Home grown BMS ideas !

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Nevilleh
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Home grown BMS ideas !

Post by Nevilleh » Sat, 12 Feb 2011, 17:12

By the way, I have just used this place:

http://www.seeedstudio.com/depot/fusion ... ?cPath=185

to make some prototype pcbs and I have to say they have done an excellent job. 10 boards for $40 (+postage) is pretty good. Pity about the size limitation, but its amazing what you can get into 100 x 100 when you try. I am thinking to use them for my next BMS iteration which will be a single board for each cell, bolted across the terminals and comms by IR board to board in a daisy chain.

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weber
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Home grown BMS ideas !

Post by weber » Sat, 12 Feb 2011, 18:19

Hi Neville,

Maybe we can pool our efforts. We've already put thousands of hours into our cell-top daisy-chain-comms boards, and it is all open source, open schematic, open artwork. Just Google "celltopbmu" (one word) and you can download the whole package from SourceForge.

We are currently using Protel 99SE for the schematic and artwork, but are considering changing to something else, e.g. KiCad or Eagle. What are you using?

We considered using IR and even RF at one stage, to avoid even the tedious daisy-chain wiring. But we settled on making sets of 8 boards joined together, but with routing so that they are only joined by thin flexible S-shaped pieces. This idea was gratefully copied from Tritium's design. So the wiring requirement is greatly reduced. But you could use our design as a starting point to add IR comms.

The flexible joins also made it practical to run an analog sense wire between boards so we can monitor the voltage drop across the high-current links.

And you needn't worry about Forth. We couldn't fit it and are only using assembler now. You could substitute your favourite processor for ours, but the new MSP430G2432 is looking pretty good, with 8 KB of flash and 256 B of RAM. Our software is pretty refined. That's where most of the hours have gone. We're particularly proud of our bootstrap loader that lets us update the software in all boards at once via the daisy-chain comms. And we're currently working on being able to reset them all by sending a break (hopefully by adding only a diode and a cap to each board). This could be important when they are buried in the bowels of a vehicle.

You can read more and see more photos by going to this page and following some of the later "Battery Management System" links.
viewtopic.php?t=980&start=1

Here they are on some Sky Energy (CALB) 40 Ah cells.

Image
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Nevilleh
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Home grown BMS ideas !

Post by Nevilleh » Sat, 12 Feb 2011, 19:10

Yes, maybe we can. I'll have a look at SourceForge to see what you have done.
I'm now using DesignSpark for pcb and schematic design. Its downloadable from here http://www.designspark.com/pcb
and is free with virtually no limitations, unlike Eagle. Promoted by RS I think. Its able to read/convert Eagle files and libraries and you can generate Gerber files for sending to manufacturers. I am a long way short of expert, but I learnt enough to do a BLDC motor controller schematic and pcb in a longish afternoon. (Boards made by seeedstudio as mentioned above).
Having built my 8-cell per board BMS and connected it to 45 cells, I never want to use wires again! Hence thinking of IR. It'd be silly for me to comment very much further before I look at your design, but I'm thinking of using a PIC micro - they can work down to 1.8V (and up to 5.5), have very low power consumption, UART on board, 10-bit ADC channels and enough memory to do most anything. And less than a couple of dollars each. But I'll go look at yours now!

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Home grown BMS ideas !

Post by Nevilleh » Sat, 12 Feb 2011, 20:07

Do I need to register on SourceForge? I couldn't find any files.

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Post by coulomb » Sat, 12 Feb 2011, 21:38

Nevilleh wrote: Do I need to register on SourceForge? I couldn't find any files.

No, you don't need to register on Sourceforge.

Start here:

http://sourceforge.net/projects/celltopbmu/develop

Oh. I've just realised that we don't have our pretty web page live; you'll have to download the files and read the index.html file.

Or this may work:

http://celltopbmu.svn.sourceforge.net/v ... ision=HEAD

It's the "download" link for the head revision of our index.html file, as checked into the repository. In my Firefox browser, it just displays the web page, complete with images. If it prompts to download, you could try saving it and reading the downloaded page, but I suspect the images won't appear.

The web page needs a little updating, I guess, but it can get you started.

Sorry, because I'm a Sourceforge developer, it's a little tricky for me to see what Sourceforge procedures are like for non-members.

[ Edit: the next step depends on how deep you want to go, and whether you have a subversion client already set up. To skim, go to Code then "SVN Browse". To read about proper subversion access (recommended), go to Code then "SVN". Weber and I find the Tortoise SVN client for Windows particularly convenient. ]

[ Edit 2: Updated web page URL to point to HEAD, rather than 220, which is only the current head. ]
Last edited by coulomb on Mon, 14 Feb 2011, 05:48, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

Nevilleh
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Home grown BMS ideas !

