Is anything such as a DC energy meter easily/cheaply available? I'm
thinking something in function similar to the plug-in energy monitors, but
for DC. I'm thinking the sort of thing that might be attached to a battery
to measure the discharge performance (such things are available for Li-ion
batteries, but very specialised), or to measure the power consumption of a
DC device like a hard drive.

It would take 3 leads: a ground lead, a DC current in lead and a DC current
out lead. Between current out leads there's a precision resistor to form
an ammeter, and between DC out and ground there's a voltmeter. The device
would perform:

Integral( I * V dt ) = Energy (joules)

ie multiply the (RMS?) voltage and current, and sum this for each
[micro|milli|]second of operation.

Perhaps some multimeters do this... anyone suggest one?

Thanks
Theo

Theo Markettos wrote:
Is anything such as a DC energy meter easily/cheaply available? I'm
thinking something in function similar to the plug-in energy monitors, but
for DC. I'm thinking the sort of thing that might be attached to a battery
to measure the discharge performance (such things are available for Li-ion
batteries, but very specialised), or to measure the power consumption of a
DC device like a hard drive.

It would take 3 leads: a ground lead, a DC current in lead and a DC current
out lead. Between current out leads there's a precision resistor to form
an ammeter, and between DC out and ground there's a voltmeter. The device
would perform:

Integral( I * V dt ) = Energy (joules)

ie multiply the (RMS?) voltage and current, and sum this for each
[micro|milli|]second of operation.

Perhaps some multimeters do this... anyone suggest one?

Thanks
Theo

What you wan is entirely available in the model aircraft world and is
called a Whattmeter (:-!)

Generally it shows volts amps instantaneous power and mA hours

E.g.

http://www.micronradiocontrol.co.uk/batt_monitor.html

The only sight problem is its summated energy is in mAh not on joules etc.

This is no big deal with a constant voltage source.

The Natural Philosopher wrote:
Theo Markettos wrote:
Is anything such as a DC energy meter easily/cheaply available? I'm
thinking something in function similar to the plug-in energy monitors,
but
for DC. I'm thinking the sort of thing that might be attached to a
battery
to measure the discharge performance (such things are available for
Li-ion
batteries, but very specialised), or to measure the power consumption
of a
DC device like a hard drive.

It would take 3 leads: a ground lead, a DC current in lead and a DC
current
out lead. Between current out leads there's a precision resistor to form
an ammeter, and between DC out and ground there's a voltmeter. The
device
would perform:

Integral( I * V dt ) = Energy (joules)

ie multiply the (RMS?) voltage and current, and sum this for each
[micro|milli|]second of operation.

Perhaps some multimeters do this... anyone suggest one?

Thanks
Theo

What you wan is entirely available in the model aircraft world and is
called a Whattmeter (:-!)

Generally it shows volts amps instantaneous power and mA hours

E.g.

http://www.micronradiocontrol.co.uk/batt_monitor.html

The only sight problem is its summated energy is in mAh not on joules etc.

This is no big deal with a constant voltage source.

heres another little tiddler that shows watt hours directly

http://www.sussex-model-centre.co.uk...xd.asp?id=5148

The Natural Philosopher wrote:
The Natural Philosopher wrote:
What you wan is entirely available in the model aircraft world and is
called a Whattmeter (:-!)

Generally it shows volts amps instantaneous power and mA hours The only
sight problem is its summated energy is in mAh not on joules etc.

This is no big deal with a constant voltage source.

heres another little tiddler that shows watt hours directly

Thanks. I'd seen those sort of devices, but they looked very specific to
Li-ion/Li-PO4 batteries (all the cell balancing stuff). Good to know they
do the basics as well.

Theo

Theo Markettos wrote:



Thanks. I'd seen those sort of devices, but they looked very specific to
Li-ion/Li-PO4 batteries (all the cell balancing stuff). Good to know they
do the basics as well.

