Adding an Amp Meter for Transformer

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Adding an Amp Meter for Transformer
Posted by AirMojo on Wednesday, June 28, 2017 12:03 PM

I'm building a panel of volt meters & amp meters for my layout's KW & ZW transformers.

I have an amp meter (15 amps AC) for each Transformer (so that's two amp meters), and two voltmeters (20 volts AC) for the KW, and four volt meters for the ZW.

I wired up the first amp meter to my KW transformer, with one post of the amp meter attached to the center (power) rail of the track connected to the KW's A post, and the other post of the amp meter attached to the KW's A post.

I did an internet search to find out how to install an amp meter, and this is the way that I understood it to be done.

I tried running a train on the track, but I do not get any reading on the amp meter--it just stays at 0.  I expected it to move at least a little... or maybe I need more of a load on the transformer (?).

Am I doing something wrong with the way the amp meter is wired ?

What's the best way to test it to make sure the meter is working ?

Here is a photo of my panel...

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Posted by cwburfle on Wednesday, June 28, 2017 12:11 PM

What sort of train were you running? If you were running a light train, especially a modern era can motored one, the train might not be drawing much current. Fifteen amps is an awful lot of current, how sensitive is your meter? 

Also, did you accidentally leave any other wires between the transformer and the center rail? They all have to pass through the meter.

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Posted by AirMojo on Wednesday, June 28, 2017 12:41 PM

I was running my Texas Special 2245 pulling the Dummy A unit (from 1954?), and 7 cars.

I'm not sure how sensitive the meter is... from the information that I found on the internet, a 15 amp meter was recommended... maybe I got the wrong ones.

I got this one... Baoman Ammeter DH-670 AC 0-15A.

https://smile.amazon.com/gp/product/B01ISHH3AQ/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

The track does have various center rail wires to the transformer, and some sidings that I can power on & off to park a train.

I only hooked up one wire from the amp meter to the track.

I need to splice into all the power wires to the track and then to the amp meter post ?

 

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Posted by Sturgeon-Phish on Wednesday, June 28, 2017 3:54 PM

The ammeter will move when a load is introduced.  Try an older train pulling a car with weight added.  As said 15 amps is too big of a scale to detect the loads you would normally see on your layout.  With my American Flyer I'd see 2.5 - 3 a at most.

If I remember correctly the ammmeter is placed inline between the transformer hot lead to the power rail if you want the amps the trains are pulling when operating.

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Posted by AirMojo on Wednesday, June 28, 2017 4:17 PM

This is a link to the reference that I found for the recommended meter limits...

https://ogrforum.ogaugerr.com/topic/how-to-connect-volt-and-amp-meters

So what range should I be looking for in an ammeter ? 0 to 5A AC ?

A link to an appropriate one would be helpful.

But still wondering if I have mine wired correctly...

My ZW transformer is connected to my Lionel Command Control... one track runs a command control Lionel Diesel GP9, the other an older conventional 736 locomotive using a command control Power Master...I use the other two ZW variable transformer posts for my accessories and turnout switches and lights.

I have not tried hooking the ammeter to the ZW yet... I wanted to start with the KW which does not use any command control stuff.

 

 

Sturgeon-Phish

The ammeter will move when a load is introduced.  Try an older train pulling a car with weight added.  As said 15 amps is too big of a scale to detect the loads you would normally see on your layout.  With my American Flyer I'd see 2.5 - 3 a at most.

If I remember correctly the ammeter is placed inline between the transformer hot lead to the power rail if you want the amps the trains are pulling when operating.

 

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Posted by lionelsoni on Wednesday, June 28, 2017 5:17 PM

Disconnect everything from the transformer's variable-voltage terminal.  Connect one of the ammeter's terminals to the transformer's variable-voltage terminal.  Connect the ammeter's other terminal to whatever was originally connected to the transformer's variable-voltage terminal.

Bob Nelson

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Posted by AirMojo on Thursday, June 29, 2017 7:31 AM

Thanks Bob !

I did that and now I am getting some movement in the ammeter's pointer... not much but some.

Will this wiring method pickup the amperage draw from the other transformer's variable and fixed posts ?

So the 0 to 15 amp AC range is probably too high ?

