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 Author Topic: BMS- battery management system arduino based  (Read 1070 times) 0 Members and 1 Guest are viewing this topic.
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 « on: June 17, 2012, 06:21:15 pm » Bigger Smaller Reset

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

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 « Reply #1 on: June 17, 2012, 07:11:20 pm » Bigger Smaller Reset

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?
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 « Reply #2 on: June 18, 2012, 01:24:48 am » Bigger Smaller Reset

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...
 « Last Edit: June 18, 2012, 01:45:54 am by RIDDICK » Logged

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 « Reply #3 on: June 19, 2012, 07:24:37 am » Bigger Smaller Reset

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.
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 « Reply #4 on: June 19, 2012, 07:43:21 am » Bigger Smaller Reset

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.
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 « Reply #5 on: June 19, 2012, 09:02:48 am » Bigger Smaller Reset

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?

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Rob
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Brunsbüttel, SH, F.Rep.GERM
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 « Reply #6 on: June 19, 2012, 09:05:35 am » Bigger Smaller Reset

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)
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 « Reply #7 on: June 19, 2012, 09:08:03 am » Bigger Smaller Reset

______
Rob
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 « Reply #8 on: June 19, 2012, 09:24:13 am » Bigger Smaller Reset

*sob* why? what does it say? did u type the "0" after the www?
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 « Reply #9 on: June 19, 2012, 09:32:38 am » Bigger Smaller Reset

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.

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Rob
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 « Reply #10 on: June 19, 2012, 09:54:56 am » Bigger Smaller Reset

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
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 « Reply #11 on: June 19, 2012, 11:30:34 am » Bigger Smaller Reset

"magic smoke event" added to vocabulary.
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 « Reply #12 on: June 19, 2012, 02:42:41 pm » Bigger Smaller Reset

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...
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 « Reply #13 on: June 19, 2012, 03:18:04 pm » Bigger Smaller Reset

seems like an awful lot of hassle, when you could just use voltage dividers...
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 « Reply #14 on: June 19, 2012, 03:41:21 pm » Bigger Smaller Reset

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