Ignition light fix
Discussion
Hi,
I posted a thread a fair while ago about my dimmly glowing ignition warning light. Just recently got the alternator checked out and all good, also put in a new battery, and renewed both 100 amp fuses. At idle I've got 14.2 V at the alternator and 13.9 V across the battery terminals but still have a dimmly lit ignition light. When turning on the main beam the ignition light dims further and recently has started to flicker and go out all together - but only sometimes.
I believe there is a fix to eliminate the dim ignition light problem - does anyone happen to know exactly what it is so I can fix this annoying problem.
thanks,
Ozstyle.
I posted a thread a fair while ago about my dimmly glowing ignition warning light. Just recently got the alternator checked out and all good, also put in a new battery, and renewed both 100 amp fuses. At idle I've got 14.2 V at the alternator and 13.9 V across the battery terminals but still have a dimmly lit ignition light. When turning on the main beam the ignition light dims further and recently has started to flicker and go out all together - but only sometimes.
I believe there is a fix to eliminate the dim ignition light problem - does anyone happen to know exactly what it is so I can fix this annoying problem.
thanks,
Ozstyle.
Leds seem to light with less PD..I used to have the glowing red LED, this dissapeared when i installed a 105 A/hr. alternator.
Fortunatly i have a mate who knows a bit about car electronics, no comparison to David Beer, but who is... He told me something interresting, i will try to explain.
At the back of my old alternator there was a thin brown wire, this was the wire that makes the red LED go out when the alternator charges. LED lights burn with only a minimal current. So having a slightly bad/corroded connection at the alternator (thin brown wire) will make your LED glow.
Make sure the thin brown wire connects without any corrosion and is firmly attached.
Fred
Fortunatly i have a mate who knows a bit about car electronics, no comparison to David Beer, but who is... He told me something interresting, i will try to explain.
At the back of my old alternator there was a thin brown wire, this was the wire that makes the red LED go out when the alternator charges. LED lights burn with only a minimal current. So having a slightly bad/corroded connection at the alternator (thin brown wire) will make your LED glow.
Make sure the thin brown wire connects without any corrosion and is firmly attached.
Fred
Fred,
when I took off the alternator to have it checked out I cleaned all the connections including the brown/yellow warning light wire attachment. I was hoping it might have been something that simple but it wasn't. When I check the resistor in the circuit wiring I'll clean the connection to the LED as well to eliminate that as a possible cause.
One thing gets me wondering though, if LED's only light up with current passing in one direction why use an LED as an alternator warning light when potentially current can flow in both directions to indicate a problem.
Griffter, I would appreciate the fix if you can remember what it involves.
thanks
Ozstyle.
when I took off the alternator to have it checked out I cleaned all the connections including the brown/yellow warning light wire attachment. I was hoping it might have been something that simple but it wasn't. When I check the resistor in the circuit wiring I'll clean the connection to the LED as well to eliminate that as a possible cause.
One thing gets me wondering though, if LED's only light up with current passing in one direction why use an LED as an alternator warning light when potentially current can flow in both directions to indicate a problem.
Griffter, I would appreciate the fix if you can remember what it involves.
thanks
Ozstyle.
Ozstyle said:
...if LED's only light up with current passing in one direction why use an LED as an alternator warning light when potentially current can flow in both directions to indicate a problem.
That seems to be the nub of the problem the battery (& hence ign circuit) can be at @13.8v whilst the alt sense is only at 12v, hence the LED will glow - a filament bulb will not. Careful choice of the resistor in parallel with the LED (required so that if the LED/bulb fails you will still excite the field coils on start up) or the the specific LED characteristics should fix the problem IMHO.Dave
Spend,
I don't know its all greek to me, and I'm no electrician. But I figure if there is a diode in the circuit that only allows current to flow from battery to alternator via ignition warning light (diode after the ignition light) then the ignition light will light up when,
a)ignition on and engine not running
b)engine running alternator belt failure
c)engine running alternator ouput drops below battery voltage
d)engine running alternator packs up
The only thing it won't do is light up if alternator is over charging - but the volt meter would indicate that.
I don't know its all greek to me, and I'm no electrician. But I figure if there is a diode in the circuit that only allows current to flow from battery to alternator via ignition warning light (diode after the ignition light) then the ignition light will light up when,
a)ignition on and engine not running
b)engine running alternator belt failure
c)engine running alternator ouput drops below battery voltage
d)engine running alternator packs up
The only thing it won't do is light up if alternator is over charging - but the volt meter would indicate that.
Just had the dash off, checked the resistor in the ignition light circuit and its 430 ohms, which seems fine. Cleaned up the connections to the LED but swapped them around to see if there would be a differnce; there was, with ignition switched on there was no illumination at all. Switched them back, same as before dim glow when running. Blows my diode theory out of the water, looks like the LED only illuminates when voltage at battery is greater than voltage coming of the alternator(D+) warning light circuit. So it would appear that alternator D+ output is less than 13.9 volts I get at the battery causing the glow.
