Here's my initial report on the Blu Shark project, conversion of a 1990s 3-rail AC Weaver/Samhongsa Sharknose diesel to 3-rail Blunami control and sound.
The dual can motors, when wired in parallel, had a stall current exceeding the rating of my power supply, 10A. Wired in series, the stall current was 4A at 18V, at the Blunami 4408 board's specified current limit.
With the motors wired in series, connected directly to the track pickups, and run with 18VDC power on the tracks, the Weaver Shark achieved a speed that's respectable for a freight hauler that ran mostly on secondary lines, probably around 45 smph, hauling 15 average freight cars (scale). Observed current reached a maximum of approximately 1A when hauling that train up a 3% grade. This corresponds to a load resistance of approximately 18 Ohms.
My layout is powered by 3 Lionel Powerhouse 180 "bricks", whose nominal AC output voltage is 18.9V without load. Loaded track voltage stays near 18V throughout the dual-track mainline. When the Powerhouse feeds a full-wave bridge rectifier and a 20 Ohm resistive load, a filter capacitor of approximately 1000µF is needed across the rectifier input to keep the ripple minimum voltage above 18VDC.
The Shark was experimentally wired with the bridge AC terminals attached to the (replaced) pickup rollers and chassis common, the aforementioned capacitor across the bridge DC leads, and the latter connected to the Blunami board DC input terminals. The Blunami motor output was connected to the two can motors in series. Its sound output was connected to the Shark's original fuel tank speaker (it was delivered with a QSI electronic horn). The Blunami board DC input voltage at idle was 24.5V, with virtually no ripple, below its 26V rating. Under load, the DC voltage does drop somewhat and there's some 120 Hz ripple, but the peak ripple voltage does not exceed 24.5 V.
In this temporary configuration, the Blunami control board and Blurail software worked flawlessly. Operation was smooth and minimal loss of speed occurred when pulling 15 cars up the 3% grade at roughly 40 smph. Some tweaking of the throttle response characteristic appears necessary, but that will await further refinement of the conversion. No 120Hz hum was heard out of the loco's speaker. Whether running at speed or creeping along, the Shark pulled smoothly.
Next up will be permanently mounting the components and adding a DC>DC buck converter regulator. I've done some work on the test bench with that, but have yet to install it in the Shark and actually run a train. The bench tests were encouraging. Once the fundamental motor control is optimized, lights and couplers can be addressed. I'll also do a complete write-up of the project, including extensive measured data for motors and rectifier, scope waveform photos, and so forth.
My tentative conclusion is that the Blunami control board is a very practical alternative to DCS and TMCC for dual can motored diesels in general freight or yard service. The tradeoff is between absolute speed and meeting the Soundtraxx 4A stall current limit, so it may not be appropriate for mainline varnish and hotshot freights. And there's no way to meet the stall current limit in steamers with large can motors. Once the Blu Shark is finished, an Atlas switcher and possibly a Weaver E8 may be up next on the workbench.
