Searching \ for '[EE] Bidirectional Current Monitor' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: massmind.org/techref/power.htm?key=current
Search entire site for: 'Bidirectional Current Monitor'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Bidirectional Current Monitor'
2009\06\10@151448 by Francois Robbertze

flavicon
face
Hi

I want to measure current on four 12 Volt DC motors in both directions.
The free turning current is about 3 Amps and can draw up to 13 Amps at full load.
This is to stop the motors at the end stops and to monitor over torque situations.

I would prefer an output that I can connect to the pic's A/D. (2.5 Volt - No Current; <2.5 Volt Current in one direction; >2.5 Volt Current in the other direction)

I came accross a few ICs and different methods (shunt, hall effect etc). that should do the job, but can not get hold of these in South Africa
Bidirectional CURRENT SHUNT MONITOR
* INA170
* AD8206

Hall Effect
*ACS715


First of all: If you turn the current around on the shunt resistor - What is the configuration - High side or low side sensing?

Can this be done with a shunt resistor and op-amps (eg. the LM358 or MCP604 that I have plenty of stock) or is it not advisable? If it is possible is there a AN or a website that I can get more info and schematics.


Regards

Francois




2009\06\10@152930 by Rolf

flavicon
face
Francois Robbertze wrote:
{Quote hidden}

You will want the ACS714, not the ACS715 (which is uni-directional).

Why can't you get the allegro part in South Africa?

Rolf

2009\06\10@155025 by Isaac Marino Bavaresco

flavicon
face
Francois Robbertze escreveu:
{Quote hidden}

I struggled with this problem some time ago.

To measure high-side currents there are some specific integrated
circuits. You may try to build your own with op-amps, but you will need
high-precision ones (very low input offset voltages) or you will get big
measurement errors.

One problem I faced (because my motor was inside an H-bridge) was that
the current sensor sometimes was in the high-side (motor turning to one
side) and sometimes it was in the low side with the polarity reversed
(motor turning to the other side).

If you don't need to use a chopper driver or you need to measure the
current only during the on period, you may put your shunt sensor between
the ground and the low-side transistors' emitter/source. This is the
easiest way.

Regards,

Isaac

__________________________________________________
Faça ligações para outros computadores com o novo Yahoo! Messenger
http://br.beta.messenger.yahoo.com/

2009\06\10@171210 by Francois Robbertze

flavicon
face
Hi Rolf

I contacted Arrow Altec about the ACS712 but they didn't have stock and
require min order quantities and delay.
Avnet Copp have stock on the ACS712 ELCTR-05B-T but this one is optimized
for 5 Amps. I don't know what will happen at 10 Amps...datasheet don't help
me exept for the sensitivity at 185mV/A vs 100mV/A for the 20Amp version.
mayme I can use a voltage devider with the ACS712 -05B?

I will contact Arrow Altec again and ask for the ACS714.

I think I'll have to go with the 20 amp version. Put the output through a op
omp if needed...?

Is there a difference in the ACS712 and the ACS714 exept for the  automotive
grade?

Regards

Francois



{Original Message removed}

2009\06\10@172220 by Álvaro Deibe Díaz

picon face
How about Sentron hall effect sensors?

http://www.sentron.ch/csa.htm

Regards,

Alvaro Deibe Diaz

-----Mensaje original-----
De: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] En nombre de
Francois Robbertze
Enviado el: miércoles, 10 de junio de 2009 21:15
Para: 'Microcontroller discussion list - Public.'
Asunto: [EE] Bidirectional Current Monitor

Hi

I want to measure current on four 12 Volt DC motors in both directions.
The free turning current is about 3 Amps and can draw up to 13 Amps at full
load.
This is to stop the motors at the end stops and to monitor over torque
situations.

I would prefer an output that I can connect to the pic's A/D. (2.5 Volt - No
Current; <2.5 Volt Current in one direction; >2.5 Volt Current in the other
direction)

I came accross a few ICs and different methods (shunt, hall effect etc).
that should do the job, but can not get hold of these in South Africa
Bidirectional CURRENT SHUNT MONITOR
* INA170
* AD8206

Hall Effect
*ACS715


First of all: If you turn the current around on the shunt resistor - What is
the configuration - High side or low side sensing?

Can this be done with a shunt resistor and op-amps (eg. the LM358 or MCP604
that I have plenty of stock) or is it not advisable? If it is possible is
there a AN or a website that I can get more info and schematics.


Regards

Francois



2009\06\10@173850 by Bob Blick

face
flavicon
face

On Wed, 10 Jun 2009 21:14:34 +0200, "Francois Robbertze"
<fastmailspamKILLspameskulaap.co.za> said:

> Can this be done with a shunt resistor and op-amps (eg. the LM358 or
> MCP604 that I have plenty of stock)

Yes. A single resistor in the negative input to your H-bridge, amplified
with an opamp. Choose a resistor so your loss will not be too
much(somewhere around 0.02 to 0.1 ohm), and set your opamp for a
noninverting gain to match your input and output requirements. You'll
want some small RC filter right before the opamp to keep some transients
out(LM358 doesn't like negative transients on the input).

