Dual DC throtttle one internal, one walkaround in a single case


videobruce

videobruce

Tower Operator
DC is not dead. Dual throtttle: one internal, one walkaround in a single case

I had a home built dual cab throttle left over from my 1st layout 15 years ago that I was planning on reusing. That design was from a book that Peter Thorne wrote back in the early 90's and was outdated. After taking a 2nd look at this 'dated' design, I decided to gut this, mostly due to the use of very heavy, bulky and inefficient transformers. It brought new meaning the the term "brick". ;)

I was aware of this design, but rejected it due to cost and the fact I already had a case with meters that I wanted to reuse;
http://thegmlenterprises.com/id18.html

So I did a search and found a guy in St Catherine's Ontario Canada (a 30 minute drive from where I live) that sells throttles. One a small hand held all in one and another a two piece walkaround. All you need for the walk around is a case (unless you don't want to bother placing in in one).

His site is here;
http://www3.sympatico.ca/kstapleton3/Index.html

His larger version is this;
http://www3.sympatico.ca/kstapleton3/821.HTM

Though, not listed, the cost for just the throttle is $45 without the handheld controller. I already had one that I wanted to reuse. You do have to supply a external power supply either AC or DC. I wanted to use a energy efficient switching supply. No more "bricks".

The rating of three amps is overly generous. Though it can supply this, I would not recommend going anything close to this if you are running full throttle for over 5 or 10 minutes due to the excessive heat the main component (a LM350) generates. Partly due to the small heat sink and what I consider the crowded circuit board used, after a 10 minute full throttle load test of only two amps, I measured a temperature of over 200 degrees on that heat sink! Way, way too high. In spite of what manufactures claim, even though electronics can run hot, there is no way anyone could ever convince me that is acceptable.

In reality, few guys will run full throttle for any extended period of time, but it should be known just how hot this can get.
Have said that, running 1.5 amp seems to be safe. Running two amps at a 50/50 duty cycle would be acceptable also. All of this is in open air, not in a closed case and no fan. After discovering the heat problem I have added a cooling fan and drilled additional holes in the base for air flow.

The power supply I used was from MPJA in Florida (It was $4 when I bought it. They have plenty of others for around $10);
http://www.mpja.com/19V-265A-DC-Desktop-Supply-Globtek/productinfo/18903+PS/


I did a few modifications to fit my needs as follows after discussing the problems with Ken on the phone. There is no provision for meters, either amp or voltage. I find this a disadvantage as I like metering and already had the meters on the case on the old supply;

1. I added taps for a amp and volt meter. The amp meter I placed in line between the external PS and his circuit broad since this didn't require cutting any traces on his board which I preferred not to do unless I had to. Ken stated the slight additional current that the board itself draws was not a concern. I proved this by measuring current before the board and after using a fixed load of four 12v light bulbs mounted in a test jig I had.

2. I tapped off of the input to the reverse relay for the 12volt track power feed for the volt meter. This way, since the meter was not a 12-0-12 volt scale, I didn't have to be concerned about reverse polarity. Measuring voltage with a DVM (Digital Volt Meter) produces fluctuating, inconsistent readings without a load due to the PWM used. Placing a load on the output solves this. When using analog panel meters, there is no problem even without a load.

3. I already had a dual brake provision. One for "service", the other for "emergency". I paralleled his design by adding the 2nd brake. I used variable 'pots' instead of fixed resisters (about $1.50 each) since I had no idea what resistance was needed.
If you wanted to get real 'fancy', you could use a 4 or 6 position rotary switch with either fixed or variable pots on each position to effectively duplicate a prototype locomotive brake with multiple positions. This could easily be added in the future, substituting the push button for a rotary switch. If you could find a 'level', it would really ad to the realism. ;)

4. Note the standoffs for the boards, the front panel LED (being fed from only one of the PS's), the holes on the base for air flow, the cable ties securing those supplies and the rear mounted fan being supplied from the 2nd supply (terminals 3 & 5).
 
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Components:

You don't have to place this inside a case. It can be easily mounted to a piece of plywood where you have your other electronics & terminal blocks located. You also don't have to have a volt and amp meter, but it makes troubleshooting easier, allows monitoring current draw o you loco's and just looks neat. :D

I like enclosed electronics to protect the components and better organize them to function. Case size has to be planned out depending on the external power supplies you use. I split open the supplies and only used the bottom half, leaving the top open. I stacked the two using larger cable ties to the bottom of the case since the only other option would be some type of brace. Cable ties hold fine.

I mounted Ken's boards on the back side of the case. Air circulation would be improved slightly if the boards were mounted on the bottom, but due to the design, they had to go on the back. I wanted to be sure the eight connections were accessible if I had to remove any and also wanted the volt 'pot' next to the heat sink accessible for fine tuning the maximum track power.

