how to power pf motor on 12v track

[mark n]

Hi all,

I love the 12v era and have a great track layout. I have been trying to find out what size motor fits into the casing so i can buy a 12v one.

I have made some bogies with 12v pick ups but find that 1: the trains run in reverse 2: the motors stop. I think due to higher voltage and 3: the motors run a lot faster than the older 12v ones. to too good when having a few trains running and flying off around corners.

Has anyone converted a 9v  to a 12v and if so what kind of motor did you buy and where. Also i live in Australia so i may find sourcing  parts a little difficult .

 

Thanks Mark

[JopieK]

Of course the motors turn faster as they are meant for 9V, they probably stop because they become too hot and then thermal resistor protection kicks-in. I thing the best way to do it is add some circuitry between the pickups and the motors (I assume you use https://www.bricklink.com/v2/catalog/catalogitem.page?P=bb0053b?). You could use something like this: https://www.google.com/search?client=safari&rls=en&q=12V+to+9v+buck&ie=UTF-8&oe=UTF-8. The only thing is that you need to think how polarity is handled. You could use diodes to decide how the current flows.

Something like this would help to differentiate between +12V and -12V and in a second step you can convert +12V to +9V and -12V to -9V.  

See: https://www.circuitspedia.com/12v-15v-dual-power-supply-circuit-diagram-using-7812-7912/. They use a LM7809 to go from 12V to 9V. Not the most efficient solution but it should do the job. It seems the part is obsolete but it can draw up to 1A.

 

You can't use this circuit 1-on-1 but I hope you get the idea. Get some components and a Lab power supply, experiment with it I would say.

[JaBaCaDaBra]

Correct but a few remarks

C5 and C6 are not correct and should be 0,1µF
Their function is to short unwanted HF signals to ground.
The IC's are more common known as UA7809 and UA7908

[mark n]

Thanks for the response.

is my understanding correct that if i use a buck converter, the motor will run fine then

[dr_spock]

 

12v to 9v buck converter should work. Some buck converters are adjustable so you can fine tune the output voltage. 

[mark n]

Thanks all, this has been doing my head in. The last thing i wanted to do was go battery 

 

[Toastie]

I am confused.

• You have a 12V layout, with a 12V DC power supply feeding the track, correct?
• If so, the 12V DC power supply has a dial that goes from -12V to 0V  to +12 V, correct?
• You have 12V power pick-up from the track feeding a 9V motor, correct?

If that is true, then I do not understand how that should work, as you would need to proportionally convert the 0 to 12V to 0 to 9V. Why don't you use a +/- 9V speed regulator then? The ones for the 9V train era with the big yellow dial sell rather cheaply.

Or do you want to run many original 12V engines on the 12V track and you just want to individually address that problem you have on each "new" train?

Best
Thorsten

 

[LEGO Train 12 Volts]

On 3/31/2020 at 5:14 PM, Toastie said:

I am confused.

• You have a 12V layout, with a 12V DC power supply feeding the track, correct?
• If so, the 12V DC power supply has a dial that goes from -12V to 0V  to +12 V, correct?
• You have 12V power pick-up from the track feeding a 9V motor, correct?

If that is true, then I do not understand how that should work, as you would need to proportionally convert the 0 to 12V to 0 to 9V. Why don't you use a +/- 9V speed regulator then?

Oh yes this is a great question and the solution suggested is the classic Columbus' egg.

Why you need 12V on the track? To feed not only 9V motors but also 12V locomotives or to manage traffic lights and electrified switches? On the contrary a +/- 9V speed regulator is surely the best solution.

In any case for my Emerlad Night I've used a 12v power pick-up and converted the 0 to +/-12V to +/-9V and run this train with old12V train set

 

 

Edited April 2, 2020 by LEGO Train 12 Volts

[Toastie]

Hi Emanuele!

How's life - and more importantly how is the family? I sure hope you are all doing well!!! Cross my fingers and hope and wish the very best!

Phew. Why am I so slow ... I think I am still missing something.

