JJC Posted November 3, 2020 Report Share Posted November 3, 2020 How many amps should a standard alternator deliver? Is there a way of checking performance other than turning the headlights on and looking at the ammeter?JJC Quote Link to post Share on other sites
RobH Posted November 3, 2020 Report Share Posted November 3, 2020 (edited) The 15ACR which was standard on the early TR6, is rated at 28Amps at 6000 alternator rpm (3200 engine revs). The 17ACR on the later cars gives 36Amps at the same speed. There is no easy way of testing them properly on the car and anyway to do so needs some test-gear like large variable resistances for loads The simple check you mention will tell you whether it is working though, and generating at least 10 Amps. With the engine off and the headlights on there should be a 10A discharge shown on the ammeter. With the engine running at above 3000rpm this should fall to zero and depending on the battery condition may even become a charge to the battery. If the discharge current does not fall or does so only partially, the alternator is not working properly. Edited November 3, 2020 by RobH Quote Link to post Share on other sites
JJC Posted November 3, 2020 Author Report Share Posted November 3, 2020 Rob - thanks that’s a great help. JJ C Quote Link to post Share on other sites
ctc77965o Posted November 4, 2020 Report Share Posted November 4, 2020 (edited) Volts is a good indicator...use a voltmeter on a ~20V DC scale...your battery and headlamps are sufficient load to ensure the voltages are meaningful. At 3200 revs you should have 13.8V measured at the battery...if you have that then the alternator and wiring are good. If you see a number greater than ~14.2 V then that is a concern about either wiring or alternator health, similarly numbers under 13V indicate that the system is not charging (could be alternator, could be wiring). Edited November 4, 2020 by ctc77965o Quote Link to post Share on other sites
ianc Posted November 21, 2020 Report Share Posted November 21, 2020 I would be very concerned if my engine had to be doing 3000 rpm in order that my alternator could provide sufficient output to drive the headlights and a few other items. On my TR4, I have narrow belt conversion and a Lucas LRA101 alternator (later sold as Unipart GXE8210) as fitted to the TR7, which it is rated at a modest 34 amps. With the engine running yesterday, it kept the ammeter in its usual very slightly positive reading with the engine at 1300 rpm and full-beam headlights (plus sidelights), both spotlights and the heater motor running. That is the sort of performance I expect of an alternator. In stationary traffic, with dipped headlights, the ammeter only goes slightly negative when the engine is running below about 800 rpm. Ian Cornish Quote Link to post Share on other sites
ed_h Posted November 21, 2020 Report Share Posted November 21, 2020 The original 18ACR on my TR6 was rated at 40 amps, but the replacement 18ACR I bought recently claimed 60 amps. Ed Quote Link to post Share on other sites
ianc Posted November 22, 2020 Report Share Posted November 22, 2020 I imagine that the passage of time has brought superior electronic components, and that this may have permitted the output of alternators to be increased without fear of damage. Three years ago, I bought a spare equivalent of the LRA101 from ATP Electronics and it is rated at 50 amps, a lot more than the original 34 amps. It has code ALT113 Left hand (although it sits on the right of a TR2/3/4 engine, it must be lefthand). The full code was 7JN19557MJ614343Y. As the unit is unused and sitting on the shelf, I cannot say anything more than that it looks good and was a competitive price. Ian Cornish Quote Link to post Share on other sites
Macleesh Posted November 22, 2020 Report Share Posted November 22, 2020 On 11/21/2020 at 4:17 PM, ed_h said: The original 18ACR on my TR6 was rated at 40 amps, but the replacement 18ACR I bought recently claimed 60 amps. Ed Just fitted one supposedly updated to 65 Amps as a replacement to the 15ACR in my 1970 TR6 Quote Link to post Share on other sites
trchris Posted November 22, 2020 Report Share Posted November 22, 2020 Hi all I hope everyone's taking there 50 year old wiring into consideration when they are upgrading alternator outputs Chris Quote Link to post Share on other sites
RobH Posted November 22, 2020 Report Share Posted November 22, 2020 (edited) Chris - as I posted on another thread, it isn't the alternator which determines the current flowing, it is the load. The alternator only supplies what it is asked for and do not forget that the battery can supply a lot more current than any alternator. The wiring is adequate for all the standard loads so if they have not been changed there is no concern if a larger alternator is fitted. What would be of concern is if a load has been increased without a commensurate upgrade of the connecting wire. Edited November 22, 2020 by RobH Quote Link to post Share on other sites
ed_h Posted November 22, 2020 Report Share Posted November 22, 2020 (edited) It seems that the main output conductor from the alternator should be sized based on the current rating of the alternator. With a severely discharged or faulty battery, the alternator may supply all the current it is capable of. I upgraded that wire to 120 strand. With PVC insulation, it is rated at 60 amps. I think 120 strand is close to AWG 6. An alternative is to run parallel wires. Many Lucas alternators have a pair of large male output spades that are electrically connected. Ed Edited November 22, 2020 by ed_h Quote Link to post Share on other sites
trchris Posted November 22, 2020 Report Share Posted November 22, 2020 I agree Ed Chris Quote Link to post Share on other sites
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