julians Posted June 24, 2004 Share Posted June 24, 2004 When I replace my dashboard with a carbon one, I also want to replace all the warning bulbs (indicator, main beam, alternator charge light) with LED's, however something in the back ofmy head is telling me it wont be that simple with the alternator warning lamp. Can I just replace the alternator lamp with an LED, or do I need some additional circuitry to make it work correctly? Link to comment Share on other sites More sharing options...
Big Brother Posted June 24, 2004 Share Posted June 24, 2004 Julians I had exactly the same idea and had a brief email conversation with Chris W The 12v warning lamp wired to the alternator also provides an exciter voltage to enable the alternator to start producing a voltage. Replacing the bulb with an LED may not allow enough current to reach the alternator. I toyed with the idea of wiring in a bulb, out of sight under the dash and then connecting a led to it. Not sure how this would need to be wired to work as a bulb can glow at low voltages, a LED tends to be on or off (to the eye) Eventually I decided to just keep it simple and fitted a single bulb to the dash. All the other warning lights fitted are LED's. Steve Se7en-Up! Link to comment Share on other sites More sharing options...
Frying Pan Posted June 24, 2004 Share Posted June 24, 2004 The new instruments (Caerbont, not VDO) have the warning LEDs integrated into the tacho, so it must be possible. Guy See some pictures of the build here. First 2000 miles completed! Link to comment Share on other sites More sharing options...
Joe 90 Posted June 24, 2004 Share Posted June 24, 2004 Most alternators have enough residual magnetism that the exciter current isn't neccessary (although sod's law applies). You can either use an LED with an integral resistor, which should have a 12V rating, or add your own resistor. For a typical 20mA LED I would use a 560 ohm 0.25W resistor. SEP field working, not spotted in 101,600 miles. Some photos on webshots, updated 10 June Link to comment Share on other sites More sharing options...
rj Posted June 24, 2004 Share Posted June 24, 2004 In some tintops, using a LED, there is a resistor parallel with the LED, say you want a consumption of 2W @ 12V this would leave you with a resistor of 72 ohms. As a safety precaution would I go for an 82 ohms. Remember it needs to be *at least* a 2W resistor, preferably 5W not to get too hot! /r Link to comment Share on other sites More sharing options...
V7 SLR Posted June 24, 2004 Share Posted June 24, 2004 There's already a diode in series with the ignition warning lamp. I removed both the lamp and diode and replaced both with what is foolishly labelled as a 12V LED from RS (diodes are current devices, but that's pedantism). In fact I replaced all my dash warning lights with them because they were flat and came with their own bezels. Problems: The indicator LED only lit when I indicated left. I realised soon after that this was because the positive voltage is applied to different "legs" of the bulb, depending upon which way you indicate. Simply add a diode in series with each wire (2 diodes) and join both outputs of the diodes together and to the LED. The other side of the LED goes to earth. In fact use the diode you've liberated from the ignition lamp, and another similar... The main beam (blue) LED is too bright and will require further current limiting before your eyes are not seared out each time you use it in the dark. It's probably brighter than my 80W main beam bulbs. 😬 I've got a pic somewhere... if interested. Link to comment Share on other sites More sharing options...
Chris W Posted June 24, 2004 Share Posted June 24, 2004 RJ If you put an additional resistor in parallel with the LED, the additional resistor will only have 2v across it (the forward voltage of the LED) NOT 12v across it. You would need to put the additional resistor across the LED AND its series resistor to have 12v across the additional resistor. V7 The K series (don't know what you have) already have the 2 diodes in line with the indicator lamp exactly as you describe. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
V7 SLR Posted June 24, 2004 Share Posted June 24, 2004 It's not engine specific, but I assume it is age related. Mine is a K (SLR) from late 1999 and didn't have any diodes in the indicator. Well, it may have had, but in operation it needed a couple to make an LED work as described. Link to comment Share on other sites More sharing options...
Chris W Posted June 24, 2004 Share Posted June 24, 2004 V7 If it had one lamp, then it must have had diodes somewhere or else the left and right indicators would be connected together through the lamp when the indicator switch is on. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
V7 SLR Posted June 24, 2004 Share Posted June 24, 2004 Possibly, but consider this: 1. Removed the lamp and inserted LED. It only lit when indicating in one direction. 2. Removed LED to measure things. Noticed that when indicating one way, ONE wire stepped 0-12-0-12 whereas the other stayed at 0v. Indicated the other way and noticed the opposite. 3. Inserted diode in series with each wire, and joined other end of diodes together, and then to LED. Other end of LED to permanent earth. Always on the look-out to remove unecessary stuff, how would I remove all diodes to make this work, or remove "some" of them? Link to comment Share on other sites More sharing options...
rj Posted June 24, 2004 Share Posted June 24, 2004 Chris W You are absolutely right; I'm just a bit tired... But you have indeed explained what I meant! Thanks for correcting me /r Link to comment Share on other sites More sharing options...
