lowest voltage that will move an OO loco

Basic electrical and electronics, such as DC/Analog control.
Phred
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Location: Queensland Australia

Re: lowest voltage that will move an OO loco

Post by Phred »

kebang wrote:
New gaugemaster controller provides excellent control at all speeds, including shunting. Very pleased!
The Gaugemaster is a truly excellent controller. The only beef I have with them is the tiny wee retaining screws where you insert your feeder wires in the back. I'm always afraid I'll somehow over-tighten and damage them. Otherwise great! :D
kebang
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Joined: Fri Jun 13, 2008 11:59 am
Location: Bohol, Philippines

Re: lowest voltage that will move an OO loco

Post by kebang »

Children now returned to UK (landed at Heathrow an hour ago) so now its back to the railway!

The Ivatt is an older mainline model so I expect it is split chassis, but at the moment its running perfectly. I shall research as Bigmet suggests. The L&YR class 5 negotiates the 4 1st rad curves I had to intersperse in my layout to make everything fit, but it does slow down considerably as it crosses them, The Ivatt also slows, but not as much
Bigmet
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Re: lowest voltage that will move an OO loco

Post by Bigmet »

When you have the time, it is worth a little inspection and tinkering to ensure all the designed sideplay of the wheelsets is available. External features that can limit sideplay such as moulded brake shoes, arches for pony truck wheels, and other detail around the wheelsets, are the sort of thing that can make a big difference to how freely a loco gets around R1. I had a look at a current Bachmann 57xx fairly recently which should have no trouble based on my past experience, but between brake shoes, sandpipes, some flash on the brake pull rod moulding and a bent pick up wiper the owner had found it was slowing on R2. Cutting away the flash and shaving the (invisible) faces of the brake shoes for a tlittle more clearance, straightening the wiper and slightly bending the sandpipes, and it was happy on R1.
Richard08
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Re: lowest voltage that will move an OO loco

Post by Richard08 »

Apropos nothing really, but I noticed in a recent review that the spec on the box (Class 45) gave the starting voltage (2.5V) as a 'feature'. Presumably to help DDC folks, but it would be interesting to see if they are consistent model to model.
Bigmet
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Re: lowest voltage that will move an OO loco

Post by Bigmet »

Richard08 wrote:... I noticed in a recent review that the spec on the box (Class 45) gave the starting voltage (2.5V) as a 'feature'...
What brand is this from? Cannot recall previously seeing anything like this on the RTR OO I own or have looked at.
Richard08 wrote:...Presumably to help DCC folks, but it would be interesting to see if they are consistent model to model.
Largely irrelevant to DCC users with current RTR OO product. We just bang in a decoder of choice, and then make the adjustments to extract the on track performance required. (For example I have my track voltage set higher than most DCC users, because a few RTR loco designs that suit my interest are overgeared and otherwise would not achieve scale maximum speed. Have main line layout, will run at express speed as appropriate, for the proper contrast with the slow unbraked freight.) The injection of long proven HO mechanism technique into RTR OO means most current product can be easily adjusted to whatever extent is required to 'work realistically', or to suit the owner's taste. (These of course are not necessarily anything like the same thing...)

As concerning performance consistency between examples of the same motor: wholly unpredictable. Quite a high proportion are like peas out of a pod, others are 'all over the place'. The latter condition unsurprising from low cost, modest precision, volume assembly. I would like to quote supporting data but my sampling is far to small to deliver any statistically valid evidence, beyond 'there clearly can be significant variation', and also as a customer there is no clue to motor sources.

(Then there is the contribution from the attached mechanisms, and sometines circuit components, which has to be assessed separately to avoid confusion. Over these last 15 or so years typically satisfactory with small variation, but with occasional outbreaks of less than optimal design, manufacturing and/or assembly technique, component choices and materials deficiencies; resulting in a range of different perceptions of 'quality'. I had the considerable joy some years ago of fettling an example of the Oxford Rail 'Radial tank' model, to 'disappear' the motor and allow sufficient weight to consistently bear on the driven wheels. On the owner's layout it then ran very sweetly and pulled well, and another visitor pontificated on this demonstration of the clear superiority of the Hornby model. He wasn't amused by the revelation that this was the Oxford item. Experience gained in past kit and scratchbuilding projects does occasionally afford amusement.)
Richard08
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Re: lowest voltage that will move an OO loco

Post by Richard08 »

Bigmet wrote:
Richard08 wrote:... I noticed in a recent review that the spec on the box (Class 45) gave the starting voltage (2.5V) as a 'feature'...
What brand is this from? Cannot recall previously seeing anything like this on the RTR OO I own or have looked at.
The new Heljan one.

Presumably this is to suggest to DCC users they should should set the start voltage to to 2.5V when fitting a decoder. Seems pretty logical, and useful, bearing in mind this thread title.
Bigmet
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Re: lowest voltage that will move an OO loco

Post by Bigmet »

Richard08 wrote:Presumably this is to suggest to DCC users they should should set the start voltage to to 2.5V when fitting a decoder. Seems pretty logical, and useful, bearing in mind this thread title.
Except that the DCC systems I am familiar with cannot read the voltage applied to the motor. The 'start voltage' setting on a decoder is a number on a scale from 0 to 'maximum' (255 on those I use) to set the pulse width as small as necessary to just get the motor turning reliably from stationary. I have never yet measured the time averaged voltage the decoder applies over the motor terminals, but I'll have to get around to it now, just to see! One of the features that characterises the best motor drive capability from decoders is a very stable minimum output, so the loco movement is a 'creep' from stationary to dead slow, and likewise from dead slow to stopped.

(The only measurement I have taken for DCC decoder selection purposes was the current draw with the motor stalled and nominal 12V applied; because 'back in the day' many decoders had pretty limited continuous current capability, and wouldn't stand regular exposure to more than about 70% of their claimed - limited - capability.)
Bigmet
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Re: lowest voltage that will move an OO loco

Post by Bigmet »

A little tinker time later, and because I had an Oxford Rail N7 on the bench I have used that to make a very rough estimate that the average voltage at speed step 1 was 300mV. The decoder output when 'on' was 14.9V, so that suggests the pulse width modulation roughly 2% on, 98% off. (My storage scope is 300 miles away with a young relative, so no more accurate or precise determination is possible.)
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