Alternator Not Charging

[Cornishman]

I noticed when driving my CSI at night that with the main beam on full that there is a slight glow to the red alternator light, I assumed that this was light from the bulb behind the blue main beam lens finding its way to the red alternator one. However, now the red alternator light is on permanently. I haven't driven the car since the light came on permanently.

A quick check with a voltmeter shows 12.5 at battery with engine off and 12.1 with the engine running. Revving makes no difference. There is 12.5v at the red single wire that excites the alternator with the engine off.
I removed the external voltage regulator and shorted it out, same thing and light is on still on.
I removed the alternator from the car and then took the white plastic end cap off, this houses the spring loaded brushes. All looked fine and the resistance across the coil was approx. 1 ohm. All clean inside.
I have reassembled the lot and run the car, light still on.
I think that this is an aftermarket alternator made by Vectronic, model QX with no other markings.
Help...
Does this brush set look correct to you? They extrude different lengths, one at 9mm, the other at 11mm, however that is enough to make contact, the springs also seem ok.
W&N have new brushes (coals) that look like they could be soldered into my white plastic end cap so I can try this, or can some one suggest where I can get brushes or an alternator repair in the UK?
Any other suggestions and have I missed something simple to check or fix it?

Thanks
Cornishman

 

[taylorcom]

This may or may not be helpful, but my on my 3.0CS, the red light comes slightly on when the headlights are on and it stays on. I had the alternator checked out in the mid-'80s and it was charging properly. After years of service, that alternator finally failed and I installed a good rebuild a few months ago. It seems to work fine, but still the red light still stays on, not on full but on half-power, when the headlights are on full.

So I'm guessing the problem may be in the sending unit.

 

[HB Chris]

I would replace them and all might be good. I had the same issue with the slightly glowing red light,

 

[Arde]

In my ignorance I have a contracontrarian opinion.
If the light glows it means the brushes are conducting electricity. It probably also means the alternator output is too low which could be indeed faulty diodes.

A higher output alternator can serve two purposes, one is to allow a higher total load and the second one is to charge the battery faster. The latter is pretty innocuous and like the writeup says all you need is thicker conductors between the alternator and the battery. A higher total electrical load will put a higher mechanical load on the engine and on the belt when such load is present. And the circuits downstream of the battery especially the ground need to be tolerant of the higher potential currents.


In short I think it is the diodes and I would not go crazy on getting 3x times more output from an alternator.

 

[Gary Knox]

This is probably not the OP's problem, but for others - If the light glows when the engine is running, it might be an issue somewhere in the 'blue wire' that connects to the Voltage regulator (or the 'L' wire on the newer 3-5 connection alternators).

That wire is supposed to 'see' enough voltage from the operating alternator that it stops current from coming from the wire that carries 12V+ to the bulb.

The blue wire acts as a grounding wire when the switch is turned on and the engine is not running, causing a full glow of the bulb. Find the blue wire under the hood and check connections - just might cure it! On my '74, the blue wire exits the harness just below the 'diagnostic plug', on the right side of the battery.

 

[lloyd]

Before replacing anything, I would carefully examine all grounds, from to or around the alternator and the alternator supports. A bad ground can ruin your day.

While the brushes look worn, they also look like they have a fair amount of usable "meat" left. Different lengths after use is not very unusual. I would examine the yellow metal rotating contact area on the alternator to ensure things are clean and not particularly worn. It may even be that the alternator brushes are different lengths if the areas they "brushed" started out at different diameters. This might occur if someone else previously popped in a new set of brushes.

When it comes to a slight warning light glow, alternator could have a common diode problem that most electrical shops could handle. Something else, I thought I read (or may have mentioned) in another post. An alternator has to spin fast enough to produce adequate voltage to accommodate the entire system. Often, as in the case of one cars, unless the throttle is blipped slightly after first starting, the alternator light glows. It is a much higher output alternator than stock and has done this for more than 10 years. (See below)

Because you tend to favor the left side of roadway, answers to some common alternator questions may be found here, try not to pay too much attention to the word "Lucas." :razz: http://www.howacarworks.com/electric...rnator-brushes

How much amperage do I need? The alternator that was provided with your vehicle should handle all of its electrical needs as outfitted from the factory. If you have added electrical components such as stereo amps, lights, compressors, winch, plow, etc. then you will need to produce more power to operate these components. Use our Amperage Load Calculator to find out how much power you now need from an upgraded alternator.


