Wiring volt and amp meters

As close to the source as possible.

No matter what devices you are send volts and Amps through-you are monitoring the Source.
But, you could monitor between the track and all those other items

if you wanted to see the actual values getting to the track.

Just remember

voltage is measured across both + & -

and Amperage is measured through only one leg   - & - or + & +

Amperage (AC) can also be measured using a snap-around meter.  Placing the probe around a current carry-ing conductor  Works without having to dis-assemble the wiring, to insert the meter.

A search for Snap-around meter should yield product.

I have this $15 Harbor Freight Clamp-On that I keep next to the layout.  It's surprisingly accurate as tested with my Fluke ammeter.

If you want to have meters wired in, I agree, as close to the source as possible. I tend to agree with GRJ, that inexpensive clamp on from Harbor Freight would likely server you as well. Only thing would be if the transformers are inaccessible and you have the meters on your panel, that is a little easier. IME you won't need that all that often, but it does look cool.

Many thanks to all who have responded.   It's obvious, but still worth saying, that the Forum is invaluable to folks like me.

Bill

One follow-up:  can someone confirm whether I'm fine with 10 amp DPDTs for distribution of power to my power blocks?

Thanks, again.

Unless you're going crazy with track power to each power district, 10A switches is all you need.  Also, you only have to switch the center rail, so in truth, a SPST switch is sufficient for simply turning track power on and off on a power block.

I recently added a clip on amp meter to monitor my 3 Lionel LW transformers, details below

Picture of the $25 Amprobe Clamp on Ammeter, 0 to 25 amps, note the compressed area of 0 to 5  amps on the left of the scale.

To amplify this area to 5 times its size, I made a simple 5 loop wire doughnut and rapped it with electrical tape.  That changes the max reading from 25 amp max to max of 5 amps for the whole range of the meter.

Five coil wire doughnut installed and meter is rotated to each of three LW transformers

Picture of 5 turn coil, LW transformer and Amprobe clip on ammeter, reading scale for 5 turn coil in service are the big numbers added on with taped on numbers.

With a clip on ammeter I only need one meter and can move it to each LW.  They all now have a 5 coil donuts.

I normally do not need it but yesterday, the 6 amp circuit breaker was throwing when running 3 trains on one loop with my relayed system.  If I had read the meter I would have seen the problem coming.

Charlie

GRJ,

Thanks again for your follow-up.   

Regarding single-pole vs double-pole, I was under the impression that to minimize DCS issues, I should be using a "star" wiring system with both hot and common wires of equal length to/from the power blocks, and equal paths through switches or other "interference" (i.e., both hot and common passing through my toggles) before the commons indeed come together at the TIU.

Thus, I assumed the double-pole toggles.    I will appreciate your futher help on this.

Bill   

PS to GRJ,

I'm also powering my switches, operating tracks and accessories from separate transformers than those powering trains/track and further assuming that to minimize DCS issues, I will keep any "common" or bus for these items separate from the commons for track/train power.

Am I on the right or preferred track, here?  Thanks, again.

Bill

It can't hurt to switch both, but most folks only switch the hot rail.  I don't power anything but operating trains from track power, switches and accessories run from a different transformer.  However, if you run TMCC and have TMCC accessories/switches, they must have a common ground with track power.

To add on to this discussion, I would like to wire in an ammeter into my control board. It's a cheap analog ammeter from amazon, and I've read that you need to have some sort of shunt across the terminals and that you can't just put the ammeter in line with the hot wire.

I'm not sure I understand why, when I use my fluke I literally just pull off the hot post and stick it in between the post and the hot wire to read amps.

The reason is that the meter movement (the tiny coil and armature) that causes the needle to move starts out as a very sensitive circuit, not capable of handling a large current. The shunt, which is a bar of metal, designed for the particular application, "shunts" or bypasses most of the current, leaving the small remainder of the current to pass through the meter movement.

More technically, the shunt is designed to create a certain voltage drop across the terminals, and the meter movement responds to a voltage in that small range.

Most ammeters have a shunt, either hidden inside or visible on the outside, mounted across the terminals. By changing the size of the shunts, the same movement can be designed to handle different current ranges.

We often use a flow of water as an analogy to electrical theory. In this case, picture a river with a fast -moving heavy flow. Then picture an island with one large stream on one side, and a small stream on the other. If you know the ratio of the two streams, it would be easy to measure the total flow by measuring the small stream and doing some math.

If the ammeter you bought has a stated rating, then it is assumed that the shunt is already installed.  Can you check and tell us the advertised rating, or show us a picture?

Arthur, thank you for the explanation. The river theory was helpful .

Here's what I've got. My Mandarin is not so good.

I've also attached the spec sheet from the site.  I assume "Can be directly connected" means it has an internal shunt already?

It says "can be directly connected", so presumably it has the shunt built-in.

If the meter you purchased has a built in shunt, it should be measurable with an ohm meter…

I did a quick search and found no useful information for determining if a ammeter is pre-shunted.
seems there is no designated markings to advise the end user.

The information states a “high current” requirement..but does not define a value for “high current”.

I built a device to read Amps for my tracks because the Z-4000 I bought was determined unrepairable-the display was fried-it reads nothing and everything.
but the outputs are clean and accurate-

so I built my Ammeter so I could see real time current draw.

it’s worked almost 10 years..and I got it for a great price.
I've since rebuilt it and added SPST to control each mainline feeder.

I use a bus bar from an electric panel for distribution..all together I spent less than $50 on it.

Now, I’m curious about the shunt and determination what value it is  

That model has a built-in shunt.  It says rated for 0 to 10 Amps.

@bhoerger posted:

GRJ,

Thanks again for your follow-up.   

Regarding single-pole vs double-pole, I was under the impression that to minimize DCS issues, I should be using a "star" wiring system with both hot and common wires of equal length to/from the power blocks, and equal paths through switches or other "interference" (i.e., both hot and common passing through my toggles) before the commons indeed come together at the TIU.

Thus, I assumed the double-pole toggles.    I will appreciate your futher help on this.

Bill   

I use a star pattern with some switchable track blocks... I only use single pole switches and switch the hot on and off to regulate the block power. No problems seen with the DCS signal.

LT1Poncho,

Thank you for your further information. 

Do you bring your "returns" back more or less on the same path as your "hot" wire and more-or-less the same length/distance but route them directly to a common bus at your control panel or power station and simply by-pass the power-block toggle?

Might I ask the general dimensions of your layout?

Thanks, again.

Bill

@bhoerger posted:

LT1Poncho,

Thank you for your further information.

Do you bring your "returns" back more or less on the same path as your "hot" wire and more-or-less the same length/distance but route them directly to a common bus at your control panel or power station and simply by-pass the power-block toggle?

Might I ask the general dimensions of your layout?

Thanks, again.

Bill

My layout is 10x12. I run hot and common from the output of my TIU to a distribution block in the center under the layout. I then run hot and common (together) to the track blocks. If a certain block is to be shut off by a single pole switch, I run that track blocks hot hot wire to a relay. The single pole switch then activates or deactivates the relay. This way the wires from the distribution block to the track blocks are similar in length as per DCS suggestions. The wires would be much longer if they themselves went to to the single pole switch. Relays help keep the wire lengths in check. Hope that makes sense.