I am working on a Mack 15 ton switcher engine kit. The body is from Jordan and I am using a powered truck from an older Bachmann 44 tonner as motive power as per Darth Santa Fe’s original idea.
I have the power truck running OK but it is very sensitive to power interuptions. Yes, the track is very clean. The body has a fair bit of added weight in the form of lead sheet. Test runs without the body revealed frequent stalling. Test runs with the body in place reduced the tendancy to stall but did not eliminate the problem completely.
My question is about installing capacitors to keep the motor alive during the brief power interuptions. I would like to know what size would be effective, and I would like to know exactly where in the circuit to install them. There is no sound (I wish there could be but there simply isn’t space for a speaker.) Space is at a premium but I have about 1/2" x 3/8" x 1/4" still available in the upper part of the cab.
Here is a picture with the body off. If you look into the lower sides of the cab you can see where the lead weight has been installed:
Here is a picture with the body loosley installed. Sorry about the focus. You can see that there isn’t a whole lot of space for big capacitors. The wires sticking out the top are for the headlight/tail lights.
I have some SMD 0603 capacitors that are rated at 100pf. My problem is that I don’t understand capacitor ratings so 100pf does’t mean much, but I am assuming that they are pretty small. I am wondering if it would be possible to wire a number of these small capacitors into a larger ‘block’ (for lack of a better word), and get anything useful out of them? How much ‘capacitance’( is that the right word? ) would I need to bridge momentary interuptions in power for a non sound motor?
I know that TCS has a capacitor power interuption device available but there is no way that it will fit in the 15 tonner, and I am trying to avoid using a ‘trailer’ as you suggested. I also don’t think I need several seconds of alternative power supply. One second would seem to be more than adequate given the current performance of the engine as long as the recharge time is fairly quick.
By the way, if anyone could enlighten me on capacitor ratings and relative functionality, that would be very much appreciated! I used to love running my boat in the dark, but that was when I knew where I was going and I could see the horizon![swg][(-D].
Dave
EDIT: It didn’t take me too long to figure out that the 100pf capacitors would be rather useless in this installation once I read the posts.
You would need a Polarity sensitive,Electrolytic,capacitor,and other components,to do what you are asking and I am rusty on that… Check out ,Elect.and DCC,Forum,on Rad Lite LED Lites for passenger cars and read the Lion’s, post…That should help you…
I checked out the Lion’s post and came to the conclusion that the solution to my problem may not come easily, if at all.
That however, is not going to stop me from investigating further. Good thing my back surgeon said I had really solid bones! I can afford to bang my head that much harder!![(-D]
TCS offers decoders with the “keep alive” built in. They’re the same size as a regular HO non-sound decoder. The “keep alive” add-on only works with TCS decoders that have a place to plug-in the add-on.
If you can find the room, go for the TCS. I had a first-run Proto 0-8-0 that came with no power pickup from the tender wheels, and it ran so poorly I never used it. I put a TCS “keep alive” in it, and now it runs great.
I have looked at all the TCS offerings, both for the add-on circuit and for the decoders that have the Keep Alive built in. They are all too large to install in the switcher itself.
I do have a TCS Z2 decoder on order which is supposed to be pretty small. It is intended for another project but when I get it I will see if using one in the 15 tonner will give me any more space. The TCS Z2 does not have the Keep Alive function. I am using a Digitrax DN135 right now.
I have the option of removing some of the weights to make space but that seems to be totally counter productive. Even then, there is only 7/16" from the front to the back of the cab. All of the TCS circuits are larger than that. Even if I put them on their sides they still won’t fit.
You won’t get any “stay alive” capacity from any single capacitor that will physically fit that little guy.
For a single capacitor, you need at least a 16 volt rating and at least 100,000 microfarads to get a second or two stay alive ability - plus a resistor and diode … which won’t even come close to fitting. The TCS modules have one farad of capacitance (one million microfarads) but use multiple 2.5 volt capacitors in series to get the size down.
Instead of the drive you used, you could have used one of NWSL / Stanton drives and had both hoods and the cab wide open which would have given you plenty of room for a decoder and stay alive module …
Thanks for the information about what capacitance I would need to get a reasonable amount of reserve power to keep the critter operating.
I looked at the NWSL Stanton drives and their model 1210 does offer the correct 6’ 6" wheelbase. Unfortunately the width of the Stanton drive’s body is just a bit too wide to fit inside the 15 tonner’s body. It is very close but in order to get the wheels at the right height the Stanton motor has to go up into the shell a bit, and it is too wide for that. I could mount the body higher above the wheels I guess. I would have to do a mock up to see if the switcher still looked reasonably accurate.
There is another small issue and that is the price of the NWSL Stanton drives. I got the powered truck I am using for about $10.00 and I have eight of them to work with. (I bought four of the Bachmann 44 toners with the two motor drive through eBay for about $20 per engine). So, being a (something that starts with a B) for punishment, I have committed myself to working with the 44 tonner self powered trucks.
My next step is to see what size capacitors I can gang together to accomplish basically the same thing the TCS 2.5 volt capacitors do. Maybe I can, and maybe I can’t, but I ain’t quitting just yet!
I just spent a bunch of time searching Digi-Key’s site for capacitors that would do the job AND fit, and as Mark gently suggested, there ain’t no such thing!!
Oh well, now I have to explore other options. The concept of a trailer is becoming more interesting, or perhaps two 15 ton Macks hitched together with one powered and the other carrying a TCS Keep Alive decoder.
I’m going to have to think about this one a bit more.
As I said in the beginning,trying to get something to fit in that little,mouse,is going to be the tuff part…When I mentioned trailer,How about,the mouses,sister,a little work caboose,behind her brother?? Just a thought!! Don’t give up,‘‘Buddy’’, I have confidence,in you…
If you run two of them together, you might not even need the keep alive, as you would then have 8 wheel pickup. But that’s pretty much the only option, even the smallest surface mount capacitors aren’t going to be of sufficient value to give any effective keep alive ability when also small enough to physically fit. You could give it a try, wutht he highest value 16V rated surface mount capacitor that will fit - the resistor and diode aren’t strictly needed, although you may have trouble programming it with just the capacitor. It may only give a fraction of a second of juice but that may be enough to keep it moving.
The only other option is to make sure all frogs are powered, and keep everything scrupulously clean - track, wheels, pickup wipers.
I think you are going to have trouble running it if you filter that track signal too much. The decoder relies on the pulse width modulation that is DCC. The modulating DCC square wave peaks from plus to minus at about 5 -10 KHz. I’m not sure about that freq range, but I don’t think that you can put enough C on it to improve power pickup without “rounding off” that signal too much. The Booster may not like it, either. I think you need a special “keep alive” circuit designed for the DCC signal.
