Finding the power usage of my project

bountyhunter, that's a very complete and clear tutorial on voltage regulators. I would suggest it be made a Sticky in this forum for all those who have continuing questions about regulators (and all those in the future who will).

How about it moderator?

If your going to be regularly testing the real wattage usage of devices with odd wave forms just do what I did years ago and take a stock mechanical KWH meter and rewind the current sensing coils with smaller wire in order to change the rate it reads at. Change it to a 10:1 and you have a KWH with a 1/10 KWH place or do a 100:1 and have a 1/10 and 1/100 KWH places.
Obviously your peak amp limits will be lower due to the smaller wire of course.

Just use a known wattage draw device for checking the calibration after you rewind it and your good to go!
$15 and bit of work and you have a full true reading KWH meter with fine WH resolution. Just run it for an hour and read the actual wattage used.

This is one I built some time ago that I rewound with a 10:1 ratio so it now works as a 0-20 amp, 0 - 240 VAC KWH meter.
I just mounted it in a old external floppy drive case and added lug terminals for the input and output. A power cord and socket would work just fine also.
If I am patient it can show the power being used by a wall power pack.
Just find out how many revolutions per KWH and calculate the time between rotations of the disk to figure out sub watt hour load readings.

crutschow said:

bountyhunter, that's a very complete and clear tutorial on voltage regulators. I would suggest it be made a Sticky in this forum for all those who have continuing questions about regulators (and all those in the future who will).

How about it moderator?

Click to expand...

It's OK with me if they want to sticky it.

Thanks bountyhunter, I've been away for a little while and saw that you posted your paper. Thanks. I've only downloaded it for now but I WILL read it later.

tcmtech said:

If your going to be regularly testing the real wattage usage of devices with odd wave forms just do what I did years ago and take a stock mechanical KWH meter and rewind the current sensing coils with smaller wire in order to change the rate it reads at. Change it to a 10:1 and you have a KWH with a 1/10 KWH place or do a 100:1 and have a 1/10 and 1/100 KWH places.
Obviously your peak amp limits will be lower due to the smaller wire of course.

Just use a known wattage draw device for checking the calibration after you rewind it and your good to go!
$15 and bit of work and you have a full true reading KWH meter with fine WH resolution. Just run it for an hour and read the actual wattage used.

This is one I built some time ago that I rewound with a 10:1 ratio so it now works as a 0-20 amp, 0 - 240 VAC KWH meter.
I just mounted it in a old external floppy drive case and added lug terminals for the input and output. A power cord and socket would work just fine also.
If I am patient it can show the power being used by a wall power pack.
Just find out how many revolutions per KWH and calculate the time between rotations of the disk to figure out sub watt hour load readings.

Click to expand...

Well, I can get my hands on a stock mechanical KWH meter but don't know if I have the skill to do all the rewinding you suggested. Don't suppose it will give me a decent reading without rewinding the thing, will it? What if I let it run for 10 hours for example and get an average? Is it a matter of the meter not rotating enough for a good reading?

Sorry for buggin all of you. I edited and deleted this so as to not upset anyone with unwanted questions that are off subject.

depending on the meter design some are literally a no brainer on how to rewind them. They have two single loop coils (one for each leg) of heavy gauge wire or buss bar going around a common laminated core.

What I did with mine was to take apart the windings and core section and remove the heavy gauge wire. Then I just used a thin layer of JB weld to make a solid insulation layer on the laminated core section so that I had a solid non conductive layer between the enameled wire and the laminated iron. Then I just rewound it with 20 turns of enameled 13 gauge wire and reassembled it to how it was before.
For that one the calibration stayed exactly the same being all I did was change the current sensing ratio so it now reads at 10 times its origional rate.

Some stock KWH meters with good jewel bearings can read below a 10 watt load with reasonable accuracy but many dont. They have a lower limit of sensitivity due to internal losses and the physical friction of the mechanical drive system for the dials or numerical readout system.

If you can get a hold of a KWh meter look it over and see if the internal layout of the heavy gauge wire is in such a fashion that it can be removed and replaced. If you can see where all the wire is routed its possible. But some designs have it all potted in plastic so they are much harder to rework.

Really it comes down to what your comfortable to work with.

So you replaced two single turns, with two lots of 10 turns (total 20)??

If you need a dual circuit yes then you would still need two independent 10 turn coils. If you dont you just use one 20 turn coil.

In the American home power systems we have a 120/240 split system. Its a 240 volt circuit with a common ground center tap basically. Each leg of the 240 volt uses a current sensing coil in the meter. However the voltage coil uses the full 240 volts.

If you want to modify a meter for single line use and still be accurate over the full voltage range then you only need one coil that gives it the ratio relative to as if it was reading the power through both single loop coils for a two line circuit.