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| Thread ID: 138986 | 2015-02-20 19:31:00 | Lucas Electrics, 21st Century version. | Whenu (9358) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 1394691 | 2015-02-20 19:31:00 | www.dailymail.co.uk | Whenu (9358) | ||
| 1394692 | 2015-02-20 23:56:00 | The joke material is endless | prefect (6291) | ||
| 1394693 | 2015-02-21 00:14:00 | The chips were down here to get the landrover moving. | Bobh (5192) | ||
| 1394694 | 2015-02-21 04:54:00 | Can I have a new distributor please? You want fries with that? |
R2x1 (4628) | ||
| 1394695 | 2015-02-21 06:56:00 | I have used a potato in the past to get home. The function of a condenser or capacitor (made from aluminium foil separated by waxed paper) in an ignition system is to absorb the current from the coil primary windings when the points open. This then causes a voltage to be generated by the secondary winding which jumps across the plugs. It also prevents the back EMF (electric motive force) from jumping the points and burning them. A potato with moisture and salts in it will do the job. The revs may be limited, but the engine should run. The potato works better on motors with few cylinders, you may have to use more spuds on a V8. Similar results could be obtained with a glass jar of salt water with two electrodes in it. |
mzee (3324) | ||
| 1394696 | 2015-02-21 07:15:00 | Haven't used a spud but I have used a radio suppressor off the generator on my Morris Oxford to get me home from Lake Chalice. | prefect (6291) | ||
| 1394697 | 2015-02-21 09:10:00 | I have used a potato in the past to get home . The function of a condenser or capacitor (made from aluminium foil separated by waxed paper) in an ignition system is to absorb the current from the coil primary windings when the points open . This then causes a voltage to be generated by the secondary winding which jumps across the plugs . It also prevents the back EMF (electric motive force) from jumping the points and burning them . A potato with moisture and salts in it will do the job . The revs may be limited, but the engine should run . The potato works better on motors with few cylinders, you may have to use more spuds on a V8 . Similar results could be obtained with a glass jar of salt water with two electrodes in it . Close, but no cigar . The capacitor and the coil’s primary windings form an oscillating L/C (inductance/capacitance) circuit and when the points open, the field in the primary coil collapses and in doing so a 'back-emf' is created in the HV coil which generates a damped HV oscillating current . That exchange of energy between the capacitor’s electric field and the ignition coil’s magnetic field produces a longer spark duration . Put more formally, the initial current flow into the coil primary when the points close produces a rising magnetic field in the coil and the capacitor both protects the points from arcing damage when they open, and also conducts the back-emf which is necessary to generate the spark . In a normally functioning ignition system the capacitor/coil combination also extends the duration of the high voltage pulse at the output of the secondary winding so that the energy output to the spark plug lasts longer than the initial field collapse pulse, continuing until the circuit’s energy is expended, then the cycle repeats . All that a potato can do is provide a substitute current path for the back-emf, and given that the voltage applied to the spud is similar to that impressed across the spark gap in the plug, then in comparison to the spark gap it will look like a low impedance/resistance path and a spark will be produced at the plug . Spark amplitude and duration may not be up to Formula One specs, but it can get you home , that is, providing you don't have one of those 'point-less' electronic ignition systems . Then you will need to unravel a potato sack and plait it into a tow rope instead . A potato cannot store energy, but it can act as both conductor for the back EMF and as a damping resistor to minimise arcing across the points, which might otherwise prevent an adequate secondary (spark voltage) output from being generated . Cheers Billy 8-{) |
Billy T (70) | ||
| 1394698 | 2015-02-21 10:53:00 | Thanks Billy T. That is the sort of reply that I expected when I was an instructor in my youth! Thinking about it I remember that it was a 1926 Durant-Rugby 4 with a Continental 4 cylinder engine and auto-vac fuel system, wooden wheels, tyres 4.50 x 21. Rear wheel brakes only. It was very reliable and never let me down, apart from the capacitor. It used to boil a lot, but the altitude was 8,000ft above sea level and was not pressurized. The thermometer in the radiator cap was missing and a jet of steam would come over the windscreen. |
mzee (3324) | ||
| 1394699 | 2015-03-01 07:38:00 | But does it need to be a low ESR (Equivalent Spud Resistance) potato? | Agent_24 (57) | ||
| 1394700 | 2015-03-01 18:08:00 | On spuds, it is usually reluctance rather than resistance. | R2x1 (4628) | ||
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