Lithium Battery Monitor 48 cell

Threads relating to the BMS system begun by Peter Perkins

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casemod
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Re: Lithium Battery Monitor 48 cell

Postby casemod » Thu Jan 03, 2013 6:03 pm

dillond666 wrote:Hi casemod,

Glad to see someone playing with my board :D I just noticed I didn't put the schematic in the KiCad files on my webpage so I'll get that fixed :oops:

The current drain on the first three cells is of the order of 0.6mA so I'm not overly worried.
I will be manually balancing periodically (supposedly). I am using 40aH per day from a 100aH pack so I reckon I'm within safe limits.

The dc-dc is probably a more correct solution though from a design point of view.
I tied myself in knots for ages thinking about the startup circuit, thinking there must be a way to do a capacitor isolated circuit. There must be an elegant way but in the end I just went with a way I knew would work.

I'm interested to see any refinements you make to the design, please post your progress on this thread.

Derek

EDIT: uploaded schematic into KiCad files.


Hi Derek,

Its a great circuit. Simle, efective and not dependent on software.
I am looking into a way to implement with greg design as a fail safe, so I can operate each or both.

I am using a 10Ah battery (at 650V), so I would run out of balance much quicker ;)

I did a change to the schematic that will "patch" this - Instead of a permanent voltage regulator zener/resistor I placed the zenner after after the opto coupler. So the idea is it will only drain/regulate if the OC is ON, about 1% of the total time, reducing to uA when the BMS is off.

I am also replacing some of your conectors with USB/Audio ports. This would make for a simple way to interconnect several units and the charger together and droping the relays. Instead a daisy chain signal is sent to the master that should disconect the master contactor if one of the packs reaches LVC or HVC. The charger would also be able to read this in case you take the battery out.

Now one problem I am having... I am new to kicad (Cadsoft Eagle user). I am adding components to the schematic, however they dont revert into the board, I only have the option to start the board from scratch. I would like to keep with my layout routing only the new components. Any advice on this?

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Thu Jan 03, 2013 11:18 pm

When you add the new components to the schematic you have to generate a new netlist.
Then you open the netlist up in CvPcb and associate the desired footprints with the new components and save it.
Then you open Pcbnew and hit the read netlist button. The new components should be there for you to route.

One time I used a schematic component with legs marked 1 2 3 with a footprint with legs marked a b c. It didn't work!
It required an adjustment to be made using the module editor. Just a little pitfall to be aware of! To an Eagle
user this method may appear cumbersome but it's pretty flexible.

Good idea with the zener, I knew it'd be simple :)

Derek

casemod
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Joined: Mon Dec 17, 2012 3:18 am

Re: Lithium Battery Monitor 48 cell

Postby casemod » Thu Jan 24, 2013 11:40 am

Ouch...! Thanks

I am making modifications on your board and was wondering if I can feed the picaxe with 3v3?
I plan to do charger identification by reading of input voltage (5V = Car BMS, 12V = Charger). The 5V need to be regulated still, so the most I have is like 4V, so working with 3v3 would be ideal.

What exactly makes the difference when the charger is identified? Shouldnt the board stop anyway if HVC is reached?

Any change to add a disable charge if the temperature goes below 1C and over 50C?

Regards

casemod
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Re: Lithium Battery Monitor 48 cell

Postby casemod » Thu Jan 24, 2013 6:14 pm

Me again :twisted:

Revised questions,

I believe the charger circuit only operates when the charger input is high, am I right?
If so will it enable the relay all the time the charger is suposed to be on and go off once the charge is completed?

I also believe that the Alarm output indicates both HVC and LVC (single wire).

Also, will the alarm output be low until either LVC or HVC are met? or it does go high all the time and only goes low at LVC/HVC?

