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'[PIC] Looking for simple way to use PIC to measure'
2010\05\31@083525 by Mark

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I am working on a project where I need to measure current for voltages
5V, 3.3V, 12V all DC voltages and some have currents as high as 60A.
I would prefer a low cost method as this is just a hobby project not
something for production. It doesn't need to be terribly accurate,
within a couple hundred ma would be fine.
I have pics 18f4580 , 18f2580, 16f88 and a few others to work with.

Thanks
Mark

2010\05\31@085222 by Marcel Birthelmer

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Current sense resistor, current sense amplifier (LT makes some nice
ones, I think maxim has some that you might be able to sample), PIC
ADC input.

On Mon, May 31, 2010 at 2:35 PM, Mark <spam_OUTmarkTakeThisOuTspamcgmark.us> wrote:
> I am working on a project where I need to measure current for voltages
> 5V, 3.3V, 12V all DC voltages and some have currents as high as 60A.
> I would prefer a low cost method as this is just a hobby project not
> something for production. It doesn't need to be terribly accurate,
> within a couple hundred ma would be fine.
> I have pics 18f4580 , 18f2580, 16f88 and a few others to work with.
>
> Thanks
> Mark
> -

2010\05\31@090211 by RussellMc

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> I am working on a project where I need to measure current for voltages
> 5V, 3.3V, 12V all DC voltages and some have currents as high as 60A.
> I would prefer a low cost method as this is just a hobby project not
> something for production. It doesn't need to be terribly accurate,
> within a couple hundred ma would be fine.

- Linear Hall cell monitoring field from wire.

- DC Shunt and measure mV.
Nees to be LOW resistance to keep power loss down.
eg ~ 1 Watt per 15 mV at 60 A.

Note that 200 mA at 60 A = 1 part in 300 = > 8 bits - so "not terribly
accurate" only works for some values of terribly.



     Russell

2010\05\31@091041 by Isaac Marino Bavaresco

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Em 31/5/2010 09:52, Marcel Birthelmer escreveu:
> Current sense resistor, current sense amplifier (LT makes some nice
> ones, I think maxim has some that you might be able to sample), PIC
> ADC input.
>
> On Mon, May 31, 2010 at 2:35 PM, Mark <.....markKILLspamspam@spam@cgmark.us> wrote:
>  
>> I am working on a project where I need to measure current for voltages
>> 5V, 3.3V, 12V all DC voltages and some have currents as high as 60A.
>> I would prefer a low cost method as this is just a hobby project not
>> something for production. It doesn't need to be terribly accurate,
>> within a couple hundred ma would be fine.
>> I have pics 18f4580 , 18f2580, 16f88 and a few others to work with.
>>
>> Thanks
>> Mark
>>    

But at 60A he will need a very low value for the sense resistor (1 mOhm
will dissipate 3.6W), and a very good amplifier circuit.

Perhaps he could use off-the-shelf Hall Effect current probes.


Regards,

Isaac

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2010\05\31@091243 by ivp

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>I am working on a project where I need to measure current for voltages
> 5V, 3.3V, 12V all DC voltages and some have currents as high as 60A

One of the few Silicon Chip articles that are available fully on-line

0-80A ammeter

http://www.siliconchip.com.au/cms/A_30551/article.html

16F84 based, using the old firmware ADC method. Would be a
snip to convert for a PIC that has hardware ADC, and probably
more accurate too

Joe

2010\05\31@091926 by ivp

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> at 60A he will need a very low value for the sense resistor (1 mOhm
> will dissipate 3.6W), and a very good amplifier circuit.
>
> Perhaps he could use off-the-shelf Hall Effect current probes

Maybe both methods, for high and low ranges

2010\05\31@194147 by Olin Lathrop
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Mark wrote:
> I am working on a project where I need to measure current for voltages
> 5V, 3.3V, 12V all DC voltages and some have currents as high as 60A.
> I would prefer a low cost method as this is just a hobby project not
> something for production. It doesn't need to be terribly accurate,
> within a couple hundred ma would be fine.
> I have pics 18f4580 , 18f2580, 16f88 and a few others to work with.

There are lots of ways to do this, each with its own difficulties.

How about a small coil and Hall sensor?  That gets around high side / low
side measurement issues and is totally isolated?  Adjust coil turns to get
desired full scale range by experiment.


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'[PIC] Looking for simple way to use PIC to measure'
2010\06\01@055126 by Alan B Pearce
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> Mark wrote:
>> I am working on a project where I need to measure current for voltages
>> 5V, 3.3V, 12V all DC voltages and some have currents as high as 60A.
>> I would prefer a low cost method as this is just a hobby project not
>> something for production. It doesn't need to be terribly accurate,
>> within a couple hundred ma would be fine.
>> I have pics 18f4580 , 18f2580, 16f88 and a few others to work with.
>
> There are lots of ways to do this, each with its own difficulties.
>
> How about a small coil and Hall sensor?  That gets around high side / low
> side measurement issues and is totally isolated?  Adjust coil turns to get
> desired full scale range by experiment.

I am certainly on the side of hall Sensor chips for this level of current.
My choice would be one of the nice chips from Allegro Micro.

See
http://www.allegromicro.com/en/Products/Categories/Sensors/currentsensor.asp
to make your selection.

Note that the current sense wire can be either a track on the PCB (although
I suspect this will not be heavy enough for 60A) or a wire over the top of
the chip body (my preferred method at this current). Some models have a
sense 'wire' built in, but it is still a PCB connection, and I seriously
doubt the current capability of a track unless you don't worry about the
voltage drop.

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