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Topic: BMS- battery management system arduino based (Read 3 times) previous topic - next topic

fca

Hi there..
i'm here with small doubt i want to build a a small device that measures the voltage of my battery bank
i have 6 2v cells connected in series to give ~12v  (~because they can go from 1,75v to 2,45v) and thi is exactly what i want to know.
So with that the voltage i won't need any voltage divider, but my first ideia (stupid one)  was this:


but with this layout i would be adding the cells voltage and at the last one i would have 12v on arduino pin, right ?

so how do i connect all this to arduino so i can read each cell individually ?

regards


fkeel

How about you do some simple math?

subtracting the reading at A4 from the reading at A5 should give you the voltage of battery 6, right?
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

RIDDICK

#2
Jun 18, 2012, 08:24 am Last Edit: Jun 18, 2012, 08:45 am by RIDDICK Reason: 1
ideas:
1. voltage divider in hardware (decreases accuracy) and undoing that division with a program and building differences in software...
2. one attiny per cell (powered by that cell), that talks to the arduino via 2 opto-coupler or some mosfets (with a smaller voltage divider that brings the voltage below Vref=1.1V)
3. 1 mechanical relay per connection (1 for the lowest minus-pole and 1 for each plus pole = 7 relay) that r connected to the arduino, so that the cell to be measured is connected to arduino ground and arduino analog pin
4. idea 3 with each relay substituted by 2 mosfets (p-mosfets should be fine for the plus-pole-relay and n-mosfets for the lowest-minus-pole-relay)...

and warning:
on ur picture it looks like a phat short circuit... dont do that at home...  ;)
-Arne

fca

Hi
@fkeel
that was a way but i would need voltage dividers after the first cell and i would loose accuracy, but so far its the only way i know how to do it..

@Riddick

Your idea 3 confuse-me i can't understand correctly  can you please make drawing or something..

Regards.

fkeel


For simplicity I would use a voltage divider for each channel (set to the same voltage ratio). Your accuracy should not be significantly influenced by that.

p.
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

Graynomad

Quote
i would need voltage dividers after the first cell and i would loose accuracy

After the second cell, but that's not important right now.

What accuracy do you need?

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

RIDDICK

oki - here comes the picture:  :)
http://www0.wgboome.org/idea3.png(i mixed idea #3 and #4)
(the minus pole of B1 must not be connected to arduino's ground)
-Arne

Graynomad

Rob Gray aka the GRAYnomad www.robgray.com

RIDDICK

*sob* why? what does it say? did u type the "0" after the www?   :smiley-eek-blue:
-Arne

Graynomad

I just clicked on the link, then thinking it was a typo tried without the 0, then tried clicking the link again.

But now it works, go figure.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

Graynomad

I think I get what you are doing there.

It's very prone to a magic smoke event if you get the sequence wrong though.

I would be inclined to control the relays with a decoder so there's no chance of the wrong relays being energised at the same time.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

fkeel

"magic smoke event" added to vocabulary.
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

RIDDICK

u can connect the arduino via a 5kOhm resistor and (further) protection diods pointing from ground to the arduino pin and from the arduino pin to +5V...
-Arne

fkeel

seems like an awful lot of hassle, when you could just use voltage dividers...
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

RIDDICK

yes, indeed... but it is a possibility...  especially if u use a long battery chain...  ;)
-Arne

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