I would use a wal wart plug to power the meters.  Those meters will not pull any amps to speak of.

http://www.amazon.com/Excelity...ords=wall+adapter+9v

Put your TVS diodes between the circuit breakers and the track. When you have a derailment, excessive current will be drawn from the transformer plus you will have voltage spikes occurring on your track power. During the voltage spikes, the TVS diode will conduct drawing even more current through the circuit breaker possibly helping it trip faster. TVS diodes also typically fail shorted. You want them after the circuit breaker in case this happens. The TVS diode will just blow the circuit breaker instead of blowing up assuming you have sized your circuit breaker properly.

TVS = Transient Voltage Suppressor.

Dear gentlemen

Thanks for you input. I never though of the wall wart, thanks for the tip TurtleLinez. Matt A the fast acting circuit breakers I use are rated at 10 amp.

Hi

This is for the folk peeking over the fence. I found this on one of the other threads. This is a Stan2004 design and will work with Digital Meters.

https://ogrforum.com/t...-digital-panel-meter

I'm curious why not use a regulated 5V wall-wart and dispense with all the separate power modules?

Hi John

Thank you for your reply on this thread. If I used what you suggested would I need just one wall wart to power 4 digital Amp meters and 4 digital volt meters?

3 1/2 Blue LCD Digital Volt Panel Meter AC 200V Item number 390221407367

Digital Electrical Ammeter Gauge AC 0~20A Current Panel Meter LCD Monitor+Shunt Item number 391035327062. This for the Post war ZW and ZW-C.

Also for the KW and MTH 4000 set up what wall wart would you suggest?

If it is possible do use the Digital meters without the DC/DC step down bucks I all for it.

Looks like it takes 9-12V AC or DC.  I don't see why you couldn't feed all of them direct, I'd probably pick a 12V Regulated wall wart for the power.  In any case, what you've picked isn't compatible with a 5V DC output.  I don't see the need for extra power modules, maybe Stan can chime in to let us know what he was thinking, I certainly could be overlooking something.

I do know that most of these meters need a totally isolated power supply from the measured voltage, so you'll want a transformer isolated supply just powering the meters that has no common connection to the track power.

The DC-DC modules in the diagram and described in the OGR thread link are indeed isolated converters...not to be confused with non-isolated $1 LM2596 stepdown buck converters.

Hi Stan2004

Thank you for your reply. So if I used a wall wart (totally isolated power supply) that was 9-12V AC or DC using a bus bar to power the meters it should work with out the DC-DC modules, right?

Thank you John as well.

Thanks Stan, I figured you had to have a reason for adding the extra parts. I looked for isolation in your description, but I didn't see it, which is why the question.  Of course, a couple posts down, you did clarify they were isolated, but I didn't read the whole thread.

One wonders if it's a problem to use isolated power in parallel for powering the modules.  I suspect the measurement circuit and the power are not isolated, but if you have the same track common for all meters, you might get away without isolated power for those power sources.  That would drop the price and complexity of the meter installation significantly.

If you need isolation, I think I'd just use a bunch of cheap wall-warts, I have tons of them, so that's not an issue for me.

I would use individual isolated supplies for each digital meter as shown in the diagram.  Or a separate wall-wart for each meter if that's practical to wire up.  The isolated converter supplies are only a few dollars each. 

I agree that given a specific situation, it may be possible to power multiple digital meters with a single isolated supply (or wall wart).  But I found the scant technical info on the digital meter listing wrt isolation, impedance, loading, etc.  Plus the isolated DC-DC modules are inexpensive relative to the cost of the digital meter module. 

But as Kris has multiple transformers and is eyeing expansion, I'd want a more general purpose instrumentation panel that is not hand-cuffed to a track wiring configuration.  That is just my opinion.

Perhaps the scrap 5V adapters from countless wireless phone chargers would be a cheap solution.

I can't argue that the bulletproof solution is to have separate isolated supplies, you'll never get into trouble that way.

Here's a cheap version: 311384000776

Dear Gentlemen

Thank you for your answer but I have more questions. This are the information that I got from the vendor:

Based on the above info this is what I found:

http://www.ebay.com/itm/370412...e=STRK%3AMEBIDX%3AIT

My main consideration is the MA what I need for this project. Example  do I need 4 or 8  these unit for a Postwar ZW, one each for the voltage and one for each Amp meter? Or can I bus bar one unit for all of the voltage and AMP units? Or am I dreaming and each voltage and AMP unit need it's own isolation unit?

Remember that those converters are fairly touchy about the input voltage, so I'd be thinking of a regulated 12VDC power supply as input to the isolation modules.  You can use one power source for all the isolation modules as they are providing total electrical isolation.  I'd probably use this identical converter as it's a lot cheaper and also with free shipping: 371304256443  $3.32.

As Stan says, the safe option is to use individual isolation modules for each meter.  I suspect, though I'd have to personally check, that for a single transformer where the common post is really common to all outputs, that you could get away with fewer converters.  However, without looking at the meters in detail to see how the power source and measurement pins are intertwined, the safe bet is to use individual converters for each meter.  Eight of the ones I mention cost around $26 or so.

Hi John

Thank you for the advise and explanation.