# DIY Keep Alive questions...



## afboundguy (Jan 10, 2021)

I purchased some supplies to make some Keep Alives and I was curious if the ratings for the resistors, diodes and zener diodes need to be adjusted if I use less super capacitors?

The model I'm going off will use 5 super caps with a 100 ohm 1/2w resistor, 1N4001 diode and a 13v 1.5w zener diode. If I only want to use say 2 or 3 super caps in some of my smaller engines (such as Plymouth Switcher) would I need to adjust everything else?


----------



## wvgca (Jan 21, 2013)

less on the number of supercaps -may- reduce the voltage rating .. indicating use of a smaller zener


----------



## afboundguy (Jan 10, 2021)

wvgca said:


> less on the number of supercaps -may- reduce the voltage rating .. indicating use of a smaller zener


Could I still use the same zener diode thought? I wasn't sure if I used something that was overrated for what I would be constructing would be fine? I've seen a lot of people using a 13v 5w zener diode with 5 super caps...


----------



## wvgca (Jan 21, 2013)

depends on the caps ...a 13 volt zener would only be applicable with five of the 2.5 volt caps ... they would add up to 12.5 volts applied .. any other voltage would need a different zener [if one is used at all]


----------



## Stejones82 (Dec 22, 2020)

Is that the new BLI Plymouth switcher? I have one and would be curious how your project turns out. I have not removed the shell yet, but there can't be much space in there. I have the DCC but no sound (if sound was even an option).


----------



## gregc (Apr 25, 2015)

at least last i checked, super-cap voltages weren't rated very high. some minimum number of super-caps are required to have a sufficiently high voltage to drive the motor. for example, at least five 2.7V super-caps (13.5V) are needed to operate near typical rectified DCC voltage (~14V - 1.5). only three 5V super caps would be needed

the zener diode is used to limit the voltage across the caps, if needed and would be rated at less than the series voltage of the caps. 

there's no need for a zener diode if the the series voltage of the capacitors exceeds the track voltage after rectification (track voltage - 1.5V).

a 1.5W zener seems high. it only passes current when the voltage exceeds it's rating. no more than 1V would be across the 100 Ohm resistor, or 10ma. 13.5 V at 10 ma is a little more than a 1/4 W.

you may want to use a 7.5V zerner if only three 2.7V caps (8.1V). typical current thru the zener would be 50 ma ( (14 - 1.5 - 7.5) / 100) and the zener needs to be rated > 0.37W (7.5V * 50 ma)


----------



## afboundguy (Jan 10, 2021)

Stejones82 said:


> Is that the new BLI Plymouth switcher? I have one and would be curious how your project turns out. I have not removed the shell yet, but there can't be much space in there. I have the DCC but no sound (if sound was even an option).


Yes... I "finished" doing the outer track on the layout and ran some engines just to see how they ran and the BLI Plymouth Switcher stalled out on a lot of the insulated turnouts so I thought about adding a stay alive but I don't know how I'd fit one in there...


----------



## afboundguy (Jan 10, 2021)

gregc said:


> at least last i checked, super-cap voltages weren't rated very high. some minimum number of super-caps are required to have a sufficiently high voltage to drive the motor. for example, at least five 2.7V super-caps (13.5V) are needed to operate near typical rectified DCC voltage (~14V - 1.5). only three 5V super caps would be needed
> 
> the zener diode is used to limit the voltage across the caps, if needed and would be rated at less than the series voltage of the caps.
> 
> ...


As much as I don't understand electricity and all the numbers I did understand that well enough thanks!


----------



## JeffHurl (Apr 22, 2021)

HOw does a stay alive work with DCC? Do you insert the capacitors down stream of the decoder (but before the motor)? Otherwise, wouldn't the signals get lost in the capacitor?


----------



## afboundguy (Jan 10, 2021)

JeffHurl said:


> HOw does a stay alive work with DCC? Do you insert the capacitors down stream of the decoder (but before the motor)? Otherwise, wouldn't the signals get lost in the capacitor?


You have to attach the blue (positive) wired side to the decoder's blue wire and then the black (negative) wire you attach to the negative ground decoder connection on the board...


----------



## wvgca (Jan 21, 2013)

in some decoders it's pretty easy, others not so much ...
in my photo that's a home made decoder, the blue that i'm holding is the positive common, and the black is the negative, whch goes to a spot right after the rectifier on the decoder [before the motor drive]


----------



## Stejones82 (Dec 22, 2020)

afboundguy said:


> Yes... I "finished" doing the outer track on the layout and ran some engines just to see how they ran and the BLI Plymouth Switcher stalled out on a lot of the insulated turnouts so I thought about adding a stay alive but I don't know how I'd fit one in there...


Just trying to be helpful as I often forget to do the obvious. My Plym Switcher came from the factory in the pre-order (via Factory Direct) and stalled at the unpowered frogs lots. Someone suggested that though new, the factory usually ships them with lots of gunk on the wheels. I cleaned them using the paper-towel with CRC on the tracks technique and that helped immensely! You, no doubt smarter than I, have probably already done this. 

That said, I am very nervous about popping the shell on that switcher. But I do want to order a Gopack for my BLI Steamer. She is running better but still balks occasionally. The stop-start of the sound eats at my nerves! The videos at the BLI site are well done and the job looks fairly simple.


----------

