2 with 1?

[johncolley]

My question has to do with fairly modern locos. There are micro-mini connectors available. I have some Stewart FT's drawbar connected, and I installed a Tsunami with sound in a B unit, but ran headlight leads to the A unit through the connecting door windows. It got me to thinking that with the low power settings I use up to 25-35 mph on 2% grades why couldn't I run a second set of leads to the motor in the A unit and run them off  the one decoder? What is risk of blowing (letting the smoke out) the decoder? Anyone out there done this? John

[Hamltnblue]

 It can be done as long as you stay below the rating of the decoder.  You're obviously not going to get as much speed either. It does seem to be a lot of work for minimum if any savings.

[selector]

I agree, the electrical logic is okay, but the practical nature of the maximum designed throughput for the decoder may be a problem just one time too many. 

Very short spikes of power somewhat above 2 amps are not likely to hurt the decoder, but pushing 2 amps through one for more than a minute (maybe much less) is going to really put you close or over the limits in many cases.  So, I think you could safely do it, but not if you are forgetful.  If you keep the car numbers low and/or grades to a minimum, you may be just fine, often running a total of 1 or 1.5 amps through the two motors.  A decoder not crowded in tight or warm confines where it can cool should be fine.

If you have sound decoders and a speaker or two installed, I would expect you to cook the decoder in short order unless you run very short trains of maybe 6-10 cars.  Depends on the tightness of the drive-trains in the locomotives and how free-wheeling and heavy your cars are.  Curves and grades just add to the amperage requirement.

-Crandell

[cacole]

With NCE D13SR decoders costing as little as $12 each in lots of 10, I think you're better off putting a separate decoder into the other loco for motor control.

[locoi1sa]

 You are taking power from the decoder to drive the amp and speaker with one motor. Controlling another motor will rob power from the decoder and cause more heat. For what its worth, why fry a $100 decoder when you really need a $12 decoder for the additional motor.

    Pete

[richg1998]

It can be done but you have to know what you are doing. Measure the motor current at 12 volts DC with the drivers slipping. Choose the appropriate decoder. Wire the motors in parallel.

I have a PCM HO A/B F3 in Lashed Up mode. Decoder in the A unit with motors and speakers in the A and B units. The LokSound v3.5 decoder in the A unit runs everything. The motors and speakers are in parallel so I can use the A unit by itself. The receptacle is in the A unit and the six pin plug hangs out the “front” of the B unit and the wiring is not seen when both are coupled together.

I can run them at HO scale prototypical speeds.

I bought a BLI HO F7 A/B set, refurbished, $100.00, no DCC or sound, DC only and intalled a Tsunami in each with speakers. I can run all four in a consist with no issues.

Rich

[CSX Robert]

Hamltnblue

...You're obviously not going to get as much speed either...

Running two motors from one decoder is not going to give you any less speed.

[Hamltnblue]

 Actually you usually will. You can only increase the throttle until the decoder hits max current.  Depending on the draw of the loco motors it should max out at a much lower speed than normal.

[rrinker]

 If the combined peak current draw of the motors is less than the decoder's limit (which is has to be, otherwise you run the risk of blowing the decoder if somethig should stall the locos), there should be no slowing - the decoder is quite capable of passing full voltage to whatever load is connected. A pais of 1/4 amp motors in parallel or one 1/2 amp motor - it's all the same.

                            --Randy

 

 

[CSX Robert]

Yea, want Randy said. Maybe I should have been a little clearer in my answer, but IF you select a decoder that is rated for enough current for both motors, then there will be no slowing. If the decoder is not rated for enough current, then you may be limited somewhat in speed, but you would probably end up frying the decoder anyway so the question becomes moot.

[jeffrey-wimberly]

 

johncolley

My question has to do with fairly modern locos. There are micro-mini connectors available. I have some Stewart FT's drawbar connected, and I installed a Tsunami with sound in a B unit, but ran headlight leads to the A unit through the connecting door windows. It got me to thinking that with the low power settings I use up to 25-35 mph on 2% grades why couldn't I run a second set of leads to the motor in the A unit and run them off  the one decoder? What is risk of blowing (letting the smoke out) the decoder? Anyone out there done this? John

I've tried multi-motor control with non-sound decoders. While it would seem to be a solution of sorts I ran into many problems with it. The decoder is set up to control one motor. When more than one is being run by one decoder motor performance issues often crop up. Issue one, when coming down a grade the laed loco will speed up a bit. The decoder will counter by slowing the motor but in doing so also slows the motor in the second unit causing a sort of back and forth rocking motion. I've had this happen with BEMF equipped decoders as well as non-BEMF decoders. The same issue would also crop up when going up a grade. Moreover the added power draw of two motors, no matter how efficient, eventually fries the decoder. You're better off putting separate decoders in each unit.

