AUSLNER Posted December 11, 2012 Share Posted December 11, 2012 I'm just curious into the capability differences between the sapphire and standard decoders and which would be better for a Flying Scotsman Tender Drive Loco. Cheers Link to comment Share on other sites More sharing options...
poliss Posted December 11, 2012 Share Posted December 11, 2012 The Sapphire has many more CVs than the standard decoder. Vstart, Vmid and Vmax for example. It's also more powerful. Link to comment Share on other sites More sharing options...
96RAF Posted December 11, 2012 Share Posted December 11, 2012 Sapphire also has more features such as auto-ops, coal/fuel burn, support for ADCC, RailCom, etc. Rob Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 12, 2012 Share Posted December 12, 2012 More importantly the Sapphire can take a higher stall current making it suitable for older locos such as Tri-ang locos and 1970's Hornby locos with the old Tri-ang motors. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 12, 2012 Share Posted December 12, 2012 The rule of thumb when choosing a decoder is can it handle the stall current of the loco motor you are fitting, get that wrong and it's fried decoder time. So when buying look at stall current first and then the whistles and bells second. Link to comment Share on other sites More sharing options...
Gregd99 Posted December 12, 2012 Share Posted December 12, 2012 The son of Triangman said: More importantly the Sapphire can take a higher stall current making it suitable for older locos such as Tri-ang locos and 1970's Hornby locos with the old Tri-ang motors.I know that it is normal to talk about stall current but is it more reasonably "slip" current that should be considered. "stall" implies the loco is stopped and jammed so hard down on the track that the wheels can't turn. "slip" is where it runs up against an obstacle and cannot move while the wheels spin on the track. Has anyone actually had a stall? I would be interested to understand the situation. I do wonder whether "slip" current would actually be less than normal running current. when the loco hit the obstacle the current would increase as the wheels still had a grip on the track. once the grip was lost and the wheels were "skidding" the current should decrease I think. Any physicists out there to correct me? Link to comment Share on other sites More sharing options...
37lover Posted December 12, 2012 Share Posted December 12, 2012 I am an Engineer not a Physicists but did study physics many, many years ago! Keeping it simple and ignoring air resistance, etc the maximum force that can be transmitted through the wheels is a direct function of the coefficient of friction [and the weight applied]. For a loco that is moving forwards the maximum force hasn't been reached until the wheels just start to "slip". As SoT said the maximum current will be when the wheels are actually prevented from turning. When the loco hits an obstacle the motor will try and overcome the resistance and the current would increase up to the slipping point and then should remain constant, not decrease. I wait to be corrected! Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 13, 2012 Share Posted December 13, 2012 A motor will reach it's maximum current comsumption when stalled as a rule, if testing for a stall the test must not last more than a second or two or the motor will burn out, a simple multimeter will record the stall current briefly or one of the very very expensive meters like a Fluke which has a facility for freezing a reading for examination. Stall current of the motor is the most important factor for choosing a decoder, then comes the size of the decoders, and finally the whistles and bells you need. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 13, 2012 Share Posted December 13, 2012 37lover has it about right. Slip current won't give you maximum current comsumption. From fitting decoders professionally I have found the stall test gives the true figure. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 13, 2012 Share Posted December 13, 2012 Stall will be the point at which the wheels stop moving, this doesn't mean jamming a loco down hard but merely stopping it with a finger in the four foot, after the stall point the loco motor will eaither burn out or the loco will slip. For a breift second or two the motor will reach it's maximum current consumption. Link to comment Share on other sites More sharing options...
Gregd99 Posted December 13, 2012 Share Posted December 13, 2012 I think I understand all of the above so the steps would be 1. motor running freely - current = x steady state 2. motor stalled - current = y (instantaneous/short) as wheels transition from free running to stall to slip 3. motor (well wheels) slipping = z steady state it would seem to me that y > z > x and y has a very short duration. so..... if the 8249 has a peak current of 1A and a continuous max of 500mA then it seems that 8249 would be suitable for stall currents (y) of 1A providing the slip current (z) was not more than 500mA. Would this align with practical experience? The rather spectacular exception to the rule would be if the stall continued for more than a short period of time. it would then seem that it would be a race to see whether the decoder or the motor burned out first. Link to comment Share on other sites More sharing options...