All what you are describing makes perfect sense, but only when the the track is permanently powered with 12V and then lets say a PF receiver does the work of adjusting motor power, right? I mean, a 7809 does really not know what to do with - lets say 6V DC applied to the track as input voltage from the LEGO 12V Transformer/power supply? Wasn't it as with 9V? The speed regulators (12V or 9V doesn't matter) apply 0 - 9/12V to change speed. An onboard 7809 makes only sense when there is > 10V input voltage. Or do you use the 7809 to max out the voltage applied to the track?

Best
Thorsten

[dr_spock]

I think the 7809 will output a lower voltage in relation to the input voltage being below the regulated input voltage range per spec sheet.

Example graph from a different linear voltage regulator model.

[Paperinik77pk]

Wow, this thread is really really interesting!!! After trying my 3D printed wheels with Technic axle on PF motor, it could be great to run the whole thing directly on 12v track!

Emanuele, you did a great converter circuit!!! Pity I've very poor electronics knowledge to fully understand it - but more or less I got the whole idea

I love that Emerald Night on 12v!!!

Edited April 1, 2020 by Paperinik77pk

[LEGO Train 12 Volts]

16 hours ago, dr_spock said:

I think the 7809 will output a lower voltage in relation to the input voltage being below the regulated input voltage range per spec sheet.

It's correct: the 7809 cuts all voltages above 9 by stabilizing them at 9 volts, lower voltages are maintained.

The only thing I have added successively to the circuit is a capacitor that stabilizes any false contacts of the pick up bricks, because otherwise the locomotive interpreted them as reversals (for this I added the green and red LEDs: to read the polarity at glance).
Having said that, the system works and the locomotive behaves exactly like the good dear 7740 set!

 

 

[bricks n bolts]

Or the other possible solution is to change the internal 9v motor to 12v, can get the right motor from here -

https://www.conrad.com/p/miniature-brushed-motor-motraxx-x-train-263-h0-6440-rpm-229021

have done this myself but in the end I just swapped most my 12v motors to 9v so I could just adjust the input power.

[Toastie]

4 hours ago, LEGO Train 12 Volts said:

It's correct: the 7809 cuts all voltages above 9 by stabilizing them at 9 volts, lower voltages are maintained.

 

21 hours ago, dr_spock said:

I think the 7809 will output a lower voltage in relation to the input voltage being below the regulated input voltage range per spec sheet.

Ahhhaaaa - thanks guys! You are ingenious!

So what about a let say just one 3 Ohm/5 W resistor in series to the motor?

• No resistor: Let's say the 9 V motor draws 1 A (that is just for simplicity) at 12 V (=> full speed) with some average load - and everything goes nuts.
• With 3 Ohm resistor: The voltage drop across the resistor would on the URI-order of 3V isn't it? The behavior would be a little off, because when the motor has more load, the voltage drop increases of course. However: All that circuity vs 1 resistor.
• Are you guys sure that the 7809 is actually regulating below its nominal input voltage? Or is there some current dependent behavior on the output (as with an e.g. 3 Ohm resistor?)

I am a chemist, and I just work here so I don't know much about electronics.

[LEGO Train 12 Volts]

12 hours ago, Toastie said:

So what about a let say just one 3 Ohm/5 W resistor in series to the motor?

I am a chemist, and I just work here so I don't know much about electronics. 

Ohhh right ...let me start by saying that I have a degree in economics and electronics is just a self-taught hobby, so please go easy on me

The solution of the resistor has been also my first choice as you can see...

...but I don't know if the resistance was correctly sized, I don't know if the voltage lowering behavior underwent variations based on the other trains already running on the circuit or the weight of the whole EN train, but I can certainly say that the XL PF Motor released a strong burning smell after not even 60 seconds of use.

If I have time I will try to post a video of how the tester behaves instead with the new solution (using the 7809) that works fine.

Let me say that my theoretical approach to electronics is not very orthodox but experimentation on the field saves me...

Edited April 2, 2020 by LEGO Train 12 Volts

[Thai bricks]

As long as you don't try to run the 9V loco in the same circuit as a 12V loco you should be good. At 9V it will already fly out of every corner, so you would not want to power it up further. That assumes no young children run it...

