Decoder Stay Alive

[Zorcan]

I am keen to fit stay-alive devices to my locos where possible.

 

I have some decoders that support this function - I made a stay alive device from a single 16volt 0.1 Farad capacitor as follows:

 

1. I wired the negative terminal to the dedicated stay-alive decoder negative feed.
2. I put a 100 ohm resistor between the positive terminal and the positive stay-alive lead to limit the in-rush current when the capacitor is charging
3. I put a reverse diode across this so that the full load of the motor is met by the capacitor when DCC decoder feed is interrupted.

 

I understand this to be the accepted circuit.

 

I could see no improvement at all in running.

 

The only difference I noticed was when switching off the DCC feed - the loco would stop then give a violent jerk about a second or so later.

 

What am I doing wrong?

 

 

[Nigelcliffe]

Would help to know exactly which decoders, and probably exactly which terminals you connected to on those decoders. 

 

The obvious issue might be whether you disabled DC running in CV29 - DC running and Stay-Alive is generally incompatible. 

 

 

Its possible that your capacitor cannot discharge fast enough (there are a few devices around which have huge storage, but are designed to trickle out power to keep a very low power circuit running for ages).   But that depends on the capacitor(s) you have selected.

I assume you're confident about your track voltage on 16v rated capacitors, if not, some voltage protection over the capacitor is required in the form of a 16v Zener diode.

 

If you have 0.1F at 16v rated, wired correctly, capable of delivering proper currents, then you should see significant run times without DCC power.  

 

 

- Nigel

[Zorcan]

Would help to know exactly which decoders, and probably exactly which terminals you connected to on those decoders. 

 

The obvious issue might be whether you disabled DC running in CV29 - DC running and Stay-Alive is generally incompatible. 

 

 

Its possible that your capacitor cannot discharge fast enough (there are a few devices around which have huge storage, but are designed to trickle out power to keep a very low power circuit running for ages).   But that depends on the capacitor(s) you have selected.

I assume you're confident about your track voltage on 16v rated capacitors, if not, some voltage protection over the capacitor is required in the form of a 16v Zener diode.

 

If you have 0.1F at 16v rated, wired correctly, capable of delivering proper currents, then you should see significant run times without DCC power.  

 

 

- Nigel

 

Thanks Nigel - I was wondering if the capacitor I used had a fast enough discharge rate.

 

I used an Lais decoder which has dedicated stay-alive leads. I measured the voltage across them before fitting a capacitor - it was a shade over 14.

 

I didn't know about the DC running issue - I will try again!!