HO Decoders in G Scale Trains

[jviss]

I am looking around at DCC systems, and decoders in particular, for my Bachmann Big Hauler Railroad.  I really like the Soundtraxx decoder, the TSU-1000, P/N 826116, for my 4-6-0 locomotives.  

I just measured over 3 Amps stall current for my new Anniversary loco chassis!  This decoder is rated at 1 Amp.  However, I never see more than about 800 mA in normal operation.

I thought for a while about building a current follower, but then a simpler solution occurred to me.  Why not put a 1A circuit breaker in the motor circuit?    BAD IDEA!  See reply umber 12, below.

A 1A, resettable C.B. can be had for about $7., quantity one.  It can handle up to 35 Volts, and trips in from 4.5 to 28 seconds.  Sounds ideal, to me; I'm assuming the TSU-1000 has about 50% margin and that the damage would be thermally-related, so 4.5 to 28s at stall currents should protect the decoder.

Has anyone tried this?

[Mark Oles]

Why wouldn't you use a DCC decoder with components designed for G scale? 

[jviss]

Thanks, that's a good question, and it nags me a bit, too.  I can't find, or figure out if there exists, a G-Scale decoder that runs the motor, functions, and produces sound as the Soundtraxx decoder does.  I find the Digitrax documentation and website to be a bit obtuse - there seems to be an assumption that people going there already know the structure of the product line, but I don't.  So, does anyone make a G-Scale equivalent of the Soundtraxx TSU-1000? 

Thanks,

jv

[Kevin Strong]

There are a good handful of sound/motor control decoders for large scale. QSI, ESU (LokSound), Zimo, Massoth, Piko all make motor/sound combination decoders designed for large scale. You can also pair a motor-only decoder with a standalone sound decoder from Phoenix (though the combo units are generally more budget friendly). Also, check in with TCS to see if they're close on releasing their large scale version of their "WOW" decoder. Soundtraxx was at one point going to release a 4-amp version of their Tsunami, but that got back-burnered a while ago, and may be completely off the stove at this point in the game. There used to be a few companies that "beefed up" the 1-amp tsunamis so they could handle about 3 amps. Basically, they put a big honkin' heat sink on the Tsunami. Personally, I'd rather spend the money on a decoder specifically designed for large scale.

I use the QSI "Titan" decoders in some of my locos, and they're great! I've played with ESU's decoders at a train show, and liked what I saw and heard. I reviewed the Piko decoder for GR a year or two back. It's okay, but comparatively limited in terms of sounds.

Later,

K

[jviss]

Thanks for the detailed reply, Kevin.  I checked out the decoder vendors you cited, thanks.  The prices are high, like on the order of two or more times higher than the Soundtraxx unit; admittedly, they handle more motor current, but otherwise no particular advantage.  In fact, I prefer the Soundtraxx.  

I should say at this point that I'm an electrical engineer, and have started thinking about this topic in engineering terms, specifically, what my requirements and desired system operational parameters are, and what behavior I want, both nominally and in extreme conditions.  

First, 'though I did do a brief test to see what is the stall current of my Bachmann Anniversary chassis, generation 5, I did not want to test it to destruction, and did it without building any elaborate test stand.  But, yes, I saw current over 3 Amps, and that was enough for me at that moment.  The voltage at that time was about 14V.  

This morning it occurred to me the idea of putting a decoder in a locomotive that can source the motor's stall current is to sacrifice the motor when the stall condition occurs; and likewise, putting in a decoder that will smoke when the stall condition occurs is to sacrifice the decoder.  Neither alternative represents a good design to me.

Stalling the motor is not normal operation!  If this happens it's because something has gone wrong in operation, or the combination of available traction and motor power is inappropriate.  

My design requirement is to have a motor that can pull within its safe operating region the load I want to subject it to, and to employ a decoder that can supply sufficient current to support this, including any normal operating mode transients.  I would further protect the motor, decoder, wiring, and contacts with some kind of circuit protection device.  

So, my BBH Anniversary loco never draws 1 Amp or more in normal operation on my layout, which is indoors and level (no grades).  I think a Soundtraxx TSU-1000 will do just fine, and I might even add a 1 A circuit breaker to protect the decoder.