Would a 0 to 5 amp AC range be better ?

Or what would be best ?

Thank you so much!

This project has been fun, but kind of frustrating too !

Ken

lionelsoni

Disconnect everything from the transformer's variable-voltage terminal.  Connect one of the ammeter's terminals to the transformer's variable-voltage terminal.  Connect the ammeter's other terminal to whatever was originally connected to the transformer's variable-voltage terminal.

 

Tags: ammeter , amp meter
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Posted by cwburfle on Thursday, June 29, 2017 9:59 AM

The ammeter on my workbench is a 5 amp. In my experience, the only load that pegs it is a Lionel HO magnetizer. 

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Posted by lionelsoni on Thursday, June 29, 2017 7:33 PM

I would have used a 5-ampere meter.  Hardly any train would draw more than that.

If you wanted to measure the total current drawn by all the loads, you would put the meter in series with the common terminal instead of a variable-voltage terminal.

Bob Nelson

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Posted by AirMojo on Thursday, June 29, 2017 9:22 PM

Bob... how do you put the ammeter in series with the common terminal ?

I have my two transformers' (KW & ZW) phased together with a wire connecting the common connections.

I have another ammeter for the ZW that I have not connected yet.

 

I found a similar 5 amp meter that will fit in the same panel hole that I made... that's a relief !

Ken

lionelsoni

I would have used a 5-ampere meter.  Hardly any train would draw more than that.

If you wanted to measure the total current drawn by all the loads, you would put the meter in series with the common terminal instead of a variable-voltage terminal.

 

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Posted by lionelsoni on Friday, June 30, 2017 12:43 PM

To measure the total current from one transformer, disconnect everything from the transformer's common terminal(s).  Connect one of the ammeter's terminals to (one of) the transformer's common terminal(s).  Connect the ammeter's other terminal to whatever was originally connected to the transformer's common terminal(s).

To measure the total current from both transformers, disconnect everything from the transformers' common terminals, but leave the common terminals connected to each other.  Connect one of the ammeter's terminals to (one of) the transformers' common terminal(s).  Connect the ammeter's other terminal to whatever was originally connected to either transformer's common terminal(s).

Bob Nelson

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Posted by AirMojo on Friday, June 30, 2017 1:42 PM

Thanks Bob !

So I only need one ammeter if I am measuring the total current from BOTH transformers.

But what if I want to measure each transformer's total current ?

I would need to disconnect the wire connecting the two together to have them phased ?

Would this cause any problems, not having them phased together ?

Wouldn't knowing the total current of each transformer be best ?

Thank you again for your help.

Ken

 

lionelsoni

To measure the total current from one transformer, disconnect everything from the transformer's common terminal(s).  Connect one of the ammeter's terminals to (one of) the transformer's common terminal(s).  Connect the ammeter's other terminal to whatever was originally connected to the transformer's common terminal(s).

To measure the total current from both transformers, disconnect everything from the transformers' common terminals, but leave the common terminals connected to each other.  Connect one of the ammeter's terminals to (one of) the transformers' common terminal(s).  Connect the ammeter's other terminal to whatever was originally connected to either transformer's common terminal(s).

 

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Posted by lionelsoni on Friday, June 30, 2017 4:40 PM

To measure the total current from each of two transformers, just follow for each transformer the instructions above for measuring the total current from one transformer.

When you are done, the only thing connected to each transformer's common terminals will be one terminal of the ammeter that measures that transformer's current.  The wire that formerly connected the transformers' commons together will have moved to connect the other terminals of the ammeters.  This node in the wiring will serve as the new layout common.  The transformers' outputs will still be in phase with each other.

Why do you have the transformers in phase?  For some purposes, it is better to have them out of phase.  What do you power with each transformer?

Bob Nelson

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Posted by AirMojo on Friday, June 30, 2017 8:22 PM

Bob... On the KW transformer, I power two conventional post-war trains, and a couple of active/motion accessories, and some lighted accessories... on the one track I have four turnout switches and I can turn the power off to either track that the switches can route the train, so I can park a train on the unpowered track.

These four turnout switches are powered, along with four other turnout switches, by the ZW transformer.

