Volt and Amp meters

Here's a basic, generic schematic that has been posted here a few times previously.

Does anyone know of a digital amp meter and/or volt meter that can run off track power instead of needing a separate power supply?

I run DCS at a constant 19.5 volts; could I resistor it down to what ever voltage the meter works on?

Thanks,

Waddy

Not many of those around Waddy, it seems most want a separate isolated power supply.  You'll do good just to find a suitable digital voltmeter for the range you want!

RTR12, I came to this thread intending to post that meter connection diagram. You beat me to it! I made that diagram a long time ago. I'm pleased to see it's been saved and put to good use. Thanks!

As the diagram shows, the ammeter is wired in series and the volt meter is wired in parallel.

You are welcome and apologies for stealing your diagram. I had forgotten who posted it originally, but I have used it several times. Including when wiring my own meters on my layout. I'll mark it for proper credit in the future!

When I first started saving these diagrams I just put them in a folder. Now I have a bunch that I have no idea who posted? I have been trying to ID them as I find the OP's and I mark all the new saves.

No apologies necessary! I'm glad you posted it! Saved me the trouble... 

Thanks!

"...could I resistor it down to what ever voltage the meter works on?"

Resistors are not used to reduce voltage. They are used to reduce current.

I suggest that you use an isolated supply for the meters (and anything else that requires an isolated supply) per the manufacturer's suggestions.  Small isolated supplies, either AC or DC, are easy to find (wall warts  for example) or to make.

"Resistor it down" was a bad choice of words.  I'm actually thinking of using a regulator and a couple of capacitors. 

Thank you!

 

use a resistor to get another range of your volt meter , it's the same as you will find in a multimeter if you switch to another range

the resistor has to be in series of your meter

for this you will have to know what is the resistance of your volt meter, and the resistor has to have a particular accuracy.

via that way you can mesure greater voltage than the origional range of your meter

good luck

Cor 

Are there any of the digital meters that will work with ac power? I run Legacy and now have analogue meters for volts and amps but I would like to put a digital meter in to read  amps, the analogue meter even with several trains running on the same track registers1 amp or less. The only time I get any readable number is if I run some of my pw A.C. Gilbert engines with the open frame motors.

Thanks

Ray

Rayin S, if you do find any, please post a link. These seem to have all but vanished. Not sure what has happened to them?

Yep, in the past, there were a number of options, and I still have several that I purchased "in case" in my parts drawers.  However, all of the low voltage AC meters have vanished from eBay for some reason.  I also have a number of DC meters that the various Chinese vendors tried to pass off as AC meters, but after some discussions, I did get refunded for those.  I guess they didn't understand, when they advertise a voltmeter as an AC voltmeter, it really should measure AC voltage!

take a bridge rectifier and connect it for your DC volt meter, you can now mesure the AC volt

it will work, but it will not be verry precise

Cor

Not even close, I went that route at first but discovered that it was never going to have sufficient accuracy.  I've toyed with the idea of building a small PCB that will measure true-RMS and output to a simple display, but it's just one of many interesting ideas.

Well it depends on what you mean by "close" or "precise" or "accurate".  In this thread I showed for about $2 in eBay parts you can make a self-powered AC digital voltmeter.  Picture from thread copied below.  The thread has a video showing it in action vs. a Z-4000 digital voltmeter readout. 

The "self-powered" feature makes it like a typical analog voltmeter where no external power supply is required to power the meter itself.  But to make it self-powered you need more than a bridge rectifier since the digital electronic must have power when the AC voltage crosses zero; hence the need for a capacitor.  The 10 cent trimmer calibrates the meter for best accuracy around the region (voltages) of interest. 

 

GUNRUNNERJOHN,I am not well versed in electronics but my query was more toward the possibility of finding a digital amp meter for the ac power. Is there a way to wire one of the digital meters to read the amps in an ac circuit? This may be a dumb question but this shows how much I know, very little. I do have a meter with analogue read out that has a clamp attachment to put  around one wire to a circuit and it will read amps. This meter is from Radio Shack it is labeled with the part number #22-602. I do not know how accurate this kind of reading is but is there some way to adapt this principal to one of the digital meters to read ac amps? Ray

The issue with digital meters is often the true RMS measurement of non sinewave AC voltages. Most of the late variable transformers vary the effective RMS voltage by chopping up the sinewave and the most inexpensive meters do not read that correctly. The usual method for inexpensive meters is to rectify the AC, store the peak voltage and scale that down by .707. So you can do that and display the result on a DC meter. But it will be somewhat inaccurate over the range of voltages measured.  For our purposes, it's probably just fine. It will be repeatable and that matters most to us.  The maximum voltage of about 18 VAC will be most accurate. I think that's the method Stan2004 uses in his post above.