Similar things are available for electrically assisted pedal cycles. I know
of one business in Surrey that retrofitted them to a hire fleet because
people were getting stranded with flat battery, mind 36V lead acid battery
has a fairly flat Voltage so they may just be amphour meters rather than
proper watthour meters.

AJH

On 17/04/2011 09:52, andrew wrote:

Similar things are available for electrically assisted pedal cycles [...]

Also, at a higher power level, for solar PV installations:

http://www.hoytmeter.com/products/MK...rgy_Meter.html

--
Andy

On Sun, 17 Apr 2011 10:32:14 +0100, Andy Wade wrote:

On 17/04/2011 09:52, andrew wrote:

Similar things are available for electrically assisted pedal cycles [...]

Also, at a higher power level, for solar PV installations:

http://www.hoytmeter.com/products/MK...rgy_Meter.html


http://www.gossenmetrawatt.com/engli...ahitenergy.htm

In message , The Natural Philosopher
writes



heres another little tiddler that shows watt hours directly

http://www.sussex-model-centre.co.uk...xd.asp?id=5148

The spec says:
€¢ Current 0-100 A peak, 50 A continuous, resolution 0.01 A
€¢ Voltage 0-60 V, resolution 0.01 V
€¢ Power 0-6500 W, resolution 0.1 W
If it's only 2.8" long, what's the size of the wires?
Will they carry 50A?
Or am I reading things wrong?
--
Ian

Ian Jackson wrote:
In message , The Natural Philosopher
writes



heres another little tiddler that shows watt hours directly

http://www.sussex-model-centre.co.uk...xd.asp?id=5148

The spec says:
€¢ Current 0-100 A peak, 50 A continuous, resolution 0.01 A
€¢ Voltage 0-60 V, resolution 0.01 V
€¢ Power 0-6500 W, resolution 0.1 W
If it's only 2.8" long, what's the size of the wires?
Will they carry 50A?
Or am I reading things wrong?

Oh yes, they will carry 50A.
probably about 10 sq mm cross section.

The Natural Philosopher wrote:
Ian Jackson wrote:
In message , The Natural Philosopher
writes



heres another little tiddler that shows watt hours directly

http://www.sussex-model-centre.co.uk...xd.asp?id=5148

The spec says:
€¢ Current 0-100 A peak, 50 A continuous, resolution 0.01 A
€¢ Voltage 0-60 V, resolution 0.01 V
€¢ Power 0-6500 W, resolution 0.1 W
If it's only 2.8" long, what's the size of the wires?
Will they carry 50A?
Or am I reading things wrong?

Oh yes, they will carry 50A.
probably about 10 sq mm cross section.

The advert says 14 gauge, which is just over 2 sq mm, assuming American
wire Gauge. Other sources say 25A continuous current, 166A ruptures it
after about 10 seconds with no insulation. 50A would get it hot enough
to need the quoted high temperature insulation.

For the intended use, the wire is acceptable, as is the internal current
sensing resisitor. The battery normally used for a model helicopter will
supply 50A for a few minutes at most. I'd be dubious about using it on a
continuous basis for more than about 20A.

--
Tciao for Now!

John.

Mike Harrison wrote:
http://www.gossenmetrawatt.com/engli...ahitenergy.htm

Thanks. Looks nice, though I hate to think what the price is (and I can't
find anyone listing it).

Apparently it uses the CS5463 chip:
http://www.cirrus.com/en/products/cs5463.html

For just over three quid plus an SPI lashup, might be more feasible for
occasional hacks.
http://uk.farnell.com/cirrus-logic/c...p24/dp/1506323

Theo

On 17/04/2011 16:25, Theo Markettos wrote:
Mike wrote:
http://www.gossenmetrawatt.com/engli...ahitenergy.htm

Thanks. Looks nice, though I hate to think what the price is (and I can't
find anyone listing it).

Very nice - I want one...

Try
http://www.conrad.com/GMC-M249A-METR..._17622_1101010

Price is less than I expected, actually.

--
Andy