# Volt / Amp Meter.



## Mickeyls (Jan 2, 2008)

I would like to set up a indoor track with a volt & amp meter to check out equipment.   I can find digital meters but I am sure I need more than just the meter.  Does anyone have a diagram of how these meters would be hooked up???


----------



## Torby (Jan 2, 2008)

You familiar with Ohm's Law?


----------



## altterrain (Jan 2, 2008)

You can pick one up at HarborFreight for about $7 (less on sale). It comes with the pointy probes. It would be easy enough to make a second set of probes with banana jacks and alligator clips (or even hooked up directly to your test track). 

For voltage just hook a probe up to each rail. For amperage you need to put the meter in line with one of the power feeds to the track. Its pretty simple.

-Brian


----------



## Dwight Ennis (Jan 2, 2008)

If you're looking for permanent panel mount meters, Micro Mark sells a voltmeter, item # 82144 and an ammeter, item # 82145.  You'll save a little if you buy the set, item # 82146.  Keep in mind that conventional meters such as these or digital multimeters won't read accurately if using DCC.


----------



## Skip (Jan 2, 2008)

Whatever you chose for an ammeter, make sure it can handle at least the amount of current you are fused for. Most handheld type multi-meters can only handle about 1/2 to 1 AMP max current, if that. Pulling 10A through your multimeter will ruin its day ... electronics surplus stores and probably RadShack in the states (we don't have them up here anymore) have relatively inexpensive panel meters which are available in the DC voltages and currents used on LS. As Dwight says though, you won't get a meaningful reading on DCC

Voltage is measure across two points (i.e. rails).   Current (amperage) is measured through something. OHM's Law:  V=I/R where V=voltage, I=current(in amps) and R= resistance (in ohms)

Power (watts)=I x V (called volt-amps on transformers)


----------



## Mickeyls (Jan 2, 2008)

Thanks for the comments.  

I am looking for a permanent panel,  For the cost of the Harbor Freight meters, I might just get a couple and mount them on  a panel.


----------



## JerryB (Jan 2, 2008)

There are a couple of potential problems with using a hand-held volt ohm meter in place of a real panel meter. First, the hand-helds are battery powered. You will need to remember to shut them off each time you use them, then turn them back on to the appropriate range for use. Failure to turn them off will use up lots of batteries. 

A second problem is that the cheap hand-held meters are usually very limited in terms of amperage, commonly an amp or two. Assuming you want a meter that will read amperage to at least to the maximum of your power supply system (say 10 or 15 amps), you will need to add a shunt and read the voltage drop across it. This is a pretty simple design and build task, but even with the correct shunt, accidentally putting the meter on the wrong range can result in its early demise. That means you will need to remember to turn the meter on and select the correct range every time prior to turning the RR power supply on. 

Hand held volt ohm meters are made for a specific purpose and aren't really well suited for the application you suggest. Add to that the fact that the cheapest hand-held meters from Harbor Freight and the like usually have a pretty limited life due to cheap construction, and you will find that real panel meters are definitely a superior solution for permanent use. There are lots of suitable analog panel meters available in the $20 range. 

Happy RRing, 

Jerry


----------



## Torby (Jan 2, 2008)

Those from Micro Mark look cool. 

I'm used to having to calculate and make a shunt knowing the resistance, or ohms per volt, of the meter movement. Looks like they've done the work for you in just the right range.


----------



## Dan Pierce (Jan 2, 2008)

There are inductive clamp current probes than can attach to a multimeter and go to over 500 amps and theseoutput a voltage to your digital meter. Very useful as no wires need to be cut. 

Also, this clamp can be atached to an oscilloscope for DCC or PWM for looking at current waveforms. Not cheap, but very useful.


----------



## Road Foreman (Jan 2, 2008)

Mickeyls,

If you go for panel mount meters, on the current meter be sure you place it in the line before the direction switch, other wise you will destroy it when you reverse direction..  Hope this helps..

BulletBob


----------



## Rayman4449 (Jan 2, 2008)

Not sure if you already have enough info for what you were looking for, but here are the meters I purchased and how I hooked them up along with some other tips. 

http://www.rayman4449.dynip.com/Powersupply-40amp.htm 

Good luck. 


Raymond


----------



## toddalin (Jan 4, 2008)

The easy way: 










http://cgi.ebay.com/20V-20A-DC-RED-...ryZ58278QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


----------



## Roland Seavey (Jan 4, 2008)

OK, 
I can wire a house but this stuff is more difficult for me. Will you please explaine to me thw reason or the two different 5V power supplies here. that just doesn't sink in for me. am sure there is a very good reason,just explaine it to me. 
Thanks 
Roland


----------



## bob7094 (Jan 3, 2008)

The easier way - no 5V power required: 




You wire the voltmeter in parallel with the power supply leads. 
You wire the ammeter in series with the power supply. The ammeter requires a "shunt resistor", 
which is probably included with the lower current capacity meters from All Electronics. 

-- Bob Mills


----------



## bob7094 (Jan 3, 2008)

Well that sucks, the links disappeared! I'll try again: 

http://www.allelectronics.com/make-a-store/item/PMD-30V/30V-DC-PANEL-METER/-/1.html 
http://www.allelectronics.com/make-a-store/item/PMD-5A/5A-DC-PANEL-METER/-/1.html 

-- Bob Mills


----------



## dbodnar (Jan 2, 2008)

Good day - I put together some notes on wiring the inexpensive Harbor Freight meters on my web page. 
Have a look and see if this makes things a bit clearer. 
Volt Ohm Meter Wiring 
dave


----------



## Dan Pierce (Jan 2, 2008)

Don not use banana plugs and jacks for more than 3 amps. Solid connections are needed for good contact in high current situations to minimize contact loss.


----------



## Semper Vaporo (Jan 2, 2008)

Posted By dbodnar on 06/22/2008 3:10 AM
Good day - I put together some notes on wiring the inexpensive Harbor Freight meters on my web page. 
Have a look and see if this makes things a bit clearer. 
Volt Ohm Meter Wiring 
dave




I cannot get the link to work.


----------



## dbodnar (Jan 2, 2008)

I corrected the link in the message above - not sure what happened.... 

You can also get there by going to http://www.trainelectronics.com/ - click on Projects then Volt Ohm Meter Wiring 

dave


----------

