Chrislock Posted March 13, 2011 Share Posted March 13, 2011 Greetings. I have recently been given a Maplins 9v power supply which I want to use to power half a dozen Cobalt turnout motors. Unfortunately the socket/plug has been cut off and all I have are the 2 wires. How can I tell which is positive and which is negative? Sorry if that sounds stupid, but I have no idea how to tell! I have a mulitmeter if that helps. Regards, Chris Link to post Share on other sites More sharing options...
Kenton Posted March 13, 2011 Share Posted March 13, 2011 what colours are the two wires? brown = +ve blue = 0v Or is this not a DC wallWart? both wires black - both 9v AC. put multimeter on 0-10v dc setting and measure volts across both wires. if -9v then the wires are opposite way round. Most WalWarts give the rating on the label. Some of them have very low (few mA) output - these are generally unsuitable for driving points. I use a 500mA 12v Wallwart to drive Tortoises - I don't know about Cobalts Link to post Share on other sites More sharing options...
66C Posted March 13, 2011 Share Posted March 13, 2011 Hi Chris Bare the ends of the wires from the power supply and keep apart when switching on the power. Switch on your test meter and select a suitable voltage range. Touch one wire with the red lead from your meter and the other with the black lead from the meter. If the reading shows a negative value on a digital meter then the black wire is on the positive output. If the needle on an analogue meter goes to the left - that is off the bottom of the scale - again the black lead is on the positive output. If a positive voltage is shown then the red lead is the positive output. Regards Link to post Share on other sites More sharing options...
RMweb Gold Donw Posted March 13, 2011 RMweb Gold Share Posted March 13, 2011 Simple test set the multimeter to the fist AC volt setting above 9v ac touch the probes to the two wires If you get a reading its AC. If nothing try setting it to DC volts and try again if you get a reading its DC if the needle quivers (analogue meters) then it was AC. No reading in either case its either duff or the fuse has gone in the plug. If its 9v Ac you could try using a couple of diodes to give two supply lines one positive half cycles the other negative half cycles. I powered tortoises using 16v AC in this way and they were strong enough to throw 0 gauge points 9v might be enough for 2mm. If that won't work you need a bridge rectifier and the wiring is more complex. Don Link to post Share on other sites More sharing options...
Edwin_m Posted March 13, 2011 Share Posted March 13, 2011 Set meter to 20 volts (or whatever) DC (sometimes marked =). Connect the red and black probe leads to the red and black sockets on the meter. Touch each probe on one of the bare wires from the power supply. Switch on the power supply. If you get about +9V then the wire connected to the red is the positive. If you get about -9V then the wire connected to the black is the positive. There is probably a white line or a rib on one of the wires so you can tell them apart. If you get a very small or zero reading then then switch to 20 volts AC (sometimes marked ~). If you now get a reading of about 9V you have an AC power supply, if it is still zero then either one of your meter probes is not making contact or the power supply is a dud. Edit: Two more people got in while I was writing this. We seem to be saying the same thing though! Link to post Share on other sites More sharing options...
Chrislock Posted March 13, 2011 Author Share Posted March 13, 2011 Sorted, thankyou all very much. The power supply is 9V DC at 400ma which I think is adequate for needs. I think Cobalts only draw about 10ma each, and I was advised that 9v would move the blades more slowly. If its no good then I see I can buy a 12V equivalent for less than a tenner at Maplins. Incidentally I cannot see any difference between the cable colours on this one - both black, Chris Link to post Share on other sites More sharing options...
corax67 Posted March 13, 2011 Share Posted March 13, 2011 Look and see if one of the two black wires has a white stripe running along it - that would normally indicate the positive feed. Link to post Share on other sites More sharing options...
naugytrax Posted March 13, 2011 Share Posted March 13, 2011 All very true about the polarity identification, but why worry? Whenever you wire up Cobalts (or Tortoises or Fulgureces) there's a 50 percent chance that the turnout will move the "wrong" way, i.e. opposite to what your control panel tells you. So you have to swap the feeds to that motor anyway. I find that the empirical approach is a lot less worry than trying to match feed polarity to direction of throw, and quicker too! Link to post Share on other sites More sharing options...
Kenton Posted March 14, 2011 Share Posted March 14, 2011 All very true about the polarity identification, but why worry? Because some of these WallWarts are not DC output. Link to post Share on other sites More sharing options...
RMweb Premium Kris Posted March 14, 2011 RMweb Premium Share Posted March 14, 2011 Sorted, thankyou all very much. The power supply is 9V DC at 400ma which I think is adequate for needs. I think Cobalts only draw about 10ma each, and I was advised that 9v would move the blades more slowly. If its no good then I see I can buy a 12V equivalent for less than a tenner at Maplins. Incidentally I cannot see any difference between the cable colours on this one - both black, Chris They should work at far less than 9v Chris. The more power used just increases the speed and strength of the throw. Link to post Share on other sites More sharing options...
Chrislock Posted March 14, 2011 Author Share Posted March 14, 2011 They should work at far less than 9v Chris. The more power used just increases the speed and strength of the throw. Kris - given the build quality of some of my points they will probably need a hefty shove to move and lock them in place! Naugytrax - I was thuinking why bother, but then having gone to the trouble of laying out a wiring diagram ... Chris Link to post Share on other sites More sharing options...
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