I trust you all had a good Christmas and New Year, though it seems an age ago already !
I am finally nearing the end of the renovation of my 1949 Shipley Flyer and have almost completed the wiring which needed totally replacing.
However I was unable to get the ignition warning light to come on and closer inspection showed that one of the wires from the warning light to the switch is what is known as – according to Google, a ‘Wire wound flexible resistor’. I have attached a couple of pics and the very fine cotton covered wire can be seen wound around what seems to be a rubber core and the fine wire is broken in severeal places, hence no ignition light !
So my question is this, can any electronics wizards out there tell me how I can tell what resistance it should be and what I could replace this resistor with as this type now seems to be obsolete. I assume it is there to reduce the the current to the bulb and prevent it from blowing when the dynamo is charging or some such thing ?
Any advice appreciated !
Regards, Mark Compton
[attachment=0:li23nvdz]Flex resistor 004 rez.jpg[/attachment:li23nvdz]
[attachment=1:li23nvdz]Flex resistor 006 rez.jpg[/attachment:li23nvdz]
Such a thing does not appear in my 1950 Scott/Lucas wiring diagram leaflet…. Anybody else got any ideas ?
Yes, your quite right Brian, I have that wiring diagram also and it isn’nt marked on it as a resistor, but the actual resistor/wire itself does appear to be an original part of the wiring in the switch.
Perhaps I should just replace it with an ordinary piece of wire and see what happens. After all it can only blow the bulb !
Why not measure the resistance of an intact bit of the wire? Extrapolation to the original length should get you in the ball-park. Its not going to be critical…..
I agree with that , then replace the resistance wire with a suitable wire wound resistor.
I would of said that the resistance was fitted to give the lamp a soft glow, and not a harsh bright light, or could it be to bias the bulb? In other words make the bulb extinguish better as the dynamo voltage rises .
Thank you all for the replies.
I will do as you say and work out what the resistance was approximately and then get a modern wire wound one.
I still cant quite get my round why or how the light is extinguished when the dynamo is charging though !
When the dynamo isn’t charging, the lamp is lit by the battery. When the output from the dynamo reaches the same voltage as the battery, the two cancel each other out and the lamp goes out.
I’m afraid that is not correct.
In basic terms, the ignition warning light is powerd by a positive polarity feed when the ignition is turned, and is “earthed” to negative polarity via the field coils of the stationary dynamo. When the dynamo begins to rotate, a positive polarity is produced in the field coils, thus depriving the the warning light of a negative polarity return, so it goes out.
As the dynamo speed rises, it would continue to produce a rising voltage unless limited by the regulator – until internal resistance levels this off at around 30 volts. (which incidentally is why you can instantly convert to a 12 volt system, given a change in regulators etc.)
Dependent upon condition and adjustment etc. of the (mechanical) regulator, this is why the warning light sometimes appears to increase its brightness until the regulator cuts in to limit the dynamo voltage output. To avoid any momentary “over-voltage”, a protective resistance is sometimes incorporated into the warning light circuit.
That’s what I said but in more basic terms!
Thank you both for the replies. I have certainly learnt a bit more about motorcycle electrics !
I shall work out the resistance as best I can and then get a modern one to put in its place. There seems to be many different types and sizes of resistor out there, I assume it matters what type I use, I’m guessing one of those little things that looks like a blob of glue with a wire sticking out of each side may not be suitable ?
Can you give me any guidance ? There is a maplins near where I live, I can ask them what they have.
Are you still using a mechanical regulator ,or are you using a more modern solid state unit?
I’m intending to try using the mechanical regulator that was on it when I got the bike as it looks to be in quite good condition and I will see how it performs, but if it gives problems I will probably go over to a solid state one as I have on some of my other bikes.
Why do you ask ?
I was thinking that you would not have to worry about the resistance if a solid state one was fitted, as explained by Stan , the resistance may have been fitted for over voltage, mind you I have never seen this arrangement before
Thats useful to know as I have just been trying to work out what resistance that little wire would have given but I haven’t been able to as it
has breaks in it all along almost up to the terminal.
Interestingly the wire wound around the core appears to of a ferrous metal as the breaks are where its rusted through in many places.
I thought it would have been copper ?
I will just have to make a guess at the resistance or change the regulator to a solid state one.
For what it is worth – and old dodge was to fit a 12 volt bulb in the warning light instead of a 6 volt one, which gave a softer glow and achieved the same effect as a wire-wound resistance.
A note on electronic regulators: “Mechanical” old-type regulators consume a fair proportion of current in operation, whereas an electronic one does not – so providing more charging capability etc.