Old BMS General Thread

Threads relating to the BMS system begun by Peter Perkins

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dillond666
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Program editor

Postby dillond666 » Sun Jul 13, 2008 3:49 pm

I.ve got the program editor but unfortunately I can't use wine to run it on my linux computer. This means I must torture myself by installing windows on my old computer :roll:
The data bus error was an easy one to miss, but I suppose a little jiggery pokery with the interconnecting leads would have fixed it if it had gone to PCB.
I had a quick look for current sensors (coulomb counting would be nice) but it seems if you need up to 500A then the resolution might not be too good (my zilla z1k has a 500A fuse in it). Luckily with lead acid, voltage is a better indication of SOC than it is with Lithium so that's a refinement for the future in my case :)

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retepsnikrep
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Postby retepsnikrep » Mon Jul 14, 2008 5:22 am

Started to add Master Hardware Background PWM code, this controls the Charger and Controller Cutback function by driving the cutback optos. Sorted a few other annoying mistakes. :roll:

www.solarvan.co.uk/Master140708.txt
www.solarvan.co.uk/Master140708.jpg

www.solarvan.co.uk/Slave140708.txt
www.solarvan.co.uk/Slave140708.jpg

Hope to finish Slave pcb this week and send off for manufacturing. Any reccomendations for a pcb maker and an initial run of 100 slave boards?

I have been thinking about one of the online Chinese sweatshop boys :shock:

http://www.pcbcart.com/cart.php

I tried the quote procedure for the one above and 100 Slave board cost came out at about £1.00 each! Pretty good I thought. 15 day lead time.

Cheaper next time round as don't have initial tooling costs. 8)
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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retepsnikrep
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Doesn't look mutch

Postby retepsnikrep » Mon Jul 14, 2008 8:36 am

Image

Been running this prototype on the bench for a couple of weeks now.

On left at bottom is a Picaxe 18X I'm using for testing with a simple program that basically is pinging the slave/s and receives the data over the opto isolated bus, displays the Cell Voltage and Pack Voltage on the LCD display which will eventually be Dashmounted on the finished systems.

The board on the right is a Slave connected to one of my old TS 200ah cells out of shot. It does not have the balancing fuction on this board as this is just a data transmission testing rig. It's working out the voltage of the cell pretty well and transmiting it to the Master. Accuracy looks like +/- 30mv over the working range according to my MM. :)
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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EVguru
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Postby EVguru » Mon Jul 14, 2008 10:01 pm

When I was working on a lead acid monitoring system, I found that a 10mv resolution per 12v block was useful. A problem I had was corrupted readings due to using opto-isolators with an insuficient common mode di/dt rating. EVs are a very challenging electricl enviroment from an EMC point of view.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

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dillond666
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agm slave

Postby dillond666 » Mon Jul 14, 2008 11:19 pm

I've been playing with schematic software (1st time) and can share my rather poor efforts. Borrowing very heavily from Peter, I have tweaked things to be suitable for monitoring 12v agm's I hope. I have not filled in the values of most of the components yet, and I had to use a PIC for the diagram, but hey......I'm a mechanical fitter not a boffin.

http://www.dillond1.pwp.blueyonder.co.uk/slavething.png

:wink:

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retepsnikrep
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Postby retepsnikrep » Tue Jul 15, 2008 4:53 am

Paul

Interesting, luckiliy my system is quite SLOOOWWW 2400baud I'll just have to suck it and see if the that causes a problem. I can change to any suitable standard 4 pin dip opto in the catalogue. I would like 16 bit resolution but can't get it so have to use 10bit :( I think that's good enough.

Dillion

Good effort, but what's the bottom opto for?

You can't drive the interrupt opto of the next slave with that unless you introduce some power. Mine powers the next opto if you look at the schematic. The slave to slave isolation is provided by that top interrupt input opto and the data bus opto's.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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dillond666
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oops

Postby dillond666 » Tue Jul 15, 2008 8:06 am

You can't drive the interrupt opto of the next slave with that unless you introduce some power. Mine powers the next opto if you look at the schematic.


You are correct of course Peter, It just hadn't clicked! I understand now.

common mode di/dt rating.


Perhaps EVguru could briefly (and in simple terms) explain what this means and the implications for the proposed design?

Every day is a schoolday for me :lol:

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retepsnikrep
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Postby retepsnikrep » Tue Jul 15, 2008 8:49 am

Dillon

IMO You need a pull down resistor (100k) on the gate of the logic level FET you are using to switch on the load, this ensures it is turned hard off. leakage current through Pic may result in it being partly on if you don't .

I am considering using a Logic level fet as well, haven't decided yet :roll:

I am concerned about noise/spikes etc from the EMI rich electrical environment of an EV causing the Cell Pics to lock up. So I may well add some extra filtering and some noise supression.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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dillond666
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fixed I hope

Postby dillond666 » Tue Jul 15, 2008 5:05 pm

Peter

I have updated my drawing including the pulldown resistor on the logic level FET(floating pins not good). I have included a 100uf electrolytic capacitor and a varistor to clamp any voltage spikes, is this roughly what you had in mind? Here is the link to the varistor

http://www.rapidonline.com/Electronic-C ... tors/64510

and my drawing

http://www.dillond1.pwp.blueyonder.co.uk/slavething.png

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retepsnikrep
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Noise

Postby retepsnikrep » Wed Jul 16, 2008 4:56 am

The Varistor is quite a good idea for your circuit as it will be running off 12V AGM's. Need to choose right voltage to allow max charge but cut anything spikey above that. The fact your PIC is behind a regulator and caps anyway will probably suffice.

My Pic is connected straight to the cells :shock:

I'm thinking more about an RC filter. But I'm open to ideas :wink:

http://en.wikipedia.org/wiki/Electronic ... ve_filters

In the Honda Insight IMA Motor as an example we have a 3 phase dc motor with commutation frequency of 0-600hz approx, on top of which is a PWM power frequency at say 15-20khz, + all the lovely harmonics :shock: It's an electrical high current noise nightmare.

I was thinking of a low and high pass RC filters to experiment with, I'll leave a few holes on my pcb to add filters. Also some inductor/capacitor filters might also help. Have to suck it and see. Filtering is a bit of a dark art IMO.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.


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