[Toastie]

1 hour ago, LEGO Train 12 Volts said:

but I can certainly say that the XL PF Motor released a strong burning smell after not even 60 seconds of use.

Was it the XL motor or that poor 1/4 W resistor? When the XL motor tries to push the EN over the track, it will draw some serious current, wouldn't it? Philo's page says the XL motor draws 1.8 A at 9V when stalled - and about 0.1 A at 9V freely running. As I am color-blind, I can't really get the resistance from the rings in your picture; it sure is 5% tolerance and the third ring is black. Let's assume the first two are red/red = 22 Ohm? And then we assume 0.3 A current going through the XL/resistor line. W=I^2 R = 2 W. That should give some nice smell - but from the resistor, right? Also the voltage drop at 12 V would be more than 6 V ???

Hey, I have learned my electronics wisdom from trial and error as well! I sure know the smell of burnt resistors, transistors ... virtually from everything, the electronic industry is providing for dummies like me!   

Where is @dr_spock when we need him?

All the best!
Thorsten

[LEGO Train 12 Volts]

41 minutes ago, Toastie said:

Let's assume the first two are red/red = 22 Ohm?

22 Ohm 1/4W correct: red, red, black and gold rings ...even if I'm not color-blind the colors of the resistances are difficult to identify (primary colors excluded) ...so has been the size of the resistance (1/4 W) the problem?

[Toastie]

57 minutes ago, LEGO Train 12 Volts said:

so has been the size of the resistance (1/4 W) the problem

Regarding the colors: I cheated (asked my daughter, they are used to that - when I am asking random people for a color, they at first have "this" look in their face)

Regarding the resistance: That are the 22 Ohms causing the voltage drop. I'd try something around 3.3 Ohms initially (a value of the "E12" Series). The thing though is the wattage, the resistor needs to dissipate as heat. The resistor you used seems to be of the 1/4 W series. I'd go for something like these: https://cdn-reichelt.de/documents/datenblatt/B400/5WAXIAL_9WAXIAL_11WAXIAL_17WAXIAL%23YAG.pdf The can dissipate 5W easily.

If that does not work (still too much voltage across the XL even at medium load), I'd increase the value to 10 Ohms or so.

Thing is: Just one part, clocking in at about €0.50 ...

But there must be somebody around here who for sure knows much better than we two 7/8 blinds (electronically-wise).

Have a nice day!

Thorsten     

Edited April 2, 2020 by Toastie

[LEGO Train 12 Volts]

In the meantime I have prepared some new material to support my solution (this is the picture of the final circuit):

you can see the unit 7809 with the heat sink and the condenser, put between the green LED and the relay, to stabilize any false contacts.

Here you can see a video which is worth more than many words:

 

Greetings

[dr_spock]

NIce, that works well. 

 

On 4/2/2020 at 7:02 AM, Toastie said:

Was it the XL motor or that poor 1/4 W resistor? When the XL motor tries to push the EN over the track, it will draw some serious current, wouldn't it? Philo's page says the XL motor draws 1.8 A at 9V when stalled - and about 0.1 A at 9V freely running. As I am color-blind, I can't really get the resistance from the rings in your picture; it sure is 5% tolerance and the third ring is black. Let's assume the first two are red/red = 22 Ohm? And then we assume 0.3 A current going through the XL/resistor line. W=I^2 R = 2 W. That should give some nice smell - but from the resistor, right? Also the voltage drop at 12 V would be more than 6 V ???

Hey, I have learned my electronics wisdom from trial and error as well! I sure know the smell of burnt resistors, transistors ... virtually from everything, the electronic industry is providing for dummies like me!   

Where is @dr_spock when we need him?

All the best!
Thorsten

I do trial by fire too.  Larger wattage resistor is your friend like dynamic brakes on a diesel electric locomotive. 

I guess size does matter. 

[LEGO Train 12 Volts]

3 hours ago, dr_spock said:

I guess size does matter. 

Nobody ever said otherwise 

[Toastie]

Folks folks folks!