Question for the Gurus. Current Sensing

Brian Carpenter

At work we have a back up 30 KVA backup generator that is supposed to start with an automatic transfer switch when the power grid goes down.· It has only been in place for about a year.· It is supposed to be execized on a monthy basis.·· anyway...· long story to get to the point.· A month ago, the generator didnt start.· Fortunately the janitor called me to let me know the power was off.· When i got there the unit said that it exceeded it cranking time.· I gave it another try and it started right up.· So we have now installed a monitoring system.· This system monitors the grid, generator and load.· To do this, all that is installed is a simple little device that is zip tied to the large conductors.· It was explained to me that it is like to little device that you can get a home depot to tell if a wire is hot by touching the insulation.· It was a great idea.· Any idea how to make one of those?

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It's Only A Stupid Question If You Have Not Googled It First!!

Brian Carpenter

i want to be able to tell when an Air Conditioner is on or off based on current

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It's Only A Stupid Question If You Have Not Googled It First!!

Mike Green

What you probably have is a current transformer. This is a coil of wire, often with a ferrite or iron core that, by tying it to an single insulated conductor carrying AC, acts as the secondary winding of a transformer with the single insulated conductor acting as the primary winding. Often these transformers have a diode and filter capacitor so what you get is a DC voltage proportional to the current through the insulated conductor.

Mike Green

There are some gadgets that look like a 3-wire tap except that there's only one socket and the plug and the center part looks like a donut. These allow you to plug in something like an air conditioner and they divide the two conductors to either side of the "donut". You can then use a clamp-on current transformer to measure the current flowing to the socket. Look in the Wikipedia for "current clamp". You'll see a description and explanation.

Brian Carpenter

Mike,
Looks like i am wrong. it senses voltage. http://www.toolup.com/greenlee/gt11.html this is similar to what i was explaining.

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It's Only A Stupid Question If You Have Not Googled It First!!

Mike Green

I'm guessing, but this probably acts as one plate of a capacitor with the power conductor acting as the other plate. This probe has a high impedance, high gain amplifier and detects the AC coupled through this capacitance.

Brian Carpenter

i think you are right. How would i go about constructing one of these? Should i buy one and tear it appart an see how it "ticks"

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It's Only A Stupid Question If You Have Not Googled It First!!

Brian Carpenter

Mike,
I am looking at a Hall Effect Sensor. Sould this work? and if so, do these require that i break the circuit and feed it in and out if the chip?

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It's Only A Stupid Question If You Have Not Googled It First!!

stamptrol

The little voltage probes work by capacitive coupling to the cable. In normal use, your hand provides coupling to ground. In stand-alone operation, it may be necessary to wrap a few turns of wire around the handle of the probe and tie it to ground.

For long term use, you'll probably need to parallel the batteries with a power supply of some sort. To obtain a signal for external logic, break the circuit of the indicating LED and add an optocoupler in series. The output of the 'coupler can be used for the external circuitry.

To the original problem, the genset might be able to be set up to try a couple of more times after an over-crank. After all, the genset is designed for emergency service and shouldn't give up so easily! If it already has multiple re-tries enabled, the system needs to be looked at to find out why it didn't start.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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sam_sam_sam

One place where·I use to work had this problem with there backup generator and turn out to be·a bad battery connection on one of the batterys it would·not give you··over-crank each time you try to start it


Brian Carpenter

When i got there the unit said that it exceeded it cranking time.

Tom Sisk

To the original problem, the genset might be able to be set up to try a couple of more times after an over-crank. After all, the genset is designed for emergency service and shouldn't give up so easily! If it already has multiple re-tries enabled, the system needs to be looked at to find out why it didn't start.

The one s·that have I seen you do not have an option to have it start·more than once with out reset it


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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 10/7/2008 12:38:46 AM GMT

lenswerks

Brian,

I like this small Zap series·- http://www.ampsolution.com/

Donnie

Brian Carpenter

Wow Donnie,
Those are great. i bought 2 to play with

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It's Only A Stupid Question If You Have Not Googled It First!!

Brian Carpenter

Donnie,
I have made progress. I will post my results in the prop forum since i am using that chip.

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It's Only A Stupid Question If You Have Not Googled It First!!

lenswerks

Thanks Brian. I'll take a look.

Donnie