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Author Topic: High side current measurement  (Read 8382 times)
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max
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« on: November 12, 2012, 09:24:47 21:24 »

Hi,
I need a circuit (not dedicated ics) to measure the high side current.
My app is battery charging max voltage is 60V and current is 30A

Regards
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« Reply #1 on: November 12, 2012, 10:00:17 22:00 »

You could use something like this
http://uk.rs-online.com/web/p/analogue-panel-ammeters/3159515/
Or a shunt that reads 0-60mv (0-60amps) then use pic/avr to dispaly the voltage another crude cheap method is messaure the volts drop accross the fuse but the downfall to this methoed is the reding could alter with temperature.
I know you want to avoid dedicated ic's but other than the meter like from RS which are not cheap I can't see another way that would be easy
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solutions
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« Reply #2 on: November 12, 2012, 10:41:02 22:41 »

You have not provided enough information, have not defined and constrained the problem, for anyone to provide anything more than a shot in the dark. There are a million ways to do it.

How will the measurement be used? What other supplies and resources are available? Accuracy?? Regulatory/safety? Noise? Linearity? etc etc etc  Most succinct is to just describe the application, but that's always a big secret in these kinds of questions.
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Gallymimu
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« Reply #3 on: November 12, 2012, 10:52:16 22:52 »

Current sense resistor (shunt) and an instrumentation amplifier or diff amp measuring across the shunt.  INA149 is a nice high voltage diff amp +/- 275V.

Agree though that more detail is necessary to have any chance of offering a suggestion that would actually work for your situation.
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« Reply #4 on: November 12, 2012, 11:29:09 23:29 »

This topic reminds me of problem in work, I was asked to add amp meter to a project, asking for details of the project, I was told you don't need that.
So took the easy way and went down RS&Farnell path and bought ready made meter, also I did not have to beg for funding Smiley

A few weeks later when product was being fully tested before release, we got one into our workshop, fall about laughing, the power supply had a 100k resistor that was very linear over the range to be monitored.
We could have done meter circuit for 100th of the cost, the prototype cost.

Thank goodness I don't need to go down the now long gone, ThornEMI  Route of bidding & begging for funding.
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element1133
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« Reply #5 on: November 13, 2012, 03:14:02 03:14 »

I know you said you wanted to stay away from dedicated ic's but this is a pretty cool device. i used it in an rf amplifer to monitor the transistor currents in the amplifier. i used it in differential mode and adjusted the gain of my diff amp to get the scaling for my current range.

http://www.melexis.com/Hall-Effect-Sensor-ICs/Triaxis%C2%AE-Hall-ICs/MLX91205-689.aspx

Regards
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wellnerson1
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« Reply #6 on: November 13, 2012, 03:32:24 03:32 »

Dear MAX,
Please refer the following documents. May be useful for you.
1. citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.131.5176&rep=rep1&type=pdf
2. http://www.ti.com/lit/an/sloa044/sloa044.pdf

With regards.
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max
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« Reply #7 on: November 13, 2012, 03:55:12 03:55 »

You have not provided enough information, have not defined and constrained the problem, for anyone to provide anything more than a shot in the dark. There are a million ways to do it.

How will the measurement be used? What other supplies and resources are available? Accuracy?? Regulatory/safety? Noise? Linearity? etc etc etc  Most succinct is to just describe the application, but that's always a big secret in these kinds of questions.

There is no secret, I have been asked to design a battery charger for 48v lead acid batteries using SCR, the
low side current sensing must be avoided, the charger must have current limited output, the current accuracy/linearity is not important +/-2A deviation is ok, the sensed current output is used as an adc input to a pic uc, the supplies and resources are arranged as required. Secondly it is not necessary to use a uC, an analog solution is also ok.
I have found some SCR based charger circuits using analog control (op-amps etc) with current limiting but all are using the low side current sensing. If there is an interest I can upload the circuits I found.
The main reason for the avoidance of the dedicated sensing ic, is the availability of special parts, so i am looking for a solution using commonly available parts op-amps etc.
« Last Edit: November 13, 2012, 04:05:10 04:05 by max » Logged

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Gallymimu
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« Reply #8 on: November 13, 2012, 06:19:04 06:19 »

That makes it easy.  Like I said, current shunt and a cheap diff amp or just an op-amp configured as a differential amplifier (the one I suggested before is probably too expensive for an application like this).

Posted on: November 13, 2012, 06:13:12 06:13 - Automerged

If you are pulsing/charging from AC with the SCR you could probably also use a current sense transformer. such as this:

http://www.digikey.com/product-detail/en/CT1040/TE2279-ND/2362758
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vovchik02
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« Reply #9 on: November 13, 2012, 07:06:42 07:06 »

Hi,
I need a circuit (not dedicated ics) to measure the high side current.
My app is battery charging max voltage is 60V and current is 30A

Regards

Simple sensor for AC and DC circuit :

http://www.lem.com/hq/en/component/option,com_catalog/task,displayserie/serie,LA%2025-200%20-P/output_type,/
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« Reply #10 on: November 13, 2012, 10:54:40 22:54 »

I have found some SCR based charger circuits using analog control (op-amps etc) with current limiting but all are using the low side current sensing. If there is an interest I can upload the circuits I found.
Max that would be good if you could looks and sounds interesting
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« Reply #11 on: November 14, 2012, 12:31:54 00:31 »

There are some people here that are assuming your uC supply is referenced to the high side, or that you have a 50V input common-mode range op amp if your uC is ground referenced....

