DCC Myth or Fact?

[wabash2800]

I haven't got around to adding DCC decoders to some of DC locos but thought I heard somewhere that a DC loco after it has a DCC decoder installed (especially a sound one) it will have less tractive effort. And I am not referring to reducing weight in the loco to make room for the decoder.

And while I am at it, let's say I have a consist of three DCC locos, for example, and only one or two have sound decoders and the others just DCC decoders without sound.  If they are all the same make/model  and normally in sinc before the decoders were added, will the sound decoders versus standard decoders make any difference in their speed? I know I can program speeds to match but was wondering if I would have to or not.

Thanks in Advance

[Hamltnblue]

wabash2800

I haven't got around to adding DCC decoders to some of DC locos but thought I heard somewhere that a DC loco after it has a DCC decoder installed (especially a sound one) it will have less tractive effort. And I am not referring to reducing weight in the loco to make room for the decoder.

And while I am at it, let's say I have a consist of three DCC locos, for example, and only one or two have sound decoders and the others just DCC decoders without sound.  If they are all the same make/model  and normally in sinc before the decoders were added, will the sound decoders versus standard decoders make any difference in their speed? I know I can program speeds to match but was wondering if I would have to or not.

Thanks in Advance

Depending on the decoder used, tractive effort may be increased.  By using features like Bemf and momentum, wheel slippage can be held to a minimum, and reducing wheel slippage.

The second part is answered by a thing called speed matching.  With no matching done the sound loco's would probably run a bit slower than the non sound.  A few adjustments of the start and max voltage would match the speed in most cases.  For more extreme cases the total time to match the non sound to sound would be about 15-30 minutes.

 

[selector]

Tractive effort could be reduced if you must remove material from the frame or weight in order to accommodate the decoder.   Sometimes the weight must be milled to remove material so that wires will have a channel, for example, or even so that the volume of a tiny decoder from a smaller scale can be inserted under the shell.  A decoder will have less density than the same volume of metal.

Crandell

[Stevert]

I don't have any hard evidence, but I would think that with everything else remaining constant, a decoder's PWM motor drive would actually increase tractive effort somewhat.  However, the old rule that you can't make a silk purse out of a sow's ear still applies.  In other words, any benefit is likely to be small, so don't expect the addition of a decoder to turn a marginally-running loco into a great running one.

The answer to your second question probably depends on which decoders you use.  For example, if your sound loco has a QSI decoder and your non-sound locos have (NCE, Digitrax, TCS, Lenx, etc) decoders, then yes, you may encounter a speed difference.  But if your sound loco has let's say a Tsunami, and your non-sound locos have the Soundtraxx non-sound decoders that were recently introduced, the speed difference should be minimal.  So I think using different decoder brands has more to do with speed difference than sound or not.

[rrinker]

 Total myth. While high frequency pulse width modulation as used in any decent qulaity 'silent running' decoder does indeed reduce the torque output of the motor, such decoders also include a torque compensation factor that counteracts the torque loss. Coupled with the ability to more gradually apply power, there is less chance of a sudden application of power making your loco loose its footing. Of course with a DCC throttle you cna crank the knob from stop to full instantly and experience allt he same poor train handlign you do with DC. DCC isn't going to make you a magically better engineer, but it's not goign to make your trains pull less. Plus let's be a bit realistic here. It may be that your old Tyco 0-4-0 with traction tires can pull 100 cars around 18" radius curves, but it's completely and utterly unrealistic. Plus when that 100 car train means the loco is only a car length from its own caboose - that's kinda silly too. I'm sure we all did it just to see what each loco could do, but if your layout can realisticalyl handle 10-15 car trains, does it matter if the loco can pull 90 or 100?

                             --Randy

 

[DigitalGriffin]

One easy question, and one complex question:

The easy question: Do they have less tractive effort?

Answer: No unless you run them on a DC track which only goes up to 12 Volts.  If anything DCC allows for better slow speed operation tractive effort if equipped with a BEMF decoder.  With BEMF there is no erractic starts or stops at slow speed due to slight mechanical variances in the mechanism.

The complex question: Mixing decoders and speeds

The complex answer: Even if both trains rain perfectly together in a consist in DC, it doesn't mean they will run well together in DCC if you mix decoders.  Different decoders have different capabilities and algorithms on how they send electricity to the motor.  At slow speeds, some use a varying "kick pulse" to ensure the motor keeps going.  Some use BEMF to measure motor speed change.  Some use neither, but allow you to adjust the pulse width.  This can lead to variations at the slower speeds even if the same value is used in CV2.

The difference however is usually small.  If you don't want to use a custom speed table, then you can adjust CV2.  What I like to do is set a speed of around 5/127 (speed step 1 in consist mode) or 9/127. (speed step 2 in consist mode)  And compare my locos there.  I then adjust CV2 so they match in speed.  (Or the mid voltage CV)

 

[rbettig]

Stevert

I fully agree that if you match a sound Tsunami with the new non- sound the locomotives run without any speed difference. (I have 2 Life like Proto 1000 RS2) equipped this way, and they are the ones that run almost perfectly.  Some of my other locomotives equipped with Tsunami sound and for ex: Digitrax, non sound, need to be "speed matched" and the results are not as good ad the two RS2..

 

 

[jeffrey-wimberly]

wabash2800

I haven't got around to adding DCC decoders to some of DC locos but thought I heard somewhere that a DC loco after it has a DCC decoder installed (especially a sound one) it will have less tractive effort. And I am not referring to reducing weight in the loco to make room for the decoder.

And while I am at it, let's say I have a consist of three DCC locos, for example, and only one or two have sound decoders and the others just DCC decoders without sound.  If they are all the same make/model  and normally in sinc before the decoders were added, will the sound decoders versus standard decoders make any difference in their speed? I know I can program speeds to match but was wondering if I would have to or not.

Thanks in Advance

I've never had a loco come up with LESS tractive effort after installing a decoder. Maybe a bit less speed but not less tractive effort. The only time I've seen one lose tractive effort was when part of the weight had to be milled out to make room for the speaker. If no weight has been removed I do not see how the locos tractive effort could be effected. If anything I've had locos pull MORE after the installation because of the better control. Somebody's been feeding you myths.