfectly. The 4-stroke lawnmower will run all day on ages-old petrol but this 2-stroke won't. Link to comment Share on other sites More sharing options...
Adrian Posted June 7, 2021 Author Report Share Posted June 7, 2021 Perhaps I need to repost now in electrical but anyway tested the alternator with the engine running and only getting 12.8 volts at the battery (more consistent but it did flicker around a bit). Does it make a difference testing once started or waiting till warmed up? Generally 0.1-0.3 A/C at the alternator but occasionally spiked to 0.4-0.5. So looks like its the alternator. Adrian Link to comment Share on other sites More sharing options...
johny Posted June 7, 2021 Report Share Posted June 7, 2021 Are you sure your meter is good as Im surprised you saw rapid voltage changes when running with the battery connected? The battery is like a large reservoir so its voltage can only be changed slowly. To see a higher voltage at its terminals youd have to be pushing a lot of current into it... Link to comment Share on other sites More sharing options...
Adrian Posted June 7, 2021 Author Report Share Posted June 7, 2021 Its only about 3 years old and whilst not an expensive one hasn't seen a lot of action so would expect it to be reasonably accurate. Maybe its time to take it to the garage! Any suggestions for a reasonable and accurate tester? fundamentally I'm getting a constant 12.5v at the battery not flickering around. Tried an AA cell battery and got 1.43v, again not flickering. The flickering only seems to happen when the engine is running which suggests an inconsistent electricity generation? Any suggestions for a replacement if needed. What amps, brand, source? Link to comment Share on other sites More sharing options...
johny Posted June 7, 2021 Report Share Posted June 7, 2021 As your video clip doesnt work what is the range of the DC fluctuations youre seeing? Your meter certainly sounds good but its always worth checking it against another if you can borrow one. I take it the fan belt is adjusted correctly and definitely not slipping? If Ive got this right you think the fluctuations could be affecting the running so try unplugging the alternator and run the engine just on the battery to see if this improves things... Link to comment Share on other sites More sharing options...
GrahamB Posted June 7, 2021 Report Share Posted June 7, 2021 I would not recommend running with the alternator unplugged as voltage spikes, normally dampened by the battery, could damage the electronics within the alternator. The alternator produces A/C which is not completely smoothed by the diodes so you will get a ripple on top of the D/C voltage. I have not tried to measure it myself but 0.5V A/C seems quire reasonable. You will only measure any A/C voltage with the engine running as it is produced by the alternator. The dashboard mounted voltmeter in my car, which is not very sensitive, is wired directly to the battery via a relay. It reads 12v with the ignition switched on rising to 14V as soon as the engine starts. I replaced the previous alternator as the voltage only registered 11V with the engine running and the lights on. I fitted a 60 amp Lucas style alternator purchased from Canley Classics. I do not know if they still sell them. Link to comment Share on other sites More sharing options...
johny Posted June 7, 2021 Report Share Posted June 7, 2021 With the alternator completely disconnected I dont think it would generate anything as the initial field supply from the ignition light would be missing. However to avoid any risk another way would be to remove the fan belt for a short run of the engine and see if theres any improvement... Link to comment Share on other sites More sharing options...
GrahamB Posted June 7, 2021 Report Share Posted June 7, 2021 Yes, I was forgetting that the initial field supply would be removed if the alternator plug was disconnected. Link to comment Share on other sites More sharing options...
Adrian Posted June 10, 2021 Author Report Share Posted June 10, 2021 Hi Chaps I took the car to the garage and they confirmed the alternator was just about holding its own at 12.6v. With regard to not running when it's hot they said ther was an air leak from a wrongly installed gasket on one of the carbs which appeared to result in almost running on 3 cylinders. I can't deny It was my fault but given my totally amateur status a wrongly installed gasket from an engine out partial rebuild is pretty good in my eyes. The garage said they were actually impressed with the restoration and presentation, apart from the gear box which I haven't touched. On the ramps they can see a leak from a couple of gaskets front and back of box AND noticed miss alignment on the mounting plate as has been identified and discussed before. The leak isn't major and will enjoy this years driving once tuned up before considering stripping it out. Just out of interest I'm going to have to replace the alternator. Given that various conversions are out there how do you know which one? Its a Valeo 436140, no idea what amperage but Rimmer replacement is 36 amps? Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 11, 2021 Report Share Posted June 11, 2021 at lat you have a solution good going. canley show as 60a lucas https://www.canleyclassics.com/?catalogue=triumph-gt6-mkiii&diagram=triumph-gt6-mkiii-alternator-lucas j paddocks dont say https://www.jamespaddock.co.uk/alternator-new-inc-fanpulley-2 Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 11, 2021 Report Share Posted June 11, 2021 and on the orig subject of old fuel lost its oomph we went to a mk2 spitty off the road and not run for over 3 years what a luverly car absolutely brilliant so off with the cover , prime the pump, pull choke and va va room fired up straight away , on 2nd crank , Pete Link to comment Share on other sites More sharing options...
Adrian Posted June 12, 2021 Author Report Share Posted June 12, 2021 Hi Pete was it standard fuel, no preservative, octane boost? Link to comment Share on other sites More sharing options...
Chris A Posted June 12, 2021 Report Share Posted June 12, 2021 Sort of related to this thread. Last night on my local news there was a report from a petrol refinery at Donges ( Loire estuary near St Nazaire). during the report they mentioned that the additives were changed according to the time of year, more (forgot what) in winter to help cold starting for instance. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 12, 2021 Report Share Posted June 12, 2021 its was common to add to diesel to stop cold weather waxing up the pipes dont know about petrols Pete Pete Link to comment Share on other sites More sharing options...
Chris A Posted June 12, 2021 Report Share Posted June 12, 2021 2 hours ago, Pete Lewis said: its was common to add to diesel to stop cold weather waxing up the pipes dont know about petrols Pete Pete I was surprised when they said to petrol, not to stop it thickening as with diesel obviously, but I assume to make it more volatile. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 12, 2021 Report Share Posted June 12, 2021 a blue rocket might help theres a few around now Pete Link to comment Share on other sites More sharing options...
Chris A Posted June 12, 2021 Report Share Posted June 12, 2021 2 hours ago, Pete Lewis said: a blue rocket might help theres a few around now Pete Yes there are, but I notice some privileged contributors are better treated, no names mentioned of course . . . Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 12, 2021 Report Share Posted June 12, 2021 3 hours ago, Pete Lewis said: a blue rocket might help theres a few around now Pete Link to comment Share on other sites More sharing options...
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