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Need some serious help / alternator / red light / battery

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biggdave1 Avatar
biggdave1 david fruge
lake charles, LA, USA   USA
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ok here is my story thus far. had a discharging battery and changed it to new, tested with a volt meter across the battery and only getting 12.31, had Alertnator tested by a alternator shop after getting a bad reman alt from a parts house. ordered NEW not reman alternator and put on MGB 74.5 still getting 12.31 when i put my volt meter on battery. Now the red light does not come on at all but a couple weeks ago it came on and would stay on even while the car was off and key was out now nothing. i am so confused because new battery and new alternator and still my test when car running and volt meter on battery is 12.31 and with lights on drops to 12.06.....

i did unplug the alternator and test getting 12V from the cable on 2 leads from the wire harness.
if this helps the alt part no# 14050 (little big litte) and the parts house and the every site about this alternator says must be tested on the car but as you all know if you disconnect the plug from the alternator then you get a reading of 0.00 because there no current to return.

HELP



Edited 2 time(s). Last edit at 2014-10-25 10:27 AM by biggdave1.

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PaulP Avatar
PaulP Gold Member Paul Peterson
Seattle, WA, USA   USA
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1973 MG MGB GT
1974 MG MGB
No expert here, but as I understand it, if the red warning light is burned out, you're not going to get any field current. Astley's book says you can check the bulb "With the ignition on, test the bulb by removing the brown/yellow wire from the alternator and touching it to ground, whereupon the bulb should light (it helps to have an assistant observe the lamp)."

Edit: What year is your car?



Edited 1 time(s). Last edit at 2014-10-25 11:33 AM by PaulP.

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29desoto Gold Member M Wayne Sanders
Otis, OR, USA   USA
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1965 MG MGB V6 Conversion "Carmine"
1973 MG MGB GT "Eliza - FIRST PLACE - MG2013"
1984 Chevrolet Corvette "The Green Weenie"
1994 Chevrolet S10 "Lil Red"
Paul, that test works. When Ole Yeller's alternator went, that's how I proved it to myself!

Good ole Astley! smiling bouncing smiley



Wayne Sanders
Rose Lodge, OR
(TD 4288)

"I don't care to belong to any club that accepts people like me"-joined Willamette Valley Club in 2011

79/65 MGB - Carmine- V-6 - T-5

This car is now very nearly completely done. Sure to find something else, but not now.........And 12 years later, I'm starting to fix things that were new when we built the car. It's pretty well de-bugged!

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biggdave1 Avatar
biggdave1 david fruge
lake charles, LA, USA   USA
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1974.5 MGB... i did run it to the parts house just now had them put there test across the battery and it did show the alternator putting out 30 amps. and was charging the battery slowly. so i guess my next question would be i have a 43 amp alternator why only 30 amps?
the red light does not come on at all now so i assume its burnt out, if the light is burtn will it reduce the amp output etc?

i have gone over the wire diagram and its a pretty simple system and checked all but the red light

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James74 James D
beach, VA, USA   USA
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1978 MG MGB "The Bee"
Red light has to be lit when the ignition is turned on. This let you know it is working, if it is not lighting the circuit will not make a complete charge. Thus the engine spark, and electrical asserioe\ will be relayed from the battery only. These little bulbs I believe were designed to last over 100 years.smiling smiley Although they might blowout in about 45 years time.

James



Edited 3 time(s). Last edit at 2014-10-25 12:12 PM by James74.

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biggdave1 Avatar
biggdave1 david fruge
lake charles, LA, USA   USA
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ok, if i understand the red light is more than just dummy light if it doesn't come on i am not getting a complete circuit thus the reason the test only reads 30amps, correct?

well the red light stopped coming on about a week ago. i did ground the line coming from alternator and it still didnt come on...... will this 1 little light keep the alternator from charging the battery?

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Jim K Avatar
Jim K James A. Krasnansky
Liberty, KY, USA   USA
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1970 MG MGB GT "Chloe"
1971 MG MGB GT "Roscoe"
1972 MG MGB "Camilla"
I don't understand reading Amps. Volts, yes, but I thought Amps relate to load?

