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Topic: Measuring multiple batteries without a common ground (Read 463 times) previous topic - next topic

RIN67630

#15
Aug 10, 2017, 07:35 pm Last Edit: Aug 11, 2017, 06:23 am by RIN67630
I don't really understand what that module does or what inputs it needs. I don't see the data sheet anywhere. What voltage in and out does it provide and what is the 24v for?

The proposed module is an industrial voltage sensor.
It is self powered by a current loop, which has been an industry standard for more than 50 years.
https://en.wikipedia.org/wiki/Current_loop

But Tom George's idea to switch capacitors is probably cheaper and easier to implement.
His schematic diagram was however drawn in a way that does not make its function easy to understand.
That arrangement is probably more self-explanatory:


You will need 24 relays for 12 readings, since the relays with two contacts of Tom George's design are not common in the Arduino world.

To read the first battery you will switch R1 and R2, that will move the capacitor away from the battery, and switch it to the measurement circuit, then wait 100mS and read the A0 input, release the relays.
To read the next one,  switch R3 and R4, wait 100mS and read A0 input again,
... and so forth until the last battery.
That isn't rocket science.

Fortunately, you have got some interesting boards with multiple relays built in, three of those seem perfect to do the job:
http://www.ebay.com/itm/5V-8-Channel-Relay-Module-Board-For-Arduino-AVR-PIC-MCU-DSP-ARM-LW-/172396554144
Since the relay module is provided with optocouplers and relay drivers, you might just wire the input 1&2, 3&4,... etc. together, since you will always drive two relays together.

So you we need 12 digital outputs; remember: the unused analog inputs A1 to A7 can be used as digital outputs as well.

Enjoy!

TomGeorge

Hi,

Quote
You will need 24 relays for 12 readings, since the relays with two contacts of Tom George's design are not common in the Arduino world.
You don't use the Arduino relay modules, you BUILD the assembly using DPDT relays to ensure isolation with the switching, thats why I included the MOSFET coil driving.

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

RIN67630

#17
Aug 11, 2017, 05:47 am Last Edit: Aug 11, 2017, 05:57 am by RIN67630
Hi,
You don't use the Arduino relay modules, you BUILD the assembly using DPDT relays to ensure isolation with the switching, thats why I included the MOSFET coil driving.

Thanks.. Tom... :)
I did it that night:

:smiley-razz:


TomGeorge

#18
Aug 11, 2017, 06:00 am Last Edit: Aug 11, 2017, 06:01 am by TomGeorge
Hi,
I did it that night:

:smiley-razz:


The thirteenth relay along the top row, COM terminal needs tightening. :) :) :)
Nice....
Everything runs on smoke, let the smoke out, it stops running....

dougp

I'm probably out of my depth here but, could this work? Essentially, mount a voltmeter for each cell and read them through I2C.

RIN67630

I'm probably out of my depth here but, could this work? Essentially, mount a voltmeter for each cell and read them through I2C.
I have imagined a solution using 12 lilypads, one on each battery, but then you have got the problem of transmitting the result in an isolated way.
No, finally the capacitor-relays solution is probably the best way to go.

dougp

I have imagined a solution using 12 lilypads, one on each battery, but then you have got the problem of transmitting the result in an isolated way.
I thought maybe since the chips linked have a differential mode that would get around the isolation problem. Oh, well.

RIN67630

I thought maybe since the chips linked have a differential mode that would get around the isolation problem. Oh, well.
On an electric car you may have quite high overall voltages.
A differential mode is usually only valid "within the rails".

dougp


RIN67630

I can't help thinking there's got to be an electronic solution to this problem.  Let me know if I'm being a nuisance

http://isolation-transmitter.com/download/JSD-TAF-1001S.pdf


Precision Optically Isolated Voltage Sensor

1-Wire voltage sensor TSV200-60i
- First one provides pulse output only: hard to process with an arduino
- Second one is fine, but SMD soldering skills and need to design a PCB
- Last one is perfect, but expensive: at least 12* 75€

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