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Old 12-06-2011, 04:35 PM   #61 (permalink)
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A big thank you to Mark for adding the files to the wiki. It all looks pretty good!
There is one change I made recently that is not shown on those files and that is the value of R7 on the controller is reduced from 2k7 to 2k2 to give slightly better performance with the received comms. It'll still work with 2k7 but the noise immunity is improved a bit (!) with the lower value.

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Old 12-06-2011, 10:27 PM   #62 (permalink)
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Quote:
Originally Posted by harlequin2 View Post
R7 on the controller is reduced from 2k7 to 2k2 to give slightly better performance with the received comms. It'll still work with 2k7 but the noise immunity is improved a bit (!) with the lower value.
I corrected the CellTop Master BOM (2k2) R7.

-Mark
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Old 02-05-2012, 07:17 PM   #63 (permalink)
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BMS + SOC meter

Quote:
Originally Posted by harlequin2 View Post
For anyone interested in building this, the relevant files should appear on the wiki soon. Its fairly straightforward, but does use all smd parts, so if you haven't worked with these before, bite the bullet and get into it! I reckon smd's are easier to assemble than thru-hole parts, once you get the hang of it.
I do have pcbs available and also can supply them with the micros mounted and programmed if you wish. Send me a PM if interested, although all the info needed to make your own is included.
A quick overview:
Each cell has its own module which bolts directly to its terminals. These modules use a PIC micro to measure the cell voltage and temperature, and the have a 6R8 shunt which can be turned on or off for balancing. The controller talks to all of the modules via a "daisy-chain" comms link and collects voltage and temperature data. It displays the max and min values on a LCD and also the total battery voltage. It also controls cell balancing via the shunts and by controlling the charger.
Have at it!
Hi

I am very interested in building your BMS, but i would like to add SOC meter for measuring current in/out of battery. That means putting shunt or hall probe on battery main cable as well as charger port input cable. That way i would know how much current passed in/out of battery at all times. Could that be done on your main board and LCD as they are? Ie, only adding some componnents and two ammeter plugs...
The problem is i have an idea, but i am mechanical engineer, not electrical. I have basic knowledge on PCB assembly, but not circuit design. Could you help me? And the rest of EV world .

TNX

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Old 02-05-2012, 08:23 PM   #64 (permalink)
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Yes, one of the reasons that I didn't add current monitoring is that Freyguy's LCD meter thing does all that and I had already built one of those.
It would be easy to add current monitoring, but working out SOC is not quite so easy - but if I stick with Li cells and consequently ignore Peukert, it would work OK.
I'll have a look into what is involved.
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Old 02-06-2012, 09:17 AM   #65 (permalink)
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yes that would be great!

Anyway i taught about measuring LIFePo cells and current from/to batteries (one sensor) and additional sensor for logging current from charger. The equation would have to deal absolute values. Adding negative attribute when current goes from battery and + when there is flow to the battery (regen and charge). Some RTC timing chip would set pace. The process would have to be continuous. Always measuring current and displaying %SOC left. So a reference has to be set. I would propose to use bottom balancing as a stage point. That way you would have 0% SOC and still some juice left for emergency crawling home.

You could just program some exponent variable koeff to account for peukert. Some assumption will be necessary though, even for LiFePo (they have some Peukert too though very small).

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Old 11-05-2012, 10:16 PM   #66 (permalink)
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Hi
Where can I find source code and schematics for the master board
Thanks
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Old 11-05-2012, 10:38 PM   #67 (permalink)
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Quote:
Originally Posted by mshalash View Post
Hi
Where can I find source code and schematics for the master board
Thanks
They are on the open source web site, but if you send me a private message with your email address I'll send you the latest files and comments.
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Old 01-06-2013, 03:41 PM   #68 (permalink)
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Hi harlequin2!

This is great work on a simple BMS. Also a big thanks to you and sawickm (Mark) for putting this all on the Wiki!

I am woking on a project using 12v AGM 15ah batteries for a little scooter. I would love to use this design and see it added to the Wiki for a 12v lead AGM option. Seems that this application could be scaled up to any AGM / SLA (ah amount) series string amount.

You mentioned in one of your posts that all would need to be done is modifying the software in the PIC. Am I wrong but would you not also need a voltage divider on the input to scale from lets say 20v down to 5v to protect the PIC? The charts I have checked out for charging AGM's their CV is around 14.5 - 14.8 volts while the charging amps taper off.

I would love to be apart of making this happen if I can. You all have done some awesome work!

Doug
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Old 01-06-2013, 03:53 PM   #69 (permalink)
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What I had in mind when making that comment about only needing a s/w mod was connecting each module to a single PbA cell ie 2.2 V. The PIC chips work down to 1.8V.
To connect it to a 12 V battery, you would definitely need to drop the voltage down. Dividing by 3 would do it - it only draws a milliamp -and you would need to change the shunt configuration.
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Old 01-06-2013, 05:12 PM   #70 (permalink)
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Wow! Thanks for the quick reply. Okay, this makes sense in regards to dividing the input voltage and the shunt resistors. I am thinking dividing the input voltage by 4. Most AGM's operating range including charging is from 11v to 15v. So, this gives a range once divide of 2.75 to 3.75. Perfect for the operating range of the pic on your BMS!

The shunt resistors are two in series and then parallel? Looks like 1 amp per series string of resistors as the board has ~2 amps of shunting capability? I might be looking at that wrong....

What program are you using to make the schematics. They are *.gbr files on the wiki. I have some time right now so thought I could work on this.

Doug

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