What super capacitor works with hornby decoders?

[Anton Stedman]

I have an 0-6-0 hornby dcc fitted engine which stops everytime it goes over an insulated track piece. 

I understand a super capacitor is needed to keep the train running.

Would a super capacitor 0.22f work well with the decoder, or do I need a different super capacitor.

Could someone please recommend a super capacitor for use in a dcc fitted hornby 0-6-0 engine.

Thanks very much.

[Fishmanoz]

Hi Anton, welcome to the forums. There is a lot of coverage of this topic already.  A comprehensive thread on it can be found at:

 

https://www.hornby.com/uk-en/forum/post/view/topic_id/21221/?p=1

 

This coverage is also pretty much independent of loco type so is applicable to your 0-6-0.

 

Finally  note though that 0-6-0s should traverse plastic frogs if the points/ Rossini’s are perfectly flat, the wheel back-to-back measurements correct, and the wheels and wipers cleaned and the wipers properly tensioned. There is lots of coverage of this too. 

[Chrissaf]

This is a better link than the one Fishy provided, but to be fair this better link was linked to in the link Fishy posted. But I feel it is best to highlight it separately, else it might have been overlooked.

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https://www.hornby.com/uk-en/forum/post/view/topic_id/13404/?p=2

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Be aware that most 'Super Capacitors' have a low rated voltage, some are only 2.7 volts but most are 5.5 volts. You need a minimum 16 volts to use as a 'stay alive' with most decoders. If you apply a voltage higher than the capacitor rated voltage you will damage it.

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To achieve the 16 volts, you connect more than one 'Super Capacitor' in series. Doing that makes the rated voltages accumulative. So three 5.5 volt capacitors in series gives the equivalence of one capacitor rated at 16.5 volts. Six 2.7 volt versions in series give 16.2 volts and so on.

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However, connecting capacitors in series reduces their overall equivalent capacitance. This is not a major issue with 'Super Capacitors' because of their extremely high individual values that you are starting out with. For example, putting three 0.22F capacitors in series gives an overall capacitance of 73.333 Milli-Farads which is the same as 73,333uF or 0.073333F.

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Three 0.1F 5.5 volt Super Capacitors in series is far more than enough for a Stay Alive (series equivalence to 33,333uF). The smaller Farad value also means that each individual capacitor should be physically smaller than a 0.22F version. However this is not always the case when comparing capacitors sourced from different manufacturers. This is important as you may struggle to find space inside a 0-6-0 loco chassis for a larger value 'Stay Alive'.

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A perfectly acceptable 'Stay Alive' can operate on a capacitance as low as 3,300uF although 6,800uF would be preferred. As you can see, three 0.22F capacitors in series giving 73,333uF is more than 10 times the Stay Alive capacitance that is preferred as a minimum. And nearly 5 times more than needed if using three 0.1F capacitors (33,333uF).

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The final design requirement for home brewed 'Super Capacitor' Stay Alives, is in-rush current protection. You MUST include a resistor and diode in series with the capacitor. However note, that the resistor and diode themselves are wired in parallel before being wired in series with the Capacitor.

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Note also, that Super Capacitors have a positive and a negative side and MUST be wired to the decoder (and to each other) the correct way round, else they will swell up and go off with a bang.

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The text above is just an overview of the salient points to be aware of.  Follow my link above and look for my posts in it to find FULL constructional details and where they connect on Hornby decoders.

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PS - If the 'Stay Alive capacitance value is too high, then the pure DC power being fed into the decoder from the capacitor in the absence of a valid DCC signal on the decoder input can cause the decoder to exhibit DC runaway. This can be more noticeable when shutting down the DCC system at the end of a play session. It has been reported on the forum by some members that large value 'Stay Alives' (when fitted) have made the loco shoot off on its own (DC Runaway) when the DCC track power is switched off.

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TIP: I write long posts. If you intend to write a reply, it would be appreciated if you didn't use the 'White Arrow in Blue Box' button. This is not a 'Reply to this post button. It is best to write any reply you want to make in the 'Reply Text Box' at the very bottom of the page and click the Green 'Reply' button. If you click the blue button instead, all you will do is reproduce this long post unnecessarily.

 

[Fishmanoz]

Thanks for improving the link to look at Chris.  Mine was the first one I looked at after doing a forum search on “stay alive”.  Then it includes coverage of electrolytic and super capacitors and how to use them in this application, has lots of links to other coverage on here, and even covers at the end a commercially available super capacitor product for those who don’t want to get into making their own. 

[96RAF]

You will require very good soldering skills to install stay alives to a Hornby decoder As there are no handy pads to attach to.

Rob

[Anton Stedman]

Thanks very much.

I have read through the other forums and found them very helpful.

Thanks for your help!

[The son of Triangman]

Also price around for the components, the so called super capacitors/stay alive kits are just normal electrolytic capacitors electronic components available more cheaply from electronics suppliers.

 

[dynax]

TBH, you might as well as buy another decoder with stay alive, save a whole load of trouble and messing about, sometimes it's just not worth the hassle to bodge a diy solution,