I don't understand why no low side sensing (not that I care, just curious why you feel so strongly against it) - you'll have a heck of a time getting the uCs to communicate, with all of them having a variable absolute voltage wrt ground, lending the possibility of toasting them just because their battery is down to 41V, while their friends are fully charged.

Has your love of the high side solution for the charging complicated the rest of the circuitry to where it's not worth it? 

Also have to ask why you are using lead batteries when most countries are starting to impose moratoriums on their use (assuming  this is not just a one off hobby thingy)
« Last Edit: November 14, 2012, 12:34:54 00:34 by solutions » Logged
zab
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« Reply #12 on: November 14, 2012, 01:39:25 13:39 »

The best choice for current measurement in ac battery charger is to use CT on primary side of the transformer. For a small ct  will meet the need.It is simple and easy available in few cents. I have practically made charger with this ways. If you like use it otherwise ignore it.
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Gallymimu
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« Reply #13 on: November 14, 2012, 03:03:25 15:03 »

The best choice for current measurement in ac battery charger is to use CT on primary side of the transformer. For a small ct  will meet the need.It is simple and easy available in few cents. I have practically made charger with this ways. If you like use it otherwise ignore it.

Can you give an example of an available current transformer, or a design than only costs a few cents?
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zab
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« Reply #14 on: November 14, 2012, 03:31:49 15:31 »

Please refer to
http://www.sonsivri.to/forum/index.php?topic=14989.0
and see  the attached pic. for ref.
http://www.sonsivri.to/forum/index.php?action=dlattach;topic=14989.0;attach=12492


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Gallymimu
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« Reply #15 on: November 14, 2012, 05:24:29 17:24 »


Sorry, I didn't mean an implementation design, I meant a design for the CT itself or a part number.  I've not seen current transformers for a few cents and was looking for some suggestion of what you were using (or built) that was actually that cheap to measure ~30A as you suggested in this thread.  I don't see any part numbers in the thread you mention (nor did I look very carefully through the two pages of discussion).  A picture of a schematic symbol with no part number isn't very helpful Smiley
« Last Edit: November 14, 2012, 05:33:03 17:33 by Gallymimu » Logged
Saber3239
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« Reply #16 on: November 15, 2012, 07:10:57 07:10 »

Small shunt resistor and INA282 will do the job
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zab
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« Reply #17 on: November 15, 2012, 10:10:51 10:10 »

Sorry, I didn't mean an implementation design, I meant a design for the CT itself or a part number.  I've not seen current transformers for a few cents and was looking for some suggestion of what you were using (or built) that was actually that cheap to measure ~30A as you suggested in this thread.  I don't see any part numbers in the thread you mention (nor did I look very carefully through the two pages of discussion).  A picture of a schematic symbol with no part number isn't very helpful Smiley

Please see the attached pic for ref. It is Chinese made ac current transformer attached on the primary side of the charger being on higher potential operating with less current. while on secondary the current will be much high with lower voltages. In this  You can use a small ct instead of big costly ct.
Hope it will clear the confusion.
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nordiceng
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« Reply #18 on: April 20, 2013, 06:16:17 06:16 »

please, let me know high voltage AC or DC , you need to provide more information about this case
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SteveyG
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« Reply #19 on: May 10, 2013, 04:08:43 16:08 »

The best choice for current measurement in ac battery charger is to use CT on primary side of the transformer. For a small ct  will meet the need.It is simple and easy available in few cents. I have practically made charger with this ways. If you like use it otherwise ignore it.

What makes that the 'best' way? There are many ways to measure the current on a battery charger, each will have their pros and cons.
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alphaville
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« Reply #20 on: May 10, 2013, 07:35:57 19:35 »

Hi,
I need a circuit (not dedicated ics) to measure the high side current.
My app is battery charging max voltage is 60V and current is 30A

Regards

Hello max,

You have high CMRR voltage. I suggest you use a single chip. Try these:

http://www.digikey.com/product-detail/en/ACS709LLFTR-20BB-T/620-1337-1-ND/2195928

http://www.digikey.com/product-detail/en/ACS709LLFTR-20BB-T/620-1337-1-ND/2195928

Regards.



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nordiceng
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« Reply #21 on: May 10, 2013, 08:26:01 20:26 »

you can use current transformer to convert high current into low current and then current measurements will be more safe
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PaulC
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« Reply #22 on: May 11, 2013, 01:48:20 01:48 »

Hi MAX
see this idea on current measurement..
http://www.mikroe.com/forum/viewtopic.php?p=212863#p212863
just as ideas
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« Reply #23 on: May 11, 2013, 06:49:39 06:49 »

Hey Max, I know you're not looking for an integrated solution but go ahead and file this one away for when you do.  I've used a lot of these in the past.

Hall Effect  aka good isolation but only reasonable bandwidth/response depending on what your shooting for

50A   100A  and they work well in parallel if you want to get into some serious amps Grin
AC
DC

high side, low side, middle side, who cares,  when the part is dirt cheap and the size of a quarter in real estate, why fiddle around with a dozen or more parts.  Wanna get fancy then use a DAC pin for scaling a VGA gain stage w/ offset on the output and poke it into the ADC.  Sprinkle a little microP code....be happy  Lips sealed

High side, high current monitoring doesn't get any easier than this:

http://www.allegromicro.com/Products/Current-Sensor-ICs/Fifty-To-Two-Hundred-Amp-Integrated-Conductor-Sensor-ICs/ACS756.aspx


H_A
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solutions
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« Reply #24 on: May 11, 2013, 10:06:42 10:06 »

you can use current transformer to convert high current into low current and then current measurements will be more safe
Please explain - "more safe"
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