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I have been trying to determine the compatibility of the Digitrax DH123D decoder with the LGB MTS System when using the LGB 50111 AC Transformer to power a LGB Central Station 1, 2 or 3.

It would not be much help to know the maximum voltage of the Digitrax DH123D decoder if I do not also know the DCC track voltage that is put out by the LGB MTS System (to know if it exceeds the voltage limit of the Digitrax DH123D decoder).

Can anyone tell me what the actual LGB MTS track voltage is?

Thanks,

Jerry
 

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Jerry,

The MTS system has a 20 volt AC transformer for power.. To get the peak voltage you multiply 1.414 times 20 volts & get 28.28 volts.. The command station probably has a bridge rectifier input & a H bridge output.. You will loose about 2 volts per section & this will give you about 24 volts track power.. As you can see this under the 27 volts the NMRA sets for HO & larger decoders.. We all know that Soundtrax in the large scale "Shay" will not work on MTS systems unless you drop the track voltage or put bridge rectifiers in the "Shay".. I you want to be real safe you could use a 18 volt transformer.. This would give you about 21 volts track power.. As long as the transformer has the same current rating there will be no problems..

BulletBob
 

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Hi BulletBob,

With a name like Bullet Bob I knew I could count on you for straight shooting. :D

With a NMRA standard of 27 volts and a LGB MTS output of 24 volts combined with the fact that the DH123D decoder seems to be working fine with no overheating, it seems that the components I am working with will most likely prove to have a long life expectancy.

Many thanks for your help,

Jerry


Posted By Road Foreman on 07/19/2008 6:33 PM
Jerry,
The MTS system has a 20 volt AC transformer for power.. To get the peak voltage you multiply 1.414 times 20 volts & get 28.28 volts.. The command station probably has a bridge rectifier input & a H bridge output.. You will loose about 2 volts per section & this will give you about 24 volts track power.. As you can see this under the 27 volts the NMRA sets for HO & larger decoders.. We all know that Soundtrax in the large scale "Shay" will not work on MTS systems unless you drop the track voltage or put bridge rectifiers in the "Shay".. I you want to be real safe you could use a 18 volt transformer.. This would give you about 21 volts track power.. As long as the transformer has the same current rating there will be no problems..
BulletBob
 

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Hi Bulletbob,

As I progress with my reading of my LGB Telegrams I am now up to 1996 and in the Spring 1996, Vol. 7. No. 1 (page 39) Heinz Koopmann stated that the LGB Multi-Train System always carries 24 volts.

Thanks again,

Jerry
 

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Hi Jerry-


As I progress with my reading of my LGB Telegrams I am now up to 1996 and in the Spring 1996, Vol. 7. No. 1 (page 39) Heinz Koopmann stated that the LGB Multi-Train System always carries 24 volts.



While Herr Koopmann's comments can be misconstrued to infer the MTS central station has a regulated output, in reality, this is not the case. If you supply 16VAC or 18VAC, the DCC track output will drop below 24V. When using a 20VAC transformer, I've also seen the track voltage above 25V.

It is hard to determine the context of Herr Koopmann's comments, but he may have been referring to the fact that DCC, unlike analog power, has a bi-polar signal on the rails at all times.

In any event, 24V is a fair assumption, especially if you are using a 6A/20VAC transfomer to supply the central station. Also note, 24V is overkill unless you need to run trains at high speeds.

Best regards,
Bob
 

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I use regulated DC as a source for my NCE system, input is 27 volts, output is 23.4 or so DCC as measured by a true RMS reading voltmeter.

Regards, Greg
 

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Hi Greg,

That is really good news to hear.

If NCE is putting out 23.4 volts and LGB claims 24 volts for MTS then that suggests to me that 24 volts is not excessive for large scale MTS/DCC.

I think this emphasizes that manufacturers should state the maximum voltage their decoders are rated for rather than the simplistic HO, O, G or whatever ratings they currently use that are (in my opinion) meaningless.

Thanks,

Jerry


Posted By Greg Elmassian on 08/06/2008 10:36 PM
I use regulated DC as a source for my NCE system, input is 27 volts, output is 23.4 or so DCC as measured by a true RMS reading voltmeter.
Regards, Greg
 

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Hi Greg,

Now you have brought up another matter.

I have several voltmeters that are rated for reading RMS. I have no idea what RMS is.