Ken provides details for a homemade handheld unit if you don't buy his ($72 for both pieces plus shipping). I used the existing 5k pot for the speed control. Values up to 50k can be used. I don't understand how such a large range can work since '0' ohms is full throttle. I then used 1 meg variable pots for adjustment of the momentum and brakes. He shows using between 100k and 500k for the momentum. I was concerned if that would be a long enough delay, so I went with 1 meg. Cost is the same, the downside is the lack of a finer adjustment. I have a larger layout, so I wanted longer delays. On a small layout, 500k would be fine. I wouldn't use a 100k though.
The same goes for braking, though 100k is ok for an "emergency" brake, but I would still stick with 500k for any other brake settings.

Components I ordered from Mouser. You can also use Digikey. MPJ does sell some components, but the selection is extremely limited, so is All Electronics since both of these specialize in 'left overs'. Overstock or over bought inventories they apparently buy elsewhere;

http://www.mouser.com/search/default.aspx
http://www.digikey.com/product-search/en
http://www.allelectronics.com/
 
Specifics:

I won't duplicate what Ken has already written on his site and in his installation instructions. Here are closeups of his board, my enclosure & handheld unit.
remember, these were from the original Peter Thorne PWM throttle from around 1990. :eek:

The two wires are off the input of the relay. This way polarity after the relay is no issue for a standard 0-12vdc meter. The trace that is under the blue wire could be cut to place an amp meter in line, but that would be somewhat risky and as I stated, current readings were very close between before the board and after.

If you note the adjustment 'pots' I 'hung' from each pushbutton switch. I suppose you could get one of those 'breadboards' to mount all three post on one board with that 10k resitor, but I didn't see the need.

One change you could do is use panel mounted pots so the adjustments can be accessible from the outside, eliminating the need to open the case if you need to 'tweak' any of them in the future. Panel mounted pots are more expensive (between $3 and $10 depending on type and quality).
 
Before someone brings this up,

I have a large number of non-DCC friendly diesels that I didn't want to part with. They all run very well, even after being in storage over 10 years. Many were custom painted and decaled. All had MicroTrain couplers added. I had/have no intention of trying to retrofit these with DCC boards.
I didn't want to get into a discussion of DC vs DCC since it's been discussed over and over. Both have pluses and minuses I was mostly aware of. What I did do was plan ahead (I hope) with my layout blocking, gapping and wiring for DCC if and when I do make the switch.

Any other input or questions welcome and I hope this helps.
 
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Thanks for the addition.
Please note, Ken does have a 1/2 speed function (that I did not use) that basically does the same thing. Depending on the resistor value used, it reduces the voltage range of the 'throttle' down by half (which should be more than enough).
 
I will add, probably due to the difference in the length of the cable between the handheld and the internal 'throttle', this apparently causes a difference in the degree of 'braking' one can have.
The longer 'service' brake time is just not there with the internal setup. Even with a 8 meg resistance (using a resister substitution box), I can't stretch the braking time out any longer unlike the handheld which has no problem.

This probably is not a problem as I'm talking about longer deceleration times to attempt to duplicate prototype braking on a large layout.
 
Hi Videobruce,

I am starting my first N scale layout using cab control to operate two trains. My plan is to use my slot car variable power supply (0-18 volts, 5 Amps) with two hand held throttle controllers instead of either two train power packs or one dual power pack (MRC Tech 4 for example).

Based on the above links, it seems that is something I can do. Is there anything else I need to consider in terms of parts or equipment? I am using Atlas coe 80 track and switchs with 8 blocks that I am mounting on a separate control board along with the turnout momentary switches.

Any advice is greatly appreciated.

Andrew
 
1. You need two separate supplies, one for each cab. I really wouldn't use that for one.
2. The supplies I used are $6 each. It is a switching supply, so the output is stable and filtered even tough you could use a AC supply. I just don't like 'bricks'.
 
I was under the impression that a single DC power supply could power two or more throttle controllers. Just dial the maximum voltage and amperage needed. Such a power supply easily runs mutlple slot car controllers with more powerful motors at faster RPMs.

If that is not the case, then my only option is to use either a double power controller like the MRC Tech 4 or two separate units as you said. I was hoping to use a smaller handheld throttle controller while keeping the power supply under the table.

Still working out the electronic plan for single/dual operators
 
Have a question on the temperature you got on the heat sink was it Fahrenheit and could a small heat sink with a fan for a cpu be mounted on that heat sink to help cool it
And does the PMW work as good as stated
 
averacpa; You do need a separate PS for each throttle. Unless you isolate both rails. But, when you cross one of those blocks, it will short out.
Go ahead and try your slot car supply. For $12 (for two) why bother taking the chance?? I know it's a PITA, especially for the way I did it with two throttles in one case. :(
Either way the supply can still be placed under the table.

MikeGTW;
Yes, the only way I measure.
You could obtain a heat sink and use thermal paste and a little adhesive in the corners to secure the HS on the chip for additional cooling. A CPU heat sink would be way too large.
I only tested it on a 3' test track. I didn't see any issues, but won't know until the layout is wired.
 
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