DCC v Analogue Loco Speed

[suerose]

Hi

I have a O gauge Terrier with a 40:1 gearbox. When built and tested on analogue, the locomotive speed round the track just fine. I have now installed a Zimo sound decoder and tested it for the first time. The speed of the locomotive has reduced considerably. This is my first decoder fitting in O gauge, up to now all my fittings have been in OO gauge and I have not noticed any significant speed reduction with them. This is also my forst attempt with sound decoders. I cheated with the OO gauge and so far ah somebody else do the sound fitting.

So is it me, does DCC reduce the power when compared to analogue.

Any help would really be appreciated before I have to consider putting a different gear ratio in it.

Regards, Sue

 

[Crosland]

What sort of power supply and voltage did you use to test it on DC?

 

What track voltage do you have from your DCC booster?

 

if you are not comparing like for like then there will be a different one way or the other.

[suerose]

Hi

The DC is a standard 12v supply, not sure of the amperage, but having just checked again, it ran very fast.

The DCC is a digitrax system with a 5amp output which runs my 4mm system just fine. This is the first attempt using it to run O gauge. So is this system not powerful enough, is it the decoder or do I need to make some alteration to the cv's somewhere.

Regards, Sue

[Adrian Wintle]

Hi

The DC is a standard 12v supply, not sure of the amperage, but having just checked again, it ran very fast.

The DCC is a digitrax system with a 5amp output which runs my 4mm system just fine. This is the first attempt using it to run O gauge. So is this system not powerful enough, is it the decoder or do I need to make some alteration to the cv's somewhere.

Regards, Sue

 

The difference would be the track voltage, not amperage. A standard 12V DC controller may put out significantly more than 12V at full throttle, while a DCC decoder will be able to use about 0.5V less than the track voltage provided by the DCC controller. What do you have the track voltage (scale) set to on the Digitrax system?

 

Adrian

[suerose]

Hi Adrian,

I have no idea what the track voltage is set to on the Digitrax as never heard about it before, it will be whatever the default value is for it.

I must admit I had assumed that the Digitrax Empire system would have run either the OO or the O gauges, or do I need a different system for O gauge.

Regards, Sue

[Ron Ron Ron]

.....I have no idea what the track voltage is set to on the Digitrax as never heard about it before,...

...it will be whatever the default value is for it.

I must admit I had assumed that the Digitrax Empire system would have run either the OO or the O gauges.....

 

 

See the bottom right hand side of the photo......

[Roger Sunderland]

Hi

 

You are really not comparing like for like.

 

1. The Digitrax 5amp system puts a voltage of around 18 volts AC into the track, it is the decoder that turns this into DC voltage to run your loco (which has a DC motor in it)

2. The amps are irrelevant as long as there is enough to operate all the locos plus other things you want to operate. The 5 amp system is ample in most circumstances.

3. Most purchased sound chips have been preprogrammed by the manufacturer/vendor to simulate the real thing as closely as possible. Things like inertia etc are built in to give smooth starts and stops. In the case of your Zimo sound decoder there will have been a maximum speed built in to be more prototypical. This is because, in real life, Terriers had a fairly low maximum speed and spent most of the time never achieving it!

 

Hope this helps.

[Ron Ron Ron]

Out of curiosity; what Zimo decoder have you fitted?

[suerose]

Hi Ron and Roger,

First, I found the switch on the digitrax, it is actually set to O/G, always has been so that should have made no difference.

 

The idea that the decoder has been preprogramed to run slower makes sense and that is what we thought might have happened. I have checked the CV29 for speed steps but it is set to maximum as far as I can work out.

This is a kit built terrier with a Maxon 352923 motor with 40:1 gearing. The decoder was bought from Digitrains who put the sound on which is a Zimo MX645. I think I may go back to them to see if the programme can be altered to give a faster speed, otherwise to get better running will have to change the gear ratio to say 30:1. Hope not necessary as will have to take the chassis apart and it runs so well on DC, actually too fast on DC but not fast enough on DCC.

I definitely have not had this problem with any of my OO gauge locos both rtr and kit built, so am confused as to why this first venture into O gauge is a mystery.

Regards, Sue

[Roger Sunderland]

Hi again

 

Changing the speed steps will not alter the speed of the loco, all this does is alter the incremental increases/decreases in speed ie the higher the number of speed steps the smoother control you have. The maximum speed of the loco is set mainly with CV5. However, in the case of sound chips(as opposed to ordinary decoders) there are other CVs that can influence behaviour.

 

If you think the speed is too low then it may be best to ask Digitrains to re programme it for you to give a higher max speed.

[Adrian Wintle]

Hi Ron and Roger,

First, I found the switch on the digitrax, it is actually set to O/G, always has been so that should have made no difference.

 

The idea that the decoder has been preprogramed to run slower makes sense and that is what we thought might have happened. I have checked the CV29 for speed steps but it is set to maximum as far as I can work out.

This is a kit built terrier with a Maxon 352923 motor with 40:1 gearing. The decoder was bought from Digitrains who put the sound on which is a Zimo MX645. I think I may go back to them to see if the programme can be altered to give a faster speed, otherwise to get better running will have to change the gear ratio to say 30:1. Hope not necessary as will have to take the chassis apart and it runs so well on DC, actually too fast on DC but not fast enough on DCC.

I definitely have not had this problem with any of my OO gauge locos both rtr and kit built, so am confused as to why this first venture into O gauge is a mystery.

