Which direction to put diodes for choke and brake buffer?

[Mark 42]

I'm working on making a simple diode brake buffer and choke.

I'm a little unsure about which direction the diodes would go into the circuit.

I'll be using it on a standard positive polarity commercial track (Pacific Slot Car Raceway)

In the attached schematic, are the choke & brake buffer diodes in the correct direction?

I know I can always reverse them if it doesn't work, but I'd like to look a little
less foolish when I try to use this the first time (I'm on a small budget, otherwise
I'd buy an adjustable controller... but I like doing experiments like this anyways)

Click the image for a larger version

[Mark 42]

BTW, in the real circuit I'll be able to adjust the number of diodes in each path.
I just wanted to keep the schematic simple for the purpose of the discussion.

[MentalKase]

Send a PM to Slapshot, its a no brainer for him.

[Mark 42]

Will do.
If I have it backwards, it will just have no brakes when I activate the brake control circuit, and won't go anywhere if the choke diodes are backward.

For tonight's race, I built a simple box with 4 diodes & 4 toggle switches. It has two wires coming out of it (input & output) and I'll just clip it in between the controller and the track. That way I can try it as a brake control and as a choke to gather data on how it works to determine what I want to do when I build a combined (dual circuit) box.

[Mark 42]

Here is the circuit with the switches in it - but I'll probably end up building
something with two rotary switches to accomplish the same thing. I need
to build 3 more of them, and add to the one I built if I want to use it for
both choke and brake adjustment.

Click the image for a larger version

[Slapshot]

I haven't worked a diode brake for a while but I believe your diagram is correct. Silver bar on diode goes to track red brake terminal other end goes to controller brake button. You can check with Jim and look at the Ruddock controller version to verify.

For choke you will need around 25-75 amp diodes depending on what you plan to run.
I have found wire wound or electronic limiter or 3rd eyes fet electronic more effective than diode chokes due to heat.

Here a couple artical and diagrams that might help.
http://www.abslotsport.com/page22.html

slot racing Mejlin has some goo pictures:
http://www.slotracingmerlijn.be/techniek/index.html




Raymond

[Mark 42]

Thanks. I think I have the brake correct (from the pics you posted), and I probably have the choke correct.
I'll have to try to get to the track early and tinker a bit - that's probably the quickest and surest way anyways.

[Slapshot]

The AB slotsport site has several scratch controller building articals that aslo has a electronic choke box.

Raymond

[Dan Ruddock]

You can also reverse parallel two diodes. This will make it work no matter what. This is what I do on my dual polarity DR-40 controllers with the brake switch. Dan

[Mark 42]

Make it idiot proof? What are you implying...

That's a great idea. Diodes are pretty cheap, even in 6 Amp they are not terribly expensive.

[Mark 42]

This turned out to be correct - using one set of diodes, I had to switch the input & output
wire to switch it from a brake control to a choke (switched which wire went to the track & controller)

I bought an electronic controller last night... but my wife will be using it, so I'll keep
working on my control boxes for me and my son.

Here is the circuit with the switches in it - but I'll probably end up building
something with two rotary switches to accomplish the same thing. I need
to build 3 more of them, and add to the one I built if I want to use it for
both choke and brake adjustment.

Click the image for a larger version

[Mark 42]

Here is the latest version (Schematic)
I have added the blue power indicator LED (ala 3rd eye), but not the FTB relay,
or the green throttle LED and white Full Throttle LED nor the red Brake indicator LED.
I don't know if the Red LED will work, and I don't know if the FTB relay will end up in
a feedback loop and stay engaged until I go all the way back to zero throttle or brake
trigger position.

[Mark 42]

The resistors for the LEDs to use 12V aren't shown - I'm starting with 470Ω
The Red/Black/White dots are where the clips from the controller and to the track attach.
I should add another one for the FTB trigger wire, but I haven't added any of that circuit yet
(I don't want to open up the controller right now - need to get the cars ready for the next
races - 2 womp cars for Wednesday and 3 Nascars for Friday)

I hooked up the red and white alligator clips to 12V (track connections), and the blue LED is BRIGHT!
I may need to use a higher value resistor for the LEDs (depending on track voltage at PSCR).
I have some spare Blue LEDs , so if I burn it up, I can fix it.

[Mark 42]

Also, I found a link that answered my initial question:

http://www.allaboutcircuits.com/vol_3/chpt_3/1.html