The Snapper's DCC Workshop - July 2023 Update - use threadmarks to find - Little & Large

[Nigel Cliffe]

....
If you wire capacitors in series their overall capacitance is lower than the capacitance of a single capacitor. They sum in parallel.

So is there some other reason you've done it that way?.....

The capacitors used are 2.7v rated, so need a decent string to get the working voltage up high enough. Yes, it does reduce the rated capacitance, but its still in the "stupidly high" arena, and I'd recommend setting the CV for maximum run time without DCC signal to prevent a Titfield Thunderbolt moment of trains running over fields and crashing downhill into pieces.

If being electrically cautious, the capacitors in the series string should each have a resistor in parallel with its terminals. That will equalise the voltages, and thus if one capacitor is towards the extreme of tolerance, you don't get an over-voltage at that capacitor.


The capacitors as used are contradicting the Zimo manual, which says a maximum of 5000uF when used on those terminals (166,000 is approx. 33 times over the maximum). The reason for the limit isn't explained, and I can't think of a reason for it, but that's what the manual says. (The current through components, and thus heating effects, could be the same with 5000uF or 500,000uF for a loco running with dirty wheels on dirty track). That it is shown working without a problem is useful empirical evidence that the instructions might not be totally correct in this detail. But, others copying will have to make their own assessment on whether its appropriate or not.


Installations I've done for others with similar capacitor banks have used a different connections to stay within the Zimo manuals statements. I've used the decoder positive and decoder negative terminals, and provided my own charging resistor, discharge diode and a zener to control the max voltage over the capacitors.



- Nigel

 

[Steph Dale]

Nigel,

Yep, it just makes a great deal more sense to me to build for reliability and use a few 25v or even 35v capacitors. Tim is safe(ish) up to about 16v, which is fine until the loco ends up on a layout that's set towards the top end of the DCC standard (24v).

I'd also be concerned about an internal short circuit failure which would almost certainly lead to the lot going pop; not pretty with that amount of energy.

I've seen what 4000uF can do as a keep alive in a larger 7mm loco and it'd be more than adequate for the loco shown here. I'd be happier having a few 500uF 25v in parallel than the solution shown here. It's more reliable and certainly safer.

Steph

 

[Nigel Cliffe]

Nigel,

Yep, it just makes a great deal more sense to me to build for reliability and use a few 25v or even 35v capacitors. Tim is safe(ish) up to about 16v, which is fine until the loco ends up on a layout that's set towards the top end of the DCC standard (24v).

I'd also be concerned about an internal short circuit failure which would almost certainly lead to the lot going pop; not pretty with that amount of energy.

I'd need to read up on which Zimo is which (its in the Zimo manuals). Some have internal voltage regulation of the capacitor terminals, so the voltage rating of the capacitors is not dependent on track voltage. Others don't, so capacitors suitable for track voltage need to be used.

The Zener I mentioned protects against over-volts, but also limits the volts from the capacitors to the Zener voltage. The Zener is protected from over-current by the charging circuit resistor. But all that doesn't go onto the Zimo charging contacts, it goes onto the decoder + and decoder ground.

Short failure is a potential issue with any capacitor bank. The only ones of mine which have failed have gone quietly. But I have seen capacitors go bang elsewhere.


- Nigel

 

[Steph Dale]

Nigel,

It'd be interesting to know what's on the decoder in terms of functionality. I'm somewhat out of touch with what Zimo are up to here, but some simple safety and reliability engineering is always worth taking into account. Mind you, I would say that; until recently it was my job...

The point is that if the caps are rated at line voltage and in parallel it doesn't matter whether any of them fail open or closed, they won't take the others in the bank with them; not the case if they're in series and fail short circuit.

Steph

 

[BrushType4]

Just heard that Zimo is insolvent.

 

[John K]

Then buy every decoder you can while you can.
They are technically streets ahead of the rest.
John

 

[BrushType4]

Maybe some good news as the website says the following;

Insolvency?

Yes, but not in reality. Due to falling behind on payments to our social security company, the latter got us into insolvency, although we had already payed our debts. There would be no problem with other business partners, but obviously this is not the case for social security companies, which we learnt from.

ZIMO had financially the best years in 2016 and 2017, and also our debt ratio is the smallest since 10 years.



ZIMO Elektronik GmbH will be under insolvency administration until January 2018, then we will get back to administrating ourselves. There will be (almost) no problems and impairments for clients and suppliers. We hope, you still have trust in us and we are trying to solve the matter as soon as possible.



In the model railway business insolvencies are practically usual. And if we are not able to declare real insolvency, we try it this way ;-)

ZIMO is, and always will be, special.

 

[SoundsLoco]

Just heard that Zimo is insolvent.

Yes and No.

I've been in contact with ZIMO this morning. There's no need to panic.

They are still in business, still trading and still making decoders. This unfortunate situation was caused by an oversight in admin.

Here's what it says on ZIMO's website.

Insolvency?

Yes, but not in reality. Due to falling behind on payments to our social security company, the latter got us into insolvency, although we had already payed our debts. There would be no problem with other business partners, but obviously this is not the case for social security companies, which we learnt from.

ZIMO had financially the best years in 2016 and 2017, and also our debt ratio is the smallest since 10 years.



