Marmite!! Posted September 13, 2006 Share Posted September 13, 2006 What should the resistance be on the ballast resistors for the RR B-Series?? Cheers Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted September 13, 2006 Share Posted September 13, 2006 What should the resistance be on the ballast resistors for the RR B-Series?? Cheers Lee, The two resistors being connected in parallel should have a total resistance of 3.8 ohms. Also the voltage given to the coil when running should be between 12 and 16 volts. Richard Quote Link to comment Share on other sites More sharing options...
fv1609 Posted September 13, 2006 Share Posted September 13, 2006 "Also the voltage given to the coil when running should be between 12 and 16 volts." This could vary with the type of meter you have. Assuming fully charged batteries. When the points are open you will read 28 volts, there will be no voltage drop as the the coil & hence the resistors are carrying no current. When the points close it with draw about 3.5 amps causing the voltage drop to 14 volts. When the engine is running the voltage is flipping from 14 volts to 28 volts. The moving coil meter will not be able to flicker up & down quick enough so it will hover & give a reading of 21 volts. Sort of mechanically averaging between 14 & 28 volts. Sometimes people have been caught out wondering why despite the resistors that the coil is seemingly running off 21 volts. It isn't but that is what the meter suggests. Goodness know what a digital meter would make of it! 1 Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted September 13, 2006 Share Posted September 13, 2006 Clive, These figures were out of the RR manual and Power EMER. From a PM Lee sent me earlier in the week, he thought he was getting around 18 volts . Richard Quote Link to comment Share on other sites More sharing options...
fv1609 Posted September 13, 2006 Share Posted September 13, 2006 These figures were out of the RR manual and Power EMER. From a PM Lee sent me earlier in the week, he thought he was getting around 18 volts. As I said it could vary with the type of meter, but I get 20 volts. It will also depend on the coil because the No.1 Mk 2 resistance is 3.1-3.5 ohms, whereas the No.1 Mk 2/1 is 4.25-4.65 ohms. I can't find voltage readings in the RR book or EMERs but I would imagine if they are quoting a voltmeter to read as low as 12-16 volts with the engine running then it must be with the No.1 Mk 2. As this has lower resistance it will draw more current that will cause a bigger voltage drop across the resistors than the higher resistance coil. Doing a bit of scribbling & by ohms law there could be a difference of 2 volts applied to the coil depending on type. But it still seems a very low figure considering the voltmeter is average the reading from full volts to dropped volts. I wonder were they actually using a moving coil meter or was it a thermal voltmeter which is very slow in response & I would have thought in the circumstances might tend to give a lower 'averaged' reading? Quote Link to comment Share on other sites More sharing options...
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