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Thread: Review of Bakatronics PWM throttle

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    Default Review of Bakatronics PWM throttle

    a 003.jpgIMG_6793.JPGBakatronics LLC sells this DC Pulse Width Modulated Speed Controller p/n FK804 for $7.95. It took me less than 45 minutes to assemble. The directions are meant for someone that has some electronic knowledge but if you pay close attention to the component shape and markings and be sure to install them in the exact same direction shown on the circuit board a novice will have no trouble. If you can attach a feed wire to N scale track, believe me, you can built this kit. I would recomend using .020 solder from Radio Shack because of it's lower melting point. There is an enclosure and a knob that can be purchased seperately. An additional DPDT switch will be required if you want to back your train up. You will have to supply a 12 volt DC power supply. A wall transformer will work as long as it's 12 Volt DC and rated at about an amp. Any N scale engine should draw less than 1/2 amp so anything over that should do for one engine. This circuit has a maximum output of 1.5 amps so concievably you could have a 3 unit lash up if you had that available from your power pack. I powered mine with a 2 amp regulated supply. Boy, does this run smooth. PWM (pulse width modulation) is the way to go! The Kado F3 crept along at about 3 scale miles per hour. Extremely impressive! the transistion to full throttle was very smooth. This would be a great throttle for switching opperations. The ony thing that I personally did not like was that the speed control would reach 60 MPH with about a quarter turn of the knob. Not a big deal, but I think I can stretch this out with a variable resistor of a smaller value and another fixed resistor. I'll keep you informed of my modification. Maybe this would react differently on an HO application. I give this 2 Thumbs UP for $7.95.

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    I use this circuit in my streetcar layouts. It is easy to build into a layout and disguise as a part of the scenery. Or incorporate it into a control panel. I have even used a nine volt transistor battery with it to run my streetcars.


    I have also built it into a Tomix Streetcar controller. It was designed to operate with four double A batteries and power their Tetsudo collection.
    01 Side by Side Comparison.jpg05 Circuitboard In The Battery Compartment.JPG10 All The Internal Mods.jpg

    The primary modification I make is to attach the variable resistor with a three wire cable to make mounting easier. I also attach a DPDT switched wired for reversing. Additionally I connect a Bipolar LED with resistor to the output of the switch to Indicate direction.

    Another good addition is to put a rectifier on the input terminals to fix any polarity issues or to use it with AC input.
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    Those little controlers are way cool! Never seen anything like it. How prototypic. Bridge rectifier is an excellant idea and should be part of the circuit, I feel. Do you also feel that the speed range on the throttle is too small? (ie: quarter turn)

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    Very nice, and cheap too!

    It would be nice for a yard switcher to tweak that so the knob itself handles direction. Centered is stop, and left or right of center is forward/backward. I might have to work that out.

    I'm having trouble with my cheap Bachmann DC throttle in that I want to use the speed knob in "switcher" mode but it's not. I've had a few reportable incidents because of that.
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    TD,
    Modifying it to work that way will be difficult. The device is a pulse wave generator. The variable resistor controls the length pulse duration. The voltage is constant. The DPDT switch that I use for direction has a center off position. Using one control for speed and anther for direction is more prototypical.

    Mike,
    Here is where to buy the mini control stand.
    http://www.1999.co.jp/eng/10072782
    http://www.1999.co.jp/eng/10072781

    The speed control is fine for me. On the one built into my layout I can use the full 270° of rotation. But that is for thirty year old Bachmann streetcars, the majority of the time I only use the first half. I also have no problem controlling locos that hit their top speed at three volts.
    Attachment 8698

    The unit built into the control stand has 180° rotation. I had to carve out 90° more than the original. The last third is not used as streetcar are not usually a high speed vehicle.
    Attachment 8697

    You might want to use one modified throttle for the yard. Or put a switch to bypass your extra resistor giving you a yard/run speeds.
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    Refer back to my opening post #1. I did change the speed control pot. It came with a 500K ohm and I substituted a 200K ohm. You will have to add 300K ohm, or there abouts, 1/4 watt resistor to the circuit to retain the original value of total resistance. This is how I did it. Hold the pot with the control shaft pointing up and the 3 electrical pins pointing toward you. Take the pin on the right and bend it up 90 degrees. Solder the 2 pins into the circuit board and then place the fixed resistor between this bent up pin and the remaining hole in the board. Now you will find that the speed control knob will need to be rotated twice as far to reach top speed. If you are interested in switching only, and would want a top speed of about 25 MPH, substitute a 100K ohm pot and a 390K resistor. This will really spread out your throttle. Don't be concerned about the buzzing coming from your motor, it's the pulse width frequency that's making it happen. There has been a discussion on this subject here in the past.

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    If I may inquire, where did you find the 2amp supply / transformer. I'm sold and ready to build one myself. I have a troller auotpulse and I have been told that these little PWM throttles make my current throttle look herky, jerkey, so they must be darn good.

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    I got this particulat transformer at an electronics salvage company here in Tacoma. I have never seen one this size before. Why don't you rob the transformer from your Troller? A 12 volt Radio Shack transformer will work also.

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    I found an old dual cab tyco transformer with ALA MRC throttle pack knobs I got on ebay for under $8.00 I plan to gut everything but the power transformer and terminal board. I intend make a pwm version of the old unit with 2 of the throttle units. I all ready bought a pair of linear taper 200k ohm pots and some 300k ohm .25 watt resistors, just have to wait for everything to arrive, I plan to take a lot of photos and get a HOW TO for uploading them right so it will make a nice step by step for anyone who might be intersted to puruse at their liesure.
    I'll keep evryone posted.