The ZW transformer also power two train routes, one having the other four turnout switches... this track runs a Lionel Command Control diesel engine, and the turnout switches are hooked up to a SC-1 command control switch.

The other ZW train route/track runs a conventional post-war 736 locomotive using command control.

The ZW also powers other accessories and lights.

Here is a YouTube link showing my 8-foot by 12-foot layout that I built about 25 years ago, and recently gotten back into it and reviving it... I'm looking forward to making more videos after some of the new additions that I'm now doing.

https://youtu.be/-Des7P0jjsI

Ken

 

lionelsoni

To measure the total current from each of two transformers, just follow for each transformer the instructions above for measuring the total current from one transformer.

When you are done, the only thing connected to each transformer's common terminals will be one terminal of the ammeter that measures that transformer's current.  The wire that formerly connected the transformers' commons together will have moved to connect the other terminals of the ammeters.  This node in the wiring will serve as the new layout common.  The transformers' outputs will still be in phase with each other.

Why do you have the transformers in phase?  For some purposes, it is better to have them out of phase.  What do you power with each transformer?

 

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Posted by AirMojo on Thursday, July 06, 2017 3:15 AM

I'm pretty sure that years ago, somewhere I read that if you are using more than one transformer that you should have them in phase... I would have to do some research to try and find this recommendation.

Why would one want them out of phase ?

lionelsoni

Why do you have the transformers in phase?  For some purposes, it is better to have them out of phase.  What do you power with each transformer?

 

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Posted by lionelsoni on Thursday, July 06, 2017 9:28 AM

"Why would one want them out of phase?"  For the same reason that your house is supplied with two 120-volt services that are out of phase, so that the return current in the neutral wire is the difference between the currents drawn by each 120-volt circuit rather than the sum.  This reduces the size of the wire needed for the neutral by a factor of 2.5 and also causes cancellation of voltage drops in the neutral wire.

If all your circuits return separately to the same transformers that supply them, there is no particular advantage in connecting the transformer commons together and no reason to prefer either phase relationship between the transformers.  But, if any of the circuits share returns, like outside rails, track-circuit-activated accessories, or non-derailing turnouts, then the commons should be, and may already be, connected, whether or not you put a wire between the transformers.

If the commons are connected and it is not possible on your layout to run a train from a block powered by one transformer to a block powered by the other transformer, then you can exploit the cancellation effect by running the two transformers out of phase.  Because the return currents subtract in this situation, you can use 14 AWG for the return wire, to handle safely the worst-case total current of 15-0 amperes.  Otherwise you should use 10 AWG to handle safely a worst-case total current of 15+10=25 amperes.

In any case, you should not deliberately run between blocks powered differently, even if the voltages are in phase, and especially from separate outputs of the same transformer.  To get safely from block to block, assign both blocks' center rails to the same transformer output.  You can do this with a single-pole-double-throw-center-off (SPDT-CO) switch to assign each block's center rail to one or the other of two transformer outputs, or to shut off the block entirely. 

Bob Nelson

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Posted by AirMojo on Saturday, July 08, 2017 6:35 AM

Thank you for your help Bob, and the other responses as well.

I'll have to see what changes I may need to make for my layout to get the amp meters working... may take awhile to get to, since my free time keeps getting taken up by so many other things this time of year.

I may be back for more questions.

So glad to have a resource like this to help me out !

Thank you all... I really appreciate the help and advice !

Ken

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Posted by webenda on Tuesday, July 11, 2017 9:16 AM

AirMojo

I'm not sure how sensitive the meter is... 

I got this one... Baoman Ammeter DH-670 AC 0-15A.

The sensitivity of a Baoman Ammeter DH-670 AC 0-15A is 0.5 amps per minor division, accuracy is ±2.5% of full scale.

Link to 5 amp version:=> https://www.ebay.com/i/162133876615?chn=ps&dispItem=1

 ..........Wayne..........

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Posted by AirMojo on Tuesday, July 11, 2017 9:49 AM

Yeah, I ordered a couple of those ones, and have them now... just need to install them in my panel, and do some rewiring on my transformers.

webenda

Link to 5 amp version:=> https://www.ebay.com/i/162133876615?chn=ps&dispItem=1

 

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