The Not just arduino group is talking about doign some group projects and one idea is power moniting in the workshop.
Has anyone else been looking into setting it up? presumably we'd need 3 x
current clamps and something to do the A/D conversion. Has anyone started gathering bits?
> The Not just arduino group is talking about doign some group projects and > one idea is power moniting in the workshop.
The easiest way is probably to hook up to the meter's data port.
> Has anyone else been looking into setting it up? presumably we'd need 3 x
> current clamps and something to do the A/D conversion.
You need to measure the voltage as well, and then multiply it by the current at a fairly
fast rate, 100 samples per cycle (5kHz) is pobably enough, but faster will give a more
accurate answer.. A lot of the workshop equipment is going to present a significantly
inductive load and multiplying average current by average volts will give significant errors.
Another thing to note is that those current clamps will be current trasnsformers (inless
you pay big money for hall effect baed ones, which are usually only used for DC).
These have a current output rather than voltage, and neeed a burden resistor across
the output to work correctly. Some of them include this internally bbut many do not.
I was looking at this and went from a simple solution to being confused .... not difficult
I geuss I am left with two question
What have we used for the existing setup "Question" anyone know ?? And what level of acuracy do we need as opposed to want and will we go with want or need
> The Not just arduino group is talking about doign some group projects and
>> one idea is power moniting in the workshop.
> The easiest way is probably to hook up to the meter's data port.
> Has anyone else been looking into setting it up? presumably we'd need 3 x
>> current clamps and something to do the A/D conversion.
> You need to measure the voltage as well, and then multiply it by the
> current at a fairly
> fast rate, 100 samples per cycle (5kHz) is pobably enough, but faster will
> give a more
> accurate answer.. A lot of the workshop equipment is going to present a
> significantly
> inductive load and multiplying average current by average volts will give
> significant errors.
> Another thing to note is that those current clamps will be current
> trasnsformers (inless
> you pay big money for hall effect baed ones, which are usually only used
> for DC).
> These have a current output rather than voltage, and neeed a burden
> resistor across
> the output to work correctly. Some of them include this internally bbut
> many do not.
Ken Boak wrote:
>It supports up to 4 current transformers. - so 3 phase not a problem.
Yes it is, it only has a voltage input for one phase. This means that the
software needs to phase shift the signal by 120/240 degrees to
synthesise the other phases before doing the RMS calculation. It will
also fail to take into account the difference in voltage between the phases,
which can be quite significant. According to the cacti graphs the figures
for unit 24 at present are:
L1 = 232.82V
L2 = 240.47V
L3 = 243.75V
An energy monitor that was only looking at L1 would be out by about 4.5%
for the power on L3
In a previous life I was taught to look at the problem/requirement before providing a soloution The second part of my comment was And what level of acuracy do we need as opposed to want and will we go with want or need
I have made a three phase current transformer, This will make the
measurements more consistent than using clamp probes and will fit into the
dis. board.
There is an old penrecorder type power meter with clamp probes on the
shelf near the bike mountain. It contains some amplifiers that are matched
to the probes. Might be an interesting thing to resurrect.
Phil
-- " et cognoscetis veritatem et veritas liberabit vos. "
> On Monday, November 5, 2012 8:49:48 PM UTC, jasper wrote:
>> Has anyone else been looking into setting it up? presumably we'd need 3x
>> current clamps and something to do the A/D conversion. Has anyone >> started
>> gathering bits?
Rather than continuously calculating instantaneous power, how about
measuring the phase angle (by timing zero-crossings) and then measure
voltage and current separately on 3 phases using a slow ADC ?
This would be much easier to calculate but wouldn't be accurate if we have
a lot of non-sinusoidal loads. However, in the workshop it might be good
enough - both because we probably only want a rough figure, and because
motors do generally present sinusoidal loads, albeit with a phase shift. A
big pile of computers would be a different matter. The welder could be an
exception, but it's a transformer rather than an inverter type so may not
be too bad.
I haven't tried this nor ever built a power meter. It's a suggestion to
invite discussion and educate me.
On Thu, Nov 8, 2012 at 9:41 AM, <cepmen...@yahoo.co.uk> wrote:
> I have made a three phase current transformer, This will make the
> measurements more consistent than using clamp probes and will fit into the
> dis. board.
> There is an old penrecorder type power meter with clamp probes on the
> shelf near the bike mountain. It contains some amplifiers that are matched
> to the probes. Might be an interesting thing to resurrect.
> Phil
> --
> " et cognoscetis veritatem et veritas liberabit vos. "
> On Monday, November 5, 2012 8:49:48 PM UTC, jasper wrote:
> Has anyone else been looking into setting it up? presumably we'd need 3x
>>> current clamps and something to do the A/D conversion. Has anyone
>>> started
>>> gathering bits?
On Thu, Nov 8, 2012 at 9:41 AM, <cepmen...@yahoo.co.uk> wrote:
> I have made a three phase current transformer, This will make the
> measurements more consistent than using clamp probes and will fit into the
> dis. board.
> There is an old penrecorder type power meter with clamp probes on the
> shelf near the bike mountain. It contains some amplifiers that are matched
> to the probes. Might be an interesting thing to resurrect.
> Phil
> --
> " et cognoscetis veritatem et veritas liberabit vos. "
> On Monday, November 5, 2012 8:49:48 PM UTC, jasper wrote:
> Has anyone else been looking into setting it up? presumably we'd need 3x
>>> current clamps and something to do the A/D conversion. Has anyone
>>> started
>>> gathering bits?
> Did I miss something? Didn't Russ say the power meter has a serial port,
> rendering all of this planning completely unnecessary?
> -Nick
> On Thu, Nov 8, 2012 at 9:41 AM, <cepmen...@yahoo.co.uk> wrote:
>> I have made a three phase current transformer, This will make the
>> measurements more consistent than using clamp probes and will fit into the
>> dis. board.
>> There is an old penrecorder type power meter with clamp probes on the
>> shelf near the bike mountain. It contains some amplifiers that are matched
>> to the probes. Might be an interesting thing to resurrect.
>> Phil
>> --
>> " et cognoscetis veritatem et veritas liberabit vos. "
>> On Monday, November 5, 2012 8:49:48 PM UTC, jasper wrote:
>> Has anyone else been looking into setting it up? presumably we'd need 3x
>>>> current clamps and something to do the A/D conversion. Has anyone
>>>> started
>>>> gathering bits?
