Minor DCC problem

[jeffrey-wimberly]

Recently I fitted an Athearn BB F7 A-B set with Digitrax decoders (DZ125's). They work fine most of the time but sometimes the lead unit won't start up on DCC (usually when the DCC unit is turned on for the first time of the day). If I switch the block to DC and give the locos enough power to just move them then shut down and switch the block back to DCC it then will start up and run just fine. Am I correct in assuming that this is because the decoder is having trouble determining whether or not the current it's getting is DC or DCC? I'm using a Bachmann DCC system so changing CV's is out at this time. Is there another way I can correct this or do I continue with the method I've been using? Starting the units separately isn't possible as the two units are hardwired together so they pick up power like a single sixteen wheel unit.

 

[Rico]

Yeah it does sound like a cv thing.
If you've hardwired them together as a unit you could likely get by with only one decoder maybe?

 

[grumpybob]

Jeffrey,

I don't know what # you have assigned to the engine, so I don't know if you have a long address or short. IE Below 127, or above. The one thing you want to do is make sure that Analog mode is shut off. So if you have an engine with an address of 127 or less, then CV29 = 2. If you have an address above 127 then CV29 = 34.

Also, I would check the amount of power coming to the tracks to make sure that you have sufficient voltage on all your rails. If you have drop offs, this can cause decoders to operate wierdly. I would suggest you meter the rails to check that out.

Bob A.

 

[jeffrey-wimberly]

Jeffrey,

I don't know what # you have assigned to the engine, so I don't know if you have a long address or short. IE Below 127, or above. The one thing you want to do is make sure that Analog mode is shut off. So if you have an engine with an address of 127 or less, then CV29 = 2. If you have an address above 127 then CV29 = 34.

Also, I would check the amount of power coming to the tracks to make sure that you have sufficient voltage on all your rails. If you have drop offs, this can cause decoders to operate wierdly. I would suggest you meter the rails to check that out.

Bob A.

You have some very good points. The address is 02, the Bachmann EZ-Command only goes up to 09. As for the track power, I checked that when this problem reared it's head. I have feeders about every six feet and all the rail joiners in each block are soldered, including the turnouts. I read steady power all around the track and my ammeter records a pull of less than .75 amps. That's from both locos together. They're Athearn's, you tell me.

 

[grumpybob]

Jeffrey,

I have had difficulty with Athearn with there older motors because of the draw. Since the Digitrax DZ125 is rated at an AMP it is possible the the initial start up of both units may be just enough to cause a problem. Your measurement of .75 amps at run may indicate that in order to run both of these engines, you need a decoder in each because at a stall you could be drawing too much power for the one decoder to function properly. With that you can assign both to 02 and not have a problem.

Just my thoughts.

Bob Adams

 

[CanuckMark]

It may be one of two different issues, either too much load on the decoder (with the two locos) or improper reading of the codes themselves.

Yeah, it is possible the Athearns paired on one decoder could be an issue. I have an single Athearn F7 that draws twice as much power as a pair of P2K Eries. The Digitrax might be going into overload.

The other problem might be the way the controller initializes the loco. There is a way that short addresses can be sent when only a single loco/decoder is throttled, especially when only one address is being used at a time - when it uses that mode the loco might not read the data string properly and not respond.

If the above sounds plausible, try this. Do a fresh start (like when you say it doesn't work). Don't move the engine. Set the controller to run a different engine (it doesn't have to exist, say #7). Run the ficticious engine for a sec, then set to control your #2 engine. (That should reset the loco number code at the rails.) Try to move the engine again, see if it works.

Mark

 

[UP2CSX]

I think Mark's second suggestion is the most likely fix for the problem. I'll be interested to hear if it does indeed fix the problem. As you know, the E-Z Command system only handles one amp so .75 amps may actually exceed one amp on starting just enough to confuse the controller without putting it in overload. One other thought. Does the same thing occur no matteer which is the lead unit, e.g., does the pair run correctly if the B unit is in the lead?

 

[jeffrey-wimberly]

Yeah, it is possible the Athearns paired on one decoder could be an issue. I have an single Athearn F7 that draws twice as much power as a pair of P2K Eries. The Digitrax might be going into overload.


Mark

Whoa! I think you missed me at the fork in the road. It's not two locos paired onto one decoder. Each loco has it's own decoder. Two loco, two decoders. Identical decoders, both programmed the same and both have the same address. It's the locos that are paired together as one unit, not the decoders. They function independently. Both locos have the new 5-pole skew wound motors. They pull very little power, turning the throttle knob one inch gets them up to 90+ scale miles per hour. Add to that that I'm running two P2K E units on the other line (DC).

 

[jeffrey-wimberly]

Since the Digitrax DZ125 is rated at an AMP it is possible the the initial start up of both units may be just enough to cause a problem. Your measurement of .75 amps at run may indicate that in order to run both of these engines, you need a decoder in each because at a stall you could be drawing too much power for the one decoder to function properly. With that you can assign both to 02 and not have a problem.

Bob Adams

Both locos have their own decoders. I don't know where this thing with one decoder came up. The measurement of .75 amps wasn't at run, it was at the max load of both locos together, so each loco is drawing about .37 amps at the most. They have the new 5-pole skew wound motors. Running they're drawing less than that. I thought something was wrong with the meter so I tested it on my Athearn PA2. It drew .80 amps at full load, what you would call maximum stall, exactly what it's supposed to. It has one of the old motors (5-pole, not skew wound).

 

[Rico]

"I don't know where this thing with one decoder came up."
Some joker earlier on suggested trying one decoder, what a rookie!
Actually what I shoukd have added that you'd need a decoder that can handle the extra load of two motors, like the larger scales.
Sorry about that chief...