Morning all

Small problem that's only just come to light. First drive out when it's been dark. Noticed that the fan on light glows dimly even when the fan isn't on, this only happens though once the fan has cut in and the turned off again (doesn't happen when car is first started and driven).
Thought this could be caused by the fan continuing turning due to air flow and the motor acting like a generator (or something like that)

So how can I sort this out easily (bearing in mind I'm an electrical numpty)

Any help appreciated, answers in the most basic form would be greatly appreciated.

Thanks as always
Nigel

quote:

---

Originally posted by jabbahutt
"Thought this could be caused by the fan continuing turning due to air flow and the motor acting like a generator (or something like that)"

---

Take the bulb out?

Or live with it, i would not worry about it

Steve

I've only just noticed it so it can't be doing any harm. Just like to know how to rectify these things to increase my dire lack of electrical knowledge.

So where in the system would you put the diode? near the offending bulb?

Thanks for the prompt replies

it needs to go just before the fan motor

Switch Bulb
+12........./ ....................X...........0v
|
|
Diode V
|
............Fan ............0v


Mmmm Site is stripping spaces before verticle lines the vertical line with the diode in should be after the switch
RD

Many thanks for that, again I've learnt something new from this site. Only another 3/4 quarters of my brain left to fill with something useful

If you really want to stop the light from glowing in this situation, the diode could be put in 1 of 2 positions.

If the diode is put in the positive feed to the fan, it will have to have a high enough current capacity to manage the fan load.

I am not sure which way the potential would be when (if) the fan is acting as a generator. ie - which side would be +ve.
If it is reverse to normal, a diode could be put in parallel with the lamp effectively shorting out the lamp to the 'reverse' voltage. This would load the motor and have an effect of slowing its rotation. Yet again the size of the diode would need to be suitable.

There is another way to do it.

If you are using a relay to drive the fan, you could use a changeover relay and ensure that the o/p that goes to the fan and light is shorted to ground when switched off.

Len

fan lamp


Thats better

Good answers but i agree with len if you have the relay then this is the best option.

Sorry to be dense but could do with some explaination of the relay solution. At present my fan is switched via a relay.

The rad switch and over ride switch are on pin 86 switching to earth

The fan and dash bulb are off pin 87

Pins 30 & 85 are 12V

So how would this change using a change over relay? would the fan and bulb be on pin 87 which in normal mode is completely disconnected? but isn't this as they are now on a normal relay?

Any further information would be much appreciated, a diagram would be great.

Many thanks for everyone taking the time to answer this.

Nigel

"Fan light glows dimly" you aint going fast enough then!!! If I get our car up to around 80 the light is quite bright; its a good indication of rad core being clear & fan ready to do its work;leave it alone IMHO.

*Presuming the bulb is seperate from the switch, all you need is a diode in the +ve lead as it goes into the back of the bulb.*where did I think that rubbish up from!!

Doh, just thought again about what I'd put then!... The light would never come on to confirm the fan is running then either lol.

Is the 'fan on' light currently coming from the terminal on the relay that also goes to the fan?..
If so you could try putting it on the low power +ve feed side that switches the relay on.

If that doesn't work there are some relays that have
diodes in them that might prevent it or as mentioned convert it to a changeover relay where in effect the fan wire is completely disconnected when the relay isin't on.

[Edited on 6/10/11 by MkIndy7]

Hi Jabba,

Just got back to the thread and I have posted a sketch of the
changeover relay wiring to prevent the lamp from glowing.


relay

Hope it helps.

Len.