Cheerful regards,

Bob

--
http://www.fastmail.fm - One of many happy users:
 http://www.fastmail.fm/docs/quotes.html

2009\06\10@174131 by Rolf

flavicon
face
Francois...

The table on the allegro site suggests the bandwidth on the 712 is
>50kHz, and the 714 is 80kHz. The devices have different temperature
ratings, and the 714 is 'automotive grade'.

As for Arrow Altec, well, I am a SA expat in Canada, so I don't know
them, but Allegro has been good to me in the past with their sampling
policy, and you can probably get mid-sized orders shipped at a
reasonable rate from sources outside of SA too.

I have only used their parts as curiosities so far, but plan to use them
in a future hobby project. They just strike me as being the perfect part
for your task at hand.

Instead of an op-amp you can also set a stable vref- and vref+ and get
your 10-bit ADC on a smaller range and get the precision you need that
way. Will be easier to manage than an op-amp on a wierd center-point.

Rolf

Francois Robbertze wrote:
{Quote hidden}

2009\06\10@175145 by olin piclist

face picon face
Bob Blick wrote:
> Yes. A single resistor in the negative input to your H-bridge,
> amplified with an opamp. Choose a resistor so your loss will not be
> too much(somewhere around 0.02 to 0.1 ohm), and set your opamp for a
> noninverting gain to match your input and output requirements. You'll
> want some small RC filter right before the opamp to keep some
> transients out(LM358 doesn't like negative transients on the input).

This will give you the magnitude of the current, not the direction.  That
may be good enough if you're controlling the H bridge and know which way the
current is supposed to be flowing.  Things could get tricky if the motor is
ever driven by the load.  You can either arrange the diodes so that negative
currents bypass the current sense resistor (except for the diode drop), or
deal with negative voltages.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\06\10@182554 by Francois Robbertze

flavicon
face
This will work because I control the motor direction. I was planning to use
relays, but maybe a H-bridge is not a bad idea at all.

What transistors/"solid state relay" would you recommend in the H-bridge for
this type of current (13 Amp full load). The motors will run free most of
the time(3-4 Amps). Half load for less than a minute and full load for
mseconds.

Regards

Francois

{Original Message removed}

2009\06\10@184621 by Bob Blick

face
flavicon
face

On Thu, 11 Jun 2009 00:25:50 +0200, "Francois Robbertze"
<.....fastmailKILLspamspam.....eskulaap.co.za> said:
> This will work because I control the motor direction. I was planning to
> use
> relays, but maybe a H-bridge is not a bad idea at all.
>
> What transistors/"solid state relay" would you recommend in the H-bridge
> for
> this type of current (13 Amp full load). The motors will run free most of
> the time(3-4 Amps). Half load for less than a minute and full load for
> mseconds.

FDS6681/FDS8812 driven by a TC4469? Too much current, you can't quite
get away with a complementary MOSFET pair like the NDS8958 but there may
be something available now that would be a better fit, I haven't looked
in a couple of years. But the TC4469 is a great driver and the input
logic allows you to wire in short-circuit lockout.

Cheers,

Bob

--
http://www.fastmail.fm - Access your email from home and the web

2009\06\10@200507 by Antonio Benci

flavicon
picon face
This is a multi-part message in MIME format.
--------------040102070904040306050607
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

I'd go with the ASC715. Fully isolated, high side monitoring with a minimal
amount of loss (1.2mohm resistance) and the output is 2.5V centre weighted.

Having used its big brother, ACS756, I can say that I was very pleased with the
performance.

Regards,

Nino.

Francois Robbertze wrote:
{Quote hidden}

--------------040102070904040306050607
Content-Type: text/x-vcard; charset=utf-8;
name="Nino_Benci.vcf"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename="Nino_Benci.vcf"

begin:vcard
fn:Antonio L. Benci
n:Benci;Antonio L.
org:Monash University;School of Physics
adr:;;BLD27 / RM118-119;Monash University;VIC;3800;Australia
email;internet:EraseMEelectronic.servicesspam_OUTspamTakeThisOuTsci.monash.edu.au
title:Professional Officer / E&IS Manager / OHS Representative
tel;work:+613 9905 3649
tel;fax:+613 9905 3637
note;quoted-printable:Albert Einstein=0D=0A=
       =0D=0A=
        =E2=80=9CIf a cluttered desk is a sign of a cluttered mind, then what=
        are we to think of an empty desk?=E2=80=9D
x-mozilla-html:FALSE
url:http://physics.monash.edu.au
version:2.1
end:vcard


--------------040102070904040306050607
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

More... (looser matching)
- Last day of these posts
- In 2009 , 2010 only
- Today
- New search...