question

teemischer avatar image
teemischer asked

Maximum Limit of DCL and CCL numbers

I have a rather large battery bank (10584ah with 7200amps of discharge limit) and venus showing wrong values: Something is limiting the numbers shown in CCL and DCL

1720970402915.png

(CCL is zero here because batteries are full, sorry for bad timing of the screenshot)

So the DCL is 3276.7 which is wrong, the correct number should be 7200amps.

(BTW, this number is obviously 2^15=32768 divided by 10)


Something seems to limit this number, it could be:

- Venus OS

- Venus GUI

- CAN BUS encoding

- BMS sending wrong values

Does anybody know where the limit comes from?

How can I dig deeper to find out?

Venus OS
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2 Answers
Alex Pescaru avatar image
Alex Pescaru answered ·

Hi @teemischer

Probably from the BMS / CAN bus messages.

According to the Pylontech protocol, protocol adopted by many manufacturers, the DCL should be encoded on 16 bits with a resolution of 0.1A

So for 7200 amps should be 72000 which is way beyond 16 bits storage. See below.

Alex

bms-ccl.jpg


bms-ccl.jpg (26.1 KiB)
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teemischer avatar image teemischer commented ·

thanks, great insights. I am not running Pylontech though, but the Victron native CANBUS protocol.

Question is: Do I have the limitation in the Victron BMS CAN protocol?

The closet I could find to a documentation is this: https://github.com/Tom-evnut/VEcan/blob/master/VEcan.ino


Also: 0.1 * 2^16 should give me 6553,6 and not 3276.7

Maybe there is another cut-off elsewhere?



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nickdb avatar image nickdb ♦♦ teemischer commented ·

Victron do not publicly publish the BMS CAN spec, it can only be requested via regional managers.

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Alex Pescaru avatar image
Alex Pescaru answered ·

Hi @teemischer

It says 16 bit signed, so from -32768 to +32767.

As for the BMS, the BCV, DCL and CCL are published by the Victron native CANBUS on the same CAN IDs. The BMS CAN bus driver is the same for all batteries.

Below a comparison table:

can-protocol-table.png


can-protocol-table.png (156.6 KiB)
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teemischer avatar image teemischer commented ·

great, thanks, that helps a lot, now I know the answer as to why I am not getting the correct CCL/DCL values into dbus.

Next Question would be: Since I cannot fix the CANBUS part of the problem, what do you suggest would be the best way to get correct values into dbus? I would be happy with fixed values that I manually set.

Possible solution, but not preferred:

I already successfully attempted to write the desired value via "dbus -y SetValue", but it gets overwritten every few seconds. My preferred choice would of course be to avoid running dbus cli commands in an infitie loop so I don't overload the GX device :-)

P.S.: I like the canbus documentation you posted and so I looked for this "Open Solar Energy" project, but googling around did not help much. Who are they and where can I learn more about them?

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Related Resources

Victron Venus OS Open Source intro page

Venus OS GitHub (please do not post to this)