Why does my new alternator have a smaller pulley?
Alternators produce more amperage the faster they spin up to their maximum capacity. Most people need the best output they can get at low speed. When the engine is idling, the alternator will not produce as much power because it is turning slower. In order to boost output at lower RPM, it is beneficial to spin the alternator faster by using a slightly smaller pulley to accomplish this. In most cases you should be able to use the alternator with the smaller pulley without having to use a smaller belt. Check to make sure that your belt is not worn, stretched, or that the tensioner has the correct amount of tension to keep the belt from slipping or having too much tension.

Why is output so low at idle?
1) Too much load - The amount of load (components using power) may be too much for the amount of output the alternator is capable of producing at that slower speed. Check the amperage output at the rear of the alternator and see if it is more or less than the amperage coming out of the battery’s positive cable. If increasing the RPM of the engine slightly causes the alternator to exceed the requirements, then it may be necessary to use a higher rated alternator, raise the engine idle speed (if possible), or change to a smaller diameter pulley to increase output at that RPM,.
2) Idle Speed - Some newer vehicles have idle speeds much lower than earlier models. This is done to help the fuel economy. On these vehicles the use of a smaller diameter pulley is almost a necessity to get low RPM output to an acceptable level. You may find that at times the load demand may be greater than the available output of the alternator. There is no problem with having this condition for short periods such as heavy bass hits from the stereo. Using an auxiliary battery to add additional reserve capacity can help alleviate problems stemming from these circumstances.
3) Pulley ratio – In order for the alternator to spin fast enough to produce the power necessary at low RPM, the pulley ratio should be correct. Changing the crankshaft pulley or alternator pulley will vary this ratio. For most vehicles the ratio should be at least 3:1. See the question “What is pulley ratio” to find out how to calculate this.
4) Wiring – When upgrading to a high output alternator it is important to make sure that the power can get to where it needs to go. The factory charge cable and ground cables were designed to handle only as much amperage as the stock alternator could provide. Using a higher amperage alternator, you need to upgrade the charge cable to handle the higher current that will be passing through or the power will be restricted. It is also necessary to upgrade the ground side as well. This would include the battery to frame, body, and engine block.

Can I use underdrive power pulleys?
The use of underdrive pulleys for the crankshaft has become popular but it has the downside of slowing alternator RPM. This will cause the alternator to have lower output at slow speeds. We recommend that the factory sized crankshaft pulley be used whenever you upgrade to a high output alternator.

Will a higher amperage alternator cause any problems with my stock electrical system?
A higher amperage alternator will not pose any problems to the vehicle’s electrical system. Amperage will flow to only those components that can use the energy and supply as much amperage as the component can consume. For example, you may have a 100 amp alternator in your vehicle and the turn signals have small wiring and will only use 10 amp of power. Upgrading to a 200 amp alternator will not affect these components. On externally regulated alternators you can still use the stock factory regulator. Of course you need to get the power to where it needs to go, so see the next question about modifications.

What modifications will I need to make when upgrading to a high amp alternator?
Almost all of the alternators we sell are meant to be a direct replacement for your factory alternator so you should not have to modify the installation. You should, however, upgrade the alternator’s charging cable and ground cables (battery to frame, body, and engine block) so that you can get the power to where it can be used. A smaller diameter alternator pulley is usually included with the alternator we provide and in rare instances a slightly shorter belt may be necessary.

What does the rated output of your alternators mean?
Our alternators are tested on our test bench to provide the best output for most driving conditions including low speed or idle operation. The specifications you see on our website reflect results as follows:
Advertised Idle Output @ 2,400 RPM
Advertised Maximum Output @ 4,800 – 5,200 RPM
These figures are alternator RPM speed. In order to calculate the corresponding engine RPM you must divide those numbers by your pulley ratio. To calculate pulley ratio, see the next question.

What is pulley ratio?
Pulley ratio is the comparison of the crankshaft pulley diameter to the alternator pulley diameter. In order to get your pulley ratio you would measure the diameter of your crankshaft pulley and divide it by the diameter of the alternator pulley you will be using. For example, if your crankshaft pulley is 6” in diameter and the alternator pulley is 2” in diameter, the ratio would be 3:1 or 6 ÷ 2 = 3. The larger the ratio, the faster the alternator will spin. CLICK HERE to go to our pulley ratio chart.


