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MG Midget and Sprite Technical Glowing Alternator Light BBS discussion at MG-Cars.net
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MG Midget and Sprite Technical - Glowing Alternator Light
| On my drive home, in the wet and dark with the headlights on, I noticed a very faint glow from the alternator light, which increased whenever I switched the wipers on. Sign of a failing alternator? AndyB |
| Andy Borris |
| Loose fan belt, maybe? |
| Dave O'Neill 2 |
| No, not the belt, the glow is too faint for that. Couldn't see the light glowing under the motorway lights, only when it was very dark. AndyB |
| Andy Borris |
| Have a look at Paul Hunt's website, charging section... http://www.mgb-stuff.org.uk/electricstext1.htm#charge |
| Dave O'Neill 2 |
| Not likely. The light is a balance between the Alt output and the system voltage from the Ign switch. It will light if either of these is substantially different from the other. If the Alt is not working, power flows from the Ign to ground through the Alt. If the Alt is working, power can flow through the Ign warning bulb to the IGN W circuit if the voltage there is low. The wiper influence is a dead giveaway that V on the W circuit is low. The wipers are fed by the G circuit, but that is fed from W, and the entire G circuit is downstream from the W where the light senses voltage. The most common point of a single failure is a bunch of W wires in multiple sleeve connectors where the IGN switch harness meets the main harness. Any high resistance fault or series of faults in the N feed to the IGN switch or the W circuits from the Ign switch can cause the same. |
| FR Millmore |
| With the original alt with 19 Amps charging I had that all the time I even had to choose between devices to use. But after I mounted a later MGB 43 Amps charging unit and I threw in some relays, fresh leads and and extra fuses I never ever had that problem again. The ign. light is like Props black hole all the time:-) In perfect order the original stuff can cope but with some corrosion on contacts and some broken strings in the wires the original set up isnt enough to cope with the situation you want to use the lights, wipers and the blower. So you can do without step-up but then you want to renew alt, wiring harnas, switches etc. Bas |
| Bas Timmermans |
| Andy, in a nutshell, yes it's a sign of a failing alternator. Get a Lucas ACR18, that will cover anything a midget has to offer Cheers John |
| JOHN HALL & JULIE ROBERTS |
| A glowing light could well be a failing diode in the alternaror diode pack. They are simple and cheap to replace if you have a soldering iron. You will get one from Wood Auto Supplies (they manufacture them there) if you cannot find one locally. Why not overhaul it. New bearings, brushes and diodes are well within the skills of a home mechanic. The numbers will be on the bearings, but from memory I think they are 6201 and 6203. |
| Shawn |
| Thanks everyone. AndyB |
| Andy Borris |
| Sorry here, and this diatribe is not directed at Andy. I'm a bit annoyed at people who jump in with no worthwhile evidence that what they say has any truth, usually because they don't know WTF they are talking about. When people take their cars to "professionals" to get fixed, they get justifiably annoyed if the "Professional" starts using random substitution of expensive parts, without correcting the problem. As a REAL professional, I take serious offense at such behavior by my "peers". I do not replace parts until I have a reasonable certainty that the part IS the problem, and a basis for that certainty. I feel the same rules apply to giving free advice to honest inquirers. Go ahead and replace the alt. Then do what Bas did, and fix all the other stuff - maybe you'll get to the place I told you to look at the start. It COULD be a bad alt, or a bad diode in the alt, or the phase of the moon. "Not likely" was my opening statement. What gives the symptoms described is what I suggested. You could, of course, measure the voltages to find out before you spend cash or effort. The Paul Hunt link posted by Dave as I was writing my first post explains it perfectly, and EXACTLY as I said it. FRM |
| FR Millmore |
| Andy - let us know if it was a faulty alternator _ I would hate FJ Millmore to be wrong. It doesn't sound like he is very often though. I was merely pointing out that if the alternoator was the problem - you do not have to replace the whole unit. Only I wasn't rude about it! |
| Shawn |
