Fan over- ride .led

[gas mart 1]

The led indicator bulb , on the fan over-ride circuit keeps blowin, its wired the same as the schematic in the bible.... electrics are not my thing....I think a current regulator diode is needed,?? but what rating is needed and where can I get one.
cheers
martin

[batman400]

Assuming it's a normal LED which needs nominal 2v supply rather than one designed to work with 12v directly you will need a resistor in series with the LED, assuming it's a standard LED a value of around 500 ohms will do the job.

If you are going to the fest I let me know and I'll bring you and handful..

[gas mart 1]

Thanks ...yes i will be at the fest. The led's i bought were 12v... they seem to work fine when connected direct to the battery....but blow when in the circuit, when the fan is switched on.

[batman400]

That's Odd if they are OK direct to the battery but blow when connected in circuit..
Does the LED blow as soon as you turn the override ON or does it come one and then now work a second time if you switch off an back on ?
It's possible that the relay is generating an reverse voltage which fries the LED in which case a diode would be needed.

[Penelope Stopit]

gas mart 1 said:

The led indicator bulb , on the fan over-ride circuit keeps blowin, its wired the same as the schematic in the bible.... electrics are not my thing....I think a current regulator diode is needed,?? but what rating is needed and where can I get one.
cheers
martin

Are you able to post a diagram of how you have wired the LED?

[gas mart 1]

It comes on once maybe twice ....then nothing, the switch and fan continue to work without any problem. I don't have the diagram with me, but it was wired as shown in the bible.

[batman400]

The fact it works then doesn't suggests the LED could be fried by the reverse voltage that's generated as the relay is de-energised.
Fitting a rectifier diode as shown below should prevent the relay killing the LED.



Alternatively replace the relay with one that includes the diode

Edited by batman400 on Thursday 6th July 14:13

[Penelope Stopit]

batman400 said:

The fact it works then doesn't suggests the LED could be fried by the reverse voltage that's generated as the relay is de-energised.
Fitting a rectifier diode as shown below should prevent the relay killing the LED.



Alternatively replace the relay with one that includes the diode

Edited by batman400 on Thursday 6th July 14:13

You are wiring it incorrectly if the diagram above is showing how your LED is wired
All the LED is informing you is that there is a voltage being supplied to the cooling fan relay

[batman400]

As the O/P couldn't remember how it was connected I've guessed
AND if the LED is wired to the relay contact it becomes a FAN ON indicator rather then a FAN over-ride indicator

Edited by batman400 on Thursday 6th July 15:29

[Penelope Stopit]

[quote=batman400]As the O/P couldn't remember how it was connected I've guessed
AND if the LED is wired to the relay contact it becomes a FAN ON indicator rather then a FAN over-ride indicator



Yes. The problem is that this method of connecting to the relay shows the coil is switched or contacts have switched, what it doesnt show is that there is power at the motor

[adam quantrill]

Another possibility if the LED is wired across the fan = relay output - when the fan is turned off it can "mill" in the airflow with forward motion. If the milling causes it to generate negative volts then the LED will become reverse biased, and too much reverse voltage can kill the LED even with a series resistor. You could add a series 1N4001 diode in series with the LED which will take the brunt of any reverse volts.

[gas mart 1]

Thanks all. for the replies...all this electrical talk has fried my brain, I am off to a 4 star hotel in Warwickshire to recover.
cheers
martin.

[batman400]

Brain Fried ??

Now that's a Lot of Back EMF.....

[Penelope Stopit]

adam quantrill said:

Another possibility if the LED is wired across the fan = relay output - when the fan is turned off it can "mill" in the airflow with forward motion. If the milling causes it to generate negative volts then the LED will become reverse biased, and too much reverse voltage can kill the LED even with a series resistor. You could add a series 1N4001 diode in series with the LED which will take the brunt of any reverse volts.

Wiring a LED to the relay output is a no goer due to it not giving the required information
Bulb failure devices were brought in to overcome this problem with vehicle lighting systems due to them giving accurate information

[batman400]

Martin,

I doubt your brain is much better after Saturday night, from our discussion (pre-raffle I think..) I understand what you have done, send me a PM and I'll see what I can do.

Hope the drive home was OK

Great to meet you both

[adam quantrill]

?

Surely it's better to wire the LED or bulb to the output of the relay as it assures you that both the thermostat is working AND the relay is working.... or is that "too much information?"

Anyhow that's how I wired my bulb many years ago, and I remember over the tun it used to glow dimply at night even though the fan was off.

[gas mart 1]

batman400 said:

Martin,

I doubt your brain is much better after Saturday night, from our discussion (pre-raffle I think..) I understand what you have done, send me a PM and I'll see what I can do.

Hope the drive home was OK

Great to meet you both

Thanks Simon
pm sent , may have gone to junk.?

[Penelope Stopit]

adam quantrill said:

?

Surely it's better to wire the LED or bulb to the output of the relay as it assures you that both the thermostat is working AND the relay is working.... or is that "too much information?"

Anyhow that's how I wired my bulb many years ago, and I remember over the tun it used to glow dimply at night even though the fan was off.

Wiring a LED/Bulb directly to the fan motor termination points is a better method, there are ways of stopping a glowing LED/Bulb caused by the fan acting as a generator