Hey all. I've dug into threads looking for this without success. I'm wondering what the current limit thresholds are for what I'm going to call an 'original' DCC++ system? What I mean by that is an Arduino Uno R3 with an Arduino R3 motor shield. The software I have installed is from the Gregg's original github link at: https://github.com/DccPlusPlus/BaseStation I have not yet tested this for myself, but a coworker with an identical setup (I built and programmed it for him) has found the mainline power tripping at approximately 3/4 amp. This value is not the track current but in the power input leads of the motor shield which should be close to the output current (nothing is 100% effiient, but the currents should be close). His and my power supply have a 2A capability. Knowing this is an open source project I don't doubt that others have modified the s'ware to get different capabilities. I wonder if the original source code was set for a lower trip level? I've briefly reviewed the project code and don't find anything that elaborates on current settings. Any and all information is appreciated Lyle Dowell
Hi, I believe the standard setup should cut-out at 800mA. It does depend on the value of the load resistors on the motor shield, they should be 0.15 ohms but some clones seem to have other values, and the setting of CURRENT_SAMPLE_MAX which is set to 300 by default (equating to cut out of 800mA). these links may help: http://wiki.rocrail.net/doku.php?id=dccpp:dccpp-en (- scroll to the bottom to the section 'Max. Current') http://www.trainboard.com/highball/index.php?threads/dcc-hardware-motor-shields.90314/#post-960418 https://www.arduino.cc/en/uploads/Main/arduino_MotorShield_Rev3-schematic.pdf EDIT: I first read your post meaning that your current was cutting out at 3 - 4 Amps(!) but now realise you mean about 0.75 amps, which would be correct for the standard setup. The links I gave should help you to adjust the setting to suit your needs... Jim
Jim, Thanks for the response. Obviously your information matches the performance. I've briefly looked at the code and see the value to adapt (current_sample_max). I don't see a setting for the main vs the program track. Do both outputs share the same setting? This would seem to be counter-intuitive to me if true. A program track output is deliberately current limited to a smaller value than the main's value to not have full main line current available for an untested locomotive, that is a new install. Again, I've only reviewed the code a bit. Perhaps the program track has its own setting I've overlooked. ========= edited to add: I had contacted Gregg a bit ago about a different subject, but his answer for that question gives the answer: "In terms of the code, it would indeed be possible to make the changes you requested but the modifications would be non-trivial. The power requirements are not the issue since DCC++ treats both channels the same in terms of current output, but the register structure is slightly different and would need to be augmented to switch back and forth between main-line and programming-track logic. Also, there is logic related to clock-cycles for the different channels that would need to be rewritten." -- Gregg I wonder if the program track track's limit point due to programming differences might be a proportion of the mainline's value. I may be able to test that in the next couple of days. I'm hoping the program track is energy limited relative to the mainline track. Gregg's response doesn't say that, but it does infer that there are differences Lyle
In some cases the programming track needs to have more "power" because some decoders.. especially sound decoders...need a bit more power in order to program them. This was true with my QSI decoders as in my regular 5amp system couldn't cut it I had to use a friends 8amp system and his programming track had a separate booster attached to it.
I understand the need for a 'bit' more current on the program track for sound decoders. What I'm a little (not a lot) concerned about is having 1 to 2 amps on the program track. With most locomotives being decoder ready and hard wiring becoming less necessary, wiring issues are less likely and current limiting on a program track as a safety issue isn't much of a concern. However, I do a lot of decoder installs for customers who bring in hard wire situations because they aren't confident in doing so. I've been doing decoder installs for close to 20 years and consider myself skilled. It's rare that I have the issues I'm concerned about, but they happen even on factory units. One example is an N-scale Intermountain F (FP ?) unit. The motor is isolated and has wires that go to a top side circuit board. Replace the circuit board with the corresponding decoder and things should be fine. However ...... when assembled in China, the solder joints for these wires at the motor may or may not have have 'strands' that contact the frame which is split frame. Both frame halves are live, so contact to the frame is quick death to a decoder if enough current is available. For a properly wired locomotive, the current on the program track is a non issue. It's for unknown units that I have concern. Lyle