I don't know yet if the decoder can sustain a stall current condition long enough for a commonly available 1 Amp breaker to trip; and, I don't know if the breaker will interfere with back EMF.

Sound reasonable?

Update: after researching circuit breakers, I will probably go with a fuse, like an ATOF automotive, 32V rating, low current fuse: much lower resistance, more choices of blow speed, much more easily sourced, and much cheaper.

[jviss]

Here's an interesting update.  I now own two (2) Anniversary 4-6-0's, one a new chassis that I put under my PRR loco, and a new Denver & Rio Grande Western "Bumble Bee" 4-6-0.  The former is the one for which I have never seen more than one Amp current, hauling eight cars plus the tender.  The most current is seen dragging this through a succession of left/right/left sections of steel track, set up that way because I ran out of straight sections (more are on the way).  The latter draws over one Amp at several points along the way. 

I was wondering why these two seemingly identical rigs are so different in operation.  I have a few hours on the former, and near zero on the latter; maybe the latter just needs to break in a bit?  Or could it be lubrication, or lack thereof?  Or maybe just a difference in motors?

[Kevin Strong]

Sound reasonable? In theory, putting current limits on the motor leads would protect the decoder. The other consideration, though, is the supply voltage. Most large scale DCC operators prefer track voltages between 20 - 24 volts. The top end on the Tsunami is listed at 22 volts. That'll work if your your track is limited to under that, but know you might have issues if you take your locos to run elsewhere. Most decoders designed for large scale can accommodate voltages greater than 24 volts.

Your risk, your reward. If it works, you've gotten two locos outfitted for what it would otherwise cost you to outfit one. If you smoke the decoder, you've lost the bet and the savings. From what I've seen online of the "beefed up" Tsunami decoders, the enemy with regard to its capacity is heat. If you can dissipate the heat via large heat sinks, you can probably get away using the decoders without much worry. Would I do it? On a 4-6-0, no. I'd rather spend the money on a decoder that I know can handle the current it's likely going to draw and not have to worry about extra steps or have that cloud hanging over me every time I put it on the track. For a small loco like an 0-4-0? Sure, so long as the track voltage doesn't exceed the decoder's maximum.

As for your two locos drawing different currents, it could be a break-in thing, it could be the motors, it could be differences between the plastic vs. metal drive train. It does, however, illustrate why you might want to reconsider using a decoder rated at only 1 amp for the locos, though.

Later,

K

[jviss]

Thanks again, Kevin.  I may have been hasty here, having purchased the TSU-1000, and the Digitrax Zephyr Xtra controller.  The controller documentation says the output is limited to 13 Volts- it's a bit vague and contradictory - but it seems it's rated for a maximum of 16. 8 VDC input ('do not exceed 16.5VDC on the next line), and the controller drops about 0.5VDC - so max to the track about 16V.   With the supplied DC power supply it will be more like 13.3VDC.  This might not be enough for the 4-6-0, plus I'm already marginal for current handling on the TSU-1000.  Yikes!  Might want to rethink this. 

Anyway, yes, I agree with your sentiment that there's comfort and more enjoyment in the confidence that you have design margin in the installation. 

[jviss]

An update on this for interested observers.

I'm returning the Digitrax Zephyr.  I like it, like the looks and the concept of a stationary cab with throttle know, brake lever, and all of those function buttons.  I just don't like that it's limited to 16 Volts and 3.5 Amps.   like the "jump ports" that allow DC controllers to be used as throttles.  I am not sure I couldn't have just added a booster to drive the track to higher voltages and currents, 'though I read the Zephyr could be used as a booster.  It would have been perfect if the Zephyr had a "G-scale" switch that allowed it to drive 24V at 5 or 8 or 10 Amps, perhaps with an external power supply.  Oh well.  I'm about to order the Super Chief 8 Amp starter set - quite a bit more money, but should suffice forever, for me.  I've also ordered a 30V 10A laboratory power supply to use instead of buying the PS2012, which at about $150 isn't a very good deal, and it's rather inflexible on output voltage, offering only 3 discrete steps of 13.8, 18, and 23V.  The lab supply has fine and coarse voltage and current adjustment knobs, a digital display for each of Volts and Amps, a built-in thermally controlled fan, and was half the price!

