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Good afternoon Adam,<br>
<br>
I've been there ... had 8 current transducers (600 amps each),
feeding into 12-bit ADCs with the transducers providing the
isolation.<br>
<br>
The problem is the current transducers can be a bit expensive
(Phidgets lists a 100 amp transducer for $40.00
(<a class="moz-txt-link-freetext" href="http://www.phidgets.com/products.php?product_id=3588">http://www.phidgets.com/products.php?product_id=3588</a>), but only
shows a 200 mA resolution).<br>
<br>
If you want, take a look at Caddock's current measuring (Kelvin)
resistors
(<a class="moz-txt-link-freetext" href="http://www.caddock.com/Online_catalog/current_Sense/current.html">http://www.caddock.com/Online_catalog/current_Sense/current.html</a>),
but they limit out at around 60 amps and will require a heatsink.
You don't want to mount these on a PC board, but rather inline with
your high current leads. This type of measurement will require
isolation ... look at isolation amplifiers, but be prepared for
sticker shock (The Analog Devices AD202 is over $50.00 each ... hmmm
price dropped since the last time I bought them). An alternative is
known as a "poor man's isolation amplifier"
(<a class="moz-txt-link-freetext" href="http://www.analog.com/library/analogDialogue/archives/34-01/haystack/">http://www.analog.com/library/analogDialogue/archives/34-01/haystack/</a>);
I've used the AD629, which is a very high impedance isolated opamp
that provides great, but not perfect isolation.<br>
<br>
A third approach is to purchase a surplus current shunt
(<a class="moz-txt-link-freetext" href="http://ctrsurplus.com/newdccurrentshunt100amp50mv.aspx">http://ctrsurplus.com/newdccurrentshunt100amp50mv.aspx</a>), as new
shunts are as expensive as current transducers. Here again you will
have to provide isolation (I'd build a board and mount it adjacent
to the shunt with the instrument amplifier and ADC right there, then
transport the information via I2C or what ever protocol you desire).<br>
<br>
Accuracy is important, but remember you will be limited by the
resolution of your ADC. I highly recommend a 16-bit ADC if you need
fine current monitoring (1.5 mA for 100 amp shunt with a 16-bit).<br>
<br>
To reduce your noise, put a low pass filter on each ADC input line
with the time constant equal to the sample rate (I sampled every 100
mS, thus I installed a 100 mS low pass on each line) ... this cuts
your random noise down. I also read each ADC 8 times ... throwing
away the first reading and averaging the remaining 7 ... and was
getting very repeatable, very accurate measurements on non-sine wave
current waveforms.<br>
<br>
Hope this helps.<br>
<br>
Regards,<br>
<br>
Rick<br>
<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 6/14/2014 11:35 AM, Adam Haile
wrote:<br>
</div>
<blockquote
cite="mid:CAG8g-TZySTsHB10d6TPCUJDdnnqM-aN4UgGrZS22iQ80ht_tRQ@mail.gmail.com"
type="cite">
<div dir="ltr">As those that saw my projects at the Maker Faire
know, I work with a lot of high current LED projects. So I'm
always looking for higher current supplies and my variable bench
supply definitely doesn't cut it so I generally use supplies
like the 5V/40A supply I used for my 24x24 matrix. But that is
even a too little for some of the projects I have planned. I'm
thinking about getting a 500 - 700W (@5V) supply (something like
this: <a moz-do-not-send="true"
href="http://www.ebay.com/itm/370888481354">http://www.ebay.com/itm/370888481354</a>)
and building it out with a few more features.
<div>
<br>
</div>
<div>Mainly, I want to add built in current sensing that would
be displayed on an LCD screen (likely all Arduino controlled).
The supply itself would be unmodified - I'm not crazy. I would
just add all that between the supply output and connectors on
the outside of an enclosure I would build.</div>
<div><br>
</div>
<div>So, my main question is if anyone has any advice for how I
could go about sensing this much current? I'm thinking about
using something like the TI INA219 (<a moz-do-not-send="true"
href="http://www.ti.com/product/ina219">http://www.ti.com/product/ina219</a>)
which, with the right shunt, should be able to handle it and
would have a nice I2C interface. I'd also like to have 2 - 4
separate outputs, each with their own separate sensor... so
each would need to handle up to 100A or so.</div>
<div><br>
</div>
<div>I realize that running the current through any PCB trace to
the shunt would probably require insanely wide traces, so is
there a good, high precision shunt that would work off PCB?</div>
<div><br>
</div>
<div>Basically, I don't know what I don't know, so I'd love any
direction that could be given.</div>
</div>
<br>
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<br>
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