cotleigh crasher Posted July 25, 2013 Share Posted July 25, 2013 Hi All My alternator failed a couple of days ago, bearings self-destructed. Got a new 100 amp one off a well known auction site, fitted it today, everything seemed fine, then about 2 miles into my journey the charge light came on, flickered at first then stayed on. The ammeter needle rises up to 3/4 up the scale, as usual, when I start the engine. I've checked the belt for slipping, checked the wiring is still connected etc. all ok Any suggestions anyone? Also, on my old alternator there was a small box attached to a wire, connected to the third terminal. What is this? I refitted it to the new alternator, should I have? Thanks in advance. Ralph Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted July 25, 2013 Author Share Posted July 25, 2013 Update: I just tried disconnecting the little box thingy, no difference. Disconnect the small wire from alternator (which goes to the charge light I believe?) light goes out Tested the voltage at the battery: 12.4 volts engine off, 14.9 volts engine running. Voltage at alternator = 14.9 volts So all seems to be well apart from the charge light being on all the time. Confused.com. Help!!! Quote Link to comment Share on other sites More sharing options...
pete3000 Posted July 25, 2013 Share Posted July 25, 2013 little box thingy is only a capacitor/coil suppressor to reduce interference on old am/mw/lw radios, you could leave it off if not needed. as far as it goes at least your bulb and charge light are normal, however if light stays on there is an voltage imbalance or problem with the alternator. The wl terminal or smaller spade terminal is needed to supply a small amount of current at 12v to the field winding of the alternator to excite the field and produce a bigger amperage on the other two larger terminals. When stationary the voltage difference on wl should be near 0v to provide a circuit and allow the lamp to light, when engine is spining fast enough the voltage rises and the lamp goes off as the voltage is being produced is close to that of the field winding. Along with this the voltage from the car is monitored and the higher the battery voltage the less field current is produced to stop the battery from overcharging if the load is low. I'd suspect the regulator pack in your "new" alternator, the alternator is providing a voltage out as you say but it may rise too high without correct regulation (via the field current). 14.9 seems too high for comfort 14.2-4 would be better. If the alternators are identical and you can't return your new one it may be worth swapping the regulators across Quote Link to comment Share on other sites More sharing options...
western Posted July 25, 2013 Share Posted July 25, 2013 W terminal is for feeding a signal to a electric rev counter. charge light on means a faulty diode in rectifier pack. Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted July 25, 2013 Author Share Posted July 25, 2013 Thanks Guys The alternators are similar but not identical so I guess a regulator swap is off the menu. I'll get in touch with the suppliers first thing in the morning and arrange a return. What a pain in the A*@%. Never mind, these things are sent to try us. Thanks for the info Great help as always. Quote Link to comment Share on other sites More sharing options...
western Posted July 25, 2013 Share Posted July 25, 2013 get them to bench test the existing alt, before you swap it. Quote Link to comment Share on other sites More sharing options...
cotleigh crasher Posted July 25, 2013 Author Share Posted July 25, 2013 get them to bench test the existing alt, before you swap it. Do you mean the new one I've just fitted? To what end? The problem is that they're in Blackpool, I'm in Devon, there's obviously postage etc involved and all the time my car is off the road. Time is of the essence, its going to be at least the middle of next week before I get the replacement fitted as it is. Quote Link to comment Share on other sites More sharing options...
western Posted July 26, 2013 Share Posted July 26, 2013 I meant the one you removed, then they can tell you what was duff in it, Quote Link to comment Share on other sites More sharing options...
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.
Note: Your post will require moderator approval before it will be visible.