Chris W Posted June 24, 2004 Share Posted June 24, 2004 V7 Ok - I did a little bit of doodling here and I believe I understand how they have wired it without diodes to make it work with a lamp AND why it didn't work with the LED. I have also now realised there is another way of wiring in an LED without the use of diodes providing you have an electronic flasher and not a mechanical flasher. (I'm virtually 100% certain you would indeed have an electronic flasher on a '99 vehicle). It would be easier to draw you a diagram so if you send me your email address I'll mail it to you. However, in words, they have wired the dashboard signal lamp across the two wires you describe and are relying on the fact that the small lamp has a much higher resistance than the indicator lamps. (typically 30 ohms for the small lamp and about 3 ohms for the two main indicator lamps on each side in parallel.) So when you switch on the, say, right hand side (RHS) indicators, current will also flow through the small lamp and down to ground through the left hand indicator (LHS) lamps. Since the small lamp has a far higher resistance than the LHS lamps most of the volts are dropped across the small lamp and only about a volt across the LHS lamps. So these LHS lamps act as a virtual ground for the signal lamp. Because they only have about 1 volt across them they do not visibly glow. When you substitute an LED, the LED will only work one way round because (unlike the lamp) it is polarity sensitive (ie: it has an anode and a cathode which MUST be connected to positive and negative respectively). So when you switch the say LHS indicators ON, the LED is reverse biased and so does not illuminate. By connecting the additional diodes as you describe, you are providing an independent path to ground for the LED cathode and ensuring the LED anode always "sees" a positive voltage and so functions perfectly. That's how CC currently do it. It occurs to me though that you could actually fit an LED (with a series resistor, say somewhere around 470 ohms to 1000 ohms) or indeed a lamp from +12v to the CENTRAL contact on the indicator switch. (providing you have an electronic flasher). If using an LED the anode MUST be connected to +12v to make this work. With a lamp it will work either way round (use a 5W lamp maximum though to keep the current down). I don't know why Caterham don't do this. I can only think that a loom with diodes already in would work with either an electronic flasher or a mechanical flasher or there may be some other historical reason of which I'm unaware. It's easier to see all of the above on a diagram than to describe it in words. Hope this helps Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Chris W Posted June 25, 2004 Share Posted June 25, 2004 V7 YHM Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
julians Posted June 25, 2004 Author Share Posted June 25, 2004 Cheers for the responses, just about to order some diodes from RS for the indicator bulb, but realise I dont have a clue what sort I need (there are millions of varieties). Can anyone specify which ones I need from rswww.com. Cheers Link to comment Share on other sites More sharing options...
V7 SLR Posted June 25, 2004 Share Posted June 25, 2004 Superb diagrams Chris. Perfectly explains what is happening. Thanks for the effort and the confirmation that I was right inserting the diodes where I though they ought to go. That electronics degree wasn't wasted on me, even though that's probably the only thing I've ever used it for. *thumbup* Link to comment Share on other sites More sharing options...
V7 SLR Posted June 25, 2004 Share Posted June 25, 2004 Julians... Gimme a little time and I'll try to dig out what I bought. Link to comment Share on other sites More sharing options...
V7 SLR Posted June 25, 2004 Share Posted June 25, 2004 Found my invoice: 1 x 265-6863 Red - Ignition 1 x 265-6885 Yellow - Dry sump pump belt 1 x 265-6908 Blue - Main beam (bloody bright - needs additional resistor) 1 x 265-6914 White - Shift light 1 x 265-6879 Green - Indicator All these are flat LEDs with integral bezels and require no resistor to work at 12V, although as I mentioned, the blue one is too bright at night (when you'll use it) so additional resistance will be required. Also, as Chris and I have determined, for the indicator please check whether you already have diodes and if not, use the current ignition one and another of the same type. Pics of my dash available upon request. Link to comment Share on other sites More sharing options...
normalbloke.29 Posted June 26, 2004 Share Posted June 26, 2004 I too have had this problem, would anyone care to forward the wiring diagram to me and the parts list? Many thanks in advance. Link to comment Share on other sites More sharing options...
