Re: Problem With New Power Monitor

[sc.smiley@juno.com]

What if there was only one Ammeter for all circuits with a rotation
switch to activate only one track at a time.  You could also install a
push button instantaneous switch to activate the meter, it does not need
to run all of the time?????  When we want to know what is going on we
could dial up a track and monitor it or push the button to see what it is
doing after dialing it up . ???

What if all of the meters were on a push button activation.  Then only
one at a time would go through the meter unless someone pushed multiples
at the same time?

From the electronic novice.

Scott

On Thu, 10 Sep 2009 19:40:10 -0500 "Ira Schneider"
<ira_schneider@Iname.com> writes:
> Hi all,
> 
> I built a new power monitor for the TTAT layout.  However, there is 
> a major problem
> for which I could use some advice.
> 
> The new power monitor contains ammeters as well as voltmeters.  
> There is
> one pair of meters for each track.  I have a single 5 VDC power 
> supply feeding
> power to all of the meters.
> 
> The problem is the internal design of the meters.  The ammeters 
> (and, as I found
> out, also the voltmeters) have the ground connection from the power 
> supply
> directly tied to one of the AC input pins.  When the power monitor 
> only had
> voltmeters, this wasn't a problem, since there is a common lead to 
> all of the
> tracks, which (by accident) I connected to the input pin which was 
> connected
> to the ground wire from the power supply.  The net result was that 
> all of the
> voltmeters, being fed from the same 5 volt supply, connected 
> together the
> common leg of the tracks, which was no problem.
> 
> However, the ammeters are a different story.  The ammeter is 
> inserted
> in series with the "hot" lead going from the transformer to the 
> track power
> controller.  Since one side of the ammeter is connected to the 
> ground pin
> from the power supply, that means that either the transformers are 
> all
> connected together or the inputs to the TPCs are all connected 
> together
> (depending on which way I wire the ammeters).
> They are also connected to the common output line from the TPCs 
> (through
> the voltmeters).
> 
> This is obviously a disaster.  When I first connected the voltmeters 
> and ammeters
> to the power supply, I noticed that the voltmeters were rather dim.  
> I thought
> the ammeters were overloading the power supply, but they weren't.  
> (The
> combined current drawn by all of the meters is around 200 ma, and 
> the power
> supply is rated at 1800 ma.)  While I was checking voltages, etc. I 
> saw smoke
> coming from the power monitor.  I eventually found the common wire 
> feeding
> the voltmeters had burned out.  That is when I started investigating 
> the connections
> of the meters.  I think this also burned out two of the voltmeters.
> 
> So far, the only solution I see, which I think is impractical, is to 
> have five different
> 5 VDC power supplies - one for the voltmeters and one for each of 
> the ammeters.
> 
> What I really need is some way to isolate the AC input signals to 
> the meters
> from the DC power supply which powers the meters, but I don't have 
> any
> idea how to do that.
> 
> Does anyone have any expertise in designing a simple circuit to 
> isolate a DC
> power supply from the load?  Or some way to isolate the AC being 
> measured
> by the ammeter from the DC power supply?
> 
> If I need to use five separate power supplies, I will have to change 
> the cabling to
> the power monitor (there is only one spare pair of wires in the 
> cable) and
> find some place for another power strip.  If I can isolate the power 
> supply
> within the power monitor, I might be able to find room for some 
> small circuits
> inside the case.  Also, the small 6 VDC (or 4.5 VDC) power supplies 
> which
> Radio Shack has (which actually fit on a standard power strip) are 
> only
> available through their stores, and no local store has either power 
> supply
> in stock.  (I am actually powering the monitor with the 6 VDC 
> version,
> and I have one of the 4.5 VDC power supplies here.  The voltmeters
> would not function on 4.5 volts, but the ammeters do.)
> 
> I will be happy for any suggestions.
> 
> Thanks.
> 
> 
> 
> 
> Ira
> 
> 
> 
> 
> ------
> TTAT members reflector.
> 
 
 
Scott Smiley
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