AC Energy Monitor

[MEXICOWANDERER]

Hope this link works


http://www.ebay.com/itm/AC-Dual-Display-80-299V-0-60A-Amp-Volt-LED-Combo-Meter-Current-Transformer-/...

[pianotuna]

Hi jc,

No, it only displays watts--but appears to be more accurate than a kill-o-watt as far as watts go. They do have other models. If I were buying again I'd get the power factor corrected unit.

[jcthorne]

pianotuna wrote:
Hi,

I chose this one :Efergy Elite

It has two sensors so I'm able to monitor all 120 volt electrical use including the inverter.

As I'm often in situations where I do not have access to the shore power breaker I find it extremely useful. I monitor the voltage on the 30 amp OEM service with a kill-a-watt unit.

They also have a power factor corrected model, and I wish I had purchased it instead.

It connects wirelessly to the sensors.

Does this unit or the power factor corrected one display volts or amps?

[wa8yxm]

The only correction to most of the current transformor comments above.

Though it may be encased in plastic, like it is on a clamp on ammeter. (Which by the way uses the same technology) it's ferrous iron in the core.

[pianotuna]

Hi,

I chose this one :Efergy Elite

It has two sensors so I'm able to monitor all 120 volt electrical use including the inverter.

As I'm often in situations where I do not have access to the shore power breaker I find it extremely useful. I monitor the voltage on the 30 amp OEM service with a kill-a-watt unit.

They also have a power factor corrected model, and I wish I had purchased it instead.

It connects wirelessly to the sensors.

[joshuajim]

All larger electrical service meters above 400a use current transformers to feed the actual meter.

[msiminoff]

I purchased a DC Volt/Ammeter from the same eBay seller about a year ago... suspect it's from the exact same manufacturer too.
Of course, since it's DC, it uses a shunt to measure current.
I installed it in the dash of my truck... works great... plenty accurate... inexpensive... very handy!
-Mark

[tenbear]

Here is the one I used. It has a photo of the current transformer in the description.

[tenbear]

I installed one, a different vender, earlier this past summer. Other than running a wire from the "doughnut" to the panel where all my meters are, it was an easy install. It has worked flawlessly ever since. I did install a switch in the AC voltage lead to turn the meter off and on.

[ktmrfs]

ken white wrote:

pianotuna wrote:
Hi,

So it uses a Hall Effect sensor?

No.

It's typically a toroid core with wire wrapped around the core. The current carrying conductor passes through the hole in the center.

And to add a little comparison, A Hall effect transducer is most often used when there is a need to measure DC current, or AC and DC current. For most AC only applications a toriod core is much simpler, and very often much "better" solution. A toroid transformer solution can be more repeatable, more rugged, less expensive, and more sensitive.

Since in this case, the source is about as close as ideal as one can imagine to a pure 60Hz, constant voltage source, a toroid transformer is a very nice transducer. No need to complicate matters with a hall device.

But then as soon as I say all this I remember my Progressive Industries EMS system with current readout and a toroid transformer for the current sense. Pretty much useless, current readings are often nonsense, usually way higher than actual, but no rhyme or reason for the error. A call to PI and they said yes, it isn't accurate at all. It was added at the last minute and they couldn't fix the accuracy issue. Why they didn't just take it out I don't know. I suspect it isn't the transformer as much as whatever detection circuit they are using, part of an IC that is the culprint. One of these days I'm tempted to see if I can figure out where the error is coming from, but it's kinda far down my list.

[MEXICOWANDERER]

Isn't it nice to know the featured meter and CT is so simple and safe? It sounds so simple some folks think it's a trick. It isn't. Shut off power at the source, disconnect the hot wire (not neutral) to be measured, slip the current transformer down it. Then run a pair of tiny wires and another pair of slightly larger wires from the meter to the current transformer region. Connect the tiny pair to the current transformer pigtail, continue running the other pair of wires to the same connection point as the wire with the current transformer and splice the two wires in (there are lots of extra connection points in a breaker box).

Too simple!

A lot of the info above is supplemental educational stuff for folks who wish to pencil out exactly what is going on. But the basic installation is a lot more "foolproof" and a heck of a lot easier than installation a DC shunt and meter.

[Gdetrailer]

MEXICOWANDERER wrote:
No.

One nick-name for these things is "Doughnut". Everything is inductive with the current transformer.

The hardest thing involved is to disconnect a hot wire and slip the doughnut down it to a convenient resting area. Much easier, faster and simpler than connecting a DC shunt.

A "split" current transformer takes care of slipping the wire through WITHOUT the need of disconnecting the wires.

SEE THIS LINK

However, current transformers are good only for AC, the do not work for DC circuits.

Current transformers are in fact a transformer, the AC lead going through the toroid is the primary winding and the secondary is the output leads. Depending on the ratio of the secondary windings you can "measure" a variety of low current to extremely high AC currents without the need to directly insert a meter into the circuit.

Allows for very remote metering of extremely high AC voltage and or AC current.

Additionally one MUST make sure if they are buying a current transformer that they know the difference between one that has a "burden" resistor or not. Current transformers MUST have a burden resistor across the output leads, this prevents lethal voltages from being present without a load attached to the leads.

[DSchmidt_2000]

Think "half of a transformer"

[ken_white]

pianotuna wrote:
Hi,

So there is no direct connection to the wire carrying the current? Sorry to be so dumb.

There is no direct connection so electrical isolation is a big benefit.

[MEXICOWANDERER]

No.

One nick-name for these things is "Doughnut". Everything is inductive with the current transformer.

The hardest thing involved is to disconnect a hot wire and slip the doughnut down it to a convenient resting area. Much easier, faster and simpler than connecting a DC shunt.