| I have had all night to think about your post FJ, and I still think you are an arrogant, self important a*se. This is a forum. People usually get a variety of possibilities here. If we were just to believe your opinions on things, you would be a very busy respondant. You may very well be right - but how stupid will you look if you are not. Think hard before accusing others of not knowing wtf they are talking about. We don't need it here. |
| Shawn |
| Agreed Shawn! This forum is to help people. FRM, as a so called REAL proffesional(what, I dread to think) your attitude is appalling. |
| JOHN HALL & JULIE ROBERTS |
| Replacing the alt might be an easy thing to do... but it may not be the first thing to try; we always like to think about things here, first (possibly along the lines of FRM). Always I ask myself: - what was the last thing I did, and did this start the problem? - was there any other event that triggered the fault? - is the problem likely to get worse, and maybe make the car unreliable or dangerous? It would seem that a feintly glowing ign light isn't a critical problem, once you've assured yourself the alternator is able to charge the battery / supply current for lights, ignition etc. Measure the battery voltage with the engine at fast idle, and is should show 13.5v or so (the headlights should be brighter with engine at fast idle than with engine off - this is a reasonable check if you don't have a meter). If it doesn't show 13.5v (normal battery volts around 12.6v with engine off?) then maybe your alts at fault. Once you've done this simple test, you'll be in a better position to go to stage 2: replace the alt or check the circuit along the lines of FRM. Always refer to the cct diagram; the 'balance' as FRM calls it is between the white wire straight from the ignition swtich and the brown/yellow from the alt. If the alt and loom are working OK, then these may be considered electrically to be the same point. If you have resistance in the loom (joints), then flow of current will translate the resistance into a voltage drop. As FRM points out, the extra current flow caused by the wipers is a sign that resistance in the loom is playing its part; this also gives a clue where to start testing - you need to invetsigate the common live feed circuit to both these elements (ign light and wipers) all the way from the alternator plug through to the solenoid post and then to where the circuits split. This is along the thick brown wire from the solenoid (incl the solenoid post), through the 4-way join (with 4 bullets and one of those bent mild steel bullet connectors protected with a synthetic rubber sheath - possibly the worst joint in the whole of the loom!) to the ign switch and out on the white. IIRC the wipers are driven off the aux circuit so the circuits diverge at this point? Check the circuit and familiarise yourself with the layout under the bonnet and dash. Then trace along the cicuit and look for voltage drop as you move from the post to the ign light. (13.6v say to earth at the battery, and falling to maybe even 12 or less after the ign switch; the biggest drop in sucessive measurements down the circuit should idnetify the main culprit.) All this should be done with the engine running; and wipers too if they make a good difference to the ign bulb glow (remove the wipers to stop them taking paint off the bonnet trailing edge?). BTW - I was thinking of upgrading my headlights last year from current halogens (60W/50W?) to something with more light. By cleaning up the solenoid post, I had (with the headlights switched on, emgine running) another 0.25V in the loom measured on the brown. I replaced the spade on the brown loom take-off wire as well. There was significant crud after 35 years in use. The increase of 1/4 volt may not sound significant, but it's (say) 13x13/12.75*12.75 in terms of heating effect at the bulb and that's nearly 5% more heat (what that means in light terms I can't say, but it felt like an uprated pair of bulbs from the driver's seat). Too much txt as always.... but HTH. A |
| Anthony Cutler |
| Andy, does the glowing decrease when the lights are switched off? Also, does it increase by adding any other load? eg heater blower, but leaving the wipers alone. Matt |
| Tarquin |
| Well, from my reading, FRM never said that the alternator was NOT bad. He said that it would be foolish to replace it unless it was known to be bad, and he said that it was foolish to advise replacement without knowing. I agree. With the faint glow of the ign light on my B, I still had around 13.5 volts in the system while it was running. So, the alt was doing its job in spite of the glow. Charley |
| C R Huff |