On decoders, I received the Tsunami TSU-1000.  It was $93.  It is a 1 Amp decoder, so marginal in the BBH 4-6-0.  Norm at Protocraft has offered to convert it for 3.5A operation for $70, exactly the difference between his price for converted Tsunamis and what I paid for mine.  Still thinking about it.  Meanwhile, I've found a G-Scale solution for mobile plus sound that's under $100: the Digitrax DH465 4 Amp HO/O gauge mobile decoder, coupled with their Sound Bug SFX006.  Street price combined this is $91.  Not sure I will try it yet, I like the Soundtraxx sound samples I've listened to, and I don't like that I'd have to invest in more gear to download sound files, and that the s/w is Windows-based (I'm a Mac user).  But we'll see.

By the way, Kevin, the Tsunami 1000 is limited to a maximum track voltage of 27V, not 22V.  Perhaps this is a revised specification?  Don't know, but that's what I see on the web site.

[Bucksco]

SoundTraxx makes a nice Large Scale sound decoder for PIKO of Germany that would probably suite your needs - http://www.piko-america.com/36220.jpg

[Kevin Strong]

My primary gripe with the Piko system is that there's no way to synchronize the chuff to the rotation of the drivers. It's all based on track voltage. With Bachmann's locos having built-in chuff cams or sensors (depending on model), it's almost sacrilegious to use voltage to control the speed of the chuff. (Did I say "almost?")

With regard to the Tsunami voltage, their user's guide states the Tsunami will go into over-voltage mode at 22 volts, and that voltages in excess of 27 volts will damage the board. I know the DCC decoder they made specifically for the Bachmann Climax has a higher voltage ceiling, as does the decoder they were at one point developing for the C-19, which has been shelved, but the small-scale boards max out at 22 volts. For most models of narrow gauge locomotives, 22 volts is more than ample. I run battery power with 14.8 volt batteries. Rarely do I ever have the top speed programmed at more than 75 - 80 percent.

Later,

K

[jviss]

Thanks Kevin.  Could you please tell me where you found the 22V v. 27V spec. for Soundtraxx?  I can't find it.

Thanks,

jv

Update: just received a reply to this question from Soundtraxx and they say that the maximum operating voltage is 27V.

Update 2: I just found the reference to 22V max in tsunamisteam_users_guide.pdf and Kevin is right according to this document, which states:

Error 10 - Over voltage fault
An Over-voltage fault indicates that the track voltage is greater than 22
volts. When this error occurs, motor control and sound will be shut off
and the error code will continue to flash until the voltage is brought below
22 Volts. Note: Tsunami’s absolute maximum voltage input is 27 volts!
Track voltages exceeding 27 volts may cause permanent damage to the
decoder.

I have asked Soundtraxx support for clarification on this.

Update 3: Kevin is right, 22V maximum operating, 27V absolute maximum.

[jviss]

More on this topic.  A fuse or circuit breaker is a bad idea in a motor circuit controlled by a MOSFET. 

I learned that many mobile decoders use MOSFETs (metal oxide semiconductor field effect transistors) as the output stage of the controller.   One of the common failure modes of MOSFETs is a large, fast voltage spike, which you will certainly get it you disconnect one leg of an inductive load from a controller!  So, above I asked "why not...?"  Bad idea! 

It turns out voltage transients are MOSFET killers, and arcing is a fact of life in electric model trains, so these decoders are working in a very hostile environment.  Good motor maintenance can reduce arcing at the motor.  Putting a capacitor across the motor terminals to suppress noise is a controversial topic, some motor controller vendors recommend it, others don't (don't know about DCC decoder vendors on this).

jv

[Hunt]

If you go with the Tsunami DCC decoder modified to support 3.5 amps it is critical to install it to dissipate the heat from both the decoder heat-sink and the added rectifier board.

Do not be surprised if the SoundTraxx decoder goes into over voltage shut-down in the 18 to 22 v range.

[jviss]

Thanks Hunt.  Have you experienced these shutting down for over-voltage at less than 22V?