04-10-2010, 10:34 PM
I know the controlers you are describing (I actually had a vic20 controlling my layout back in the early 80's- it was the predesessor to the c64- 3 1/2 whole k of ram!!)
most of the overheating and noisyness was due to the low switching frequencies then in use(often mains frequency lock ie 50 or 60 hz), these days they tend to run into the 10's of khz
`pulse power' controllers were even worse- they when on `pulse power' were basically going from fullwave rectification to 1/2 wave rectification for the dc - which meant the pulses were now 1/2 mains frequency (i.e 25 or 30 hz)
what I am thinking of doing is basically the same as the `motor driving circuit' rom a dcc controller, so the pwm concept is well proven (how many dcc locos are out there now???) ;-)
the difference is the peak voltage would be much higher- but for microseconds only, and the average voltage seen by the motor remains at the usual 0-12v as seen by a normal dc motor by limiting to duty cycle from 0% to say 10% being the 0-12v range.
for safetys sake(in case the switching circuit failed for some reason and applied a 100% duty cycle to the rails), a simple zener based crowbar circuit would save the loco engine, lights etc from letting the magic smoke out...
(edit to add- note that pulse power mode on those throttles is not pwm- totally different animal altogether)
most of the overheating and noisyness was due to the low switching frequencies then in use(often mains frequency lock ie 50 or 60 hz), these days they tend to run into the 10's of khz
`pulse power' controllers were even worse- they when on `pulse power' were basically going from fullwave rectification to 1/2 wave rectification for the dc - which meant the pulses were now 1/2 mains frequency (i.e 25 or 30 hz)
what I am thinking of doing is basically the same as the `motor driving circuit' rom a dcc controller, so the pwm concept is well proven (how many dcc locos are out there now???) ;-)
the difference is the peak voltage would be much higher- but for microseconds only, and the average voltage seen by the motor remains at the usual 0-12v as seen by a normal dc motor by limiting to duty cycle from 0% to say 10% being the 0-12v range.
for safetys sake(in case the switching circuit failed for some reason and applied a 100% duty cycle to the rails), a simple zener based crowbar circuit would save the loco engine, lights etc from letting the magic smoke out...
(edit to add- note that pulse power mode on those throttles is not pwm- totally different animal altogether)
poopsie chicken tush