| I had an alternator issue. During a long drive the pulley nut came loose and allowed the fan to rub the alternator (and also chewed up the key slot in the pulley). I also noticed that my volt meter was only showing 11 volts. So I retightened the pulley the best I could and tried to limp home (still showing a discharge). I made it home and ordered an alternator (assuming that mine had got hot and died). I never tested the anything. So I installed the new alternator and ... still didn't show a charge. A simple loose connection (at a junction box) was the problem. Had I taken a few minutes to break out the voltmeter, I could have saved myself $60. Luckily, I need an alternator for my other car (that previously had a generator) so not all is lost. But I could have saved a little time by not assuming my two issues were related. |
| Trevor Jessie |
| Im taking this thead in a differant direction so hold on. Auto pilot...pure and simple, Have you ever considard how many decisions you make on a daily basis that would be considard as an Auto pilot response...an automatic response to a given situation. I certianly cant condem others that just automatically fault the alt in this case, look at treavor, had it not been a juntion issue and it was the alt. should he have still questioned his auto polit response....Its only when the auto poilt is wrong do we ever really raise questions....So does that mean we should abondon our built in auto polit, absolutly not, can you imagine how long and unproductive your life would be if you didnt have a built in auto polit. So just becaause the auto piolt is wrong from time to time,,,,its just life, Sh*t happens, I had a low tire the other day, I filled it and it went down agian...was I correct to assume it might have a nail embedded...Yes of couarse I was ...was that the problem ...Nope! loose tire stem, but the last 10 times it was a nail...in other words I think its human nature to base a decision on past experiance...just because you assumed it was a worn out alt that had 100,000 on the clock, I think it was a valid guess that fits into the scope of human decision making. Yes you can test and retest to the extreme and spend many countlss hours in the process....But Frankly Ill trust my auto pilot most of the time so I can acomplish the task of living. Prop |
| Prop |
| On the subject of check the obvious 1st.....I had a dimly glowing ignition light that I could only see on very dark nights.......then i found if i turned the dashboard lights off, it went away. Small amount of light leaking from the gauge lights to the ignition lights. Doh ! |
| Dean Smith ('73 RWA) |
| The ignition light would glow on one of mine when travelling at speed. It turned out that the front mounted radiator fan was spinning in the air flow and giving a back feed to the ign light. |
| robnrrugby |
| "It turned out that the front mounted radiator fan was spinning in the air flow and giving a back feed to the ign light." Are you serious? I don't see how this is possible. |
| Trevor Jessie |
| Good point, Trevor. IF the fan was in the circuit, it should have been running. IF it was not in the circuit, how was it feeding into the circuit? I am puzzled, too... David "smoke and mirrors" Lieb |
| David Lieb |
| leccy fans are usually perm live and switched to earth by the thermo switch. So it could work like a generator and feed back up the live wire? *maybe* |
| David (davidDOTsmithAT stonesDOTcom) |
| Hi Andy take the bulb out ! oh and while your at it fit a zetec simples ! just a thought :-) |
| Darren 2 litre frogeye |
| In order to feed, it would have to have a complete circuit including earth, no? My temperature sensor switches earth, but it is being "read" by a relay which switches power to the fan. David "it takes two to tingle" Lieb |
| David Lieb |
| <The ignition light would glow on one of mine when travelling at speed.> The key here is travelling at speed. The air flowing into the fan could have been making the fan turn faster and speeding up the motor, thus creating voltage and feeding back through the system. Also, if the ground on the fan was not good enough, electrickery will take the path of least resistance. Ever experienced stray voltage off of a water pipe? |
| Tim Michnay |
| If you have the +12v to one side of the fan, and no connection on the other side... then the fan may generate an EMF when turned at speed... but the connected side would still be at +12v and the other side at somewhere around 0v to minus a few volts (but it's not connected to anything, so no current flows). I doubt the fan (when connected) would be able to generate an significant power such that it would make any difference to the ignition circuit. You can see how much power/current is required to blow air through the radiator; can you envisage the incoming air causing the fan to overspeed such that it would not take any power from the alternator? Having said all that... I recall some similar experience with a Scimitar (glass fibre body, famed for earthing problems...) A |