[johncolley]

Thanks to all who replied. I should have added that the reason I was considering doing this is because I tried using a Digitrax DS164D in the A unit and it is practically impossible to speed match the two units. The Digi uses CV's 2, 5, and 6, whereas the Tsu uses CV's 2, 209, and 210 with different effects on the last two for top speed and trimming instead of the normal high and mid. I Guess the best answer is to start a change jar for the second Tsunami and bite the bullet, eh?John

[rrinker]

 Or use a 28 step speed table instead of start/mid/max since the Tsunami doesn't really do that. I was able to match a Quantum Rev-U to a DH123 well enough with start/mid/max. It wasn't perfect at each speed, but it doesn't have to be. Close is usually good enough.

                                       --Randy

 

[Texas Zepher]

johncolley

why couldn't I run a second set of leads to the motor in the A unit and run them off  the one decoder? What is risk of blowing (letting the smoke out) the decoder? Anyone out there done this?

I have done many units in this manner.   I originally did it because decoders of the early 1980s era were so expensive and large they required the space available in a "B" unit. Back then the decoder was $60 and the Athern BB locos were $19 each.  It made sense to use a single decoder to power both the A & B with it.     As a prior poster noted this is also how PCM does their AB sets.  There is a decoder in one unit that has three sets of wire between the units.  One for power, one for the motor, and one for the speaker. The decoder in the A unit controls the motor and the sound in the "B" unit.

The reason I don't like to do this is just because of the wires.  I hate seeing the wires between the units and I hate dealing with two units connected together when doing repair maintenance.  I even hate the ones with plugs because they are so hard to get together and apart.  I know that the first thing that is going to break on the PCM units is that wire.    I suppose the plug part is not an issue when one has a perminant layout where the locos are just taken out and kept on the layout.   Mine come out and return to their boxes often.

 

[richg1998]

 I normally leave my PCM units connected together and I take them in a model train carry box so not an issue for me. The couplers are still connected and the plug stays inserted.

The diaphragms hide the wires quite well. Most people have no idea the A & B units are connected.

MY BLI A & B units with Tsunami are on the same address and operate quite well.

Another fellow in our club has two near identical diesels that do not consist very well with each their own address. He runs them under one address quite well.

Rich

[Hamltnblue]

johncolley

Thanks to all who replied. I should have added that the reason I was considering doing this is because I tried using a Digitrax DS164D in the A unit and it is practically impossible to speed match the two units. The Digi uses CV's 2, 5, and 6, whereas the Tsu uses CV's 2, 209, and 210 with different effects on the last two for top speed and trimming instead of the normal high and mid. I Guess the best answer is to start a change jar for the second Tsunami and bite the bullet, eh?John

 

The Tsunami should be the slower unit since it's sound.  Use that as a base and keep it stock.  Then try to match the second decoder to that one.  If necessary you can do a full speed table but it's usually not necessary.

[jwhitten]

johncolley

Thanks to all who replied. I should have added that the reason I was considering doing this is because I tried using a Digitrax DS164D in the A unit and it is practically impossible to speed match the two units. The Digi uses CV's 2, 5, and 6, whereas the Tsu uses CV's 2, 209, and 210 with different effects on the last two for top speed and trimming instead of the normal high and mid. I Guess the best answer is to start a change jar for the second Tsunami and bite the bullet, eh?John

 

 

Why not just get two small motor-only decoders, even N or Z scale to get the size down. As long as they'll produce the amp-oomph you need, doesn't matter if they're big or small. Then use your sound decoder in sound-only mode (pull the motor leads if you have to). Then your motor decoders can operate as a matched set and you can tweak the cv's to get good speed matching between the units. Set the sound decoder to the same address as the motor decoder and let 'er rip. Should run fine.

 

John

[Texas Zepher]

johncolley

I should have added that the reason I was considering doing this is because I tried using a Digitrax DS164D in the A unit and it is practically impossible to speed match the two units. The Digi uses CV's 2, 5, and 6, whereas the Tsu uses CV's 2, 209, and 210 with different effects on the last two for top speed and trimming instead of the normal high and mid.

It should still be possible to speed match them.   Have you tried one of the computer programs that matches the decoder to a graph on the screen?  Set the graph program one, then the other.

Hamltnblue

The Tsunami should be the slower unit since it's sound.

??? Care to explain that statement.