Will a high output alternator have a shorter lifespan?
The high output alternators we design should be able to provide a long life. However, the more current that is produced by an alternator, the faster the brushes may wear. If you are using an alternator more toward its peak capacity it will tend to use more brush material. Luckily, replacing brushes on most alternators is relatively easy and very inexpensive. Even if you are running the alternator at peak capacity it should provide you with years of good use before you may need to do any maintenance. http://www.qualitypowerauto.com/pages/AlternatorFAQ.php

http://www.qualitypowerauto.com/pages/AlternatorFAQ.php

 

[Ohmess]

Cornishman -- your alternator is not putting out sufficient voltage. It should be between 13.5 and 14.2 (mine runs around 13.9 volts) with the car running; not 12.1

This is why the red light is glowing. The red light illuminates off the battery voltage when the key is turned on, with the opposite side of the circuit connected to the alternator. When the alternator operates, the voltage from the alternator cancels the voltage from the battery and the light goes out.

With your battery at 12.5 (which is the measurement with the car not running), and the alternator putting out 12.1, the voltage from the alternator is not completely cancelling out the battery voltage. This is why the light is on, but only dimly. It will stay on as long as this imbalance occurs, and because you state that the voltage does not increase with engine revolutions, it appears this imbalance is only going to get worse.

I think you are correct in that your brushes should be the same length. They are not expensive; I would solder in a new set and see if that does the trick.

Because you have an external voltage regulator, you should be able to measure the output from the alternator directly (before the regulator). I don't recall exactly, but I believe the alternator should put out somewhere between 14 and 15 volts before the regulator. If you change the brushes and still are not getting something in this range, then you probably have a diode problem. Again, brushes are cheap; start there.

 

[jmackro]

Cornishman -- your alternator is not putting out sufficient voltage. It should be between 13.5 and 14.2 (mine runs around 13.9 volts) with the car running; not 12.1 ..... If you change the brushes and still are not getting something in this range, then you probably have a diode problem. Again, brushes are cheap; start there.

I agree with Ohmess - the alternator is not putting out.

But I disagree that the brushes should be changed. As lloyd wrote, the brushes do wear unevenly, and your's still have enough "meat" to work OK. I would go directly to checking the diodes.

 

[Cornishman]

Thank you

Thanks for all of the tips.
I took the alternator to the specialist who asked for the regulator also, upon taking that out I found a bare patch of wire, burnt or wear. That may have caused some of the issues.
However the repair shop said that the rectifier had failed and also the stator! So it will be fully rebuilt. Total bill will be approx £100 so not the end of the world but it is always nice to fully diagnose and fix it at home.
Parts due back tomorrow and then due to test fit on Sunday. I will let you know.
Best wishes
Cornishman

 

[Cornishman]

Back together - fixed?

Alternator fitted and back together, all works fine. Correct voltage on the multimeter.
But, the other warning lights now don't work, the ign charging light and oil, handbrake work fine, the others eg full and dip beam warning lights don't work at all. I wonder if when the alternator gave up as a final farewell it overloaded the circuits and blew those bulbs? Any other better suggestions as this does not hold too much water?

 

[jmackro]

I wonder if when the alternator gave up as a final farewell it overloaded the circuits and blew those bulbs?

I really doubt "it overloaded the circuits and blew those bulbs" - as I recall, a lack of voltage - not overvoltage - was your issue.

Not sure what the issue is. Are you saying that the only lights that don't work are the full and dip beam warning lights? If so, it is probably something unique to the headlight circuit, a bad ground, or both bulbs decided to fail at the same time (which is unlikely).

 

[Cornishman]

Just the warning lights

The actual headlights work, but not the warning lights in the dashboard.

I too suspect that something else caused this combine failure eg dash earth. As the lights in the dash are difficult to get at I hoped that I could find a reason why they don't work rather than trial and error.

I will have a close look at the weekend and report back, but all ideas welcome.

Best wishes
C

 

[Ohmess]

One of the first things I did when attacking the melted wiring in my car was clean up the ground on the inside of the fender, to the left of the fuse box. There were perhaps five wires connected to that ground; clean up the connectors and the connection point on the fender wall with phosphoric acid, and replace the screw with a new one.