How ro measure standby power?

[Wayne]

I have 2 transformers, 12Vac output. One is wire wound and the other is
electronic. How can I accurately measure the standby power consumption of
either using a digital multimeter? Standby secondary load current is a few
milliamps. I've noticed the wire wound gets fairly warm on standby.

Thanks for any help,
Wayne.

 

[John Fields]

On Thu, 08 Apr 2004 15:57:55 GMT, "Wayne"
<noprivatemailthanks@abc.com> wrote:

I have 2 transformers, 12Vac output. One is wire wound and the other is
electronic. How can I accurately measure the standby power consumption of
either using a digital multimeter? Standby secondary load current is a few
milliamps. I've noticed the wire wound gets fairly warm on standby.

---
With an ordinary digital multimeter you can't, since you need to
measure the difference in phase between the input current and voltage.

--
John Fields

 

[Joerg]

Wayne, one rather crude method would be to hook up an old mechanical power
meter and count out a few revolutions of the disk. There is usually a note on
the face plate telling you how much "billable" energy is consumed per
revolution. Now you'd have both the energy use per revolution and the time it
took for these revolutions to happen. While it may not be very accurate as to
the phase errors this should at least tell you how many pennies these devices
add to you monthly electricity bill.

This assumes that the power meter is in good shape and able to rotate on these
small currents. But when I did that a long time ago I tested it with a weak
resistor of known value and found it worked pretty well in my case.

Regards, Joerg.

 

[Tam/WB2TT]

"Wayne" <noprivatemailthanks@abc.com> wrote in message
news:7Eedc.528$ED.387@news-server.bigpond.net.au...

I have 2 transformers, 12Vac output. One is wire wound and the other is
electronic. How can I accurately measure the standby power consumption of
either using a digital multimeter? Standby secondary load current is a few
milliamps. I've noticed the wire wound gets fairly warm on standby.

Thanks for any help,
Wayne.

Wayne,
If you have such, go to a place that rents tools, and rent a wattmeter. Or

maybe you can borrow one from an appliance repair person; perhaps even take
your circuit to their store, and measure it there.

Tam

 

[James Meyer]

On Thu, 08 Apr 2004 15:57:55 GMT, "Wayne" <noprivatemailthanks@abc.com> posted
this:

I have 2 transformers, 12Vac output. One is wire wound and the other is
electronic. How can I accurately measure the standby power consumption of
either using a digital multimeter? Standby secondary load current is a few
milliamps. I've noticed the wire wound gets fairly warm on standby.

Thanks for any help,
Wayne.

Put together a small box that either power supply will fit into.
Cardboard would be OK. The box needs to have no open holes in it for air to get
in or out. Of course you need to pass the power wires into the box, but seal
the holes with something.

Put an ordinary thermometer into the box so that the bulb is inside and
the graduations are outside where you can read them.

Put one of the supplies into the box and turn it on. Watch the
temperature inside the box and wait until it stops rising and record that
temperature.

Put the other supply in the box and repeat.

Then replace the supply with a small lightbulb and connect the bulb to a
variable power supply, AC or DC, whatever you have. Adjust the power supply so
that the temperature rises to the same reading as one of the supplies. THEN use
your multimeter to measure the current and voltage going to the bulb. Adjust
the bulb voltage again to match the temperature of the other supply and read the
voltage and current.

Multiply the voltage and current readings and you will have the standby
power for both supplies.

This is a simple but very accurate method to make a wattmeter. It's
also known as a calorimeter.

Jim

 

[Wayne]

"Joerg" <nospam@nospam.net> wrote in message
news:407595A6.3C57D7A8@nospam.net...

Wayne, one rather crude method would be to hook up an old mechanical power
meter and count out a few revolutions of the disk. There is usually a note
on
the face plate telling you how much "billable" energy is consumed per
revolution. Now you'd have both the energy use per revolution and the time
it
took for these revolutions to happen. While it may not be very accurate as
to
the phase errors this should at least tell you how many pennies these
devices
add to you monthly electricity bill.

This assumes that the power meter is in good shape and able to rotate on
these
small currents. But when I did that a long time ago I tested it with a
weak
resistor of known value and found it worked pretty well in my case.

Regards, Joerg.

Thanks, this would do it. I will install a temporary single outlet on my
switchboard and switch off the breakers for everything else to factor out
any leakage currents. Then plug in one at a time and count the revolutions
(or part thereof) of my meter against time.

It may take a few hours I feel.

Wayne.

 

[Wayne]

"James Meyer" <jmeyer@nowhere.com> wrote in message
news:lrlb70dbjcglli4jg2aldt2orql0oo6s33@4ax.com...

On Thu, 08 Apr 2004 15:57:55 GMT, "Wayne" <noprivatemailthanks@abc.com
posted
this:

I have 2 transformers, 12Vac output. One is wire wound and the other is
electronic. How can I accurately measure the standby power consumption of
either using a digital multimeter? Standby secondary load current is a
few
milliamps. I've noticed the wire wound gets fairly warm on standby.

Thanks for any help,
Wayne.


Put together a small box that either power supply will fit into.
Cardboard would be OK. The box needs to have no open holes in it for air
to get
in or out. Of course you need to pass the power wires into the box, but
seal
the holes with something.

Put an ordinary thermometer into the box so that the bulb is inside and
the graduations are outside where you can read them.

Put one of the supplies into the box and turn it on. Watch the
temperature inside the box and wait until it stops rising and record that
temperature.

Put the other supply in the box and repeat.

Then replace the supply with a small lightbulb and connect the bulb to a
variable power supply, AC or DC, whatever you have. Adjust the power
supply so
that the temperature rises to the same reading as one of the supplies.
THEN use
your multimeter to measure the current and voltage going to the bulb.
Adjust
the bulb voltage again to match the temperature of the other supply and
read the
voltage and current.

Multiply the voltage and current readings and you will have the standby
power for both supplies.

This is a simple but very accurate method to make a wattmeter. It's
also known as a calorimeter.

Jim


Jim,

Thankyou for this excellent approach. I will see how it goes first by using
my electricity meter.

Wayne.