Dear all, recently I discovered the great possibilities of DCC++. It shouldn't be a surprise that I want to build it for my own layout. I should solve all the issues with my current analogue setup. The question I have is quite a elementary one; how do I protect the motor shield and arduino from a short? The railroad is powered with 12 volts and I assume that short circuits will occur. I ordererd the R3 motor shield from arduino. I couldn't find any information so far unfortunatly. The only kind of a solution i found (picture below, see link) is quite an ugly one and there must be other ways of protecting our nice locomotive roster / arduino. There isn't a loop btw. Many thanks Laurens
DCC++ will shut down track power in a short circuit. if you want more protection, you can always put a fuse in series between the DCC++ base station, and the track connection. ~Travis
Laurens I, too, sought an answer for the DCC++ base station ..... since I was using a base station between several test beds I ended up making a portable circuit breaker using an NCE EB1 (which I use on my layout) in a loco case enclosure using a push button ..... now when a short occurs I can see the LED blink, and after rectifying the short push the button and reset the circuit without shutting down the base station. Hope this helps. Steve F
dear Travis, I assume that the DCCplusplus base station is capable (or will be capable at a certain point in time) of receiving feedback from decoders. So there will be sensors on the shield (or uno). You can't protect any sensor by means of software, there is a very real chance of roasting them if the railroad shorts. There needs to be an onboard or dedicated protection. The single use nature of a fuse is not something I fancy since transistors are very capable of doing a good job. Dear Steve F, That is an very interesting solution. Are there by chance any diagrams or blueprints available? The complete ones I found tend to be quite expensive (relatively), since their price triples when taking shipping from the USA to Europe and tax / customs fees into account. Laurens
The base station code uses the current sensing capability of the motor shield. When it senses a draw of current above the set threshold, it shuts down output. You have to send an On command to start things back up. Commercial base stations behave the same way, although not all require you to send a command to turn output back on. Some motor shields, like the Pololu MC33926, have built in short circuit protection that kicks in faster than a DCC auto-reverser - such as the Digitrax AR1 - can react, so you need to take that into consideration if you need a reverser for a reverse loop or a turntable. Any approach to DCC short circuit protection that works for commercial DCC base stations should work for DCC++. That includes the 'automotive tail light' approach - when a short occurs the current feeds through the tail light illuminating it to indicate that you have a problem without causing your base station to shut down.
I use series light bulbs for short circuit protection and happy with the results. I found the 12V bulbs at Home Depot in various wattage and settled on 8W bulbs. There is some voltage drop across the bulb but not enough to make a difference. I regularly run 4 unit consists without issue. If there is a short the bulb lights but the short doesn't take down the DCC system. I have about 40 bulbs; one for each block except for blocks that use auto-reversers.
You might want to consider using one of the polyswitch resettable PTC devices: http://www.littelfuse.com/products/resettable-ptcs.aspx
I use the NCE EB1 when I only have one district. DCC Specialties PSX family if I need several districts http://www.dccspecialties.com/products/powershield_x.htm The only reason I don't use DCC specialities them for 1 district is they are like twice the price but once you get a PX4 which is 4 districts and you can find them for ~$30 per district so not much different.
what has the decoder got to do with it? the over-current shutdown is built into the base-station. i agree that software isn't as fast as it could be, but i have tested it with a 18V 20A dead-short. it shutdown well before the screw-driver welded to the track. but to play it safe, i plan on fuses (low current) at each track feeder. I had not considered those, but upon research, i will likely buy some to test out. Thank you. ~Travis
I assumed that feedback received from the decoders will be picked up by the shield and I worried that that processes the feedback might get fried with a large current. I didn't have any time to watch the hours of video on dccplusplus until yesterday evening. The short protection built into the software only gets mentioned once in one of the last videos about the base station and another time in a software video, which i didn't watch at first since I'm planning to use jmri instead. It might be handy if information about the software short protection gets included in the documentation. Thanks for the tip, that seams an ideal solution.
to be honest, i thought it was in the documentation, but as i just looked through it, i don't know as it is. I guess i found out by reading through the code. I have thought about drafting a variation of the documentation on my own website, but wasn't sure if i had the time to maintain it, with all my other projects going. I may take a stab at it at some point though. ~Travis