| Anthony Cutler |
| I have had the same effect from an electric fan - before I added a relay. I am no electrician, but my reasoning was that when the fan is being spun very fast by the incoming air flow, being unregulated,it produces more than 12 volts. So at this point the positive side of the loom is raised above the normal range of 10 - 14 volts. If it was only producing 12v it would have no effect but at the significantly raised voltage the "imbalance" is picked up on the ignition warning light as an excess charge. Guy |
| Guy Weller |
| Trevor, I'm never serious about these cars. (does a 'serious spridget enthusiast' count as an oxy-moron?) Apologies, I should have mentioned more in my 2 line post. I was seeking to suggest that the issues created by PO wiring bodges, in this case a GRP flip front, corroded common earths, lack of relays, toasted cables, scotchloks and the like, can give odd, almost amusing, effects. Suggestions that this observed effect lacked plausibility are not unwelcome, however I do feel it is inarguable that these were made from a position of insufficient pertinent knowledge in this instance, such was the dire state of the spaghetti formally known as a wiring loom. Tie wrapping the fan stopped it, removing the tie wrap and unplugging the fan supply cable it stopped it, un-tie-wrapping and replugging started the glowing again. I don't want to be accused of being a troll but the subsequent 7 post debate on two lines of information about what was a nail of a car that was weighed in 10 years ago due to being beyond redemption, may indicate that we need to get out more. Though I am glad that Guy saw a similar effect, (ie it's not a 'senior moment' by me). Although I am not implying that his car is a 'nail...beyond redemption'.....err or that he has Italian wiring (I'll stop digging now) ;) rob |
| robnrrugby |
| Hi Guy Agreed - if driven, it might have >12v across its terminals. But a couple of things (and a correction of my earlier post): - the polarity of the induced EMF will be opposite of that to the case when it was a motor (enyone remember the left and right hand rules for field/current/EMF for motor and generator?!) - if only one terminal is connected, then this will provide the reference for the system and this terminal will be at the loom voltage and the other terminal will float; so there is no current flow to light the bulb. - my memory of Scimitars is now clearer: many of us had a Kenlow, with a bulb across the motor to show when the fan was running. If the fan was switched off, the bulb would still of course be across the terminals. So when the fan was wind-milling at speed, it would generate EMF and a current flowed through the bulb and it would glow. This is different from the ignition light glow, as it's not connected across the motor (but between the +12v ignition ciruit and alternator output (plus diode in series). HTH A |
| Anthony Cutler |
| Ant, I think you will find that the wind-driven fan rotates in the same direction as when it is being electrically driven so the induced EMF is not opposite is it? And as for Rob's reference to Italian wiring -- I had an alfa 156 on which the passenger window would lower when I switched on the radio. Not every time, but amusing enough at about 1: 3 times. They are on completely different fused circuits so there was no apparent logical explanation. Other than the Italian bit that is! Other than that I never had any electrical problems - 180,000 miles on the original; clutch it was a great car |
| Guy Weller |
| Anthony, If the fan is rotated by wind in the same direction as it is driven by 12V then the EMF produced will be of the same polarity. In the powered case the back EMF resists the 12V so that for instance the case of an unloaded motor the back EMF will be almost 12V, the difference between the back EMF and 12V and the current flow giving the power to overcomes losses in the unloaded motor. If you then load the motor, the speed reduces and so does the back EMF, you then get a greater voltage difference and more power generated. I seem to recall this was all discussed a few years ago. |
| David Billington |
| BTW Andy- Did you ever fix your issue? Let everyone know so we can all be proved wrong! |
| Tim Michnay |
