Lucas Lord of Darkness rears his ugly head

[tdafforn]

Hi all
Have been commuting to the station for 3 months in the lotus and had my first problem yesterday.
Got in the car to go home and turned the key, the starter turned once and then smoke started filling the Tacho. turned off the ignition and opened the bonnet. More smoke and the wire from the solenoid to the coil looks toasted.
Managed to rig a feed from the battery to get me home, but now have to sort out the mess..
Question I have. I have 2 wires going to the +ve side of the coil. One is white one white with yellow stripe. Both seem to have 12V when the ignition is on although this could be a result of the wires shorting as the sheaths have melted . Why do I have two feeds?
I take it one is 12v for feeding the coil, the other I am unsure about. Is it for the tacho (would explain the smoke) or for a ballast resistor circuit.
the book shows one feed to the coil and one to something on the side of the coil (is this the ballast resistor for cold starting?). My coil has only one +ve terminal.
should I have a ballast resistor?
should both feeds be 12v when the ignition is on, surely with a resister circuit one should have 12v only when the starter is turning.
Alternatively if the two feeds are coil and tacho, then the coil feed seems to be coming from a small connector on the solenoid which doesn't seem to be live when the ignition is on..
Could this mean that the coil has been recieving its 12v feed via the Tacho?
so many questions..
Anyone any ideas?
Tim
'73 +2 S130

[john-c-elan+2]

Hi Tim, your car being late model wud have originally had a coil with ballast resistor. The ballast resistor was (as it left factory) a small delco one bolted directly onto the + terminal of coil. There was a white & yellow wire coming off solenoid and connecting to + on coil, and a white to the ballast resistor on the same terminal on coil. Coils that have a ballast resistor are usually only 6 to 9v. The idea being that when cranking the coil wud be getting 18v (12v from solenoid, and 6v via the ballast resistor)to get a fatter spark for starting. The white & yellow is only providing power when cranking.
If you are now using a 12v coil and no ballast resistor then you must disconnect the white & yellow from solenoid & coil - this is what I have done. Otherwise the coil will be getting 24v on cranking ! Yes the white does get to the coil via the tacho. I expect you have a workshop man ? There is a decent wiring diagram in it for +2s130 - non federal that show it pretty well.

[types26/36]

wud be getting 18v (12v from solenoid, and 6v via the ballast resistor)

Otherwise the coil will be getting 24v on cranking ! .

Huh! ????????
Well with that voltage our headlight would be BRIGHT

[nebogipfel]

That's an interesting take on how ballast resistor ignition works

Might be an idea to review that again!

[M100]

Has he been gulping down some jungle juice?

24v, from nowhere?

[john.p.clegg]

John
I think you may of gathered from the replies that you have got that one a little wrong.
!2v is supplied to the coil during cranking(which drops the supply voltage anyway) to produce a nice fat spark,the coil (6v) is fed a 12v supply while running,dropped to 6v or so by the ballast resistor....

John

[poiuyt]

So let me see...
If I add two additional wires I'll get 48 volts! That would sure spin the hell out of the starter!

Better have another look at Ohms law.

Steve B

[john-c-elan+2]

I stand corrected !

[dlbarnes1]

It sounds like the original coil and ballast resister were replaced with a 12V coil (no resister) in which case the wire from the solenoid should have been left unconnected and tied off.
Possible explanation for the failure:
If there was a ground fault in the tach, it would normally have been protected by a fuse in the circuit coming from the ignition switch. In this case the connection from the solenoid probably allowed the ignition circuit to fail back to the fault at the tach.
In the arrangement with a ballast resister, the resister would limit the fault current in a failure like this and possibly fail like a fusable link before the rest of the circuit cooks.

Dave 72 Sprint DHC

[tdafforn]

Opened up the tacho and it is toast..
Have undone the loom and the wire from the solenoid to coil and the coil to tacho are also toast...
Will replace these and check that non of the other circuits got damaged..
Looks like I need a new tacho though!
Any idea how much these are to recondition?
Cheers
tim

[rgh0]

Tim

With luck the only circuit inside the tacho thats toast is the current sensing loop. If thats the case you should be able to replace it yourself at no cost.

regards
Rohan

[tdafforn]

If the "loop" is a toriod of copper wires then this is the toasty bit in the Tacho...
If I wanted to mend it myself, where would I get a replacement?
Tim

[rgh0]

Tim

You should be able to unsolder the 2 ends of the burnt out current sensing loop that the ignition current to the coil runs through. Then unwind the burnt wires and replace with a similar sized insulated wire with the same number of turns and provided nothing else cooked in the tacho when this wire burnt out then it should be OK again.

Rohan

[dlbarnes1]

Tim
When you make the repair, remember to not connect a wire from the solenoid to the coil as long as there is no resistor in the ignition circuit (12V coil).

Dave 72 Sprint DHC[/u]

[theelanman]

tim
saw this and thought of you!!!!

http://cgi.ebay.co.uk/Lotus-Elan-Rev-Co ... dZViewItem

cheers
gareth