Can someone please help me in choosing a panel meter and shunt?

I would like to remotely monitor the total current draw of 14 incandescent light bulbs via a round (old-school) Simpson 2" panel meter.
The bulbs are not easily viewable from their control location and the meter's purpose is to conveniently alert to a potential burned-out bulb or bulbs.

The bulbs are common PAR38 halogen "landscaping" lights. All 14 bulbs are in one parallel circuit but the bulbs are slightly mismatched in that 7 bulbs are 70W @110V) and 7 are 90W (@120V (according to their boxes) for a total of 1120 watts. Their supply voltage is 110VAC. Therefore, some means to adjust the meter reading would be beneficial. I also intend to convert to LED bulbs someday after I use up my stockpile of 70+ incandescent bulbs!

Please note that I don't need .001% accuracy and I don't want a circuit that uses an Arduino to log and analyze the electron phases of each individual bulb and compares them to the solar bitribulation of Jupiter's moons! (This is not to offend anyone. I'm thoroughly impressed with anyone's ability to design such a circuit but I don't need the unnecessary complexity and added expense that such unneeded features will add.)

Many Thanks!
Harvey

Simpson 2" round meter datasheet: file:///C:/Users/Hartman-PC/Desktop/PRINT%20JOBS/round_datasheet.pdf
Simpson shunt datasheet: file:///C:/Users/Hartman-PC/Desktop/PRINT%20JOBS/currenttransformer_datasheet.pdf

 

Do you already have the panel meter or are you planning on buying one?
At 120V, a 1120 W load will draw a current of 9.33A . A 10A moving iron meter in series with the supply will do the job.
Keith

 

Thanks Keith for your reply.

I'm planning to buy a new meter (and shunt if required) and I'd like to go with one of the 2" Simpson models due to its "old-school" appearance.

Also, I'd prefer not to run 110V @10A through my control panel if possible. Thus my thoughts for using a separate shunt for remote sensing. (The bulbs and meter will be powered separately.)

 

Also, since I'm dealing with incandescent bulbs, will I need to incorporate some kind of in-rush buffer to avoid spiking the meter's needle each time the bulbs turn on?

 

Any analog meter like those linked to will not respond to any inrush current. I wouldn't worry about that. You also linked to a Current Transformer data sheet, the problem with most current transformers is they start at about 50 amps. On the bright side you can loop the primary through a CT several times. Here is an example of what I mean.



The red primary wire is looped through three times making a 60:5 into a 20:5 meaning twenty primary amps will produce a 5 amp secondary output. Keep something in mind when using a CT. The lead length can't be too excessive you may want to read up on CT burden resistance. Most CTs have a 5 amp secondary so you just use a 5 amp full scale analog meter with them and do a scale conversion. For example if I use a 50:5 CT (very common) ...



and I loop the primary twice I now have a 25:5 CT and if I loop it 5 times I now have a 10:5 CT. Again, keeping the leads short. One thing about a CT and analog meter is they are just about bullet proof. Something very important when working with a CT. While you get a low current out proportional to primary current the reverse is true of voltage. A 50:5 CT has a ratio of ten to one 50 / 5 = 10 so that means if the primary conductor is a 120 Volt line the voltage on the output leads is 120 * 10 = 1200 VAC. You always want the CT terminated before you run a primary current through it.

So I would buy a 50:5 CT and then a 0 to 5.0 amp analog meter movement. Then do the math when looking at the scale.

Ron

 

You mentioned excessive wire length between the CT and the meter. My meter will be 118ft from the CT (via 16ga stranded wires. Will this be excessive?

 

And those wires (which are unshielded and already buried underground in conduit with other wires) will probably be susceptible to crosstalk (both giving and receiving)!

 

Have you checked the price of a new Simpson panel meter lately? That's an item I would be buying from a surplus dealer, or a ham radio swap meet.
Here's a discussion on making your own current transformers: https://electronics.stackexchange.c...ow-to-build-very-low-cost-current-transformer

 

You mentioned excessive wire length between the CT and the meter. My meter will be 118ft from the CT (via 16ga stranded wires. Will this be excessive?

In a word yes, for a more detailed explanation give this a read. You will see the term I mentioned earlier "Burden Resistance" and how it comes into play.

Nice thing about a CT is the low cost but they have their limitations.

Current transducers which come in several flavors but normally cost more have their merit. Your first link pictures a similar on the left side of the page. Many current transducers will output a DC current like 4 to 20 mA loop or a DC voltage proportional to the primary current. All of these solutions come with a higher cost than a simple CT setup.

Ron

 

If the excessively long wires between the CT and control panel meter (and the fact that those wires will be in close proximity with many other wires carrying 24vac control signals) it looks like crosstalk interference is going to be a problem. Maybe I should look at another means of remotly monitoring the bulb's current? Or convert my control circuits to DC?

Harvey