junkuser Posted February 9, 2011 Share Posted February 9, 2011 Does anyone know the correct resistance of the coil in a Lucas starter solenoid as used on Spitfire 4?Of the two I have, one is 2.6 Ohms and the other 11.6 Ohms. Not sure if one has a high resistance joint or the other has shorts between the windings. Both work but at very different reaction times.Just that I was looking at an aftermarket solenoid which has a resistance of 2 Ohms and was wondering what is a reasonable load to put on the switch contacts and thought Lucas would be a good guide. Link to comment Share on other sites More sharing options...
junkuser Posted February 12, 2011 Author Share Posted February 12, 2011 Still have not been able to find any other solenoids to check the resistance so would appreciate anyone measuring the resistance of the ones on their cars for me.The resistance between the small terminal that the starter switch wire goes to and frame is what I am after.Thank you for your help. Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 15, 2011 Share Posted February 15, 2011 just checked mine and its 4ohms nothing like a bit of variation to throw a spanner in the plan I have a lucas spec manual hiding somewhere If I find it I will copy the page Pete Link to comment Share on other sites More sharing options...
junkuser Posted February 15, 2011 Author Share Posted February 15, 2011 Thank you Pete.4 ohms sounds good.Just worried what the arcing does to the contacts of the starter switch as they open so figure the lower the current in the circuit you are breaking the less the arcing. (Hope this is logical.)The lowest current through the solenoid compatible with efficient functioning of the solenoid seems desirable especially in a 48 year old ignition/starter switch.Would be interesting to see if the Lucas book has the resistance specified. Link to comment Share on other sites More sharing options...
thebrookster Posted February 16, 2011 Share Posted February 16, 2011 No idea what the resistance should be, however assuming it works via V=IR, then you surely would want the resistance to be low, so as to increase the ampage?? Link to comment Share on other sites More sharing options...
thebrookster Posted February 16, 2011 Share Posted February 16, 2011 Also, have a wee gander at the coil voltage thread on this section, Pete Lewis has just posted some info that could be useful?? Link to comment Share on other sites More sharing options...
piman Posted February 16, 2011 Share Posted February 16, 2011 Hello Junkuser, 4 ohms gives a 3 amp current at 12 v, perhaps a bit high? However low resistance measurement with multimeters is usually fairly inaccurate. It is not just the current that you are breaking, although a lower current is better, but the high voltage induced in breaking the coil's circuit which causes the arcing. (Which is why S.U. pumps, for example, have a capacitor or diode to kill the voltage).Alec Link to comment Share on other sites More sharing options...
junkuser Posted February 16, 2011 Author Share Posted February 16, 2011 Thank you Alec.The discharge from the windings on breaking the circuit is an interesting point.How does the type of winding effect the voltage of this discharge?i.e. would a thinner, shorter winding give a different voltage to a longer, thicker winding of the same overall resistance?How would these different windings effect the magnetic field generated and thus the efficiency of the operation of the solenoid?Don't now how this all works.Was interested that the Lucas solenoid with the 11.6 ohm coil worked but not sure how the slower contacting would effect the life of the solenoid's contacts.As an aside, in my youth, I rigged up a temporary starter switch on a Riley 9. Put a return spring in an old pull-push switch which had a a metal knob.If you didn't slip your fingers of the knob to let it disengage you received a good boot. Link to comment Share on other sites More sharing options...
piman Posted February 17, 2011 Share Posted February 17, 2011 Hello Junkuser, it's a phenomenon known as inductance, I don't think physical dimensions so much, rather than the number of turns on the coil. I mentioned S.U. pump as an example but of course that is making and breaking at a high frequency. Your ignition switch does far less work, and are pretty reliable over many years. Having said that, didn't the TR7 have a relay between the starter solenoid and the ignition switch?Alec Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 17, 2011 Share Posted February 17, 2011 cant get at my lucas spec manual ...guess there's something on line but !!!these solenoids , there being two families the old with the rubber prime cover and the newer version with a smaller plastic prime cover or a solid one that cant be hand primed,in the trade they were often used to control high current loads other than starter motors' , more on trucks maybe, and also abvailable as 6v 12v and 24vare you sure the 11ohm one is not 24v as that would make some sense ??does it have a lucas number on it ???if the currnt draw thro' the ign switch is of concern save the day and fit a normal 12v simple relay to feed the main solenoid and use the key switch to just trigger it .... just a thought Pete Link to comment Share on other sites More sharing options...
junkuser Posted February 17, 2011 Author Share Posted February 17, 2011 They are both stamped 12V Pete.The 2.6 ohm one has a die-cast body and is stamped 6 69 Lucas ST 950 764 1E 12VLThe 11.6 ohm one has a steel body and the stamping is very light and difficult to read but I can make out Lucas 760 4B 12V and 59.So looks like one is from 1969 and the other 1959. Both are the rubber capped type as used on cars with manual transmission. (Those used on automatics had a metal cap fitted instead of the rubber to prevent accidentally starting the engine in drive by manually activating.)Using a relay to activate the solenoid would save load on the aging starter switch contacts but thought this overly complicating things and would see what standard was. Interesting that a relay was used as standard on TR7 Piman.Thank you for the contributions, Mal. Link to comment Share on other sites More sharing options...
piman Posted February 18, 2011 Share Posted February 18, 2011 Hello Mal, "starter switch contacts"I misunderstood, I thought it was the ignition switch start contacts you were worried about?The solenoid doesn't affect the arcing of the main high current starter motor contacts, unless the mechanism is very slow in action. They will arc as they are making and breaking current over 100 amps or more depending on the size of the motor.I remember seeing on a Caterpillar diesel engine which had the positive and negative cables running a couple of inches apart physically move outward due to the start current in the cables.Alec Link to comment Share on other sites More sharing options...
junkuser Posted February 18, 2011 Author Share Posted February 18, 2011 Sorry for my confusing use of English Piman.It is the starting contacts in the ignition switch I am referring to.I just wanted to make sure that this aftermarket solenoid a friend asked me to repair for his Cortina was within Lucas specifications as I have one of the same type and brand on the Spitfire at present.Put it on the Spitfire when I had a problem with the coil and the only spare I had was a ballast type so required the extra contact to bypass the ballast whilst starting. Thought I may as well leave it on so in the case of any future coil problems, if on the road, I could just put on whatever coil was available with appropriate replugging of the wiring. Link to comment Share on other sites More sharing options...
.thumb.jpeg.b15b81ef10abeea1c3039ae03c4a9f3a.jpeg)
Recommended Posts
Archived
This topic is now archived and is closed to further replies.