Made the jump to DCC

[Cooped]

I've just done it, bought an NCE powercab DCC controller. Works great with my nice new Athearn Big Boy, but the 2 Bachmann locos I have with chips in seem to struggle. I have a N+W J class and a Berkshire. Both of these exhibit loud humming when trying to start up and don't start moving until you reach about speed step 40 (in 128 steps mode). I thought I'd read something about a possible humming that could be fixed by changing the start voltage in the CVs. I tried that, but it didn't seem to have any effect.

Any advice as to how to fix this?

Thanks
Dan

[Jim Banner]

Do your Bachmann locomotives have DCC decoders in them?  If so, what kind?

Jim

[Cooped]

Hi Jim

yes they do have decoders in them. Not  sure what kind exactly, they are the factory fitted ones. I don't think they are particularly 'high end'. I noticed on the paper included with the Berkshire that it supported 28 step speed control with no mention on 128 step so I tried both again on 28 step speed with basically the same results, loud humming sound before it starts to  move.

Dan

[ABC]

All Bachmann 1 amp decoders support 128 speed steps.

[Jim Banner]

All Bachmann 1 amp decoders support 128 speed steps.

You have to be very careful when you say this.  It all depends on what you mean by "support."  If you mean that the decoder can produce 128 different speeds, then no, it cannot.  If you mean that sending it a command to do one of 128 different speeds and it will respond, then yes it can.  Setting your command station for 128 speed steps and then sending out commands for step 1, step 2, step 3 or step 4 will all cause these decoders to produce speed 1 of 28.  Steps 5, 6, 7, & 8 will cause it to produce speed 2 of 28.  And so forth.  In this sense, it supports 128 speed steps.  It just does not use all of them.  On a bit level, 128 speed steps uses 7 bits of data while 28 speed steps uses 5.  All the decoder does is ignore the top two bits.  Whether you set your throttle/command station for 28 or 128 speed steps, you will get virtually the same response out of this decoder.

As far as setting start voltage, CV2 can deal only with values between 0 and 31.  If you put in values over 31, it just repeats the steps over again.  Same story as the speed steps.  CV2 uses only the first five bits.  The rest are ignored.  If the locomotive needs 40% throttle to start (or 40 out of 128 steps, which is close to the same thing) try an initial value of 10 and work up or down from there.

The noise is a little bit harder to deal with because it is so subjective.  Let's pay a mind visit to my H0 layout.  Today we are running three locomotives - an old Bachmann sidewinder (flat motored) Consolidation from the 1970's, an Athearn F-7 from the 1980's, and an Atlas/Kato RS-3 from the 1990's.  First we run the Consolidation.  I understand that some of these were not too bad.  But mine sounds rather like a chainsaw with a belly ache.  It is noisy by anybody's definition.  Then we run the Athearn F-7.  Much better.  It has had the Pearl Drops treatment and been well run it.  We sit around talking about how quiet it is.  Finally we run the Atlas/Kato RS-3.  This locomotive is QUIET.  On good track, it is silent except for an occasional click as it runs over a turnout frog.  Suddenly the F-7 doesn't seem as quiet as it did before.  How do you look at this?  One reaction is to enjoy the silence of the Kato.  The other is to regard it as rather unlike a real locomotive which can be deafening. 

I have some Bachmann standard diesels that came with DCC on board and I don't mind the bit of noise at all.  To me, it is just the prime mover winding up as the engineer advances the throttle and starts his train moving.  The same noise might be very disturbing in a steam locomotive.  I don't know.  All my Bachmann steamers have "silent drive" decoders, either Tsunami or Digitrax.  They both still make motor noise - just ask my dogs - but it is pitched too high for me to hear.  To me, they are silent.  Bachmann decoders are not silent because silent decoders are generally not compatible with the radio frequency noise suppression circuits Bachmann uses to meet international standards.

If the noise bothers you, may I suggest replacing the original decoder with a silent drive one.  These can be had for less than $20.  For a few more dollars, you can buy one with BEMF control.  This modern marvel of technology can produce low speed performance almost beyond belief.  Diesel switchers that can pick up a caboose and not only avoid spilling the conductor's soup, they don't even cause waves in it.  Steam locomotives that start reliably at step 1 on the throttle and move on down the track at one or two miles per hour until you advance the throttle.  You suddenly have a whole new appreciation of the valve gear.

Even if this does not fully answer your questions, I hope it at least gives you somethings to think about.

Jim   

[Cooped]

Thanks again. Both run much quieter on DC so I think I'll try upgrading the decoders. I'm very fond of the idea of BEMF control, it's one of the reasons I wanted to upgrade to DCC in the first place.

Dan

[ScottyB]

I've never liked the noise coming from the stock Bachmann decoders, so I always replace them.

It has something to do with the frequency that is being sent to the decoder.  Sometimes if you remove all references to DC control from the decoder, that can solve it too.  With the stock decoders, I believe changing CV 29 to a value of 2, and CV 50 to a value of 4 solves this.

Good luck!
Scott