Richardtr3a Posted January 31, 2006 Report Share Posted January 31, 2006 My car has failed to start on 3 weekends. So lastweek end, I put the charger on the battery for 15 hours at 1.5 amps. Then a friend towed me out of the garage and up the hill for about 100 yards. The engine fired up and ran well. However the ammeter was showing a charging rate off the scale. After a 12 mile run and a stop for 2 hours at a friends house I set off up the dual carriage way from Monmouth north to Ross on Wye. The ammeter still showed the same massive charge and half way home something serious went wrong and the ignition light came on fiercely and the lights were only running on the battery, which is 7 years old. After tailing a fast saloon almost all the way home I pulled up at the house and left it until the morning. Surprisingly the engine turned over and the car started enough to be put away in store for another two weeks. My question is has the overcharging hurt the dynamo. Why did the control box allow this level of charge, and is the battery at fault. Shall I take all three in to the local auto electrician for testing, or just give up and replace all three. If I replace one at a time, will I run the risk of damage to the new part? The car was fine when I put it away before Christmas. I would be grateful for any help from someone who has a greater understanding than I have. Yours Richard Quote Link to post Share on other sites
unclepete Posted February 1, 2006 Report Share Posted February 1, 2006 Richard Have you fitted an alternator? If you have, the original ammeter will not work. Check the voltage regulator. If you still have a dynamo then it sounds like there is something shorted out to give such a high ammeter reading but not enough to blow your main fuse. The wiring on a 3 is very simple and should not take an autoelectrician long to work out what is going wrong. Unc Quote Link to post Share on other sites
Steve R Posted February 1, 2006 Report Share Posted February 1, 2006 Richard I had a problem like this a few years back, I drove to the MOT test,Passed and then the car wouldn't start again. Turned out to be the control box. I found that a rivet that connected the conducting bars together, on the underside of the box was loose, causing arcing. I would check the box over,make sure that the contacts on the top are clean and that they can move ok. Good luck. Steve Quote Link to post Share on other sites
Nigel Lay Posted February 1, 2006 Report Share Posted February 1, 2006 Richard, Gut feeling is control box, dynamo should be OK. As Steve pointed out, besides contacts which tend to cause 'no charge problems' the most common fault is corrosion on the rivets which can lead to your symptoms. If you can get a genuine Lucas so much the better but now most are made in Asia/Far East and Lucas have franchaised their name so it say's Lucas on the box but IT IS NOT! When I changed the control box on a friends TR3a last year we went through 4 until we got a good one. The build quality was appalling. Best of luck - Nigel (with TS952) Quote Link to post Share on other sites
Richardtr3a Posted February 2, 2006 Author Report Share Posted February 2, 2006 Thank you for the help. I also feel that it is the control box and my concern now is whether to change it for the new one I have in the garage or will I cause damage to the new one. I do have a genuine old stock Lucas one also with the wrong fittings for my loom. I am keen not to remove the dynamo unless really necessary. It is very cold where I keep the car. Richard Quote Link to post Share on other sites
marvmul Posted February 2, 2006 Report Share Posted February 2, 2006 When the ammeter needle stays off the scale, it may be stuck there because of the initial fast movement to the + side of the scale. Ticking on the ammeter should free it. If it is really that much charging, it's the control box allowing that rate of charging by shunting the full battery voltage or dynamo output voltage to the dynamo field winding (small wire on the dynamo). The dynamo can be ruined and stop charging, the ignition light comes on when the dynamo output voltage is much lower than the battery voltage, when it is bright, the dynamo output is probably zero. The initial problem is probably a sticking contact point in the control box, thus sending the full battery voltage to the dynamo field winding. Quote Link to post Share on other sites
Don Elliott Posted February 3, 2006 Report Share Posted February 3, 2006 Take the black cover off the control box and press a few times on the contact points. This often solves the problem. In addition, take a small metal file (not sandpaper) and pass it between the contact points to remove the residue of the arcing. This will help as well. The reason for not using sandpaper is that we don't want to leave any sand embedded in the contact surfaces since sand is a very poor conductor. Quote Link to post Share on other sites
Richardtr3a Posted February 6, 2006 Author Report Share Posted February 6, 2006 Thank you Marmul for the diagnosis which seems to be correct to me . The ammeter was not stuck and did move when I put the lights on. I did flick the points in the control box but exactly what is going on in there is not clear to me even after reading the workshop manual; more than once. The dynamo has only covered a few thousand miles and was in perfect shape. Anyway it is spares day at Stoneleigh soon and I have something to buy now which I definitely need, rather than parts which may be useful one day. Thank you Don for the suggestion about the points but I have a new control box in my store and I am a bit depressed to find out that although it is a Lucas product, it may be made under license in China and be of dubious quality. The one in the car is not very old and clearly was stuck open. I was hoping that it would settle down as I drove along. I never had all this trouble when I used it every day. Thank you for the help so far Richard TR3a TS28894 Quote Link to post Share on other sites
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