| Hi David & Guy Well... do you remember A-level physics? You used the left-hand rule for motors and right-hand rule for generators (Fleming?). This would suggest that, for a given machine, the EMF for a generator would be in the opposite direction than the current for a motor. I recall also from A-level phys that, as a DC motor spins up, the rotation of the coil induces a back EMF such that (with no friction or windage losses) the motor would have a finite top speed when the back-EMF induced equalled that of the supply voltage. I can't remember the previous debate. A |
| Anthony Cutler |
| Anthony, I think you are correct and I agree with that but I see a point of confusion. In the case of the motor being used as a generator when rotated in the same direction as its motor use the polarity will be the same but when connected to a load the current will flow from the + side through the load whereas in motor use it flows from + through the motor. |
| David Billington |
| what's wrong with the fan on the water pump anyway? easier to understand ;-) |
| David (davidDOTsmithAT stonesDOTcom) |
| Gee, I thought we had already covered that one often enough ;-) Let me see, the mechanical fan is least effective when it is needed most (at idle when stopped in traffic). It is least needed at speed when it exerts the greatest load on the engine. Electric fans, properly installed, do not load the engine when not in use, only engage when needed, work at full efficiency at idle, what's not to like? David "all my cars have electric fans" Lieb |
| David Lieb |
| I wasn't getting into the discussion about whether an electric fan is good or bad, whether it should go in front of or behind the radiator or even the effects of induced back EMF - of which I have no understanding whatsoever. I simply commented on why I thought it might make an ignition light glow. Many years ago and long before alternative energy was fashionable, I had 3 such wind-driven radiator fans set up on a pole behind the goat shed. They trickle-charged some old wagon batteries as a back-up for when the mains supply failed. |
| Guy Weller |
| Oh good, thread drift! I just saw that one of the "10 most brilliant products of 2009" is a Honeywell wind turbine in which the blade incorporates magnets which pass copper coils in the housing to generate electricity rather than losing efficiency to a drivetrain. Sounds like a winner! http://www.popularmechanics.com/technology/upgrade/4332392.html David "now to develop a Sarvonius version" Lieb |
| David Lieb |
| David, I think I've seen the same detailed on some DIY wind generator sites a few years ago where people were winding there own coils and using super magnets. BTW I thought the purpose of the engine driven fan was to drive the car along once it was upto sufficient speed. The engine gets the car upto that speed then the wind through the rad is sufficient to drive the car along on its own via the engine fan. ;). Also BTW (serious comment) larger cars tend to use, in the past at least, engine drive thermostatic fan as the power required to drive the fan(s) was too great to be economically practical for motors |
| David Billington |
| Now this would be a cool solution!! http://www.dyson.co.uk/fans/?sicampaignppc=google&sicampaigntopic=airmultiplier&gclid=CNfZp8jhv50CFVtm4wodiWObkw Carl |
| C Bintcliffe |
| Why is it none of the people in the video showed the least sign of having their hair ruffled? |
| J Van Dyke |
| David Agreed. First finger is 'field'; seCond finger is Current; and thuMb is Magnetic field. So swapping hands we have current flow in reverse direction, which makes +ve terminal remain so. I was indeed confusing current flow with EMF. A |
| Anthony Cutler |
| Good question, JVD. Next question. How long before Prop wants to make a supercharger out of one? David "always a fan" Lieb |
| David Lieb |
| The diff went "pop" so I stopped worrying about the alternator light! AndyB |
| Andy Borris |
| Aha, another broken axle shaft thread coming up. David "can we make some controversy out of it?" Lieb |
| David Lieb |
| Sure ting, Prof Lieb! That's gotta be the most bizarre case of a bad connection fixing the problem that I ever heard. FRM |
| FR Millmore |
| Well on that basis, if you have a problem with the car, hit your thumb hard with a hammer. De Bono would approve. A |
| Anthony Cutler |
| the youtube videos for the fan are more impressive....I guess http://www.youtube.com/watch?v=h8IH4or_3XY |
| J Van Dyke |
This thread was discussed between 09/10/2009 and 20/10/2009
MG Midget and Sprite Technical index
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