33 replies to this topic

[minipower101]

http://pages.ebay.co...id=321206568306

[minipower101]

They do this with a 6v or 12v bulb. Would I need the 12v if this is suitable? Thanks

[Dan]

Yes, ideal and you need 12v. Although you can get those lamps with the correct symbols on too. Stop using Ebay and try an auto electrical supplier!

Re the above, as Ethel says my second post about resistances was taking specifically about current limiting resistors packaged with LEDs. I thought it was clear from the flow of the thread, as it was a reply to a question, but if not I apologise.

It doesn't need rectifying really, either a bidirectional LED or simply a blocking diode would do. I was going to mention this originally but deleted it in favour of directing the thread to posts by Doug where it's all explained. The only thing it can really warn you of when reversed is a resistive wiring fault on the battery side of the bulb. The alternator voltage can't really climb above the bus voltage, because the alternator output is connected to the bus where the battery is. The difference between healthy battery and boiling battery is only about 0.4v anyway which won't light any lamp enough to see in daylight. So blocking it for protection would be enough.

But as said a filament lamp does a better job.

Edited by Dan, 13 April 2014 - 08:31 PM.

[minipower101]

Great, cheers. I'm sorry, but i don't really understand the diode bit do i still need to wire something along side that 12v warning light?

[Dan]

Nope, that's all to do with LEDs. The bulb is fine by itself. Ignition live feed to one terminal and brown/yellow cable to the other.

[minipower101]

Ideal :) thanks so much everyone.

[dklawson]

Sorry... I have been gone for several days.

 

I will try and post a linked image and offer a couple of quick comments.  The picture is not mine, it is borrowed from the VW forum "The Samba".

 

 

What the image is showing is a conversion to do away with the incandescent charge warning light.  It addresses the voltage spike Tiger mentioned and shows the basic wiring.  Of course... it isn't Mini specific so I will add some comments regarding colors.

 

IGN to Fuse.  - I consider the fuse optional.  It won't hurt but should not be necessary.  On the Mini, there will be a white wire going from the ignition (IGN) switch to the old red charge warning lamp socket.

The first diode (1 amp/200V triangle pointing to the right with a vertical bar).  Is for circuit protection (as Tiger mentioned in his post).  Once you remove the incandescent bulb socket, the diode goes to the white wire.  Diodes have marking bands and the band goes towards earth.  So... the side of the diode that does NOT have the band connects to the white wire.

The next two parts are a 100 Ohm power resistor (typically ceramic) and another diode (the green triangle with vertical bar).  The green diode is your indicator lamp.  Buy an automotive LED lamp (rated for 12V) and use it in place of the green diode shown above.  The automotive LED will already have the dropping resistor Ethel mentioned so you will not have to calculate or worry about the LED's resistor value.  The power resistor provides the load that Dan mentioned.  The automotive LED will already include the voltage dropping resistor that Ethel mentioned.

The blue wire shown in the picture above Will be the brown/yellow wire on the Mini which is connected to the small alternator terminal.

 

How does this work?  You have removed the incandescent bulb and its socket.  The power resistor provides the necessary resistance to current flowing to the alternator to energize its windings.  The automotive LED is wired in parallel to the power resistor and will turn on and off correctly without having to carry the current necessary to energize the alternator windings.  The first diode protects the other elements in the circuit from the reverse voltage spikes that might otherwise cause the LED to fail.

[Captain Mainwaring]

You're missing the series current limiting resitor.

[phil hill]

You're missing the series current limiting resitor.

 

 

  Buy an automotive LED lamp (rated for 12V) and use it in place of the green diode shown above. 

 

Already covered Cap'n !!

 

Phil.

[minipower101]

Thanks dklawson. Really good info :)

[Captain Mainwaring]

 

You're missing the series current limiting resitor.

 

 

  Buy an automotive LED lamp (rated for 12V) and use it in place of the green diode shown above. 

 

Already covered Cap'n !!

 

Phil.

 

 

LED's don't just turn on and off - stick a zener to act as a crowbar so that the LED just turns on and off, but why?  I use intelligent charging controller on big gensets, They'll tell you everything you need to know, alternator output, condition, field voltage, temp, stator resistance, the whole lot.

Rather than all this pissing around with hobby electronics, just fit a voltmeter, or am I being simplistic? 

Edited by Captain Mainwaring, 14 April 2014 - 10:50 PM.

[dklawson]

I don't think the OP is doing anything to monitor voltage with this LED conversion.  As I understand it, he is making a "modern" dash with a bright LED to replace the incandescent bulb.

 

Neither of the diodes shown above are Zeners.  The purpose of the "non-LED" diode is for circuit protection, not to produce the voltage for the LED or any form of voltage monitoring.

[Captain Mainwaring]

I don't think the OP is doing anything to monitor voltage with this LED conversion.  As I understand it, he is making a "modern" dash with a bright LED to replace the incandescent bulb.

 

Neither of the diodes shown above are Zeners.  The purpose of the "non-LED" diode is for circuit protection, not to produce the voltage for the LED or any form of voltage monitoring.

 

Ya, can see your point, a zener would provide all you need in one package ........ http://www.evilmadsc...o-zener-diodes/

[tiger99]

No it would not, in fact a zener diode is not wanted anywhere near this circuit.

 

By the way, the reason for recommending a bridge rectifier, to make the LED behave much like a bulb, is that there is a rather common failure mode involving a high resistance ignition switch, which can cause a voltage reversal, and as that particular problem is associated with bad starting and running, and various other problems, detection by the warning light is useful. What happens with a bulb is that, when the fault occurs, as you bring the engine above idle the lamp goes out, as normal, but as the revs increase towards the upper limit, the bulb starts glowing again, becoming brighter as the revs rise. It is because the voltage at the field excitation rectifiers in the alternator (the 3 smaller diodes) has risen above the voltage downstream of the ignition switch, and the alternator is trying to power the ignition circuit via the bulb.

 

I have seen that happen on several cars, including one Mini, and in each case the ignition switch had to be replaced, which cured a multitude of problems.

[Captain Mainwaring]

Replace the lamp with a DC relay  and power the LED via the relay - job done. KISS