Power Thomas and his friend trains with a 9 volt using a buck PWM

[Dan_in_MN]

Hello

I joined this forum to get help designing a circuit to power my daughters trains with a 9v battery but reduce the current to around 1.5-5 volts.  They normally run on 1.5 volts.  The reasons why I want to do this is.  1.  Because I can....    2.  I think the battery will last longer. (I may be wrong here.) 3.  I'd like to have a variable output to have either predetermined voltages, or using a pot so the engines have 3 or more speeds.

I have a YouTube channel.

 You can see why I want to do this on there.  My daughter, Lilyana, is totally into these engines.  Having this feature would win me Daddy of the Year!  (not that I don't have that title already.  )

I'm thinking about using this chip: http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=163044417&uq=635548853418180909&CSRT=14532559758389010054

I don't think those little motors take more than 500 mA.

That's about where I am at the moment. 

I know a bit about electronics.  I've wired up simple 555 blinking light circuits.  I can solder fairly well.

I'd like some input, thoughts on this project.

Thanks for reading and watching my poor quality off of the cuff video!

Dan

[Skimask]

Short answer...9v battery won't last for squat.
9v battery internal resistance way too high to push any significant amperage out for any length of time.
Buck regulating 9v down to X, now you get to add in any inefficiencies of the regulator in addition to the internal resistance of the battery itself, causing it to die off just that much quicker.
About the only thing that might be worth it would be to switch to a single cell LiPo.  Would get around double the capacity (compared to most alkaline batts) and a bit more than double the voltage (3.7v average vs. 1.5v average).
But now you're talking about protection circuits, specialized chargers, etc.etc.etc.

[Dan_in_MN]

Thanks for the reply!  See, I knew who to ask!  I'll find some other project to use on my "spare" time!  LoL!

[Zero999]

I joined this forum to get help designing a circuit to power my daughters trains with a 9v battery but reduce the current to around 1.5-5 volts.

You've got that wrong. I think you meant you want to reduce the voltage to 1.5V to 6V.

They normally run on 1.5 volts.  The reasons why I want to do this is.  1.  Because I can....    2.  I think the battery will last longer. (I may be wrong here.) 3.  I'd like to have a variable output to have either predetermined voltages, or using a pot so the engines have 3 or more speeds.

One of the easiest and efficient ways to do this is to use a 6V battery and PWM (this can be done with a 555 timer) to vary the speed.

[dannyf]

A 9v battery wouldn't last very long, especially at 500ma.

You can build a simple converter from chips like LM2596, or to buy one off ebay for a couple dollars. You should explore the possibility of power the motors off a beefier battery (like for a home alarm system or motor cycles) or off a wall wart - they sell for a song and typically good from 1a - 2a.

[rob77]

what kind of batteries are powering those little engines ?  if a 9V battery fit's then , it would have enough space to fit 4xAAA and a PWM controller with 555 as Hero999 suggested.

the current is turning the motors, not the voltage. the voltage is only determining how much current you can push through by PWM you can control the average current through the motor and therefore the speed. furthermore the PWM controller made of a NE555 will be in the $3-4 range including the 4xAAA battery holder and the batteries itself

[Seekonk]

Motors when they are operated slowly like to be pulsed for smooooooooth low end torque.  A 555 is a perfect project for this.  There must be hundreds on the internet if you search 555 train control.