K-Line reverse unit max current?

Being un heatshinked - less than 1A continuous.

Again, what happens is, those BJT transistors unheatsinked heat up, and then they are higher resistance, so they heat more, and then they increase resistance- until they smoke for that direction.

Put another way, no way in heck could I in good conscience tell you running 4 motors on that, for anything other than a 10 second test bench was a "good" idea.

You want a Williams 6A, or one of the K-line ones that used relays, or a Dallee unit.

Holy Cow!  If you like the smell of burning electronics, connect six motors to that one!   I agree with Vernon, many times running one or two motors those end up with smoked driver transistors.  They are strictly a low power reverse board, and certainly not suitable for what you're envisioning!

I'd be looking for something like the QSI relay based reverse board,  They have 10A relays and 6A diodes, it would be a lot more likely to survive the experiment!

Well, so much for this being an easy project...

However, forewarned is forearmed. I'll see what reverse units I can find.

Thanks for the suggestions.

You could also hook the motors in series-parallel.

Each A or B unit has the motors in series and all three units are in parallel with each other.

The reverse unit sends out twice the voltage and "sees" the current for three motors.

Question for the experts: Can the power transistors be upgraded to ones that can handle more current? Could they be mounted off-board and with decent heat sinks?

@Arthur P. Bloom posted:

Question for the experts: Can the power transistors be upgraded to ones that can handle more current? Could they be mounted off-board and with decent heat sinks?

Not worth the trouble, and even with a heatsink, I seriously doubt it would do six motors!

@Jark K. Remol posted:

However, forewarned is forearmed. I'll see what reverse units I can find.

Drop me an email to my profile email address, I can fix you up with a QSI reverse board that will do the trick with no mods.

While we're at it, does anyone actually have documentation on the K-Line circuit boards or motors, etc.? Specs or parts lists? Or is that just wishful thinking?

Wishful thinking.

At long last, finally got the ABA set running together! Managed to take what could've been a simple project and made it overly complicated. Sorta.

Added the power trucks from another engine and swapped the silver covers from the original dummy trucks. Decided I wanted to not only connect the motor power from the E-unit to all the trucks, but also wanted to connect all the track power connections too. Ordered some 4-pin connectors and waited for them to arrive.

Bought a nice E-unit from Gunrunner John. Built a platform for it out of leftover Erector Set parts. Ground off the enamel where a heat sink would attach.

Then the fun began. The trucks had red & black wires for AC power from the track, and yellow & blue for DC power to the motors. The 4-pin couplers had red, blue, green and black wires. The E-unit had orange, brown, yellow and blue. To complicate matters, the yellow motors wire from the 'front' truck needed to be connected to the blue wire from the 'rear' and vice versa. Included a couple of extra wires for lighting later. Also, only male wire couplers at the front of an engine, and female at the back, so they can only be connected together where they will travel in the right direction with each other.

So, made a cheat sheet to keep all the connections straight. Figured consistency was my friend.

Ran into problems when I tested them. Set up an oval test track on my living room floor. I could get the leading A unit (with the E-unit) to run by itself. I could get the A-A set to run fine. But if I put the leading A unit and the B unit together, I'd get a short. Checked my cheat sheet and my wires, and all looked correct. Did find a couple of loose connections that I re-soldered, but that didn't solve the short.

Made a test consist with a gondola between the leading A and the B. Used some of the extra connectors so I could connect them individually. The DC power wires worked fine. But once I'd connect either of the AC power wires, I'd get a short. Had to wait a work week to try again. Used a multimeter to check the connections from the wire couplers to the center rails pick up and to the wheels. Discovered that, while the A units were wired with red going to the center rail, the B unit had black going to the center. One more round of re-wiring the B unit.

The results:

Thanks for the advice from all. Once I get power going to my main layout, I'll see just how many passenger cars this thing can pull!