ECR Posted September 17, 2002 Share Posted September 17, 2002 Electrics always give me problems and so in an attempt to be better informed I would like to know what the wires connected to my alternator do. I have 4 wires in total. 2 thick and 1 thin which attatch through the plug, and In addition to this I have 1 more wire which is connected to the alternator a little distance from the plug. The two thick wires presumably carry power to the battery. The first (plug) thin wire feeds the warning light (does it ?) What does the second thin wire do ? I discovered that this wire had burnt out recently (with no apparent problems to the car) and had to unwrap the loom to replace it. I traced it back to the bulhead where I discovered that it had been clumsily spliced into one of the 2 thick alternator wires. As my loom has been modifiel by a (presumably ?) qualified electrician when I converted to ecu driven distributorless ignition I am just wondering if I have discovered a "botch".. or whether this is correct. Your thoughts/explanations would be appreciated Edited by - ecr on 18 Sep 2002 12:02:28 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 17, 2002 Share Posted September 17, 2002 Are the two thick connected to the same point? This is not unusual and gives more current carrying capacity to charge the battery. The ignition light wire provides the excitation charge to the field coils. The remaining wire is usually ignition switched so that no current flows until the key is turned. If you use a master switch (and never forget to switch it off when you leave the car) then the last wire can be joined to the battery line so that the alternator is ready to go as soon as the master switch is activated. Some racing alternators are single wire where the excitation is provided by the connection to the battery and there is no other switching. Link to comment Share on other sites More sharing options...
ECR Posted September 17, 2002 Author Share Posted September 17, 2002 Yes the two thick wires are connected to the same point. Any ideas as to what would have caused the wire to burn out ? Why would I not have noticed any problems with a wire bunt out like this ? Would you normaly expect to see this wire spliced to a thick brown ? Link to comment Share on other sites More sharing options...
PeterS Posted September 17, 2002 Share Posted September 17, 2002 Peter mentioned if you never forget to switch off the master switch when leaving the car. However, for the K series, the ecu doesn't like being switched off. It will revert to its factory settings and unlearn all that it has been finding out about the engine and your driving. Maybe your engine doesn't suffer from this Roger. I just mention it as the thought hadn't crossed my mind till all this was explained to me. Link to comment Share on other sites More sharing options...
Chelspeed Posted September 17, 2002 Share Posted September 17, 2002 The wires are there to hold the smoke in. So called experts will tell you it's all about electrons but this is clearly rubbish. When the plastic skin is rubbed through what comes out? Electrons? I think not. It's smoke. The bigger the wire the smoke it holds so the more comes out when it breaks. Obvious really and something us mechanical engineers can understand too if only we can resist the goobledeegook put around by the sparkies. Link to comment Share on other sites More sharing options...
ECR Posted September 17, 2002 Author Share Posted September 17, 2002 Thanks for that Graham The clever bit is how they get the smoke in there in the first place...and, I suppose, why it doesn't spill out when it is in storage on the reel. If you find an answer to that please let me know. 😬 In the meantime if anyone can answer any of my previous questions.... Peter Turning off the master switch does not affect my ECU (otherwise there would be little point in fitting one ) Link to comment Share on other sites More sharing options...
Ian Macquarie Posted September 17, 2002 Share Posted September 17, 2002 Back to the original question. On a 1990 DeDion Xflow One thick wire goes from Battery to alternator. The other one goes from alternator to the rest of the loom. The thin wire adjacent to the thick ones is the ignition light. The separate thin wire goes from the alternator to the battery. It would seem to have no purpose as it is electrically connected to the same point on the alternator as the two thick brown wires. On my car it broke on several occasions with no apparant effect on anything. Ian Edited by - ian macquarie on 17 Sep 2002 17:25:59 Link to comment Share on other sites More sharing options...
Julian Thompson Posted September 17, 2002 Share Posted September 17, 2002 "However, for the K series, the ecu doesn't like being switched off. It will revert to its factory settings and unlearn all that it has been finding out about the engine and your driving." I wish my MEMS had been this clever. I think mine must have been at the back of the brain cell queue - it couldnt even "learn" how to idle....... 😬 Link to comment Share on other sites More sharing options...
ECR Posted September 18, 2002 Author Share Posted September 18, 2002 Thanks Ian My chassis/wiring is a 1990 De Dion X Flow exactly the same as yours. It's a puzzle why that wire is in the loom at all. I wondered if when the wire broke (yes it has on my car many times) it earthed itself and that caused the burn out. Perhaps someone will be along soon and tell us what that wire does... If it electrically connected to the same point on the alternator as the thick browns (I have not checked that on my car yet but will) then I have a wire that is connected to the thick brown wire at the alternator end and also at the bulkhead end. Doesn't make much sense Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 18, 2002 Share Posted September 18, 2002 Have a look at the regulators section Link to comment Share on other sites More sharing options...
stevefoster Posted September 18, 2002 Share Posted September 18, 2002 Liked it Peter, esp the bit about the regulators lasting for many, many years... Unless fried or vibrated to death in a Seven. How PC is this quote from it... "Many "tamer" drivers (like your wife, if she's anything like mine) will often start the car and drive for some time before making it to 1100 rpm for the first time." /Steve My racing pics, 7 DIY, race prep. Updated often here Hants (North) and Berkshire area club site here Edited by - stevefoster on 18 Sep 2002 15:20:29 Link to comment Share on other sites More sharing options...
