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#7
9th May 2021, 07:47 AM
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Makes sense to me Ray, as that's how the control works on our older train fleet with DC traction motors:
- Shunt (a high amp starting current to get the motor past the friction point (starting current) - Series (armatures powered in series for maximum torque during low-medium speed acceleration - Parallel (armatures switched to parallel for med-high speed acceleration) - Weak Fields (now this is an interesting one - DC motors use permanent magnets. As more power is applied through the armatures, they create a stray magnetic field which acts as a resistance to the propelling field between the armature and permanent magnets. This gives the motor a maximum rpm as the stray magnetic field and the field created by the armature and permanent magnet balance out. A tricky bit of magnetic manipulation called field weakening (not sure if it's electro magnetic, or some sort of current fiddle) can then be applied which artificially reduces the strength of the stray magnetic field to allow the motor to spin even faster).
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Cheers Marty  ____________________ Current: 2001 Audi S8 - Brilliant Black with Black interior, C5 RS6 rims (whenever I actually put them on...), Solar Sunroof, Tinted side and rear glass, RNS-D, Grom, Bose, clunky old phone in arm rest! 2002 Audi S8 - Project Replacement head coming arrived  thanks to MJSilver with Black interior. All features as the '01, with the 'S' mode auto shifter. Dodgey rear tint (need to find a way to get rid of that). Family: 2009 Volvo XC90 V8 R Design - has a louder more obnoxious exhaust than the S8, sounds great! Love this thing - Q7 was double the price, and certainly not double the car! Sold: 1997 Audi A4 - Hamilton's Club Sport, Achat Grey (will miss the old girl) 
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