can bus networks

so I did't own a car for over 10 years or so, used ebikes.
Now getting older and getting back in to ice vehicles.
I find that can bus is used to control just about everything in cars. I had no idea, didn't even know what
a can bus was. I was vaguely aware you could send multiple signals down wires. But now I see the
huge amount of data can be transmitted/recieved and used for control
The issue with ebikes is monitoring battery cells, its the black hole of information in electric cars and ebikes.
So how to monitor lots of cells is very much a work in progress for everyone.
I think can bus will move over to ebikes at least in some simple form, theres too many wires to use cell log type devices.
There would certainly be a market for a simple can bus setup for multiple lithium cells.
Anyhow.....there still remains the real black hole which is how to monitor multiple parallel cells, as far as i'm aware no-one is
doing it, not even tesla, from memory some modules have 23 cells or so in parallel and they are monitored as one cell, thats what
I call a black hole of intormation, the information is just not there, you can get some info from voltages and capacity to predict if there is a bad cell or three, but really there is no detailed monitoring of individual cells.
I often see people saying tesla monitors all the cells, but the reality they dont, no one does as far as I know.
Who will solve this problem ?

whatever said:

the real black hole which is how to monitor multiple parallel cells, as far as i'm aware no-one is doing it, not even tesla, from memory some modules have 23 cells or so in parallel and they are monitored as one cell, thats what I call a black hole of intormation

Click to expand...

Cells in parallel simply **cannot** be monitored independently

without disconnecting them from their group, physically impossible in effect the group becomes a single unit electrically.

Nothing to do with the EV brand, or the comms protocol between mcu and the remote sensors.

If the packs were built so they could easily be "atomized" then the cells could be tested as individuals as a periodic inspection procedure.

But cost of skilled labor in wealthy countries. . .

The real solution will be getting away from tiny cells, just one string of large prismatics, as I believe with the LFP blocks used in the Chinese Teslas.

Seen banks where each cell is over 1000Ah, that greatly simplifies things.

CAN bus is just a communication protocol (and associated interlink hardware specs). There isn't any definition of the information that is sent over it that makes it specifically useful for battery monitoring, or anything else on a bike, etc. The interlink hardware might be a bit more suited to noisy electrical environments than some others.

You can use any communication protocol and hardware to do what you want to do, that is suited for the environment in question.


The stuff that you want to do is already done, to one degree or another, by existing hardware, such as BMSs' you can buy right now (Daly, etc), and controllers you can buy right now, etc. You'd need to develop the central management unit for your specific bike design, that talks to all these things and requests the information you wish to compile and integrate to make the bike operate the way you want it to.


Some OEM systems (bosch, shimano, bionx, etc etc) may even already integrate data from the entire bike (but since it's a locked-down proprietary OEM system, no one outside their developers actually know what all it does). Some of them use CANbus, some use their own comm system, some use other comm standards.



Regarding monitoring individual cells within a parallel group...you're stuck with that, as long as they *are* a parallel group, because if they're wired as one cell, they behave as one cell and can only be monitored as one cell.

To change that, you would need to completely redesign and overcomplicate the pack so that each cell is individually shunted and voltage monitored, with it's own "relays" (of whatever kind) to disconnect it from the pack to test it's separate voltage and other properties under automated control. This will add a relatively huge amount of volume, wiring, cost, and wasted power (to run the additional electronics, and in voltage drops under loads across the "relays") to the pack, for very little information gain in such small packs as are used on small EVs like ebikes.

there still remains the real black hole which is how to monitor multiple parallel cells

Click to expand...

Its basic electrical theory. Cells in parallel act as one cell. Just the same in total resistance of a parallel resistor network.
As its been said, you cannot monitor a single cell in a parallel group unless you disconnect that single cell. Same goes for resistors in parallel.

thanks for replies, very useful and informative.
Yes there is a real issue on how to know what is the health of each cell in a parallel group.
I suspect that some bright spark will work out a way to be able to 'see' each cell even though its still in parallel.
If you say it cant be done..........then someone will do it.
Electricity is a weird beast, I believe someone will work out a way to do it.

As explained it can be done, but only by disconnecting cells from the rest of the group while performing whatever the tests are you want to perform.

Automating that process so that can be done while the pack is in use

pointless IMO, too much complexity, too many points of failure.

Even NASA sending machinery into space

does not see value in trying that, does not decrease but increases the risks of failure.

If **you** really want to, just do it as a scheduled maintenance procedure, manually.

But then, the way packs are constructed, 99.99% cannot do the separation easily.

