Any Electronics Wizzards out there?

ezdays

ezdays

Out AZ way
Feb 3, 2003
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Arizona
bigbluetrains.com
Yeah, that's the way my MRC power packs work and I love them. I started to build my own until I saw those. Even though I had most of the electronic parts, I couldn't build one that looked and worked that good with that many features for what I paid.

Don
 
Paul Davis

Paul Davis

New Member
Dec 29, 2002
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42
Edmonton, Alberta, Canada
members.shaw.ca
Actually you wouldn't even need to do that. All you'd need to do is take the first 5V (5.6V if you include the drop over a shockley bridge rectifier) to run the electonics making sure that the motor doesn't run if the track voltage is less than 5.6V.

If the power pack can deliver 18V then set the duty cycle to 3V/(18V-5.6V) * 100 = 24%

at 23% duty cycle the motor will always receive 23% of the track voltage less 5.6V. So at 5.6V the motor will receive (5.6V-5.6V)*.24 = 0V. At 12V the motor will receive (12V-5.6V)*.24 = 1.54V At 18V the motor will get (18V-5.6V)*.24 = 2.98V

Using the 12V power pack is only going to allow the motor to run at half speed which may not be what you want. You could fix this by setting the duty cycle to yeild 3V at 12V and then adding feedback to decrease the duty cycle when the motor voltage is 3V so the 3V stays constant from 12V to 18V. The powerpack would control the motor from a throttle setting of 47% to 100% on the 12 V powerpack and 31% to 67% on the 18V powerpack

To get more range on the power pack so you can have finer control you could add a dc-dc converter for the 5V. This would let you start running the motor with a track voltage of about 1.5V while still providing the 5V for the electronics. It would allow you to control the motor from a throttle setting of 13% to 100% on the 12V powerpack and from 9% to 67% on the 18V powerpack
 
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