Thanks

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Fri Jan 25, 2013 12:47 pm

Hi,

There are no spare pins to do a temperature input as I recall but I'd need to check though.
I do like the idea of the temp check. I only charge after a hard drive when the weather is really cold as that ensures the cells are not too cold. There is a risk however that the charge can complete and then 8hrs later it automatically attempts to charge the now too cold battery pack. The firmware could be changed to disable this feature though.

The Picaxe 08M2 can operate down to 1.8v. but I am unclear why you want to identify the charger by reading a voltage. It won't save you any pins and seems a little overcomplicated.

"What exactly makes the difference when the charger is identified? Shouldn't the board stop anyway if HVC is reached?"
The charger side of the firmware only comes into play when the power is supplied to the charge power input on the BMS (detected using the opto). The Picaxe knows it's in charge mode so when the heartbeat signal from the Maxim chips is not present the Picaxe knows that the cell voltage is too high and disables the charger relay.

"I also believe that the Alarm output indicates both HVC and LVC (single wire)."
Correct.

"Also, will the alarm output be low until either LVC or HVC are met?"
Yes (unless it is chirping to let you know what mode it's in)

Just to clarify, when I am charging, the 12v power to the BMS comes from a laptop PSU that is connected to the 240v input on the charger. When I am driving the 12v input comes from the car dc-dc converter. That's why there are two separate diode isolated power inputs on the board and the opto to tell the Picaxe what mode to be in.

Derek

casemod
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Joined: Mon Dec 17, 2012 3:18 am

Re: Lithium Battery Monitor 48 cell

Postby casemod » Sat Jan 26, 2013 2:49 am

Many thanks. I am just wondering why 2 relays for the charger then, the Alarm relay could also control the charger, or is it a special feature on the charger relay, like do not allow to continue charging after the BMS has cut the first time?

As with temperature my issue is Regeneration. My wife does night shits and she drives with -5 and below very often. I don't want my batteries taking 15KW of power at those temperatures, instead it would be more logical to divert power to a heater.

I have done the new PCB however cant get all the footprints on the board and now the JAVA auto-router isn't working... I think I am just going to send the PCB I posted before until i get this thing sorted ;(

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Mon Jan 28, 2013 11:09 am

"I am just wondering why 2 relays for the charger"

One of the relays controls the charger on/off on my Zivan charger.
The other relay is used to switch on the alarm buzzer, which beeps on
low cell voltage and beeps at "switch on" to tell you whether you're in
charge mode or drive mode.

I don't use the autorouter on KiCad, it's easier to do it all manually.

"My wife does night shits"

How unfortunate for you!.......mine just talks sh*t :lol:

Derek

casemod
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Re: Lithium Battery Monitor 48 cell

Postby casemod » Fri Feb 08, 2013 11:53 pm

He he he... The usual, just let them talk :mrgreen:

No wonder you do it by hand, it ends up being easier. Is a good software but still has a lot to go!
I ordered the version I posted on the forum before. My boards are somewhere between here and china now lol.

I just "finished" the car. Failed MOT.
Why? Because the power steering was "inadequately" modified. I bippassed the rack to work as a manual, how serious that is :twisted:

Doing a fully electric PS now. I hope I dont need to put a dummy hydraulic pump on there now. :lol:

GregsGarage
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Re: Lithium Battery Monitor 48 cell

Postby GregsGarage » Sat Feb 09, 2013 1:27 pm

casemod wrote:I just "finished" the car. Failed MOT.
Why? Because the power steering was "inadequately" modified. I bippassed the rack to work as a manual, how serious that is :twisted:


My car is fully covered underneath for aerodynamics. Keeps the MOT man from looking too closely. :twisted:
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

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dillond666
Posts: 139
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Location: Central Scotland

Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Sun Feb 10, 2013 12:37 pm

I had been toying with doing a BMW Z3 conversion. I identified the power steering as a potential nuisance, so I
ordered an electric hydraulic pump from a Vauxhall Astra on Ebay just for a little tinker. I have not received it yet
as the seller is shockingly inept. It might be a possible avenue for you to explore?


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