Re: Problem With New Power Monitor

[Steve Wise <swise@aoot.com>]

Another alternative is to use analog meters.  They need no separate 
power.  But they are more expensive from what I've seen.  ~$20 vs $80 
each.  Digital LED meters are easier to read at a distance though.

sc.smiley@juno.com wrote:
> 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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