ZIMO Elektronik GmbH will be under insolvency administration until January 2018, then we will get back to administrating ourselves. There will be (almost) no problems and impairments for clients and suppliers. We hope, you still have trust in us and we are trying to solve the matter as soon as possible.



In the model railway business insolvencies are practically usual. And if we are not able to declare real insolvency, we try it this way ;-)

ZIMO is, and always will be, special

 

[John K]

Nice positive spin, but it is the Zimo website.
I’m stocking up on the next six MX645s that I know I’ll need.
John

 

[Ressaldar]

Hi Tim,

I'm installing a Zimo MX696 into a split headcode Heljan Class 37, a new decoder for me - it is in two parts and not the easiest of decoders to initially get your head round but I have managed the Swiss mapping for the lights and my friend wants the roof fan to be able to switch on/off - I have wired it up to FO6 with the intention of 'Swiss mapping' it, but am stuck as to how I can make it on/off. Any thoughts?

regards

Mike

 

[TheSnapper]

Hi Mike

I haven't used an MX696 - looks a bit cramped!

Can you use a high F Key for the fan, such as 21 onwards?

Alternatively, as with the Heljan Western installation, I had the fan switching on & off with the sound (so you would map FO6 to the F1 key) - would that be acceptable? Also wire it to the low voltage output (assuming there is one on your version)

Tim

 

[Ressaldar]

Hi Tim,

many thanks for your reply. I tried wiring the fan in the same manner as the lights, but the voltage was far too great and unfortunately, the 5V option that is on the MX695 is not present on the MX696 so I think that Plan B will come onto play - don't wire up the fan, you cannot see the rotation anyway.

I'll just tidy the wiring up this afternoon and seal the speaker with silicone and call it a day.

regards

Mike

 

[SteveB]

Hi Tim,

many thanks for your reply. I tried wiring the fan in the same manner as the lights, but the voltage was far too great and unfortunately, the 5V option that is on the MX695 is not present on the MX696 so I think that Plan B will come onto play - don't wire up the fan, you cannot see the rotation anyway.

I'll just tidy the wiring up this afternoon and seal the speaker with silicone and call it a day.

regards

Mike

Hi Mike

You can reduce the voltage using CV60 and eliminate the functions that you don't want this reduction to apply to using CV114 and CV152. The fan sound can then be moved to whatever function controls the fan using CV300.

Hope this helps.

Regards

Steve

 

[Ressaldar]

Hi Steve,

many thanks for your input, I will make myself a strong black coffee and study the manual and your suggestions.

regards

Mike

 

[TheSnapper]

Recently I did a couple of DCC installations for Heather .

Loco #1 - a 2251 0-6-0, solid resin boiler, working inside valve gear, lovely build, but no room!





The motor just fits!




After pondering for a considerable while, I decided to carefully open out the opening to accommodate a “piggy-backed” decoder & stay-alive unit (Zimo MX645 & SC68).
This is the original opening:



This is the modified opening:




Also had to remove the elegantly crafted motor restraint:




To avoid clutter, this is the procedure I use to remove unused wires from a decoder:





I wired up the SC68 Stay Alive unit to the decoder, then secured them together with Kapton tape.
They were then secured to the motor using a cable tie, which also acted as the replacement motor restraint.:




Choosing a suitable speaker and location was a bit of an issue, but eventually decided on a Zimo cube mounted at the front of the chassis:




Routed the wiring to simulate internal conduit or cabling:



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End of Part 1
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[TheSnapper]

Loco #2 – a 5700 Pannier Tank, solid body, , another lovely build, but not much room!



Motor only just fits!



I ruminated over this one for a long time.
I did think about installing the decoder & stay-alive unit in the coal bunker, but as far as possible I prefer to keep everything on the chassis, to simplify wiring.
After much deliberation and e-mail exchanges, I was assured that nothing was planned to be installed between the chassis, so decided on there:




In order to hide the installation as much as possible, I wanted to fit it as low down as possible, so I fabricated a Plastikard platform to support the decoder/stay alive combo..:



…which was shrink-wrapped in black for camouflage:



and fastened to the tray with strong double-sided tape:




I had to route the wiring to avoid rubbing on the axle, so I drilled a hole in the tray, and protected it with shrink-wrap to shape it out of the way:




Speaker choice & placement was reasonably straightforward:






It turned out to be a neat job, which I was quite pleased with after all:




The decoder installation is virtually invisible when the body is fitted:


This is a beautifully built & finished model, and runs & sounds good too!

 

[Dan Randall]

Excellent idea to remove the unused wires and re-shrink wrap the decoder Tim. (I didn't even know you could buy replacement shrink wrap!). Both have been noted for the future.


Regards

Dan

 

[Kev T]

I've always shied away from completely enclosing the decoder, due to worries about overheating. Have you had problems with heat in decoders? Your way has significant advantages if temperature isn't an issue.
cheers
Kev

 

[TheSnapper]

Hi Kev

I've never had a problem with decoders overheating, despite some being enclosed as above.

I daresay, if power-hungry motors are used it could be an issue.

Tim

 

[3 LINK]

Hi Tim,

Always enjoy reading these topics of yours, food for thought so they say.

Funnily enough my next loco build will be the jltrt 2251, I notice that you managed to open out the resin firebox, can you tell me how you went about it? I always thought the resin was next to bullet proof, although I have never had any trouble drilling the holes for the hand rails.

Regards,

Martyn.