neilsjuke Posted September 20, 2002 Share Posted September 20, 2002 the small wire to the battary may be a battary voltage sensing wire but should not be con to the large terminal(possable that lot at dartford useing up old looms ) ther are two type of alts battery sensing and machine sensing .if the main feeds were open circit( Batt sw) when on load this would burn out this wire Ie try to turn the starter over with cut out in of. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 26, 2003 Share Posted May 26, 2003 Same question again. I have three thick wires connecting to the alternator (which are all joined together at the other battery end) and one thin one which used to connect to the alternator some distance from the other three. This wire seems to go directly to the +ve terminal of the battery as well (via the kill switch). Mine has fallen off again but this time, it's taken the terminal off the alternator with it so I can't reconnect it easily. Thisng is, it doesn't seem to be any different without it. It is not the light wire as that still works fine. Do I need to reconnect it or can I just cut it back and insulate it? This is a +ve wire and smokes if it gets in contact with an earth. Thanks Alex Alex Wong www.alexwong.net _________ / __ __ / ___ _//__T/__/_ ___ / (_) (_)/ /`-'/o/ _______ /o/`-'/ / /// ( VDU7X ) // / /___/--_________/--/___/ Edited by - Alex Wong on 26 May 2003 09:58:58 Link to comment Share on other sites More sharing options...
Chris W Posted May 26, 2003 Share Posted May 26, 2003 Re the resetting of the ECU. Since getting my SV 1.8K last February, I have disconnected the battery many times (and sometimes for extended periods) while fitting various gizmos. Apart from having to resynchronise the immobiliser plippers, I have never noticed any difference on reconnecting the ECU. The car drives exactly as before (very well) with no apparent resetting needed. I have seen a number of postings about this from time to time... any comments? On the EU3 K series there are only 3 wires that connect to the alternator. A thick brown one which connects to the battery positive (at the starter solenoid) and carries the charging current to the battery. A brown/yellow which connects to the ignition light (and carries the field excitation current) and a white/red which connects to pin 35 of the ECU (the larger of the two connectors and is the "alternator sense", ie: the ECU knows the alternator is functioning. In simple terms, the field excitation current is needed to initially "make" part of the alternator into an electromagnet to enable it to function. Once the alternator starts moving, it can self generate its own field current and this is used by the regulator to control how much charging current is fed to the battery under various load conditions. Chris 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 27, 2003 Share Posted May 27, 2003 Thanks. I think that the wire is redundant in my setup as the ECU does not pay any attention to what the alternator is doing and the light works. More importantly, the car seems to be fine without it connected. Thanks again. Alex Wong www.alexwong.net _________ / __ __ / ___ _//__T/__/_ ___ / (_) (_)/ /`-'/o/ _______ /o/`-'/ / /// ( VDU7X ) // / /___/--_________/--/___/ Edited by - Alex Wong on 27 May 2003 11:10:16 Link to comment Share on other sites More sharing options...
Roland Posted May 27, 2003 Share Posted May 27, 2003 Different vehicle but... I have just converted my GMC truck from Generator to Alternater. My 1942 truck does not have a warning light so I thought...dont fit the little wire then. The Alternater did not output more than 12V !!! (14 needed to charge battery) I then added a warning light...14 V !!! Link to comment Share on other sites More sharing options...
Chris W Posted May 27, 2003 Share Posted May 27, 2003 The warning light often doubles as the same circuit for the "field excitation current". The +12v you were measuring was probably just the battery voltage as without the lamp you wouldn't have any field current. Some older alternator circuits used to put the ignition light in series with the field current (rather than in parallel as now). This meant if the bulb ever blew, you couldn't get the alternator to charge the battery. Tough fault to spot. Chris 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
EFA Posted May 27, 2003 Share Posted May 27, 2003 Roger, The alternator fited to all X-flow and VX 16V Caterhams is a LUCAS ACR type alternator. This has the classical ACR type plug with two thick wires and one thinnner wire. The two thick (6mm² +) wires connect to two spade terminals on the back of the alternator which are actually connected inside the alternator. These thick wires then run to the battery +ve and the +ve feed into the main car loom respectively. The third thinner wire on the ACR plug runs to the -ve side of a warning lamp, other side connects to an ignition fed +12v. IF the alternator is an ACR type and has a 4th wire this is a field exciter and its purpose kick start the rectifier. The alternator will often work with this wire disconnected. On a more recent alternator such as the BMW alternators on the K series, the principle is the same exept loom power is derived from the battery termianl or the back of the starter motor on the permanent +12V feed. Therefore there is only one wire running from the alternator in this case. Fat Arn Visit the K2 RUM website See the Lotus Seven Club 4 Counties Area Website here Link to comment Share on other sites More sharing options...
Tony C Posted May 27, 2003 Share Posted May 27, 2003 I agree with Chris W concerning ecu resetting. My understanding is that disconnecting the battery has no effect on the ecu "memory". To reset the ecu it's necessary to turn ON the ignition and depress the throttle fully six times before turning OFF the ignition. This is from Simon Lambert concerning my 1.8 140bhp K-Series in my new (March 2003) SV. I also understand that if you de-activate the immobiliser before disconnecting the battery negative terminal - it will still be in that state when you re-connect the negative battery terminal - stated in the Owners Handbook. BRG SV 😬 aka Deep Throated Link to comment Share on other sites More sharing options...
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