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    If you want to make one (or both) of these a "walk around" throttle Doug, you can mount everything in the main chasis box with a DPDT relay for reversing the direction. Then mount the pot and a switch in a small hand held box to control it.

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    yeah mike I gave that some thought, but I just don't have the need for the walk around right now, allthough I may build in a provision for a future one as an option. Idealy I would like to design a case /box for the main power transformer and thrack connections, with a sort of cradle to hold a couple smaller handheld boxes (each containing a direction switch and throttle knob), the a removable connector on the front face of the main cabnet, and a connector for "jump" cables for remote conections. sort of like with a DCC system. the main cabnet would be like the booster box, but with a built in pair of mini pannels, and the have the ability to "daisy chain" more at convienient loctaions along the lay out. possibilities are limited only buy the wallet and imagination.

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    Check out the old model railroad electronics books by Peter Thorne or Paul Mallery. They might have ideas on how to do your remote controls cheaply and easily.
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    Icon10 I decided to build two

    Micheal,

    https://www.nscale.net/forums/attachm...chmentid=10912

    thanks for all the help, I used your circuit protection with the low side of a GE1157 automotive builb wired in serries on one of the output wires, now with any train running I can lay a coin on the track "creating a dead short" and all that happens is the train stops and the lights element begines to glow...GENIOUS! Thanks, combine that with your 200k pot/300k resistor mod and at top speed my locos are running close to a prototypical 70-80 scale mph...about 45 (+ -) at half throttle, with signal locos, double lashups about 2-3 throttle for 45. not bad considering I spent under $35.00 to build two handheld throttles with there own power supply. NICE!
    Merry Christmas and a Happy New Year to all !
    Last edited by oval4ever; 23rd Dec 2010 at 08:06 PM.

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    So, where are the pictures?

    And a Happy Bunch O' Holidays To All!
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    ok photo's are added to my last posting, I went another way, and just built two hand-held throttles in radio shack boxes, the orrigional plan to build these into the tyco twin pack I brought proved to be impractical at best, if no foolish, (too crowed in there for safty), I also gutted the packs transformer and rectifiers and mounted them under my bench work and extened the power leads with 16awg wire to the terminal strips you see for convienence also this also shows the light bulb cicuit protection, Micheal turned me onto .basicly it's the same as ChicagoNW's throttle but in a simple everyday projectbox. Of corse you can nad to it with polarity indicators useing the bi-polar diode and end other options to build it to your needs and taste....enjoy. eventualyl I plan to build one more for a seperate yard control that the troller 1 amp you see in the photos is currently puling duty for.
    Last edited by oval4ever; 23rd Dec 2010 at 08:15 PM. Reason: oppps

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    well I have an update, ater trying the handheld with mikes 200k pot 300k resistor mod I went beack to stock configuration. the locos just seemed to oppeating in a "chocked to death" mode with the reduced varriable resistance, not sure why. I also foun something cool that i will get up in a pic ASAP. I built a total of 3 throttles, 1 for each main line, and a 3rd for my internal yard. for a connector and a coiled cord I found something cheep and very durable. A cobra/uniden type CB radio microphone extention cord. has a male 4 pin plug at one end and fe-male at the other. I just deslider the end of my choice and attached it to the end of the straight cord I orrigionaly ha connected to the throttle then wired in the mic cord. the extention cords are very cheep, not sure why but.....cheeper than a replace mic cord with just one end....I paid only $12.80 for all three cords shipped, the seller is an ebay store owner so I have included a link to his auction .
    http://cgi.ebay.com/ws/eBayISAPI.dll...K%3AMEWNX%3AIT

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    well I have an update, ater trying the handheld with mikes 200k pot 300k resistor mod I went beack to stock configuration. the locos just seemed to oppeating in a "chocked to death" mode with the reduced varriable resistance, not sure why. I also foun something cool that i will get up in a pic ASAP. I built a total of 3 throttles, 1 for each main line, and a 3rd for my internal yard. for a connector and a coiled cord I found something cheep and very durable. A cobra/uniden type CB radio microphone extention cord. has a male 4 pin plug at one end and fe-male at the other. I just deslider the end of my choice and attached it to the end of the straight cord I orrigionaly ha connected to the throttle then wired in the mic cord. the extention cords are very cheep, not sure why but.....cheeper than a replace mic cord with just one end....I paid only $12.80 for all three cords shipped, the seller is an ebay store owner so I have included a link to his auction .
    http://cgi.ebay.com/ws/eBayISAPI.dll...K%3AMEWNX%3AIT

    for me the extention cord was perfect as i wanted my connection to be "in-line" if you prefer to do something with a pannel or facia mount you can get a chassis mounted mic jack, that has a square flange and mounts with 4 screws, and just save the male end of the cord for something else, or re-sell it.

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    Default bakatronics pwm kit

    just built the bakatronics pwm kit did anyone notice the transistor getting really hot or is it normal

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    If you have double checked your assembly and the trains run as expected Mike, I'd say not to worry. They do get hot but different people will have different opinions of how hot is too hot. I do not have any throttles in my possesion at this time to check but maybe Doug will have some answer for us.

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    It does happen. The electronics should not be hot enough to melt plastic.

    If you are worried about the heat, here are a couple of thing you can do. lessen the load on the throttle (Don't double or triple head your trains). Or you can attach a heat sink to the tab. The hole is for a screw or bolt to attach the heat sink. Heat sinks can be as simple as a sheet of 1/8 inch thick aluminum or a complex casting with many fins. Make sure the case you put the controller into has some ventilation holes into it. I have a MRC that would shut down because it would overheat. I cut some ventilation slots into the sides and the shutdowns stopped.

    If heat is a constant problem Bakatronics has a higher amperage version of their PVM throttle.
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