Post by Nevilleh » Mon, 14 Feb 2011, 11:53

Sad to say, still couldn't find any files on SourceForge. But the second link you provided yielded gold and I downloaded the circuit diagram, thanks. I'll have a look and get back to you.

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Post by coulomb » Tue, 17 May 2011, 04:12

weber [url=http://forums.aeva.asn.au/viewtopic.php?t=900&p=11813#p11813 wrote:here[/url]] Here's a sorted list of all the ratios (with factors of 10 ignored) available with the E12 series plus "16". You get much better resolution from the E12 series by adding the single value "16" from the E24 series.

So for example you want a 2.26 ratio. You look down the left hand column of each pair below and find the closest, which is 2.25 (4th from the top in the middle pair of columns) and you see, immediately to the right, that it is obtained by 27 and 12. You then adjust by whatever factors of 10 you need.

I wish I knew how to make columns line up, with this web interface.
I figured this out some months ago. You surround the text with [ FONT=Courier ] and [ /FONT ] (as always, without the spaces).

Like this:

Resistor ratios
1.067     16/15       2.200     22/10       4.556     82/18
1.125     18/16       2.200     33/15       4.615     180/39
1.182     39/33       2.206     150/68      4.667     56/12
1.191     56/47       2.250     27/12       4.681     220/47
1.200     12/10       2.353     160/68      4.700     47/10
1.200     18/15       2.438     39/16       4.756     390/82
1.205     47/39       2.485     82/33       4.821     270/56
1.206     82/68       2.519     68/27       4.848     160/33
1.214     68/56       2.545     56/22       4.853     330/68
1.220     100/82      2.553     120/47      5.125     82/16
1.222     22/18       2.564     100/39      5.455     120/22
1.222     33/27       2.600     39/15       5.455     180/33
1.227     27/22       2.611     47/18       5.467     82/15
1.250     15/12       2.647     180/68      5.556     100/18
1.333     16/12       2.679     150/56      5.556     150/27
1.375     22/16       2.683     220/82      5.600     56/10
1.424     47/33       2.700     27/10       5.641     220/39
1.436     56/39       2.750     33/12       5.667     68/12
1.444     39/27       2.857     160/56      5.732     470/82
1.447     68/47       2.938     47/16       5.735     390/68
1.463     120/82      3.030     100/33      5.745     270/47
1.464     82/56       3.037     82/27       5.893     330/56
1.467     22/15       3.077     120/39      5.926     160/27
1.471     100/68      3.091     68/22       6.250     100/16
1.500     15/10       3.111     56/18       6.667     100/15
1.500     18/12       3.133     47/15       6.667     120/18
1.500     27/18       3.191     150/47      6.667     180/27
1.500     33/22       3.214     180/56      6.667     220/33
1.600     16/10       3.235     220/68      6.800     68/10
1.688     27/16       3.250     39/12       6.818     150/22
1.697     56/33       3.293     270/82      6.829     560/82
1.741     47/27       3.300     33/10       6.833     82/12
1.744     68/39       3.404     160/47      6.912     470/68
1.745     82/47       3.500     56/16       6.923     270/39
1.765     120/68      3.636     120/33      6.964     390/56
1.773     39/22       3.704     100/27      7.021     330/47
1.786     100/56      3.727     82/22       7.273     160/22
1.800     18/10       3.733     56/15       7.500     120/16
1.800     27/15       3.778     68/18       8.000     120/15
1.829     150/82      3.830     180/47      8.148     220/27
1.833     22/12       3.846     150/39      8.182     180/22
1.833     33/18       3.900     39/10       8.182     270/33
1.951     160/82      3.917     47/12       8.200     82/10
2.061     68/33       3.929     220/56      8.235     560/68
2.063     33/16       3.971     270/68      8.293     680/82
2.074     56/27       4.024     330/82      8.298     390/47
2.103     82/39       4.103     160/39      8.333     100/12
2.128     100/47      4.250     68/16       8.333     150/18
2.136     47/22       4.444     120/27      8.393     470/56
2.143     120/56      4.533     68/15       8.462     330/39
2.167     39/18       4.545     100/22      8.889     160/18
2.195     180/82      4.545     150/33      9.375     150/16


It turns out I still had to take out some spaces between columns. When you look at the HTML code generated, the spaces turn into a series of   commands (no break spaces). The number of these commands is significantly less than the number of spaces in the original text, so some truncation happens. It looks like when the number of consecutive spaces is smaller, it doesn't have a chance to screw up as much.

Weird.

I find this table quite useful. Search engines, please take note of these keywords: resistive voltage divider table ratio spreadsheet (this was originally generated from a spreadsheet).

[ Edit: advice on how to convert from a voltage divider ratio to a resistor ratio (just subtract one) is here ]

[ Edit 2: Then again, the above is possibly made completely redundant with this page: Resistor Value and Ratio Calculator ]
Last edited by coulomb on Mon, 16 May 2011, 19:46, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

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