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Author Topic: my first big project - BMS - is it possible?  (Read 9865 times)
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Scooter?!? What the ... Okay, I never opened that link, thought we talking a car.
Anyway, whole thing could fit on three 80mmx80mm PCBs, so not too big.
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In a link, I posted above, data sheet for MAX11068. I didn't look myself earlier, 82 pages...., yet now I get curious and open it. It took a moment to find out on page 10 all analog front end in full details, plus a lot of useful information.
 Instead of electromechanical relay - MOSFET multiplexer. The same company produce a chips, high voltage mux, MAX378/379.
http://www.maxim-ic.com/datasheet/index.mvp/id/1085
It's not 150V, but could be other producers/manufacturers. Or just one ! electromechanical  relay to switch a half battery.

 It never hurt to study/research first what is already exist on a market, instead of inventing a bike. smiley



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A Mux doesn't give you the detailed voltage needed for ech battery.
You need contacts across each battery with ground isolated from the string of battery ground so that the arduino 5V input limit is not exceeded.
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Yes, I understand.
There is quote :
Quote
The MAX378 8-channel single-ended (1-of-8) multiplexer
and the MAX379 4-channel differential (2-of-8) multiplexer
Looks like this "differential" is a key, one channel - input, another - commutate a ground. It's all shown on page 10.
Exactly like you try to design it.
 And I just dig up one create on their web site: MAX4800, 8x - 200V switch.
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I had some reading to do to understand what you guys are talking about smiley

Crossroads; I understand your scematic, and it makes sense to me.

From what I understand from the rest, I derive that the other chips wouldn't need the relays, because they switch like a transistor (or Mosfet?). correct?

The part I don't understand, is the high voltage issue; I thought, though they are in series, if every cell is connected (with both poles) separately (like measuring them one after another with a voltmeter) the maximum voltage involved should be 1,4 V -or- the voltage of one cell?
Or am I wrong when I assume that? Or missing something?

sorry if my questions seem stupid.. I'm learing a lot here.

Turok
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High voltage: With the relays, yes, each relay would only have its batteries voltage only, thus no high voltage. The arduino and its relay coil controls and relay select logic will have its ground at the -terminal of the battery being measured.

I am not convinced the mux will work. You will need a series of the chips. They will all need a common Ground, which will connect to the arduino ground, for the arduino to be able to control them.  Then once you get past battery 3,  you have a higher voltage on the battery (5.6 on battery 4)  than the arduino can read.

To handle the higher voltages as go you higher up in battery voltage (with respect to the mux ground), you will need higher power supply voltages (and the spec seemed to show you need both a very +supply and a very low -supply:
"The MAX4800/MAX4801/MAX4802 allow a peak-to peak analog signal range from VNN + 10V to VPP - 10V."

For batteries 1-8, you will have 11.2V.
Then 9-16 will have 22.4.
17-23, 33.6
24-31, 44.8
32-39, 56
40-47, 67.2
48-55, 78.4
56-63, 89.6
64-71, 90.8
72-79. 102
80-87, 113.2
88-95, 124.4
96-103, 135.6

(should be 142.8, missed a couple tenths somewhere).

so VNN must be at least -10V and VBB must be > 152.8V, with respect to battery system ground.

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edited: read next posts O'K, you are right. I didn't notice that analog +-10V limits, been happy to see +200V max voltage.
And also couldn't find any multiplexer, that operate higher than 80V. It's strange. smiley-confuse
The only couple "improvements" I'd suggest, it replace electromechanical relay  on solid state, that will minimize space and increase speed of the "homemade" mux front-end.
 And second, opto-isolate  analog input of the arduino, so processor or "core" would be on ground safe level, capable do other stuff - monitor some additional sensors, display info on LCD and take some commands from control panel or serial link. In order to do it, build a "floating" board, that would include own dc/dc convertor and analog opto-coupler that shown on:
http://ruggedcircuits.com/html/circuit__24.html
or
http://www.vishay.com/docs/83708/appn50.pdf

There is a SSR:
http://www.vishay.com/solid-state-relays/
 
« Last Edit: July 25, 2011, 12:07:31 am by Magician » Logged

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Is there are double version of an SSR? Otherwise you are replacing a 10-pin device with the equivalent of a 12-pin device, and I am not sure 2 of these would fit next to each other in a 12-pin socket even. 2 parts would be 17.4mm long. 
I think the parts I suggested originally were 9mmx14mm,126mm^2, vs 132.5mm^2 for 2 SS relays.

turok, what are you thinking in terms of other sensors, a display etc?
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You suggested Panasonic, it's only for:
Quote
110 V DC, 125 V AC
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From Farnell link that I posted in Reply #7, the only relay I posted:

Coil Voltage VDC Nom:5V
Contact Current Max:2A  <<< 2A
Contact Voltage AC Nom:125V
Contact Voltage DC Nom:30V  <<< 30V DC
Coil Resistance:250ohm
Contact Configuration:DPDT
Coil Type:DC, Sensitive
Coil Current:20mA
Nom Operating Power:70mW
Relay Mounting:PCB
External Height:5.4mm
External Width:14mm  <<< 14 mm long
External Depth:9mm  <<< 9mm wide

« Last Edit: July 24, 2011, 11:15:55 pm by CrossRoads » Logged

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Quote
The LH1513 relays are DPST normally open switches
(2 form A) that can replace electromechanical relays in many
applications
And price only $2.79*

edited:
compare to
Quote
Prijs per Eenheid:  3,59 € 
« Last Edit: July 24, 2011, 11:32:12 pm by Magician » Logged

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Yeah, okay, those might work well.

But check the Farnell price for Belgium!
http://be.farnell.com/jsp/search/browse.jsp;jsessionid=PV2ZSN41GJJCACQLCIRJN4Q?N=0&Ntk=gensearch&Ntt=lh1513&Ntx=mode+matchallpartial&suggestions=false&ref=globalsearch&_requestid=24479

5,14 Euros for Qty 100+

compared to 3.59 Euros for Qty 1 relay.

Now, since this is for a motorbike/scooter, the SSR might make much better sense.
Why not keep searching, see if some other more reasonably priced alternative can be found.
« Last Edit: July 24, 2011, 11:55:30 pm by CrossRoads » Logged

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It's for OP to look in details, I just satisfy my curiosity  smiley
BTW, MAX4800 will works, I get confused with analog voltage, but when I re-check again:
Quote
Analog Switch
The devices allow a peak-to-peak analog-signal range
from VNN + 10V to VPP - 10V. Analog switch inputs
must be unconnected, or satisfy V NN ≤ (V COM_ ,
VNO_) ≤ VPP during power-up and power-down.

It's mean if we set VNN to -10, and VPP to 190V
Quote
The V PP and V NN high-voltage supplies are not
required to be symmetrical, but the voltage difference
VPP - VNN must not exceed 200V.
Analog switching range would be 0 - 180 V. 
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I don't think MAX4800 will work - as I said earlier, its Gnd must be at Arduino Gnd for channel selection controls to work - and then you will have >5V coming out of the mux going to the Arduinio, which will smoke the arduino.
Not to mention extra components to create <=10V and >=152.8V from wherever.
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Of course, it will works only with "floating" opto-analog boards, that I mention as second improvement somewhere earlier.
 Advantage to go for this switch is high timing performance,   I really impressed by 107 us check-up time for 12 cell battery by MAX11068,  = 9 us per cell !
It capable get dynamic cells data, when battery extra loaded by starter motor and internal resistance of cell show up in bright light on stage.
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