DC Throttle Recommendations

[garethashenden]

I need a new DC throttle and I’m not sure what to get. I have a MRC Tech 4 260, which I probably have had for 20 years. It’s giving very erratic outputs. 21V at full throttle one way, 0V the other. Try again and get .3V, or 12V, but almost always 0V in reverse. Maybe an electrical wizard could fix it, but that’s not me.

Anyway, I want something more sophisticated than a 9V battery for use on my workbench when building and troubleshooting locomotives. Eventually everything gets DCC, so I don’t need to run a layout with this. Just on the bench. I don’t know what’s available, what’s good, etc. I know there are variable DC power sources that aren’t hobby specific, but from a quick glance they don’t seem to have a way of switching the polarity. So what should I get?

[mark.hinds]

I bought one of Rich Weyand's "CoolerCrawler" DC controllers back in 2019 from Railwire member haasmarc .  It isn't pure DC though, but pulsed.  Still, if you are interested, you might try contacting him. 

MH

[u18b]

I've been a big fan of the Varipulse throttles.

http://www3.sympatico.ca/kstapleton3/Index.html

[peteski]

DKS designed this inexpensive throttle, but some assembly is required.
http://www.davidksmith.com/modeling/projects/throttle.htm

But then again, both this and the throttle Mark pointed to are PWM throttles which might not play well with DCC decoders.  I would avoid PWM (square pulse) type throttles.

If you want a throttle ready to use, then how about a Kato throttle?  While it does not provide filtered DC output, as I understand it plays well with DCC decoders.

Oops!  While that was true of the older Kato throttles, according to info in this thread it appears that Kato "improved" the design by making it a PWM type throttle, so never mind that one.

Well looks like I don't have any good recommendations for a ready-to-use simple DC throttle. I would just build my own, but I actuall use that 9V battery on my workbench and I find it adequate for a simple go/no-go tests.

As for as wiring your own reverse polarity switch, it is not a difficult thing.  The DKS' webpage I liked to earlier has a clear description on how to wire such switch.

[mmagliaro]

How adept are you at basic soldering?   eBay is loaded with nice cheap variable regulated power supply boards priced between $5 and $15 that even have a digital voltage meter on them and the pot control for the voltage (speed).  All you need to do is hook up something like a 12-16 volt AC transformer to them.  You could get a cheap "wall wart" for the 16V ac so you don't have to do any dangerous wiring on the end that plugs in the wall.  The output will be smooth, regulated, no pulse, no PWM. 
Something like this:
https://www.ebay.com/itm/112197166870?hash=item1a1f78e716:g:YhkAAOSwx2dYIKPI

I guess my plan "B" would be to just hunt down an old used MRC pack similar to your 260 if you liked that one before it went bust.
--
And finally, my seat-of-the-pants guess on your power pack is that the direction switch has gotten dirty or just plain worn out, which explains the erratic all-or-nothing voltage output that seems to change when you flip from forward to reverse.
I know you said you can't get inside and fix it.  I'm just throwing that out there in case a friend of yours is nearby who is
handy with simple electronics.  Mailing it to one of us to tinker around with it would probably cost more in postage than it's worth.

[randgust]

Right now I've got no fewer than six completely different DC power supplies:

1:  A 'new old stock' MRC Throttlepack 500N that I've had for decades.   The solution on these is to add a SECOND rheostat on the output so you literally have two rheostats in series.   Then you can really control the slow speed as best you can.   MRC used to sell the rheostats separately, they still show up on Ebay, I've put them on every DC power supply I own.  Works fine with decoders, too.

2:   An even older MRC Dual Loco Pack that I had all the way back to HO, it feeds the transistor throttles, and while I can set toggles to go 'direct drive' to the track, the only time I do that is to run straight DC on decoder-equipped dual mode locomotives.

3:   Another ancient pack:  A Cama walkaround throttle that's been my favorite for decades, I bought a second one for backup.   It's a typical single-transistor square wave deal, but the 'secret' to these was that if you reduce the input DC voltage to the minimum of what you need for each train, the square waves go down, noise goes down, arcing and dirt go down, and everybody is happy.  I'll kick it way down for switching, way up for a four-unit set of F-units.

4:   High-tech in the DC era:  I got one of the PSI 550 Cabtrollers about 1980 and that one is pure fun as it has full momentum and braking, you have a separate brake lever and you can even power-brake with it just like a real locomotive.  It's a REAL challenge to operate on my layout as you have to anticipate power needs and speed well in advance just like a real train.   Like the Camas, if you control the input voltage it is much quieter and causes less track dirt.  It's a square wave unit but I've never put it on a scope to watch it.

(Note that both 3 and 4 will NOT WORK AT ALL with any decoder-equipped locomotives, I blew up a Bachmann 44-tonner board the moment I tried it when I didn't realize it was dual-mode DCC/DC and hit it with those square waves.   It never ran in both directions again, even on DCC or DC)

5:   Really low-tech - I built a straight DC power supply from Radio Shack parts for fixed voltage to my workbench, and have a test track with a pair of MRC rheostats on it, jumper plugs, and volt an ammeters on it.  I jacked that into the track DC when I really am struggling to monitor motor performance.

6:   New on the block:   Nothing I did before could really control coreless tiny DC motors (Faulhaber and several others).   On a recommendation, I got a Blue Snail Z power supply that runs off of an internal 9V transistor battery.   Freakin' thing is amazing.   I can run my tiny Nn3 locomotives on that thing at a crawl, and it will also run a regular N scale locomotive.   Very handy on my T-trak module testing.   Way cool, love it.   I do 3.5V Solarbotics 25:1 gearhead motors in series with a 100-ohm resistor and this allows them to crawl as well.


