Chris Berridge Posted January 21 Report Share Posted January 21 I've had my TR5 a couple of years now and it's been reliable until my last trip. It started fine, did about 25 miles in daylight; and then I stopped for fuel. Tried to restart and nothing. I've changed the battery for a standard lead acid, as I didn't know how old it was. There is no current drain as far as the multimeter says, but on tick over the charge voltage out at the battery is only about 13.3V. I know this is low for modern cars but is this too low for TR's? I suspect the alternator is next on the list to change but could it be the voltage regulator? Does anyone know what a healthy alternator charge voltage is? And how I can work out if it is the alternator or regulator? Quote Link to post Share on other sites
RogerH Posted January 21 Report Share Posted January 21 Hi Chris welcome to the forum. You seem pretty sure that it is the Alternator and or regulator. Unless you want to stay original why not go over to a later Alternator. More amps and less complication. If you want to stay original why not buy a nre regulator and see if that does the trick. And possibly a new Alternator if not. As the car starts on the battery why would a suspect Alternator stop you in your tracks !! 7 Did you find a problem that could stop you. Roger Quote Link to post Share on other sites
RobH Posted January 21 Report Share Posted January 21 (edited) 13.3V isn't bad at tickover I would have thought. If your TR5 has the early Lucas 15AC-type alternator with a separate regulator, the lucas spec for that is 13.6 to 14.4 volts at 3200 engine rpm. (= 6000 alternator rpm). If the voltage is within spec perhaps it was just the battery which failed? The 15AC is bit weedy- 28A max output similar to a dynamo, so if you have added extra things which draw appreciable current it might struggle. Edited January 21 by RobH Quote Link to post Share on other sites
Chris Berridge Posted January 22 Author Report Share Posted January 22 Thanks for the replies. The alternator has no name on it and doesn't look the same as in my trusty Haynes manual so I am guessing it is after market kit, possibly with an internal regulator, as It doesn't look like the Lucas model on the Moss site. As for being stopped in my tracks, my logic is if on the run, I was draining more out than going in, that would lead to the situation maybe? Apart from a new radio, everything else is standard. For a while before that, whenever I stopped and then restarted the battery almost died then had a lease of life and turned over. I might take RobH's advice, start it, take it for a run and see what happens when I get back home and try a few starts, if all is ok, it was the battery. If not then it's a new more powerful alternator as per Roger H's advice. Thanks guys. Quote Link to post Share on other sites
RobH Posted January 22 Report Share Posted January 22 All alternators should give a similar output voltage to suit the battery Chris, so if you get (say) 14v or more at 3500 rpm it is probably working OK. Quote Link to post Share on other sites
elclem1 Posted January 22 Report Share Posted January 22 Dodgy connection especially earths. But as said new battery? Quote Link to post Share on other sites
trchris Posted January 22 Report Share Posted January 22 Hi Chris The quick check would be car running load the electrics , headlights, heater fan on raise the revs and check using volt meter at battery you should have a reading of around 14.2 volts if not points towards alternator if ok battery or possibly starter motor lazy Chris Quote Link to post Share on other sites
PodOne Posted January 26 Report Share Posted January 26 Almost dying and then being ok suggests a loose connection. After 50+ years it's likely something is loose, corroded or oxidised. As Clem suggests I'd first check, clean and tighten all the earth points esp the battery strap to the starter/body and then the low tension ignition circuit/switch. Andy Quote Link to post Share on other sites
Chris Berridge Posted January 27 Author Report Share Posted January 27 Thanks guys, I ran a check today. Started the car after a week and the battery was 12.7V, I started it, ran the engine to warm and checked at tick over (1000 RPM) and at 2700 rpm, strangely the charging voltage was still only 13.3 at both speeds. Now for the funny bit, I am a chartered electrical engineer but i've never understood electricity! I have to think of volts as pressure and current as flow. With only 13.3 to 12.7 the current flow must be quite low. But if the battery didn't need charging surely you'd expect the voltage difference to be quite low? Thanks Pod one i'll check but it never does that from cold, only when warm and not since I changed the battery, so I have my doubts about a loose connection Thansk trchris, that makes sense as I checked it with nothing running so low current drain other that the ignition. I'll gove that a go tomorrow Quote Link to post Share on other sites
Jim F Posted January 27 Report Share Posted January 27 You might find this useful as a ground/earth checklist... https://www.ovtc.net/uploads/9/5/1/6/9516577/tr6_ground_points_hr.pdf Quote Link to post Share on other sites