Educate me here.



Jim K is a grease-stained wretch

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ingoldsb Avatar
ingoldsb Silver Member Terry Ingoldsby
Calgary, AB, Canada   CAN
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1971 MG MGB
Okay - let's explain how the whole thing works.

Many of the generators you built back in school had permanent magnets that spun. The magnetic field of the permanent magnets cut across the windings of the device and that induced a voltage.

The problem is, there are no permanent magnets in an alternator (AC generator) - so how does it work. Very simply, they use an electromagnet instead of a permanent magnet. The electromagnet is called the field coil. The neat thing about this is that, by varying the current through the field coil, you can control the alternator's output - that is the job of the regulator.

The field coil can be energized from the alternator's output. However, this leads to a Catch-22 situation. If the alternator is just starting to spin, it has no output. And if it has no output, it can't energize the field coil. So, spin it as much as you like, you don't get anything out.

To bootstrap out of this state, you need to initially provide external power to energize the field coil. Once the alternator begins to produce current, it can then take over the job of energizing the field coil and the external power source can be removed. In an automotive system, this is done by supplying power to the field coil via a small indicator lamp. If the lamp is glowing, then you know that the alternator is not yet in a self sustaining state. However, if the lamp doesn't glow when the alternator is at a standstill, then you also know that something is wrong and the field coil isn't getting the initialization current.

To recap, you should see the following:

1) Engine off, ignition on - the red lamp should glow brightly. If it doesn't, unplug the connector from the alternator and ground the brown/yellow wire. If the lamp comes on, then the problem is in the alternator - usually bad brushes (which is how the field coil gets its power). If the lamp doesn't come on, you have a faulty wire or connection, or the warning lamp bulb is burned out.

2) Engine on - the lamp should go completely, 100% out (not dimly lit or flickering) at about 1100 RPM. The lamp should remain completely off at all RPM above about 800. If this does not occur the most common problem is a bad rectifier pack.



Terry Ingoldsby
terry.ingoldsby@DCExperts.com

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HiPowerShooter Avatar
HiPowerShooter James Booker
Lake Winneconne, WI, USA   USA
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1973 MG MGB
Electricity seems very difficult for most people to understand. You can't properly see it, you can't properly feel it and you can't taste it or smell it so what is it? It travels quite well through metals and generally poorly through non-metals. It doesn't behave quite like anything else.

But this is not quite true: fluid flowing through a system of pipes can behave in many respects like electricity flowing in a circuit. The 'obvious' exception to this is that if you pierce a pipe full of water, the water comes out.

Try piercing the insulation and touching the conductor: you will soon find the electricity coming out! The main difference is that water will fill any space whereas electricity will 'fill' only a conductor. Yes - the analogy is not perfect, but it is helpful and understanding will come not only from the similarities but also from the differences.

Pressure...
In a water system we measure water pressure in feet (foot head). In an electrical system pressure is measured in volts. There is quite a close analogy between feet and volts in this context.

Flow...
Water flow can be measured in many units but we are using feet, so let's keep to cubic feet per second to measure flow rate. The electrical equivalent is Amperes (amps).

Volume...
In our water system volume is in cubic feet. Electrical equivalent is Coulombs, which is not that commonly used. So one Coulomb per second is one amp. Flow and volume correlate nicely - cubic feet per second is clearly a flow rate.

Resistance and Ohm's law...
In an electrical system resistance is measured in Ohms. There is no name for the water equivalent. So what is it? In electricity, if a pressure of one volt will drive a flow of one amp then the resistance is one Ohm. Two volts would drive 2 amps through 1 ohm: pressure divided by current equals resistance.
In the water system resistance doesn't equate to anything useful as an aid to understanding. However 'resistance' is just that: the amount that the pipe 'resists' the flow of water. Double the water pressure and the flow will double. Double the length of the pipe and, if we didn't change the pressure, we would expect the flow to halve. This, in common sense terms, is exactly what Ohm's law says! Increase the pressure and the flow must increase. Increase the resistance and the flow must decrease. So Ohm's law is Pressure/Resistance = flow. Or Volts/Ohms = amps.

