Area Representative paul richards Posted March 20, 2012 Area Representative Share Posted March 20, 2012 My 1.8k has recently and occasionally started to run on for a few seconds after switching the ignition off. I am familiar with running on when radiator fan is operating, but this is not the case. The running on is also accompanied by an intermittent problem with the ignition (charging) warning light not lighting up. Car runs fine and meter across battery indicates 12.2 volts static and 14.2 volts when engine running, so appears to be charging OK. I'm not good on electrics and this has me puzzled. Link to comment Share on other sites More sharing options...
Q Catcher Posted March 20, 2012 Share Posted March 20, 2012 My 1.8K runs on, sometimes quite enthusiastically. It's done it all the time I've owned it and I've always put it down to being one of Caterham idiosyncracies. It never goes on forever, but I've mused that if it does, I'll just stall it in gear. That'll show it who's boss. Maybe. Link to comment Share on other sites More sharing options...
Benedict. Posted March 20, 2012 Share Posted March 20, 2012 To stop your engine(s) running on, try removing the alternator warning light bulb (Temporarily, just to check - NOT PERMANENTLY) Honestly! When I first acquired my previous seven, I had a running-on problem and cured it with a diode in the line between the "charge" light and the alternator, such that the lamp could illuminate and provide power to initiate the field windings on the alternator, but not allow current to flow "back" through the bulb and hold in relays that keep the ECU (etc) switched on. I posted about it (under my alias at the time of my last seven "Dai-X"); hang on, I'll have a quick search. *opens another window and does a search* Ah - there it is: Quoting ME as "Dai-X": Sorted it at last ❗ Got even more confusing last night as found that when the ignition was switched off with the engine running, the ignition-switched 12V lines behind the dash had ~3.5V on them Proved that, unlikely as it may seem, that 3.5V is enough to hold closed every 12V relay I could find so decided that that this erroneous 3.5V was holding some relays in - I'm guessing the ones in the MFU that switch the ignition/injection etc and keeping the engine running from the permanent 12Vs that feed these realy contacts. Spent aaaaages trying to find and understand how the flippin'eck 3.5V was arriving here when the engine was running and eventually had a light-bulb moment - ah there's a smiley for that: *idea* Having previously completely ruled out the alternator (after only considering the main output) realised that it could be the alternator warning light - When the engine/alternator are not spinning this light is on, as the top of it is connected to the ign-switched 12V and the bottom to the "starter" cct of the alternator. It uses this supply to initiate the field windings (IIRC). This "input" then rises to 12V thus extinguishing the bulb (as it has 12V either side now). In my case, this 12V from the alternator was then "getting through" to the ign-switched 12V lines, obviously dropping ~8V accross the warning light leaving enough voltage (and supplying enough current) to hold some relays on. Take the bulb out and the engine switches off fine on the ignition key. Shove a diode in series with the bulb, "pointing at" the alternator and bingo - it now works as it should. Turn the ignition key off and the engine dies instantly while the ECU stays powered for a short while while it does something to the AICV (maybe another question answered there) and then goes off. Blimey that was 6 years ago ❗ The whole thread is here Cheers, Ben Edited by - _Benedict_ on 20 Mar 2012 18:51:46 Link to comment Share on other sites More sharing options...
Area Representative paul richards Posted March 20, 2012 Author Area Representative Share Posted March 20, 2012 Q I think you'll probably find your running on is when the fan is working and they all seem to do that. Ben Interesting. Seems like you are on the right lines. Could it be that the 3.5 volts is not only causing the running on, but also causing the light to remain out. Probably won't be able to get round to it for a couple of weeks, but I think I'll fit a diode and take it from there. Can't do any harm. I wonder. Could it be that the alternator normally has a diode in it (or similar) and this has failed 🤔 Link to comment Share on other sites More sharing options...
