Aide De Memoir, Cv Settings For Speed And Voltage

[Deleted member 1986]

After scratching about for yet another scrap of paper, something to write with, calculator and complete brain fade as to which formula or equation needed to be used to calculate what CV, I came up with these, hope they will be useful to others.

 

[stockers]

Took me a few minutes to get my head around what that lot was saying. Yes, I see where you are coming from but it all looks very complicated.
Speed steps are often not used in a linear progression, usually the steps are biased to the lower speed settings to give finer slow speed control for the likes of shunting.

 

[Greg Elmassian]

What are you measuring these voltages with? Since these are all pulse-width modulated, these are at best an approximation of voltage.

But what you get varies depending on the decoder itself. Are you going to make one of these for each decoder and at each of 3 voltages?

Sounds like a large amount of work.

Greg

p.s. voltage to an LED means nothing, it's current, so I cannot see what that table does at all. Voltage makes sense to incandescent bulbs.

 

[stockers]

I think you will find they are arithmetical estimates Greg.

 

[dunnyrail]

What I failed to realise with the DCC Steps is that they are an approximation of the Voltage Supplied. Thus for example on a Massoth and probably others too, CV5 at each input Number is 1/255 of the Track Voltage. So what Arthur has superbly done is to give us Tables showing the effect of these Calculations.

For me the problem is that I wish to restrict a Locomotive to its scale Max Speed for my line. This is 40KPH. So what I do is set CV5 to a number roughly in the 80 margin. Then I use the App Scale Speed to check on a measure 2 Yards. Then I play around with the CV to get it closer to my desired Max Speed.

What I failed to understand (realise) and Arthur has graphically illustrated this is that my 40 KPH will be different on a Lower Voltage DCC. Well worth remembering if you visit another line and wonder why your Loco is either Sluggish or Running away a little.
JonD

 

[ntpntpntp]

Voltage to an LED means nothing, it's current, so I cannot see what that table does at all. Voltage makes sense to incandescent bulbs.

I think the idea is the table shows the resistance value required to run the LED at 20mA assuming the LED forward bias voltage is as listed.

Seems about right, I typically use 1k resistors as a good enough approximation, given I'm running on NCE gear at around 18V and I aim for 15 mA through LEDs unless they're high power.