sam93 Posted September 9, 2011 Share Posted September 9, 2011 Hello,Today I coverted my dynamo setup on my herald 1200 to an alternator. It came from a spitfire which was rusting in peace in a scrapyard. At the alternator I have a large yellow wire connected to one of the large terminals, a thin yellow wire with a green strip which is connected to the small terminal, and large brown wire which is connected to the other large terminal, and is connected to positive side of the battery. Where the control box was I insulated the black wire on it's own, joined together the thin yellow and thin yellow/green strip, and then the 3 large brown and 1 large yellow were linked together.So that's the setup, however I don't think it charging properly, as with the engine at idle I measured 12.58v across the battery. As I didn't think this was high enough I disconnected the wires at the alternator, left the engine on idle and took a voltage between one of the large terminals and the small terminal. The result fluctuated between 12.5v and 10v, would this suggest that the alternator does not work ?, also the charge warning light does not turn off/ go out at any rev. Link to comment Share on other sites More sharing options...
Jordon T Posted September 10, 2011 Share Posted September 10, 2011 Hi Sam93,Having gone through the process of replacing my dynamo for a higher voltage alternator, i got through 3 second Hand alternators which all read similar Voltage readings to yours. :( To start with Here a fantastic link which helped me with my conversion, this is just in case your in any doubt of your wiring :)http://www.northcotts.clara.net/tsscdevon/technical/alternator/alternator.htmlYour battery should be reading around 12.6V when the engine is switch off, Then when you start it it should be reading around 14V. ;)I think your best bet is to take you're alternator and buy an exchange unit from your local motor facotrs, Midwest, Monmore, Motor aids etc....thats what i did with mine. :)Regards Jordan Link to comment Share on other sites More sharing options...
GarthT Posted September 10, 2011 Share Posted September 10, 2011 2880 wrote:As I didn't think this was high enough I disconnected the wires at the alternator, left the engine on idlemight be wrong here, but I thought that disconnecting the alternator while the engine is running is a bad idea, as it can damage the alternator, possibly the diodes?Someone may be able to clarify.I'd go with Jordan's idea. I bought a 2nd hand one that didn't work then went for a brand new 75A uprated one. £60 no exchange on eBay. Link to comment Share on other sites More sharing options...
piman Posted September 11, 2011 Share Posted September 11, 2011 Hello Garth, yse you are right, do not disconnect the alternator on a running engine. If you start an engine with the alternator disconnected it won't charge, it needs the 12v feed from the warning light to the WL terminal on the alternator for it to start charging.Dave the two large (internally connected terminals are the alternator out put and the small is the warning light connection which goes to the field regulator. You won't get any meaningful reading there. You simply measure beteen the main output and earth. Alec Link to comment Share on other sites More sharing options...
sam93 Posted November 12, 2011 Author Share Posted November 12, 2011 Hi, I've just wired in a brand new 65 amp alternator, by following the linked instructions. Still not working though, I'm currently fault finding, is there any obvious things that I should look for ?Help required ASAP !!!Thanks,Sam. Link to comment Share on other sites More sharing options...
sam93 Posted November 12, 2011 Author Share Posted November 12, 2011 Hi, everyone I've now made the alternator work, it was the 12v supply from the warning light that was the problem. However I've now got a new bigger !! ProblemThe ignition switch no longer cuts the engine, it even still runs with the battery disconnected, so it's obviously the alternator providing the spark ..... But how ?????Please help, ASAPThanks,Sam. Link to comment Share on other sites More sharing options...
thescrapman Posted November 12, 2011 Share Posted November 12, 2011 You must be supplying the coil with a permanent live, so I suspect either ignition switch is wired wrong, or you have connected up the wires that went to the control box originally wrong.CheersColin Link to comment Share on other sites More sharing options...
piman Posted November 12, 2011 Share Posted November 12, 2011 Hello sam, do not disconnect the battery with the engine running, you risk damaging the alternator.Alec Link to comment Share on other sites More sharing options...
sam93 Posted November 13, 2011 Author Share Posted November 13, 2011 Hi all,Just thought I'd let you all know that i've now solved the problem. The cause was that, when I built in my new dashboard with the extra gauges, I changed the charge light to a LED. I've got a rough idea why it was causing the problem, but if someone knows exactly why it was the cause, I'd be interested in the explanation. Sam. Link to comment Share on other sites More sharing options...
Clive Posted November 13, 2011 Share Posted November 13, 2011 I suspect it is reducing the current too much to energise the alternator. Sorry, was going to post that yesterday, but got distracted Link to comment Share on other sites More sharing options...
Nick Jones Posted November 13, 2011 Share Posted November 13, 2011 Yes LED will reduce the current too much. That's one place you have to use an ordinary bulb. Might get away with it on a 3 wire alternation - don't know for sure.Nick Link to comment Share on other sites More sharing options...
sparky_spit Posted November 15, 2011 Share Posted November 15, 2011 2880 wrote:The ignition switch no longer cuts the engine, it even still runs with the battery disconnected, so it's obviously the alternator providing the spark ..... But how ?????Please help, ASAPThanks,Sam.Wow! You've discovered perpetual motion? Link to comment Share on other sites More sharing options...
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