Mg haggerston Posted January 29, 2018 Report Share Posted January 29, 2018 who designed ammeters and oil pressure gauges! Have had trouble with both,but over the last year ammeter has driven me crazy it always registers plus 15 Amps with engine running,but when I switch main beam it goes up to 25 amps , but with engine off it registers minus with an electric load , is this something to do with alternator diodes or rectifiers acting up, Faulty earthing or light switch,any help would be most appreciated. Michael. Quote Link to post Share on other sites
Mike C Posted January 29, 2018 Report Share Posted January 29, 2018 That's normal if your ammeter has been wired to measure the total output of the alternator, like my 1969 TR6 is . For normal running it uses about 15 amps to run the Bosch fuel pump plus miscellaneous electrics. Switch on the lights and it generated extra current for the lights, in your case 10 amps=120 watts for the main beams. I can't see any problem with your alternator system. Note I modified my alternator to 45 amps output and fitted a 60 amp ammeter-that's about as far as I'm prepared to push the existing wiring with the total alternator output going through the dash mounted ammeter. Later TR's with a voltmeter avoid this problem. If originality is not important and you're not happy with the ammeter set up you could change to a voltmeter to monitor alternator performance. Quote Link to post Share on other sites
RogerH Posted January 29, 2018 Report Share Posted January 29, 2018 Hi Michael/Mick, ideally the ammeter should only see the battery charging current - hence +/- 30 amps. Not a good idea to have all the current whizzing about behind the dash. Roger Quote Link to post Share on other sites
Mike C Posted January 29, 2018 Report Share Posted January 29, 2018 Thanks Roger- I agree , it's one of the jobs on my list for next winter but in the meantime I keep a wary eye on how long the charging rate stays above 30 amps after start up and a wary nose sniffing for any burnt wiring smells. Seems OK in the short term. Quote Link to post Share on other sites
Mg haggerston Posted January 29, 2018 Author Report Share Posted January 29, 2018 thanks Mike C, I always thought if you switched on high draw it would have a negative result,I've learned something new, I'm a sucker for originality,so stuck with ammeter. Thanks Michael. Quote Link to post Share on other sites
Mg haggerston Posted January 29, 2018 Author Report Share Posted January 29, 2018 hi Roger, top tip for safety,take ashtray out of dash top so you can see smoke !!! Quote Link to post Share on other sites
RobH Posted January 29, 2018 Report Share Posted January 29, 2018 Michael- that is happening because the feed for the fuel pump has been taken direct from the battery -shown as red on this sketch. (presumably via a relay so it only comes on with the ignition). If you don't want the standing 15A shown you need to move the pump feed to the other side of the ammeter so it is fed direct from the alternator - shown as green If you do that the ammeter will register the pump current as a discharge until the motor is started but after that will only show the current into/out of the battery. Quote Link to post Share on other sites
Mike C Posted January 29, 2018 Report Share Posted January 29, 2018 Thanks Rob. Saved this to my 2018 winter works file. I'll probably take the feed to the pump from the ammeter feed wire from somewhere in the engine bay. Quote Link to post Share on other sites
Mg haggerston Posted January 29, 2018 Author Report Share Posted January 29, 2018 rob h,Thanks ,will have a poke around tomorrow,as you can see electrickery is not my strong point. Michael. Quote Link to post Share on other sites
cp25616 Posted January 30, 2018 Report Share Posted January 30, 2018 Good info Rob H. Thank you. Alan G Quote Link to post Share on other sites
TR 2100 Posted January 30, 2018 Report Share Posted January 30, 2018 Michael, Is this on one of your 6s, the Spitfire or the Stag? And - we are talking about an ammeter, not a voltmeter? AlanR Quote Link to post Share on other sites
pinky Posted January 30, 2018 Report Share Posted January 30, 2018 hi, I found the amp meter a night t mare, good in its day with old battery's changed it for a volt meter, pink Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.