Model Railway Forum

He's right, you can't use any old capacitor because it will be subject to voltage reversals when the loco changes direction. What you need is a non polarised capacitor, as stated earlier by Stese. A normal polarised electrolytic capacitor won't work and could possibly explode.

The suppression capacitors that are normally connected to the motors aren't electrolytic, so they are safe where current reverses but they are of very low value and don't give any "stay alive" action.

Stese wrote: ↑Wed Jul 27, 2022 10:55 pm teedoubleudee, don't most locos already have this in the form of suppressor capacitor?

1. As Rog has said, suppression capacitors are of a very small value, typically measured in pico farads and have no "stay alive" potential. They are non polarized.

2. Total capitance value increases when connected in parallel, so if all locos are connected to live track power then the capacitance value equals the sum of all and will be available to every loco so connected.

3. Under NO circumstances should polarized capacitors eg electrolytic type be fitted in any circuit where full reverse voltage could be applied as they WILL explode - search the net for video confirmation.

teedoubleudee wrote: ↑Thu Jul 28, 2022 12:57 pm

Stese wrote: ↑Wed Jul 27, 2022 10:55 pm teedoubleudee, don't most locos already have this in the form of suppressor capacitor?

1. As Rog has said, suppression capacitors are of a very small value, typically measured in pico farads and have no "stay alive" potential. They are non polarized.

2. Total capitance value increases when connected in parallel, so if all locos are connected to live track power then the capacitance value equals the sum of all and will be available to every loco so connected.

3. Under NO circumstances should polarized capacitors eg electrolytic type be fitted in any circuit where full reverse voltage could be applied as they WILL explode - search the net for video confirmation.

The capacitor on a 8-pin plug arrived today. It is a non-polarized capacitor - 220micro farads - 35v 105DegC on the outside.
Their advert does emphasise that 'ordinary' capacitors can't be used in any circumstances. They don't mention non-polarized. Probably because they cost only around £1 each (or less in bulk) for the biggest size they offer and a blanking plug is cheap too.

Interesting. Does it actually work?

Viscount wrote: ↑Mon Aug 08, 2022 9:50 pm Interesting. Does it actually work?

My limited testing suggests it does not work! Having watched a video from Strathpeffer Junction about stay alive on DCC it seems the size of the capacitor is far too small to make any observable difference.

My limited testing was to run a loco with it fitted on a rolling road and then pick it up. The wheels stopped immediately, the same as without the device.

I couldn't see how it would work at that rating. Thanks for confirming!

It may help the loco to get over specks of dirt on the track, I certainly wouldn't expect the wheels to keep turning for any length of time.

Rog (RJ) wrote: ↑Tue Aug 09, 2022 10:05 am It may help the loco to get over specks of dirt on the track, I certainly wouldn't expect the wheels to keep turning for any length of time.

I would have expected the wheels to keep turning at least a 1 turn. There was no visible movement, unlike stay-alive units on DCC.

I tried this years ago in N gauge steam, tanks! very small space available so used 47uF non-polarised surface mount times four, this is my report at the time :-
COMPARING two 060 tanks one fitted with 4x47uF across motor and other not whatever difference there is is not immediately obvious so more detailed studies are required.
Loco Setting Seconds/pole Seconds/rev Stalls
060T w/o caps 5.5 4 115 0
060T +caps 4.25 3.5 115 0
These are about the limits of slow running when warm with clean wheels and track on the mainline chimney forwards.
When shunting in the yard both loco’s stall occasionally on bad bits of track (dropped joints) and also on direction reversals, I really couldn’t tell the difference.
CONCLUSION
Either my half sine control is already superlative or the amount of capacitance (200uF) that can be fitted is inadequate but there was no measurable difference in performance and as noted for longevity inductors or other measures are required to prevent wheel pitting.
I CONCLUDE THEREFORE CAPACITORS DO NOT HELP MY LOCOMOTIVES AND WILL NOT BE USED.

Hello there,

Worst case scenario, a Triang/Hornby "Nellie" from the 1970's complete with clanking XO3/4
https://www.youtube.com/watch?v=MJOXNQWUxoc
maybe it'll embed, you just never know
https://youtu.be/MJOXNQWUxoc

And a very very simple homemade controller.
If you'd like to know more ......

Cheers