Measuring mains current with 1-wire

Dear Joel Winarske, Phil Malone, and Anders Sandell - I ran across this new
product (ACS750
Current Sensor) from Allegro Microsystems. that looks like a good marriage
to a DalSemi 1-Wire DS2450 ADC (a dV/dI at 20 mV/A is 1 VDC change over 50
A; right in the "ball-park" for the DS2450, and not an unreasonable amout of
current to monitor the mains:

http://www.allegromicro.com/sf/0750/index.asp#sample_request

And the ACS750 has an Ultra-Low Power Loss: Resistance = 130 micro-ohms,
which beats dumping volts (and power losses/dissipation across a "sense
resisitor"). Another "plus" is that it requires no opto-isolation from the
mains.  I have four samples of each Allegro ACS750 "on-the-way"; I'll let
you know what I figure out, after I conjure up a breadboard and same Java
code for a Tynamo TINI/TStik servlet.

>From the FAQ on the ACS750:

What are the differences between the -100, -075, and -050 versions of the
ACS750?

The ACS750xCA-075 and the ACS750xCA-100 are physically the same part, but
they are tested using different test programs. The sensitivity of both
devices is ~20 mV per ampere. Both devices share the same specifications at
25ºC, but certain parameters, such as linearity and accuracy, are itemized
to particular temperature ranges on the data sheet. For example, the
operating temperature range of the ACS750ECA-100 is de-rated to allow
performance through 100 A, and the specifications of the ACS750LCA-075 are
guaranteed through the full automotive temperature range of -40ºC to 150ºC.

The only difference between those two versions and the -050 version of the
device is the sensitivity. For the -050 version, sensitivity is set to ~40
mV per ampere.

Can the ACS750 family sense both dc and ac currents?

The ACS750 family uses Hall effect technology, which is capable of sensing
electrical currents having both dc and ac components. As the data sheet
states, the bandwidth of the ACS750 is 13 kHz typical. There is usually a
phase lag of at least 45º on the output for ac currents at frequencies
exceeding 13 kHz. For transient current signals, the response time can be
expected to be ~25 µs.

NOTE TO MYSELF: Hmmm... so the phase shift for figuring the power factor on
the mains at 50 and 60 Hz, should not be a problem. The application that I
have in mind is for stepper motor control/monitor at a range of about 300 Hz
to 3 KHz.

The DS2450 ADC may be found at:
http://pdfserv.maxim-ic.com/en/ds/DS2450.pdf

Best regards, Kelly Smith

-----Original Message-----
From: Kelly Smith [mailto:[email protected]]
Sent: Saturday, January 24, 2004 12:10 PM
To: 1-wire-software-development-6tN4nzCoH/[email protected]
Cc: dan-ak7mA/[email protected]
Subject: RE: [1-wire]Measuring mains current with 1-wire


Dear Joel - Re: "Are they (Smart Watt) actually shipping product?"

...via Dan Diesso (dan-ak7mA/[email protected])

Best regards, Kelly Smith

-----Original Message-----
From: 1-wire-software-development-admin-6tN4nzCoH/[email protected]
[mailto:1-wire-software-development-admin-6tN4nzCoH/[email protected]]On Behalf Of Joel
Winarske
Sent: Friday, January 23, 2004 8:11 AM
To: 1-wire-software-development-6tN4nzCoH/[email protected]
Subject: Re: [1-wire]Measuring mains current with 1-wire


A while back I had sent them an email and never got a response.  Are they
actually shipping product?

----- Original Message -----
From: "Kelly Smith" <[email protected]>
To: <1-wire-software-development-6tN4nzCoH/[email protected]>
Sent: Friday, January 23, 2004 6:51 AM
Subject: RE: [1-wire]Measuring mains current with 1-wire


> Dear Anders - You might want to consider this:
>
> http://www.smart-watt.com/
>
> Best regards, Kelly Smith
>
> -----Original Message-----
> From: 1-wire-software-development-admin-6tN4nzCoH/[email protected]
> [mailto:1-wire-software-development-admin-6tN4nzCoH/[email protected]]On Behalf Of Phil
> Malone
> Sent: Friday, January 23, 2004 6:24 AM
> To: 1-wire-software-development-6tN4nzCoH/[email protected]
> Subject: Re: [1-wire]Measuring mains current with 1-wire
>
>
> Hi Anders...
>
> A separate issue for you to consider...
> If you are intending to infer the power consumption of your house from the
> current reading you take, be aware that your reading will not take into
> account the Power Factor of your inductive loads.  Such items as heat
pumps
> and washing machine motors do not have a pure resistive load, so if you
just
> take RMS current and multiply it by the nominal house voltage you will get
> readings that are too high (by 20% or more).
>
> The only way to get a Real Power measurement is to continually (maybe
1khz)
> sample both current and voltage then multiply and accumulate the values.
> Although there are several 1-wire devices out there that do this, but I'm
> pretty sure they are reading the voltages another way, and then simply
> outputting the resulting power reading on  the 1-wire net.  I don't think
> 1-wire is fast enough to actually  take the V I readings as often as
> required to get any accuracy.
>
> Didn't want to rain on any parade, but I just went through this myself,
and
> ended up having to purchase a REAL POWER meter to do the job for me.
> Unfortunately it's not i-wire, but it has a pulse output that's easy to
> interface to.
>
> Phil.
>
> At 08:10 AM 1/23/2004 +0100, you wrote:
> >Hi,
> >
> >I wish to measure the mains current into my house with a 1-wire based
> >solution.
> >
> >I am planning to use a current transformer (CR3110 from CR Magnetics,
> >http://www.crmagnetics.com/pdf/3110.pdf) which will deliver 0-5v over a
> >burden resistor and a dallas DS2450 1-wire A/D converter which will be
> >read by a Linux based computer.
> >
> >The Current transformer vill deliver 0-5v AC (50Hz), is it possible to
> >measure that with the DS2450 or will i have to use a AC to DC converter
as
> >well (like the MX636) ??
> >
> >Regards,
> >Anders Sandell
> >
> >
> >_______________________________________________
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>
> Phil Malone
> Adaptive Internet Technologies.
>
> Email:     webmaster-Ba39baAHJJtWk0Htik3J/[email protected]
> Portfolio: http://www.mr-phil.com/portfolio.htm
> Phone:     (301) 387-2331 (Deep Creek Lake MD.)
>
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