Normans_Ghost Posted June 26, 2004 Share Posted June 26, 2004 Chris W, whilst your on the subject, I was going to fit 2 time relay's into the indicator circuit so that they woulkd self cancel after say 30 seconds and would be operated by 2 push buttons. I couldn't find any inexpensive relays only fully programable ones at £50 each. I tried interior light relays but they didn't work. Your thought would be mose welcolme. [i overcome the led problem the simple (idiots) way by putting two leds in dash, one on left of s/wheel and other on right.] norman verona 1989 BDR 220bhp Mem No 2166 Curmudgeon in an Elise, (and 7 and Elan) Link to comment Share on other sites More sharing options...
Chris W Posted June 27, 2004 Share Posted June 27, 2004 Norman I have already designed and fitted such a circuit to my 7 with the switches mounted on my (removable) steering wheel. There is a photo on my website (click below). The circuitry is fairly involved for these as I used one switch for left and one switch for right. One activation switches the indicator On and another activation of the same switch turns it OFF. Further, pushing say the RHS switch while the LHS is flashing will turn OFF the LHS and switch ON the RHS, which is what you need for a turn at a junction followed immediately by another turn to the other side. Finally, if one forgets to cancel the indicators, they self-cancel after a pre-set time (I have mine set to about 25 secs). Operation of the hazard switch or indeed operation by the original indicator switch (if one wanted to keep it as a back-up) are unaffected. The steering wheel switches are connected to the circuitry by a very small RJ11 (US telephone) plug and socket together with some standard flat telephone cable which has enough slack to enable the steering wheel to turn without interference. I thought it would be a very simple circuit but once I listed out the functional requirements, it started getting more and more complex. But it's been fitted for about a year now and works perfectly. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Normans_Ghost Posted June 28, 2004 Share Posted June 28, 2004 Chris, I think I can do the wiring for the relays but which relays should I use. I'm happy with a 20 sec on only, as I use indicators sparingly (only when turning left/right off main roads, rst of time car position tells which way I'm going) norman verona 1989 BDR 220bhp Mem No 2166 Curmudgeon in an Elise, (and 7 and Elan) Link to comment Share on other sites More sharing options...
Chris W Posted June 28, 2004 Share Posted June 28, 2004 Norman I didn't use programmable relays (which as you point out are ludicrously expensive). I designed a circuit which incorporated a push ON, push OFF circuit with switch debouncing components (or the circuit would get confused), timer circuitry and a cross-coupling network so that one can switch from LHS to RHS or vice versa with just one push. The actual relays I used to switch on the indicators were just small, inexpensive SPST versions. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Normans_Ghost Posted June 28, 2004 Share Posted June 28, 2004 Chris, OK thats all a bit too much for me, When I was trained alternators wern't in use yet. I was thinking of a push once switch which would energise a timer relay which in turn would power the flasher unit for 20 seconds. I would have 2 switches and 2 relays. Therefore, touch the RH switch and the RH indicators would work for 20 seconds, touch the LH and the LH would work for 20 seconds, touch both and you've got hazard warnings! I tried Vehicle Wiring Products, SVS and Maplins and no one had a relay to suit. Searching the net, I found a manufacturers who had programmable relays available through City Motor Factors at about £50.00 each. At this point I wired it up as normal. I know my way is flawed in so much. that both sides can flash together, but it should be simple to wire utilising most of the existing circuit. Take existing wire from switch and put on feed from relay, then supply 12v feed from push switch to relay (and probably 12v & earth). Am I oversimplyfying this? Any idea where I can get a simple inexpensive 20 sec relay? many thanks, norman verona 1989 BDR 220bhp Mem No 2166 Curmudgeon in an Elise, (and 7 and Elan) Link to comment Share on other sites More sharing options...
Chris W Posted June 28, 2004 Share Posted June 28, 2004 Norman Your method would work with the obvious flaw (as you point out) that both flashers can be ON together. What happens when you want to do a left followed immediately by a right? You could fit a third button which breaks the power and thus stops the flashing but there are "cleaner" ways of doing it. You won't find any inexpensive timer relays. It's much cheaper to build a timer circuit that controls an inexpensive relay. A couple of £'s of components will do the job based around the ubiquitous 555 timer chip. This part is the easy bit. It's the getting it to work like a proper flasher that adds the complication. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Normans_Ghost Posted June 28, 2004 Share Posted June 28, 2004 Chris, sounds like an article coming on. That's beyond a mere mortal like me. but I can follow a diagram and instructions. norman verona 1989 BDR 220bhp Mem No 2166 Curmudgeon in an Elise, (and 7 and Elan) Link to comment Share on other sites More sharing options...
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