Spend,
I'm with you now, I got confused. I was under the impression that a resistor in the circuit was incase the warning light failed, thus the alternator would still get initial excitation from battery voltage - but this is for a filament warning light not LED, obviuosly the resistor has an other function with an LED circuit.
I'm with you now, I got confused. I was under the impression that a resistor in the circuit was incase the warning light failed, thus the alternator would still get initial excitation from battery voltage - but this is for a filament warning light not LED, obviuosly the resistor has an other function with an LED circuit.
If the LED (or filament bulb) blows, the alternator still needs 'exciting'. The resistor ensures the magnet part of the alt (field coils) get kick started if the light fails - so you still get charge from the alt. It just so happens that the LEDs are far more sensitive to small differences than a bulb (and different LEDS have different characteristics).
Quick fix is with the resistor, but a stabilised voltage is good for your instruments - then you really want to move the heater blower to another circuit tho (Chim only?). These issues are only applicable in the very early cars, TVR fixed them in later models. If you keep your battery charged so the alt doesnt need to charge the battery, you may not even notice this 'flicker' BTW.
Dave
Quick fix is with the resistor, but a stabilised voltage is good for your instruments - then you really want to move the heater blower to another circuit tho (Chim only?). These issues are only applicable in the very early cars, TVR fixed them in later models. If you keep your battery charged so the alt doesnt need to charge the battery, you may not even notice this 'flicker' BTW.
Dave
If an LED is a must, this circuit will do the job
Using Tyco VF4 series 12 volt 40 amp Relay or one of similar specification
Tyco VF4 link - https://www.digikey.co.uk/product-detail/en/te-con...
Coil Resistance - 90 Ohm
Nom Turn On Voltage (Max): 7.2 VDC
Turn Off Voltage (Min): 1.2 VDC
Although the above is named a 12 volt relay its operating voltages are wide apart from 12
12 volt relays have carried on working without problems after withstanding 18 volts for several hours when a vehicles alternator has been overcharging
As can be seen above, the Tyco VF4 series will pull-in at approx 7.2 volts and hold-in down to approx 1.2 volts
Is important to view the chosen relay's specification if not using a Tyco VF4 series as specifications vary from manufacturer to manufacturer
Wiring a 100 ohms resistor in parallel with the Tyco's coil gives
TYCO 90 Ohm Plus 100 Ohm Resistor In Parallel = 47.368 Ohms
Current = 12 divided by 47.368 = 0.2533355 Say 0.25 amps
Wattage = 12 x 0.25 = 3 = Same as the original 3 watt bulb
100 ohm resistor link - https://www.ebay.co.uk/itm/Wirewound-Cement-Resist...
Replacing the original 3 watt bulb with the Tyco relay coil circuit gives approx the same alternator field exciter current
The LED is simply switched to earth through the relay contacts
The relay is energised by forward and reverse voltages
Should an alternator diode fail and apply a voltage to the alternator field with engine not running (ignition off), the LED will warn the driver
The warning lights and gauges circuit's show how the relay earths during a reverse voltage condition with ignition turned off (circuits have been simplified)
Using Tyco VF4 series 12 volt 40 amp Relay or one of similar specification
Tyco VF4 link - https://www.digikey.co.uk/product-detail/en/te-con...
Coil Resistance - 90 Ohm
Nom Turn On Voltage (Max): 7.2 VDC
Turn Off Voltage (Min): 1.2 VDC
Although the above is named a 12 volt relay its operating voltages are wide apart from 12
12 volt relays have carried on working without problems after withstanding 18 volts for several hours when a vehicles alternator has been overcharging
As can be seen above, the Tyco VF4 series will pull-in at approx 7.2 volts and hold-in down to approx 1.2 volts
Is important to view the chosen relay's specification if not using a Tyco VF4 series as specifications vary from manufacturer to manufacturer
Wiring a 100 ohms resistor in parallel with the Tyco's coil gives
TYCO 90 Ohm Plus 100 Ohm Resistor In Parallel = 47.368 Ohms
Current = 12 divided by 47.368 = 0.2533355 Say 0.25 amps
Wattage = 12 x 0.25 = 3 = Same as the original 3 watt bulb
100 ohm resistor link - https://www.ebay.co.uk/itm/Wirewound-Cement-Resist...
Replacing the original 3 watt bulb with the Tyco relay coil circuit gives approx the same alternator field exciter current
The LED is simply switched to earth through the relay contacts
The relay is energised by forward and reverse voltages
Should an alternator diode fail and apply a voltage to the alternator field with engine not running (ignition off), the LED will warn the driver
The warning lights and gauges circuit's show how the relay earths during a reverse voltage condition with ignition turned off (circuits have been simplified)
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