setting factory defaults on a decoder

[pdlethbridge]

I used my NCE power cab to reprogram a couple of digitrax decoders. Both were reprogrammed using option 7 on the programming track. I noticed that as each CV was reprogrammed, the motor would turn slightly. Is this normal? And after the programming, the engine still would not run. I tried both decoders. The motor must work otherwise why would it turn while reprogramming?

[Yampa Bob]

I'm being nice today, instead of a "stomp", I'll just give you a "bump". 

When I change addresses with my EZCommand, the loco moves a bit, but of course it runs when I'm done. 

[pdlethbridge]

This was using a dh123 on a bowser 'old lady' 2-8-0. The engine runs fine on analog but it won't do a  thing on DCC. I've tried 3 decoders. I wired the orange and gray to the motor leads of the  DCC ready dc71 motor, red wire to tender and black to engine frame. The motor would turn slightly when setting program defaults on the programming track.

[Yampa Bob]

So you just ignored my little "jab" huh? Have you tried running it with your EZ Command yet?

Do the left pickups on the loco connect to the frame?

[Jim Banner]

How old is your old lady?  I mean the one by Bowser.  If it was manufactured last century, it has the OLD dc71 motor which was NOT DCC ready.  If it was bought as new old stock, it may not have the new dc71 motor.  If it was bought "as new" then the previous owner may have bought it for the DCC friendly new motor and swapped motors before reselling it.  Now that Pittman has lost interest in the hobby market, that may be the only way to get the new motor.

The only way to tell is to disconnect the decoder from the motor and use an ohmmeter or a battery plus a test light to see if either of the motor terminals is connected to the frame.  If one is, then you have a difficult job ahead of you.  But at least you were trying decoders with built in short circuit protection.  Otherwise you would have three crispy critters to throw on the junk pile. 

[pdlethbridge]

Jim, I used a brand new DC-71which has the skewed armature and wires on each bush, a very DCC friendly motor

[Jim Banner]

The new DC-71 is indeed DCC friendly.  But being an open frame motor, it draws a bit more current than a can motor.  Enough more that the manufacturer recommends using a 2 amp decoder.  The DZ123 is a one amp decoder, so that is why it is refusing to run this motor - it sees it as a short, or at least as an overload, which shuts it down.  But better to have the decoder shut down than burn up.

for more information, click on the link below:

http://www.bowser-trains.com/hoother/motors.pdf

[pdlethbridge]

I was using a DH 123

[Jim Banner]

Sorry about that.  The DH123 is closer, but still no cigar.  It is rated at 1.5 amps continuous, 2 amps peak.

NCE recommends their D15SR for Bowser products and as a direct replacement for the DH123.  It is rated 1.3 amps continuous, 2 amps peak.  I know you are trying to avoid measuring your motor's stall current, so there is no guarantee that the D15SR will work either.  As mentioned in your first post the motor kicks when you are programming it so it is not a dead short.  (The kick is normal.)  But it may be drawing a bit more current than anticipated.

After installing the DH123 decoders, did you try running the locomotive on address 03 before changing the programming?  By running on the default address you can be sure the decoder is either working or not working before adding programming problems to the mix.  If you did not successfully run on address 03, you could try that now by programming an 8 into CV08.  That should reset the decoder to factory defaults. 

[pdlethbridge]

I reset all the decoders to the factory defaults and using address 3 I got nothing. I assume that the cogging is normal and indicates a working decoder. Why would the NCE decoder (1.3amps / 2amps) be better than the dh123 (1.5amps / 2amps)

[Jim Banner]

Why would the NCE decoder (1.3amps / 2amps) be better than the dh123 (1.5amps / 2amps)

I am not sure that it would be better.  On the other hand, I am not sure that it would not be better.  It is just the decoder that NCE recommends for Bowser locomotives.

One possible difference between these decoders could be in the way they handle overloads.  Neither Digitrax nor NCE is too forth coming with this information.  However, based on their external behaviour, one can infer that Digitrax uses two schemes in their DH123.  One scheme limits the instantaneous maximum current to 2 amps.  If the stall current of the motor exceeds 2 amps at any time, even for an instant, then the decoder shuts itself down and stays shut down until the power is removed.  So if the initial pulse of power to the motor exceeds 2 amps, the motor will never start.  Thus the importance of knowing the stall current of the motor.

The other scheme is based on overheating.  If the average current exceeds about 1.5 amps then the decoder overheats and shuts down until it cools off again.  The locomotive will run for a while, then stop, then after a time run again.  The exact current at which this happens varies with how much cooling the decoder gets, the temperature outside the locomotive, and the other sources of heat inside the locomotive.

The NCE D15SR decoder may use only the over heat shut down protection.  I don't know, I am just guessing.  If is does not have over current protection then an instantaneous start current of say 2.3 amps would not shut this decoder down even though it would shut down the DH123.  The average current to keep the motor running once it is started is probably only 1 amp or so which is within the capability of both decoders.

Now when Pittman says to use a 2 amp decoder, what do they mean?  A decoder rated for 2 amp average current?  A decoder rated for 2 amps peak? Or what?  As you have no doubt noticed, many manufacturers give only one current rating for their decoders.  That rating seems to be an average current rating.  Many times these decoders get used in applications where the stall current is higher than the decoder's rating and initially they work just fine.  Other companies, NCE and Digitrax among them, tell you both ratings.  In this case, the peak current rating is usually 30% to 50% higher than the average current rating.  Based on all of this, when Pittman says you need a 2 amp decoder (one rating only) I interpret this as a decoder rated for 2 amps continuous, 2.6 or more amps peak.  In light of our other knowledge, it would seem that such a decoder would be needed for its high peak current rating rather than its high continuous current rating.

I suspect that the NCE D15SR would work because (a) NCE says it will and (b) I suspect it does not use an over current protection scheme.  I believe it would be worth a try, but as I said before, I just cannot give you my personal guarantee that it will work.

[pdlethbridge]

Very interesting. Other than the humongous g scale decoders, does any one sell a 2-3 amp unit that would fit the old lady's tender?

[Yampa Bob]

Ummmm, no comment. 

[pdlethbridge]

you are soooooo bad!

[Jim Banner]

MRC makes a decoder that they call an H0/G decoder.  It is their AD321 and is rated for 3 amps.  It is about the size of an older H0 decoder, 50mm x 20mm x 7mm (2" long, a tad over 3/4" wide and 3/8" thick.)  I use these in single motor G-scale applications, such as in Bachmann Big Haulers and they work just fine.  They are also relatively cheap.  Even though MRC's list price is something like $40, you can buy them for $28 and change at Trainworld and other places.  If you are looking for them on the web, check under G-scale decoders, where most places list them.