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DT
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I bought a few items from Tony's Train Exchange. First off is the RRampMeter.



Maintaining and analyzing the electrical system of a layout requires accurate measurements of the voltage and amps. When dc was used a standard meter was all that was needed for these measurements. With DCC use of a standard meter most of the time will not give you an accurate measurement. Tests have shown that meters not designed to read the DCC wave forms can be off by as much as ±50%. Even meters that are “true RMS” may not be designed for the frequency range of DCC. The RRampMeter was designed to fill the need for a highly accurate DCC meter to measure of both voltage and amps. The RRampMeter is designed as a flexible tool to monitor and analyze the electrical operation of a layout. It is designed to work not only DCC power but to make accurate measurements of ac and dc. The RRampMeter has an amazing 2% accuracy.


The meter automatically senses and switches the type of power. Only a "true RMS" meter can accurately measure DCC voltage and current.

Easy walk-around measurements of layout voltage drops, accurate booster output setup to optimum voltages for decoders and sound units.
- Inexpensive device that accurately measures DCC Volts/Amps.
- Also measures AC and DC Volts/Amps.
- Rated at 10 or 20 Amps, costs less than DVMs that cannot measure DCC.
- Measures true RMS Volts/Amps, +/- 2%.
- Suitable for all scales.
- No batteries required (if measuring over 7 volts).
- Designed for Left/Right-hand use.
- PCB length 5.63"; Enclosure length 4", width 2", height 1.25"



Amperage must be measured in series by connecting the left set of contacts or clip leads to the input power supply or power source while the right set of contacts or clip leads are connected to the load or isolated track section where current is to be measured.

Voltage can be measured from the left or right set of contacts or clip leads. If measuring voltage only, then either end of the RRampMeter may be used accurately.

Showing a nice and steady 16 volts at my command station:

It sometimes flutters to 15.9, but doesn't go below that.

On the other side of the layout:

This photo is taken about 10 meters away (along the track). It shows that my oversize BUS wires and feeders do the job perfectly. No voltage drop over this distance.

Set up with a spare piece of track not connected to the rest of the layout to test the current drawn from a loco:

This is the Hornby King Arthur Class and it draws about 0.15 amps with wheels slipping and about 0.1 amp when running normally. When completely stalled at full voltage it draws 0.5 amps which is the limit of the decoder. No problem there. I tested some older Hornby locos that draw well over 1 amp when stalled. Interesting.

I'm going to mount this to my control panel. It will measure the overall voltage and current used throughout the layout. It will show if there is any overload or hopefully any situation that may lead to an overload. I'll connect up a test track to the current tester and have a dtdp switch to select either the layout or the test track for selective analysis of individual locos.
 

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Doug,
An interesting bit of kit. I assume from the fact it works with DCC at a much higher frequency than mains AC, that it will also allow AC measurement at 50Hz as well as the American 60Hz mains frequency?
Regards,
John Webb
 

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QUOTE (Doug @ 3 May 2007, 16:38) <{POST_SNAPBACK}>I bought a few items from Tony's Train Exchange. First off is the RRampMeter.

Pity you didn't come to us! We stock two type of RRampMeter. I came across it several years ago when it was only available in its very basic form, but it has been an extremely reliable piece of kit. I have it permanently connected on one of my DCC layouts but it can also be used on an analogue system.

Regards

John R
Bromsgrove Models
 

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QUOTE (Doug @ 3 May 2007, 16:38) <{POST_SNAPBACK}>This photo is taken about 10 meters away (along the track). It shows that my oversize BUS wires and feeders do the job perfectly. No voltage drop over this distance.

Was any current being drawn at the time? No voltage drop when no current is flowing doesn't prove very much, which is why I'm thinking of building a box with a meter and a switchable resistance across the rails so I can see how the voltage changes as I switch it in.

And to my simple mind, why can't I measure DCC voltage with a DC meter on the outputs of a bridge rectifier? The absolute reading will be wrong due to the voltage drop over the rectifer, but most of the time I'm only interested in how the reading changes when the resistor is switched in.
 

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DT
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You guys have got me thinking... off to the garage for some tests.

First off, to confirm that it is correctly measuring standard AC, I measured the output of an AC transformer with my multimeter. 17 volts on the dot. The RRampMeter measures 17.0 volts AC too.

Secondly, I added a load to the RRampMeter - a halogen bulb connected to the output terminals. The bulb had a current draw of 1.75 amps. The RRampMeter measured 15.2 volts DCC at the command station and 15.2 volts at the same distant point 10 meters down the track. The bulb warmed up rather quickly.

So I maintain that the thick 6mm DCC BUS is doing it's job very well.
 

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QUOTE (Doug @ 4 May 2007, 09:23) <{POST_SNAPBACK}>So I maintain that the thick 6mm DCC BUS is doing it's job very well.

Certainly is! I plan to build the test box I mentioned above to find out whether my rather thinner bus wires are up to the job. My layout is N gauge and much less than 10m long so I'm hoping my wiring is sufficient.

Interesting that the command station has dropped 0.8V compared with the no-load situation...
 

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QUOTE (Edwin @ 4 May 2007, 08:52) <{POST_SNAPBACK}>Was any current being drawn at the time? No voltage drop when no current is flowing doesn't prove very much, which is why I'm thinking of building a box with a meter and a switchable resistance across the rails so I can see how the voltage changes as I switch it in.

And to my simple mind, why can't I measure DCC voltage with a DC meter on the outputs of a bridge rectifier? The absolute reading will be wrong due to the voltage drop over the rectifer, but most of the time I'm only interested in how the reading changes when the resistor is switched in.

You can, but it's still a good idea to add a smoothing capacitor. The reading will not be very far out since the voltage drop across the regulator will not be very high under no load (minimal load of the meter).

Andrew
 

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QUOTE (Edwin @ 4 May 2007, 08:52) <{POST_SNAPBACK}>The absolute reading will be wrong due to the voltage drop over the rectifer, but most of the time I'm only interested in how the reading changes when the resistor is switched in.

Not very scientific but perfect & simple for what is required !
 

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QUOTE (SPROGman @ 4 May 2007, 15:23) <{POST_SNAPBACK}>You can, but it's still a good idea to add a smoothing capacitor. The reading will not be very far out since the voltage drop across the regulator will not be very high under no load (minimal load of the meter).

Andrew
Variation in rectifier drop is a good point, probably also explains the voltage drop at command station outputs mentioned by Doug a couple of posts back.

Thinking some more, I'll probably put a highish-value resistor across the meter anyway so that I get the full rectifier drop all the time (I'll have to experiment with the value). Then when I switch in the much lower value (but higher power!) resistor across the meter, I can be confident that any extra voltage drop comes from the wiring.
 

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QUOTE (Edwin @ 8 May 2007, 10:17) <{POST_SNAPBACK}>Variation in rectifier drop is a good point, probably also explains the voltage drop at command station outputs mentioned by Doug a couple of posts back.

Yes, the rectifier in the booster will have a variable voltage drop depending on load current. The same thing happens in decoders with respect to the voltage available to the motor or function outputs.

Andrew
 
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