RobH Posted January 27 Report Share Posted January 27 Open circuit, the terminal voltage on a fully charged lead-acid battery is typically about 12.8volts. 13.3v applied should result in a small 'charge' current which could be as large as C/50, so for a 50Ah battery that could be circa 1A. 14.7v applied (which is the max specified alternator output) could give around C/15 or about 3A. The actual current will depend very much on the construction of the battery and the condition of the plates. Because the battery is already fully charged, this current isn't actually charging it any further of course. It is just causing electrolysis. On a partially charged battery, the current drawn at those same voltages will be much higher. Within its current capacity, and above minimum revs, an alternator acts as a constant-voltage source and the battery acts as a variable load so the alternator sets the voltage you read. That is why a voltmeter doesn't tell you much about the state of the battery when it is on charge. Quote Link to post Share on other sites
roy53 Posted January 28 Report Share Posted January 28 On 1/26/2024 at 8:10 PM, PodOne said: Almost dying and then being ok suggests a loose connection. After 50+ years it's likely something is loose, corroded or oxidised. As Clem suggests I'd first check, clean and tighten all the earth points esp the battery strap to the starter/body and then the low tension ignition circuit/switch. Andy I had exactly this on mine. i connected a jump lead from battery earth to a head stud and perfect starter operation. Thus proving my earthing problem. Roy Quote Link to post Share on other sites
Waldi Posted January 28 Report Share Posted January 28 On 1/27/2024 at 6:02 PM, RobH said: Open circuit, the terminal voltage on a fully charged lead-acid battery is typically about 12.8volts. 13.3v applied should result in a small 'charge' current which could be as large as C/50, so for a 50Ah battery that could be circa 1A. 14.7v applied (which is the max specified alternator output) could give around C/15 or about 3A. The actual current will depend very much on the construction of the battery and the condition of the plates. Because the battery is already fully charged, this current isn't actually charging it any further of course. It is just causing electrolysis. On a partially charged battery, the current drawn at those same voltages will be much higher. Within its current capacity, and above minimum revs, an alternator acts as a constant-voltage source and the battery acts as a variable load so the alternator sets the voltage you read. That is why a voltmeter doesn't tell you much about the state of the battery when it is on charge. Thanks for explaining Rob, it’s like with psychology, if you read about it things become clearer, and you understand why things are like they are. Waldi Quote Link to post Share on other sites
John L Posted February 2 Report Share Posted February 2 I still have the 15AC alternator setup, but i fitted a Calcium battery about 4 years ago now, so far so good, I do top it up occasionally with my Ctek charger, will I expect to see a different battery charging voltage with the engine running as in your test above, I perhaps dreamt or was told that these batteries needed a higher charging rate than the current existing one, am I correct or was I really dreaming.....? John Quote Link to post Share on other sites
RobH Posted February 2 Report Share Posted February 2 47 minutes ago, John L said: I perhaps dreamt or was told that these batteries needed a higher charging rate than the current existing one, am I correct Lead -acid batteries with calcium doped plates need a slightly higher charging voltage than the average old-style alternator can supply John. This is to ensure they reach the fully-charged state. Your use of a Ctek should ensure that. If it isn't done, the battery will never reach full charge and the capacity will be lower than specified. Eventually this will become permanent. Generally these batteries have plenty in hand so the user may not notice, but the life of the battery will probably be shortened a bit. Quote Link to post Share on other sites
Chris Berridge Posted February 3 Author Report Share Posted February 3 Thanks, lots of useful information. Point noted about the earth but not sure why the starter would only do that when the engine is warm and has done a few miles. It'll be intresting to see if it still does it with the new battery. I've alway tended to put the CTek on the day before I use it so it always starts ok from cold I'll look into Waldi's advice. I agree that a volt meter tells me nothing about the battery but as that is new now, I can discount that. The ammeter on the dashboard barely moves whatever I do which is a bit surprising as I recall from old they were quite sensitive. Unfrotunately the previous owner did a lot of DIY with the wiring so not easyto trace through. Quote Link to post Share on other sites
RobH Posted February 3 Report Share Posted February 3 9 minutes ago, Chris Berridge said: The ammeter on the dashboard barely moves whatever I do which is a bit surprising as I recall from old they were quite sensitive. If it's working and properly wired, that should give a largish + swing immediately after starting, as the battery re-charges. With the engine off it should also show about 10A discharge if you turn the lights on. If it doesn't do either it must be wired wrongly or else the pointer mechanism is stuck. Quote Link to post Share on other sites
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