Old BMS General Thread

[retepsnikrep]

Ethan. What is the Euro cost of your 200 cells though? What does the bms come to as a percentage? Peter

[arnolde]

Peter,

Since they are only 10Ah, and I'm really shopping for the cheapest, it will only cost 2000-3000 EUR. I dont expect to go to the moon with it, but 20-30km would be ok.

If it were a 10.000 EUR pack, I wouldnt blink an eye. But having the BMS cost 25 to 33% of the total cost... *shudder*

Ethan

[GregsGarage]

Ethan,

Look at it this way though. The BMS is only 25-33% of your pack price because you are going for a small pack 20-30km range. Probably the right choice to see if it all works without spending too much. But if you later decided to double or triple the size of your pack for more range by adding more cells in parralel you can still use the same BMS and then the cost becomes a smaller percentage of your pack price.

[Cogito]

I realize that you have come a long way but I thought that you might be interested in this link. No optocontrollers needed

http://www.linear.com/designtools/batte ... Qgod7z4Biw

Someone in Norway has just offered a Think car converted to lithium for sale. He wants to buy up others for the same conversion. To capacities on offer. Claims to have adjusted the BMS to cope with lithium charging.
Du you think that anyone here would know about this:Actia BMS and Siadis program on the Siemens motor controller?

This is a money making venture so he won`t share too much. He is part of making the Thor EV, Europes fastest?

Anyway, good luck and I have enjoyed what I can understand on this thread.

[arnolde]

Cogito,

thanks for the link but that is a product that is not available yet. When it becomes available, it will be great, but unfortunately it's not yet.

Regards,
Ethan

[retepsnikrep]

I had a free day today so after tidying the garage I bolted 5 Digital Slaves together and started testing them in a bit more depth whilst I wait for my Battery trays to be made.

The Master was talking to them at 4800baud and calculating Pack voltage (5 Cells) from the data they sent it. My DMM measured 16.77V BMS made it 16.80V within 30mv so pretty pleasing.

www.solarvan.co.uk/bms/VoltageTest.jpg

I then pulled the power jumper off the third slave and it correctly identified that as a "Cell 3 Data Error"

www.solarvan.co.uk/bms/DataError.jpg

Software took a bit of tweaking, but now I have that up and running I can simply copy the tweaked bits into the main Master software.

One of the issues was that the Slaves start up with the outputs in a sort of floating limbo neither high or low, and this caused problems on the Master Data Bus until I added some pull high and low commands.

Oh and I nearly forgot, I fixed that duff first Master Board by replacing the main Pic so it's available.

Nice update Greg glad it's working to plan so far

[Roger Crier]

Could you not use your spare populated master board as part of a redundancy system in the event of a failure......

[retepsnikrep]

Roger, you could but It should not be necessary. I'll flog the spare instead.

Update for today, what happend to the forum/site ealier it went AWOL

I have the Master up and running in a fashion for the first time with the Master software Ha Ha.

It's talking to the slaves and I have my charger connected to the 5 test cells at 200ma just to boost them up a bit.

I added some hystersis to the Digital slaves as well, as they were hunting at the load switch on point.

The comms is working to the Master fine, but the Master software has a shed load of bugs as I expected. The display is working pretty well now, and gives you all the basic info you need, the pack temp sensor and dash buttons inputs also works which is good.

At the moment the Master thinks one of the cells is Over the Abs Max V 3.80v which it isn't, and the data it is recieveing says it isn't, but it still thinks it is, Oh well time to scratch my head, got a + & - mixed up somewhere.

www.solarvan.co.uk/bms/MasterFirstRun.jpg

It's doing something at least, but even the Digital Slaves on their own rapidly balanced the cells to within 50mv of each other which was very pleasing, even with the Master off line. I'm pleased with the Slaves. Just got to finish Master software and wire it all up. Well I've got plenty of time this week to tinker with Master Software. The only tweaking left to do with Slave software is to reduce the delay to the minimum to give maximum pack scanning speed. Must add the decimal points into the display!!

Software versions for the Digital Slaves and Master I have been working on today.

www.solarvan.co.uk/bms/SlaveSimpleDigital_v07.txt

www.solarvan.co.uk/bms/Master110908_v04.txt

[arnolde]

Update: havent finished the layout yet because I am still investigating alternatives, but I have done some calculating and got some prices:

Production of 17 pcs 100x160mm boards with 12 slaves each, incl. mounting & soldering of all the components: 883 EUR (devide by 200 slaves = 4,40 EUR each)

Components for 200 slaves: 2,60 EUR each (from rs-components)

Makes a grand total of 7 EUR per slave, fully industrially made, no sweat (plus 19% VAT)

Peter, are you offering your spare Master for sale? What would you be asking?

Ethan

[wjdennis]

Hi, Peter. I was just reviewing the Master code. If I'm reading it correctly, it issues a gosub to Warning: only when Warnings > 0. But let's say that some warning condition happens and a LED gets turned in in Warning: If the condition then goes away the next time through the MainLoop and Warnings = 0, then Warning: is never called to turn off the LED. Did I see that correctly, or did I misread the code?

Bill Dennis