Capacitance...
In a water system a tank has capacitance. You might think then that capacitance is cubic feet.... Wrong, we have seen that coulombs is cubic feet. Cubic feet/coulombs is the amount of water/electricity you put in the tank/capacitor to raise the pressure/voltage to a certain level.
Do you see then that capacitance in an electrical circuit equates to the base area of the water tank. Capacitance equates to square feet. In a water (electrical) system, volume (coulombs) is base area (capacitance) times feet head (voltage). In a capacitor, 1 coulomb stored in a 1 Farad capacitor raises the pressure to 1 volt. In a water system 1 cubic foot stored in a tank of base area 1 square foot raises the pressure to 1 foot. The analogy is quite close! Consider also that in electricity, the capacitance between two plates is directly proportional to their area so you might expect area and capacitance to be related.



"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

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biggdave1 Avatar
biggdave1 david fruge
lake charles, LA, USA   USA
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Terry my brother i do know how the alternator produces a current but forgive because i haven't had an MGB in about 13 yrs and just getting back into it so i am rusty to say the least. you cannot test a lucas system like the systems of today but i need any good advice i can get.

recap: i have a new alternator not a reman one (part# 14050 fittings little big little) and a new battery. the red light does not come on at all so my question is will that little issue stop the alternator from doing its job.... from the wire diagram i am looking at it should not have anything to do with the production of the alternator other than a warning lamp etc.

had the new battery and alternator tested today because i am freaked out by the red lamp not lighting up and the test was the alternator is putting out 30amps... is this sufficient for my B? i am still running wires and trying to get to the red lamp as we speak...

guys i am sorry for sounding dumb but hey i guess i am when it comes to this kind of issue

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Steven 67GT Avatar
Steven 67GT Steven Rechter
Jackson, CA, USA   USA
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In reply to # 2833616 by biggdave1 you cannot test a lucas system like the systems of today

Yes it can. There is no difference except for the simple Lucas output connector that seems to baffle discount auto store parts clerks.


quote=biggdave1,2833545,2833616]
recap: i have a new alternator not a reman one (part# 14050 fittings little big little) and a new battery. the red light does not come on at all so my question is will that little issue stop the alternator from doing its job.
[/quote]

Yes. As Terry stated if the red dash light does not come on then the field coil is not energized. Result no output from the alternator. Test the light bulb, it may be bad.


quote=biggdave1,2833545,2833616]
the alternator is putting out 30amps... is this sufficient for my B?
[/quote]

Marginal. Sufficient so long as you do not make short runs with you headlights, heater fan, wipers and radio on.

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biggdave1 Avatar
biggdave1 david fruge
lake charles, LA, USA   USA
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Steven i got it, thank you..... the little red light not coming on is my issue. not allowing the Alternator to work to it full capacity, not allowing a complete circuit...
this little red light is a devil on my sholder today

so if the red light is not burn out what the heck is the issue?

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PaulP Avatar
PaulP Gold Member Paul Peterson
Seattle, WA, USA   USA
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1973 MG MGB GT
1974 MG MGB
Terry - I probably know enough about alternators to be dangerous, but it seems like if Dave could back probe the yellow/brown wire at the alternator and connect a test light from there to battery positive that would serve as a temporary substitute for the dash light. With that connected and the engine running he could then he could see if he gets 13.X v acrosss the battery and verify the dash light (or associated wiring) is the problem.


Does that any have merit?

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HiPowerShooter Avatar
HiPowerShooter James Booker
Lake Winneconne, WI, USA   USA
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1973 MG MGB
Have you gone through all of the connections and ensure they all have good, clean, tight connections? At the alternator, check to see if there is any trickle potential...ie a innervation or close quarters charge sharing between pins? I'm not sure I would be looking at BIG components, rather something that is robbing charge from "someone" else. Do you get any static charge from the body? Seriously...a tiny static shock when you touch a door frame or something?



"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...



Edited 1 time(s). Last edit at 2014-10-25 01:18 PM by HiPowerShooter.

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biggdave1 Avatar
biggdave1 david fruge
lake charles, LA, USA   USA
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got the red light out, not burnt at all...so i am lost now!

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