Fishmanoz Posted December 13, 2012 Share Posted December 13, 2012 I've had the misfortune of watching stall current in action. The motor was an X04 and the wheel quartering was out causing it to bind. It bound then continued on a few times and finally came to a halt on a point but with current still going to the decoder which was rated at 1Amp. I made the mistake of turning up the controller at that point and the result was 2 puffs of smoke from 2 diodes in the bridge rectifier in the decoder. So I can report stall current in this X04 was in excess of 1Amp. It was very clever to do all of that on a point, making me think it had lost contact or even shorted out. I was wrong. Many thanks to Richard at DCC Concepts who replaced the decoder under warranty, even though it was clearly my fault. Link to comment Share on other sites More sharing options...
Gregd99 Posted December 14, 2012 Share Posted December 14, 2012 This seems consistent with some of the comments above. A hard stall, if prolonged, will most likely either cook the decoder or the motor. Link to comment Share on other sites More sharing options...
poliss Posted December 14, 2012 Share Posted December 14, 2012 Mark Gurries of the NMRA puts more emphasis on Motor Slip Current draw than Stall Current draw due to the improvements in the transistors used on decoders. https://sites.google.com/site/markgurries/home/decoders/decoder-motor-ratings Link to comment Share on other sites More sharing options...
Fishmanoz Posted December 14, 2012 Share Posted December 14, 2012 He seems to be right in my case poliss. Clearly the motor drive transistors were still operating otherwise there would have been insufficient current being drawn to blow the bridge rectifier. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 15, 2012 Share Posted December 15, 2012 Certainly on a stall the transistors will keep working as poliss has said they have improved a lot. However peak current is generally reached at stalling point. This of course can show in a slip where a loco stalls for a brief part of a second and then slips. Current draw during a slip will be high but peak point will be at stalling point. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 15, 2012 Share Posted December 15, 2012 Transistors of course will play their part in the destruction during overload. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 15, 2012 Share Posted December 15, 2012 The bog standard Hornby decoder will be fine for fitting to most ringfield drive locos post 1974 if the motor and magnet are in good fettle as current draw is usually less than 500ma. Motors like the X.03 and X.04 require something beefier, I use a micro decoder with a 1.5amp peak stall current and continuous 1amp cuyrrent draw, it's made for Z and N gauge locos but is perfect for the job. Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 15, 2012 Share Posted December 15, 2012 This X.04 powered loco is fitted with just such a decoder. http://i157.photobucket.com/albums/t43/thetriangman/DSCF0019-2.jpg http://i157.photobucket.com/albums/t43/thetriangman/DSCF0015-5.jpg Link to comment Share on other sites More sharing options...
The son of Triangman Posted December 16, 2012 Share Posted December 16, 2012 This Hornby R.066 Duchess of Sutherland made in 1977 with ringfield tender drive has the standard Hornby decoder fitted, stall peak current of the motor was 420ma on test. I decided to cut current consumption down as the original bulb was using 60ma, an LED was fitted into the bulb socket of the loco, and a loco to tender plug fitted of the type Hornby currently use to run the function control from the decoder to the LED. http://i157.photobucket.com/albums/t43/thetriangman/duchess4.jpg http://i157.photobucket.com/albums/t43/thetriangman/duchess2.jpg http://i157.photobucket.com/albums/t43/thetriangman/duchess3.jpg Link to comment Share on other sites More sharing options...
CobaltUK Posted January 5, 2013 Share Posted January 5, 2013 Surely even a 20mm quick blow glass fuse could be found space and there are smaller devices these days. For a hard wired decoder it wouldn't add much time to the work. Link to comment Share on other sites More sharing options...
poliss Posted January 5, 2013 Share Posted January 5, 2013 Fuse not needed. You are testing what the power consumption is so you can choose a suitable decoder. Just don't stall the motor for more than a second. Link to comment Share on other sites More sharing options...
CobaltUK Posted January 5, 2013 Share Posted January 5, 2013 poliss said: Fuse not needed. You are testing what the power consumption is so you can choose a suitable decoder. Just don't stall the motor for more than a second. Misunderstanding. No it was aimed at never risking an expensive decoder (eg sound decoder) emitting "puffs of smoke" in a terminal fashion. Link to comment Share on other sites More sharing options...
CobaltUK Posted January 5, 2013 Share Posted January 5, 2013 CobaltUK said: Misunderstanding. No it was aimed at never risking an expensive decoder (eg sound decoder) emitting "puffs of smoke" in a terminal fashion. In everyday use. Link to comment Share on other sites More sharing options...
poliss Posted January 5, 2013 Share Posted January 5, 2013 All good decoders cut out if they are overloaded. Link to comment Share on other sites More sharing options...
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