DC energy meter

[Theo Markettos]

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

[The Natural Philosopher]

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.

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]

heres another little tiddler that shows watt hours directly

[Theo Markettos]

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

[andrew]

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

[Andy Wade]

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

[Mike Harrison]

[Ian Jackson]

In message , The Natural Philosopher writes

[The Natural Philosopher]

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

[John Williamson]

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.

[Theo Markettos]

find anyone listing it).

Apparently it uses the CS5463 chip:

just over three quid plus an SPI lashup, might be more feasible for occasional hacks.

[Andy Wade]

Very nice - I want one...

Try

is less than I expected, actually.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Theo Markettos saying something like:

Why pay fifty quid?

[Theo Markettos]

Eighteen (note the postage). Which is about the going rate for those sent-from-Hong Kong gadgets (best to be 17.99 to avoid VAT and duty). Trouble is there's zero documentation on what they actually do (other than the spec, which on this one is a little clearer than most).

Theo

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Theo Markettos saying something like:

I'm thinking of that one for electric bicycle monitoring. There are a couple of much more expensive alternatives, of course.