Voltage Drop

[djp]

Hi All,
        Just a question about an issue that has me baffled. I've got a Bachman K4-6-2 DCC onboard engine. Has been working really well for the past 6 years. Lately i've found a voltage drop eveytime i start her up. The drop remains and increases as i increase the throttle. Track voltage is 14V. Drops to 12V at 1/4th throttle to 1/2 throttle. Drops to 10V at full throttle. This is with about 8 rolling stock and by itself as well. Any ideas? I have lubed all the gears,rods and wheels. Thanks.

[Joe Satnik]

Dear djp,

Great question.

There is some kind of (abnormally high?) resistance between your controller and your track. 

Could be loose or dirty connections, or a cable that has been flexed to the point of breaking nearly all its internal copper strands.

As you command your loco to take (draw) more amperage from the controller, it passes through some kind of high resistance which drops the voltage.

Current x Resistance = Voltage  (IR=V)  a.k.a. "Ohm's Law".

Hope this helps.

Sincerely,

Joe Satnik

[Hunt]

Check the drag of all rolling stock.   

[Hunt]

Examine wiring to and in tender.

Remove any lighted or DCC decoder equipped rolling stock. Then check voltage level.

[djp]

Joe and Hunt,
Thanks for the quick reply's. My mistake i did not furnish you with all details.
I have 6 other steamers pulling the same rolling stock that run on the same layout but there is no drop in Voltage.
I have run the 4-6-2 by itself and removed all other engines from the layout including lighted rolling stock. I've unplugged the tender wires and cleaned the terminals with isopropyl alcohol. The only thing not done is open up the tender.
Could it be that the decoder has finally decided to call it quits?
Thanks.

[Joe Satnik]

Sounds like it could be on the motor side of the decoder.

Can you easily unplug the decoder?

Is there a dummy plug available to troubleshoot the motor and chassis with a  DC powerpack?

Possiblities, not in order:

1. Short in output of decoder.

2. Short in wiring from decoder to motor.

3. Bad brushes, dirty commutator or shorted motor windings.

4. Motor wiring not isolated from chassis or wheel pickups.

5. Mechanical binding in chassis, either driver wheels out of quarter,

driveline out of alignment, wheels or wheel bearings dragging, etc.

Hope this helps.

Joe

[Hunt]

The motor may be about to fail.

Have you put a drop of Motor Bearing Lube on the motor bearings?

[Len]

How often do you run this loco? If it gets run regularly, and this is starting after 6 years of use, my first thought would be the motor brushes are wearing out. Second though would be the insulation on the motor windings is starting to break down.

Either way, it would mean replacing the motor.

Len

[djp]

Hi Guys,
            I just replaced the decoder with a spare one i had and Hey Presto !!! we are in business.
Everything back to normal. Joe, i guess your option 1 was the culprit.
            I was just wondering instead of tossing away the decoder if i could reset it and see if i could salvage it. Coz in India a $20 decoder costs $40, so any chance of keeping it is a bonus.
            I have the MRC Prodigy Express but i'm not sure what make the decoder is. Anybody have any ideas? Its the Bachman K462 Spectrum. Engine is about 6 yrs old.
            Thanks.

[Joe Satnik]

Hi, djp.

Check to see if the problem follows the decoder by plugging it back in, or plugging it into another loco. 

It's a possibility that a short was cleared by moving stuff around in original loco,

e.g., 2 bare wires touching (shorting), jostled into not touching.

Hope this helps.

Sincerely,

Joe Satnik

[electrical whiz kid]

For what it is worth, every I find worn brushes to be a culprit in any brush type (series wound, universal, etc), the unit over draws, runs hot, sparks, and makes terrible sounds...
I would isolate the motor from the DCC component, and just run it at straight DC; see what happens.

[Hunt]

. . . i'm not sure what make the decoder is. Anybody have any ideas? Its the Bachman K462 Spectrum. Engine is about 6 yrs old.
            Thanks.

It is a Bachmann decoder Lenz based.

The factory installed Bachmann non-sound decoder in the HO K 4-6-2 Pacific DCC on Board is the result of a partnership between Bachmann Industries Inc., USA and Lenz Elektronik GmbH, Germany

CV 8 = 101
CV 7 = 46

[djp]

Hi All,
Joe, you hit the nail on the head with your suggestion. I swapped decoders and once again came out tops. The supposedly faulty decoder is doing great in another loco and the K4-6-2 is doing great again with the swapped decoder. So i am back in business and have stored my spare decoder away for a rainy day. This is one really weird phenomenon. I installed a MRC decoder in the K4-6-2.

Hunt, thanks for all the suggestions which shows that so many things can be the reason for a problem like this.
Appreciate your info on the Lenz Decoder and the CV's. Can those two CV's and values be changed at the same time or do i have to do it one at a time? Does it need to be done only on a program track? or can i do it on the main track [I can remove all my other loco's]. The reason i'm asking is coz there seems to be a problem with my "Prog Track function" on my MRC.

Len and Electrical Whiz Kid, thanks for your suggestions too. They are the other possibilities to consider for a problem like this. Appreciate it.

[Hunt]

. . .
Hunt, thanks for all the suggestions which shows that so many things can be the reason for a problem like this.
Appreciate your info on the Lenz Decoder and the CV's. Can those two CV's and values be changed . . .

It is a Bachmann decoder built in partnership with Lenz.

Both CVs are Read Only.  You cannot change them
CV 7 Manufacturer Version No     46      is assigned by manufacturer
CV 8 Manufactured ID               101      is assigned by NMRA

[djp]

Thanks again ALL for the help and info.