Regards, Sue

 

In O/G it should be putting out a nominal 20V. (HO = 15V, N = 12V). It is possible that there is some motor tuning that can be done through the decoder, but I'm not familiar with Zimo decoders.

 

Adrian

[pauliebanger]

There are two ways to reduce top speed with ZIMO decoders.

 

The 'universal' way by reducing CV5. This can be set in the range 1-255, higher numbers giving higher top speed (subject to the motor's capabilities and the track power). 

 

Reducing the value in CV5 can prevent the higher speed step sounds being played (the lower ones continue) so is not the prefered solution for sound decoders.

 

CV57 is the reference voltage CV, the purpose of which is actually to allow the decoder to maintain steady speeds over track without a properly regulated power supply. However, a side effect of this is that if set so that the 'reference voltage' is lower than the track voltage by a good margin, the top speed can be limited but without 'slicing off' the top speed sounds. The intervals between the change thresholds of the driving sounds are compressed to fit wholly within the available voltage range.

 

So, read CV57. If its value is in the order of, say, 80 - 90, consider increasing it to 150 -160 (equivalent to 15 or 16 volts under load). Do remember the earlier advice that Terriers had a, rarely achieved, low top speed so if it turns into an express locomotive, reduce CV57 to tame the beast.

 

Kind regards,

 

Paul

[suerose]

Hi Paul,
I contacted Digitrains as we bought the decoder from then, they suggested exactly the same, change CV57 (never even knew about that one before) to 140. So just changed and it now goes just the same as on DC.

Thanks to everybody for your help and advice, it is really appreciated.

Regards Dave & Sue

[Phil S]

Before 'sending it back', I would suggest emailing the supplier, and asking them what value is programmed into CV5 (max Speed) by them.... or alternatively, and FIRST: read the manual and discover how to READ the value back, if your system supports read-back.  (Overlapping replies: you have since found it to be the setting of CV57)

so what follows is 'generic' for other readers with similar speed differences...

 

If it does not support 'readback', then you can simply TRY a series of values in CV5, until you find one which is about the same as the loco is now, and then alter it until it matches the range you want!   (Reading CVs is NOT a requirement to program new values into them)  If necessary write the values you prefer down ona  piece of paper 8-)

 

From what you have stated, you do not perhaps, possess a Multimeter ot Voltmeter ..... It is a very useful tool to have, whether working in DC or DCC, and they can be bought from 5GBP uprwards.

Admittedly, like many tools, paying a bit more will buy a better, more useful, and accurate (Multi)meter.  When fitting your own decoders, the use of a meter is ALWAYS a good idea - it can save decoders from destruction!!

 

Once you have a meter, you willbe able to find the ACTUAL track voltage when your loco is/was running under DC/analogue ... and as Andrew Crossland said

"What sort of power supply and voltage did you use to test it on DC?, What track voltage do you have from your DCC booster? ,if you are not comparing like for like then there will be a different one way or the other.

 

DO NOT ASSUME that the '12vDC' Controller was outputting only 12Vdc maximum!!!  Older Tri-ang Hornby units were labelled as 14-16Vdc output, others similarly. I have an H&M DC60 which outputs about 20Vdc .. especially when very little current is being taken: THese older, PRE-ELECTRONIC CONTROLLERS did not 'regulate' the voltage, and the quoted value will be the 'lowext maximum' - occuring at the maxiumum current output.

 

When measuring the DCC voltage, many meters may also give an 'inaccurate' result when used on their AC range - as this is usually calibrated for Mains-derived ac supplies (50Hz)

If measured, with a bridge rectifier and dc voltage range, you will get a good indication of what voltage the motor and lights are being supplied with.

 

Some basic CVs:   CV1 = 3 by default, a running number between 1 and 100 or 127 depending on controller (Also called Basic or Short Address)

                              CV2 = Starting Voltage at Speed Step 1 ... can be set to the lowest value at whiuch the loco keeps moving. 

                              CV3 = Acceleration - the higher the number, the more sluggish the acceleration

                              CV4 = Deceleration - the higher the number, the more sluggish the braking 

                              CV5 = MAXIMUM SPEED       NB: On our 'G Scale Shunting Puzzle, we se this to between 1/4 and 1/2 of the Maximum (unrestricted) speed, or it is too fast!!!

 The NUMERIC RANGE used for each of these values varies with different makes of decoder: they should have come with a sheet giving the range, and default values  eg 1-64, 1-255, 1-1024

 

SOUND decoders also often INCLUDE TIME DELAYS before actions take place - to match in with the 'sound picture'.  An SWT HST decoder takes 1.5 circuits of my 8m x 5m layout to stop, and about 30 seconds or so after 'starting' before the engine will move!

 

You might also have a SHUNTING SPEED on an 'F' button - which REDUCES THE MAXIMUM SPEED for easier shunting - and 'releasing' reverts to the normal full speed range.

IN this shunting mode, the acceleration and deceleration values are usually reduced, as well.

[suerose]

Thanks everybody, your answers have been very useful, Digitracks solved to speed problem as I changed CV57 and it worked. I have heard from them today that the sound projects are mainly for 4mm scale, so it is expected that some user changes to various CVs for larger scales are user determined, so I will enjoy playing with different combinations that some of you have suggested.

It is really good that there are members of the forum who are so helpful, and it is really appreciated.

regards

Sue & Dave