And, I also have a Digitrax Zephyr DCC system that I use primarily on my T-trak modules, frankly, I hate the thing, but it serves my purposes of setting up and testing decoders for customer projects.    After 15 years in IT and microprocessing, I really hate struggling with unnecessary technology, so I'm still 'mostly' a DC guy that has learned a second language.

I have a standard four-pin plug system on both my big layout and on my T-trak and portable modules so that I can plug both walkaround throttles and packs into a layout somewhat interchangeably; throttles have power in and track out; packs have accessory power out and track power out.

If you've never tinkered much with 'pure' DC vs square-wave throttles, a pure DC throttle essentially controls current and resulting voltage by the use of a series resistor.  You'll see a lot more difficulty controlling trains up and down grades as load changes and the voltage equation flips, and even more trouble trying to speed match multiple units as the current changes as they load up, so speed does go all over the map.   On square wave, they essentially 'fire the motors' at a given RPM with pulses, and if you reduce the pulse amplitude by reducing peak voltage, most of the pulse noise and heat problems go away.   I never could get multiple units to match speed under pure DC even if they were all the very same mechanism, but with the pulse wave throttles I can creep 3-4 similar units and watch the mechanisms run in perfect sync from startup to full slip.   It just works, one of my better accidental discoveries.   I'm not an electrical engineer, but I'm always experimenting, and adopt based on results rather than theory or recommendation.

[haasmarc]

I bought one of Rich Weyand's "CoolerCrawler" DC controllers back in 2019 from Railwire member haasmarc .  It isn't pure DC though, but pulsed.  Still, if you are interested, you might try contacting him. 

MH

The CoolerCrawler is still available.  As far as it working with DCC decoders, I am building a small layout for my 90 year old dad who had to move into assisted living last year so he lost his layout.  I am using a CoolerCrawler and running BLI DCC locos, both steam and diesel, and it works just fine so far.

[mike_lawyer]

If you are just using a DC pack for testing at your workbench, you can pick up an MRC Tech IV for pretty cheap used.  I have one I purchased secondhand for just this purpose, as I use DCC on the layout.  I have been satisfied with it.

[mrp]

I have an old (35-40 years?) NTRAK simple throttle, MOD II if you want it. Just pay the freight.
It is a simple transistor throttle. I don't think it does any type of pulse power.
Just tested it and it still works. It needs an additional 12 VDC input.

Michael Pennie

[peteski]

Going back to the original misbehaving throttle, I suspect the problem is defective speed control potentiometer (colloquially called rheostat). It is probably an off-the-shelf part that can be purchased for couple of dollars.

[garethashenden]

Thanks for all your suggestions. To clarify I'm most concerned with testing locomotives during the construction stage, before decoders get fitted. A mixture of coreless and cored? motors are used, so really I need something that plays well with both of them. I do have one of those Blue Snail controllers. I like it but I find the battery doesn't last very long. I should probably get a power supply for it.
I will pull the MRC throttle apart and see if it can be fixed. I'm pretty good at soldering, but not so good at knowing what components are what.

[brill27mcb]

Why not just get a common blue Kato "S" power pack (not the newer "SX")? It's a very basic pack that uses a bridge rectifier to make full-wave rectified DC and puts it through an amplifying potentiometer/transistor circuit. Very basic, providing 0-15VDC, up to 1 amp. If you want to smooth out the full-wave rectified DC, you can simply add a large capacitor across the "dress snap" connections for turnout control switches, which are conveniently located on the side of the pack.

Rich K.

[peteski]

Thanks for all your suggestions. To clarify I'm most concerned with testing locomotives during the construction stage, before decoders get fitted. A mixture of coreless and cored? motors are used, so really I need something that plays well with both of them. I do have one of those Blue Snail controllers. I like it but I find the battery doesn't last very long. I should probably get a power supply for it.

There are plenty of inexpensive "wall-wart" power supplies you coudl use to power that Blue Snail.  Here is a good selection (most for under $5).  1 Amp should be plenty for what you use the throttle for.
https://www.goldmine-elec-products.com/products.asp?dept=1007
Or, depending on how much of a hoarder you are, you could have a suitable wall-wart supply which you kept from some discarded electronic item.

I will pull the MRC throttle apart and see if it can be fixed. I'm pretty good at soldering, but not so good at knowing what components are what.

I think TRW community will help you in troubleshooting. 

[mmagliaro]

garethashenden:
Can you clear up some questions about what you wrote?
"21V at full throttle one way, 0V the other. Try again and get .3V, or 12V, but almost always 0V in reverse. "

I am interpreting this to mean you get  21v in forward, 0v in reverse.  And if you try again, you get 0.3v in reverse, or 12v in reverse,
but almost always 0.  Is that right?  Does it always give you 21v full throttle in forward, but something random in reverse?
Or were the 0.3 and 12 numbers for forward?

I agree with Peteski that the speed pot is suspect here, but  it's either the speed pot or the direction switch, depending on your answers.
Both are cheap, easy to change parts if you want to fix this thing.

I have fixed a few MRC packs like this, and the speed pots are often wonky - either acting like you describe, or having a "dead spot"
 in the rotation somewhere.

[garethashenden]

No, never getting anything in reverse. At first I got 21V forward, and ran a locomotive at half throttle. It worked fine. Put it in reverse and nothing happened. Then I started testing the output at the terminals, just in case there was a wiring problem with the track. Going forward I got a little power at full throttle, something around 0.3V, and nothing in reverse. Turned it on and off a few time and exercised the direction switch. Then got 12V one way and 0V the other. Around this time I decided it was broken, posted this thread, and went to bed. I need to find my set of inch Allen wrenches and open it up.