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using mobile decoder without motor; simulate motor load with a resistor???

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using mobile decoder without motor; simulate motor load with a resistor???
Posted by SpringStreet on Thursday, February 13, 2020 10:37 AM

Apologies if this has been discussed before; I've searched for but not found prior discussions.  If I use a mobile decoder without a motor attached, do I need to simulate the normal load of a motor for the decoder to operate properly? (I assume this would mean a resistor in place of a motor, but what value?) 

Examples of this situation: using a few extra mobile decoders I have for passenger car lighting only. Or: keeping an older loco's original mobile sound decoder in place for sound purposes (disconnecting the motor from it), and adding a newer mobile-only decoder for better motor control (yes, there might be added issus of having the sound sync with speed properly, and programming gets more complicated, etc.).

NCE's website mentions adding a 47K 1/4 watt resistor to simulate motor load for one of its mobile decoders if it is used for lighting only, but I'm wondering if that's generic information for any decoder, or perhaps specific for the particular NCE decoder mentioned in NCE's help files. I've not found any guidance yet from other decoder manufacturer websites.

Thanks for your help.

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Posted by RR_Mel on Thursday, February 13, 2020 11:37 AM

Motors have low resistance so anything from 2K up should work.  I use function only decoders for my lighting, cheaper and physically smaller.
 
 
 
Mel
 
 
 
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Posted by rrinker on Thursday, February 13, 2020 12:54 PM

 The problem with using a lower value similar to an actual motor is then you need to use a fairly high wattage resistor, which can get hot, unless you also remember to go in and program the speed table, or at least CV5 max to something low. If CV2 is 0, then CV5 can be as low as 1. 

Anything in k's should be fine and not get hot. The whole need is to put some sort of a load pulse on the program track to ack and read back CVs - the decoder will normally pulse the motor. NCE's value should be fine but smaller will be OK too. 

"Like an actual motor" are resistors of say 100 ohm. You'd need a 2 watt resistor to handle full track voltage, and it would be generating right at 2 watts of heat, too. a 5 watt would be better at 100 ohms. ANd that much heat enclosed in the loco or car shell is  not good. There's no reason for it, a larger resistor won't get nearly so warm and will still do the job.

                                           --Randy


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Posted by MisterBeasley on Thursday, February 13, 2020 1:43 PM

It's been a while since I did this, but my recollection is that a resistor is only needed to program the decoder, even if you're just setting the address.

I would disconnect the resistor after programming, since you shouldn't be applying any power to the "motor" anyway.

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Posted by Mark R. on Thursday, February 13, 2020 1:47 PM

MisterBeasley

It's been a while since I did this, but my recollection is that a resistor is only needed to program the decoder, even if you're just setting the address.

I would disconnect the resistor after programming, since you shouldn't be applying any power to the "motor" anyway.

 

That's what I've always done. A 100 ohm resistor for programming, then remove the resistor for operation. Chances of me having to re-program again down the road are pretty slim. You could even leave the resistor in place as long as you don't advance the throttle while that particular address is accessed.

Mark.

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Posted by gregc on Thursday, February 13, 2020 1:57 PM

Mark R.
100 ohm resistor for programming,

so the controller (e.g. PowerCab) can sense the current drain used to communicate back to the controller

greg - Philadelphia & Reading / Reading

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Posted by SpringStreet on Thursday, February 13, 2020 9:19 PM

Thanks for all the helpful replies. One follow up question: what would happen if the resistor is left in place and the throttle is accidentally increased off of step 0? Heat problems? Decoder damage? Something else? Nothing? I'm wondering about the convenience of leaving the resistor in place versus any risk that entails. Thanks very much.

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Posted by RR_Mel on Thursday, February 13, 2020 9:32 PM

SpringStreet

Thanks for all the helpful replies. One follow up question: what would happen if the resistor is left in place and the throttle is accidentally increased off of step 0? Heat problems? Decoder damage? Something else? Nothing? I'm wondering about the convenience of leaving the resistor in place versus any risk that entails. Thanks very much.

 

Assuming full throttle 12 Volts DC, 12 Volts 2000Ω = .006 Amps or .072 Watts.  No problem.
 
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Posted by gregc on Friday, February 14, 2020 4:43 AM

SpringStreet
I'm wondering about the convenience of leaving the resistor in place versus any risk that entails.

a S-9.2.3 Service Mode Basic Acknowledgement requires at least 60ma, or a 200 Ohm resistor at 12V.

a 100 Ohm resistor would draw more than a Watt (1.4 = 12^2 /100)

greg - Philadelphia & Reading / Reading

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Posted by BigDaddy on Friday, February 14, 2020 7:15 AM

SpringStreet
One follow up question: what would happen if the resistor is left in place and the throttle is accidentally increased off of step 0?

What happens to the voltage on a DCC system when you increase the throttle?  Nothing

Henry

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Posted by rrinker on Friday, February 14, 2020 9:34 AM

 But the apparent voltage at the motor terminals of the decoder increases. If the resistor is left connected, everything will be fine if the decoder is set to an absolute minimum top speed, with CV5 set to 1 or 2. Then even if you acciently turn it to full throttle, the resistor won;t get hot.

                                  --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by richg1998 on Saturday, February 15, 2020 11:57 AM

I did that some years ago. I adjusted one or two CV's. Don't remember which ones so the resistor did not get hot. I used a Tsunami Micro. Bruce Petrarca, Mr. DCC  use to have a DCC site with the explantion. His site is gone.

I had put a DZ125 in a Mantua 0-6-0, turned it around to become a 2-6-0 oil fired cab forward and put a Bachmann Vanderbilt oil tender behind it with the micro in it. It worked very well.

I found photos of a NG cab forward 4-4-0 made around 1900 I think.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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Posted by rrinker on Saturday, February 15, 2020 12:20 PM

 NPC #21. Really crazy loco that had some serious design flaws, but it was the first in many things, not just the first cab forward. One of the first if not the first locos designed as an oil burner, and the first to use a marine boiler, which explains the really odd appearance. Then tender was insteresting - two tanks on wheels, one water, one oil. 

 Perhaps a little bit the inspiration for the Kemtron cab front to convert a Lil Joe to a cab forward.

 Got any pictures of that Mantua cab forward conversion?

                                     --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by BigDaddy on Saturday, February 15, 2020 5:50 PM

rrinker
But the apparent voltage at the motor terminals of the decoder increases.

There you go, I post my thoughts and find out how much I have to learn.Ashamed  How do lurkers find out what they don't know?Hmm

Henry

COB Potomac & Northern

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Posted by richg1998 on Wednesday, February 19, 2020 3:14 PM

No more Photo Bucket, Sorry. I still have the photos. The Kemtron front inspired me though. It did come out nice.

Rich

 

 

 

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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