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Reading/Using an Ampmeter

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Reading/Using an Ampmeter
Posted by Trynn_Allen2 on Wednesday, January 30, 2008 4:27 PM

So I now have an Ampmeter and was wondering, what is the best setting to read the Output of a Digitrax system?

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Posted by locoi1sa on Wednesday, January 30, 2008 5:00 PM

  None. DCC is a square wave DC almost but not quite AC. If you are looking for an amperage output you will have to be fast before the booster breaker trips. If you want to test the wireing just do a quarter test. Boosters trip in miliseconds so you will have to have some kind of load to regulate the output before the booster trips. Any amp meter I have seen will not register before the booster trips.

  If you are having problems post a symptom so we can work on it.

       Pete
 

 I pray every day I break even, Cause I can really use the money!

 I started with nothing and still have most of it left!

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Posted by DigitalGriffin on Wednesday, January 30, 2008 5:25 PM

As a general rule of thumb, you could hook your amp meter in series with the power supply lead.  (Providing your Amp meter has a AC amp reading setting)  Yes this works, as the amp meter just uses transistors to switch the input as the current switches direction.  It doesn't matter if it's square, sinusoidal or whatever.  That only matters with voltage.

Hold on...there may be a product on the market...brb

EDIT: here you go...

http://www.tonystrains.com/products/tteexclusive_measure.htm

 

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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Posted by larak on Wednesday, January 30, 2008 9:42 PM
 DigitalGriffin wrote:

 It doesn't matter if it's square, sinusoidal or whatever.  That only matters with voltage.

Hold on...there may be a product on the market...brb

Um ... that's not strictly true. The scale (or readout) is only calibrated for one waveshape,

unless it is a true RMS type meter or wheatstone bridge. Simple ammeters are just voltmeters across low value resistors.

The mind is like a parachute. It works better when it's open.  www.stremy.net

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Posted by Phoebe Vet on Thursday, January 31, 2008 6:54 AM

 locoi1sa wrote:

None. DCC is a square wave DC almost but not quite AC. If you are looking for an amperage output you will have to be fast before the booster breaker trips. If you want to test the wiring just do a quarter test. Boosters trip in milliseconds so you will have to have some kind of load to regulate the output before the booster trips. Any amp meter I have seen will not register before the booster trips.

If you are having problems post a symptom so we can work on it.

Pete

DC Direct Current (one direction only plus OR minus)

AC Alternating current (reversing direction alternating between plus AND minus)

DCC is ALTERNATING current. The fact that it is a square wave does not make it "almost AC" whatever that means. All digital signals, AC and DC use a square wave.

An ammeter measures load. It cannot be used across the supply. It cannot be used on the booster unless it is series with the load. Different loads will result in different readings. The amp rating on your booster is not a measure of continuous flow, it is a limit. It cannot supply a flow greater than that. That is why an 8 amp booster will not hurt your 1.5 amp engine.

You really do not need an ammeter. To test your system wiring, remove all loads (engines and all cars with lights or decoders) and measure AC voltage between the rails in each block. It should be the same in every block. Since most AC voltmeters are calibrated to measure a sine wave, it will not be super accurate measuring a square wave, but it will be close enough for your needs. If you are a nitpicker and need exact measurements, get an oscilloscope.

If adding more engines or lighted cars causes your engines to run slower, then you have exceeded the amp limit of your booster.

The reason that your booster circuit breaker trips when you put an ammeter across it is because you have just created a short circuit, just like when you put the quarter on the tracks.

Dave

Lackawanna Route of the Phoebe Snow

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Posted by DigitalGriffin on Thursday, January 31, 2008 9:38 AM
 larak wrote:
 DigitalGriffin wrote:

 It doesn't matter if it's square, sinusoidal or whatever.  That only matters with voltage.

Hold on...there may be a product on the market...brb

Um ... that's not strictly true. The scale (or readout) is only calibrated for one waveshape,

unless it is a true RMS type meter or wheatstone bridge. Simple ammeters are just voltmeters across low value resistors.

I'm sorry I should have been a lot clearer.  Modern day clamp on (not in series) ammeters can do this using a series of induction coils and diodes.  But they are a lot more expensive.

 

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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Posted by Phoebe Vet on Thursday, January 31, 2008 11:12 AM

I'm sorry, you are right.  I forgot that there are inductively coupled ammeters available that measure actual flow through the wire they surround.  We didn't have them at NSA when I was stationed there.

I guess I was still picturing someone connecting the ammeter across the power source and trying to get a reading before the fuse blew.

Dave

Lackawanna Route of the Phoebe Snow

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Posted by BlueHillsCPR on Thursday, January 31, 2008 1:23 PM
 Phoebe Vet wrote:

I forgot that there are inductively coupled ammeters available that measure actual flow through the wire they surround.  We didn't have them at NSA when I was stationed there.

I guess I was still picturing someone connecting the ammeter across the power source and trying to get a reading before the fuse blew.

That's why I LOVE my Amprobe! 

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