Benedict. Posted March 20, 2012 Share Posted March 20, 2012 Quoting Paul Richards: Ben Interesting. Seems like you are on the right lines. Could it be that the 3.5 volts is not only causing the running on, but also causing the light to remain out. Probably won't be able to get round to it for a couple of weeks, but I think I'll fit a diode and take it from there. Can't do any harm. I wonder. Could it be that the alternator normally has a diode in it (or similar) and this has failed 🤔 I suspect (though have no memory one way or the other now) that you may find the alternator lamp may be glowing faintly, as it has ~8V across it, as opposed to 12; have a look at night ❗ 😬 Before you do mess about fitting the diode, I would be inclined to prove it one way or the other by just removing the bulb. You'll then know if it's worth the effort. I'm very sure that it isn't standard to fit such a diode, I think it's just a fluke of the way Caterham wire things that it happens to hold in the correct relays. Cheers, Ben Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 20, 2012 Member Share Posted March 20, 2012 Interesting explanation: is there a suitable LED that could replace the ignition warning bulb? Jonathan Link to comment Share on other sites More sharing options...
Johnty Lyons Posted March 20, 2012 Share Posted March 20, 2012 as the top of it is connected to the ign-switched 12V and the bottom to the "starter" cct of the alternator. It uses this supply to initiate the field windings (IIRC). So please explain since you have stated it yourself how the field windings are getting excited with a diode in place as Your posting confuses me. *confused* Link to comment Share on other sites More sharing options...
Benedict. Posted March 20, 2012 Share Posted March 20, 2012 Quoting Johnty Lyons: So please explain since you have stated it yourself how the field windings are getting excited with a diode in place as Your posting confuses me. *confused* Hi Johnty. If you'll permit, let me go through the whole thinking process. Apologies if the initial bits are the proverbial "Teaching your Granny to suck eggs" Firstly, under normal operation, when you first switch the ignition on, it puts 12V on one side of the lamp. The other side is connected to the field windings thus "activating" them, as with current flowing through them, they are now effectively a magnet. As this current is also flowing through the bulb, it lights up. When the alternator starts spinning, when the engine is running, it now generates it's own 12V (OK closer to 14) which it also supplies locally to energise it's field windings. This means that the bulb now has 12V on bothsides of it (ie 0V across it), so now goes out. The problem here however, is when the ignition switch is turned off. This switch takes away the connection from the battery/alternator 12V to all the ignition switched circuits. You'd expect them to drop to nothing and everything switch off. However, the bulb in question now has 12V at the alternator end, and it's other end is connected to the ignition switched wires. Electrically, this means that the 12V from the alternator is conected through a resistor (the bulb) to these wires, and therefore to the coils of all the relays that power the ECU, fuel pump, etc. In practice, this proved to leave 3.5V across these coils. Experimentally I ascertained that (very surprisingly) 3.5V was enough to hold in every 12V relay I could find to test. This suggested to me that the power "leaking" through the bulb was causing the engine to run on. I proved this by disconnecting the bulb and the engine instantly stopped, and never failed so to do. Quite a few other people found this as well. OK, sorry, this is getting quite long. The diode. To solve my problem and still have the lamp function as it should and provide the initial excitement for the coils I decided to use a diode. This diode was connected in series with the lamp, such that it would conduct electricity in the "direction" of the alternator. That is to say that before the engine started, it would allow current to flow from the 12V from the ignition switched wires, through the lamp, through the diode and though the field windings. When the alternator starts, the light still goes out as you have 12V on both sides of the lamp/diode pair. However, when you turn off the ignition switch, current can no longer flow from the alternator field supply to the lamp as the diode is preventing this. There is no voltage at all "leaking back" (horrible term, but it seems to describe things quite well), the relays all open and everything stops. I hope I've clarified things and not made them worse, Cheers, Ben Link to comment Share on other sites More sharing options...
Benedict. Posted March 20, 2012 Share Posted March 20, 2012 Quoting Jonathan Kay: Interesting explanation: is there a suitable LED that could replace the ignition warning bulb? Jonathan Unfortunately LEDs only work on such a low current (you have to limit it with a series resistor, though these are sometimes "built in" and quoted for certain supply voltages) that this fails to suitably excite the field windings. In practice, you need to use a resistor of similar resistance (and power dissipation capability) in parallel with the LED (and it's limiting resistor) to get the functionality as well as the funkyness of the LED. You can put the above mentioned diode in series with all the above to prevent run-on, if this is happening by this means. Cheers, Ben edited for speeling... Edited by - _Benedict_ on 20 Mar 2012 20:41:37 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now