You can still get analog meters on ebay for AC volts or amps. And they can easily be wired into your layout power. It's just the digital ones that seem to have vanished. The analog meters require no external power either, like most of the digital ones I have seen in the past, before they became extinct. 

Harbor Freight has a small digital clamp on meter for about $14 that is good for taking readings around the layout. I think they call it a 'mini' amp meter or something like that. If you are interested in something like that I can post a link.

RTR12,

I am interested in these meters, would you please post the link. I would like to see exactly what these are and if they might suffice for what I desire to see.

Thanks

Ray

These are very cheap meters, but will probably work fine.

http://www.ebay.com/itm/AC-Ana...hGFy3zbBArAZhk1ELl9A

http://www.ebay.com/itm/AC-15A...6:g:cxwAAOSwJQdW8msz

If you buy Simpson meters, etc., they will probably perform marginally better...

http://www.ebay.com/sch/i.html...p+Meter&_sacat=0

http://www.ebay.com/sch/i.html...t+Meter&_sacat=0

Ray

Just FYI. da bay I ordered AMP and Volt gauges both AC and DC about  a week ago just to experiment with on a project. These are the cheap china analog gauges also . Cost a little more than the plastic housing ones.  All of these are in metal round housing and I liked that look. You can see them o0n one of  CJACKs sites.

Larry

 

In addition to the links cjack posted, here are a couple more: 

0-15 Amp Analog Ammeter here's a 0-20 Amp version and here's a 0-30 Volt meter and another 0-30 Volt one

A couple of these (volt and amp) are from the same vendor. They are not exactly like the ones I got a few years ago, but similar. If you want to do a little more searching the meters I got were HUA 85L1 type as shown in the lower left near the indicating pointer on the dial. I can't find the listings for the ones I got, too long ago I guess, but they were all from the same vendor.

I still search around every so often for the digital meters, but no luck so far. 

In case anyone reads this page, I found some digital Volt and amp gauges on Amazon. they are powered by AC or DC 8-12V and will read 0-10AAC and 0-600VAC. 

Yeeco 0-10.00A Digital AC Ammeter Amp Panel Meter

Yeeco AC 0-600V LCD Display Digital Voltmeter Volt Panel Meter

So $24 to do both current and voltage.  if that were cut in half I'd be interested.  "+/- 2 words" I think is "+/- 2 digits" which may be fine with the ammeter but for the voltmeter unacceptable.

Have you purchased these and tried them out?

A meter with a 600vac face might be way too large, i.e it might not be accurate enough if not digital.

The stability of digital reads can be fickle, can't be zeroed well, or are slow to showing change per build. You also want one minimum imo. Slow or sensitive, that fraction always works in your favor. 0-99.9v or even 0-99.5v in accurate half volts...would likely be fine. It's likely never going to 30v on a bad day.

 120vac is way too much also. At 50v half of the meter would still never see use (until something was out of phase anyhow ).

 A 20-30v face would be great; note ZW 20v full throttle, so 25v ZW max with the +5v whistle boost. The 5v extra in fast accidents likely wouldn't kill a 20v meter, but hard to say when excess heat takes it toll ...it's just a tiny electric coil & a spring. (traditiinal analog anyhow..ie. how long at 25-27v? 0.2 sec. or 2 min ???)

 

Where can I buy meters like the one pictured in the drawing?

Here is a very simple AC/DC digital voltmeter I have been using for some time. 

From way back in the day--Meter wiring. Top row three 0-30 range VAC meters wired "across the line" (parallel) with power jumpered up from the amp meters below and connected to the common white separately.

 The AAC units below, 0-15 range, are connected "in-line"( series) with heavy enough color-coded wire to read/carry the full 10 amp load of the particular power district being monitored.

Meters are Der 670 units assembled in Taiwan of Japanese components and were distributed by a New Zealand Electronics Company. Cost about $12 each + air fare from multiple destinations . Analog meters, much less Digital, in the desired range were not easy to find in the early days of the Forum.

Photos are very old-1997 layout under construction.