Your post suggests that I could use my RMS meters to measure MTS/DCC voltage. Is this correct?

**************************************************************************

Also I recently bought an Aristo-Craft CRE55468 regulated 24 volt DC power supply. Later I bought an Aristo-Craft CRE-55467 24 volt controller. I think the power supply was originally intended as a DCC power supply. I have yet to use either.

Would there be any advantage to using the CRE55468 as a power supply for a LGB MTS Central Station?

Thanks,

Jerry


Posted By Greg Elmassian on 08/06/2008 10:36 PM
as measured by a true RMS reading voltmeter.
 

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Jerry,

RMS is Root Mean Square.. This is the standard measurement for AC voltage.. Greg used a "true RMS meter", the differance being able to measurer any AC wave, such as the almost square wave DCC signal.. A RMS meter will measurer the voltage, but not correctly.. Can not help you with the Aristo-Craft stuff..

BulletBob
 

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Jerry-
I've "Googled" the term "true RMS voltage" in the past and I've gotten good results.

http://www.kpsec.freeuk.com/acdc.htm

Remember, even if a meter is listed as a 'true RMS' meter, it may only be accurate within a given freqency range. The low end Fluke meters I checked online are only accurate within lower frequency ranges, e.g., frequencies between 50/60 Hertz, 45/500 Hertz, etc. The meter specifications are usually in your manual. To accurately read a DCC signal, you'll need a meter with a significantly higher frequency range.

Also note, some Fluke meters include a 'possible damage warning' if used at frequencies above 50/60 Hertz. Again, read your manual.

Good luck!

Best regards,
Bob

PS - You can always rectify the DCC waveform, filter it, and read the resulting DC voltage. Remember to add back the 0.7V drop for each resistor. You could probably build a small circuit board with "clip-on" leads for a few bucks.
 

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Jerry,

Go to Tony's Train Exchange & look for the RRAmp meter.. Get the rev # 4 for large scale.. Will do every thing you want & then some..

BulletBob
 

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These guys have it all correct. I should really have been more specific so I did not confuse things Jerry.

Virtually all meters that read AC (as in alternating current) must be RMS, that's the standard way of measuring AC, rather than peak. It's a better way to really measure the real energy since it is changing constantly.

When I said "true rms", what I should have really said "I have an AC voltmeter that will accurately read the RMS voltage of the DCC waveform, which your ordinary Radio Shack (for example) will not since it reads RMS only at 60 Hz"

But that was way too much typing, so I cheaped out !!!

Regards, Greg

oh, the 24v regulated supply can be used for anything, it would be a good source for a DCC system.
 

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Most meters only read RMS of a "Sine" wave, regardless of frequency... I don't think that DCC power is sinusoidal, ain't it more like a square wave?

Take a look at it with an oscilloscope.
 

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Yep, absolutely, an even more difficult wave to measure. The cool thing about DCC is since it's a square wave, it does not need a lot of filtering (like big electrolytic caps) to smooth out the sinusoidal curves... but of course that's one of the reasons they designed it that way.

Regards, Greg
 

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Hi Greg (and others),

Thanks for the explanation. It (RMS and/or DCC voltage) is not a big issue for me. I just thought that if I already had a meter that I could use that it would be nice but it is not something I would spend any money on.

I appreciate the additional information. Perhaps it will benefit someone else.

Jerry



Posted By Greg Elmassian on 08/08/2008 1:38 PM
These guys have it all correct. I should really have been more specific so I did not confuse things Jerry.
 

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I'll give this one final piece of advice, if you get into a situation where you do need a good amp meter, then it's worth buying this, because it measures volts and amps, DC and AC, and it will read a lot of amps...

Regards, Greg
 

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Jerry-


Hi Greg (and others),

Thanks for the explanation.



You are welcome.

As I mentioned in another thread, the RRampMeter IV is a very nice tool for the DCC enthusiast. The Tony's Train Exchange website is also a helpful tool for DCC beginners.

Best regards,
Bob
 

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Jerry,

On the Digitrax system you can get real close by measuring rail A to Gnd & rail B to Gnd on the DC voltage scale & add the 2 voltages together.. The reason this works is because the DCC voltage is a bi-polar signal.. 1 rail goes 0 to 12 volts positive & the other rail goes 0 to 12 negative..

BulletBob
 
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