Absolutely cannot be done without separating, limitation is not human cleverness but the laws of physics

thanks john, yes I am building a pack that is easy to replace cells and monitor temp of all the cells.
But you miss my point: you say it cant be done, I say it can be done without taking the pack apart, I have no doubt there are
many people trying to solve this problem at present, maybe it has already been solved.........who knows?
Yes the law of physics must be obeyed and they will be how the problem is solved.
Lets see if I cant think of someway to do it, however rediculous, just for the heck of it.
What would be valuable information to know:
for example cells voltages at any instant
The electrical signals are being switched on/off quite rapidly its not a constant flow of current, so is there a way to use this
switching to look at each cell, while still connected in parallel?
I dont have a good understanding of how the voltage/current varies over time when current is turned on/off, but there would be some miniscule time delay between each cell. This is just being theoretical here. Thats one way to get info on each cell, that miniscule time delay of voltage rise or decline of each cell could be used ( considering electrical signals transfer at some high proportion of the speed of light its not likely to be a good way to do , but in theory its possible.
There might be another option, going back to the start of the thread was about can bus networks, each network has a terminating resistor so that signals are not reflected back along the wires causing interference. Maybe that could actually be used to gather information on the cells in parallel, maybe sending a particular type of signal ( given frequency etc), that might reflect back off each cell, giving a voltage profile or other information. These sort of signals are in fact used in optic fibres to gather information at a distance. I'm sure there would be some information could be gathered in that way.
So lets not say it just not possible for no particular reason, people will used physics to find a way to monitor parallel cells, there are probably many different ways to do it, which have not been worked out as yet. Or may have been worked out in another field but not applied to this problem as yet.

heres my easy to dissassemble, and easy to feel temp of each cell pack
under construction
( its made of two of these packs, 48v 15ah )
One side has wires that disconnect easily, the other side is flat face of cell,
so that can feel temp with hand easily. Complete pack is made of two of these

It doesn't address the issue of parallel cells being disconnected but does allow the series strings
to be disonnected and a new cell added very quickly

whatever said:

I say it can be done without taking the pack apart

Click to expand...

I never said that!

Just that any **parallel connections between cells** must be opened, in order for any measurement to "see" them as individuals.

Otherwise electrically they **are** one big cell, just like pouring shot glasses of water into a cup.

No one with a clue is trying to overcome THAT "problem".

However that has nothing to do with "taking a pack apart", unless the connections are spot-welded.

So for the **actual** problem - how to test individual cells - the answer is simple. Do not spot weld your pack, and make it easy to separate the paralleled cell groupings.

Or even better, do not connect any cells directly in groups! Put them into modular 1P sub-pack strings at your desired pack-level voltage, and then connect those sub-pack modules in parallel to get to the Ah capacity you need.

Say you want 60Ah total, then using 20Ah cells, you only need 3 strings, only 4 connections need to be opened in order to do your cell-level testing.



> The electrical signals are being switched on/off quite rapidly its not a constant flow of current

No idea what this is about. If you mean while the pack is in use, being discharged

these are not "signal" level currents, but high amp power flowing

> a way to use this switching to look at each cell, while still connected in parallel?

There is no switching going on. And switching **means** between a connected state (closed) an disconnected, isolating the two sides from each other (open).

And no, doing so is going to not just halt the operation, but is expensive, risky, increasing failure risk geometrically with each component added to the system.

Again, there is no good reason to want this during operations - it is a scheduled maintenance procedure while the system is not in use.

> that miniscule time delay of voltage rise or decline of each cell could be used

Accurate voltage measurement for testing/benchmarking purposes require the cell to be isolated, at rest, for at least an hour.


> each network has a terminating resistor so that signals are not reflected back along the wires causing interference.

What "network"? CANbus networks are completely separate from the power circuits, no connection between the two at all!

And again putting resistors, or diodes whatever into either, are going to both interfere with desired operations, and increase failure rates, as above.


> sending a particular type of signal ( given frequency etc), that might reflect back off each cell, giving a voltage profile or other information. … I'm sure there would be some information could be gathered in that way.


You really need to be clear what the overall point is, sounds like you're not sure even what you are wanting to measure, much less why.

What do you mean by "monitor" here?

whatever said:

heres my easy to dissassemble, and easy to feel temp of each cell pack under construction

Click to expand...

Yes temp sensing has nothing to do with the circuits carrying the flowing current, so parallel cells has never presented any issue for that measurement.

Same with cell wall hardness, cell volume and density, shock / vibration, linear distance between the cells, etc

thanks for your feedback john,
I have to disagree after doing some research on what research has been published on testing cells while still connected
in parallel I can say there are many people researching this area, its rather imprortant.
Here is an example, if interested in what research is going on, have a look at the references in the article linked.
https://www.sciencedirect.com/science/article/pii/S0378775316300015

references are at bottom of the article

The differences in current flow within a parallel group leading to uneven cell ageing thus reduced overall pack lifespan is indeed a major issue,

but nothing to do with what I inferred you to be talking about in your OP.

My apologies if that was my mistake.

here is a really detailed article on current flow variations of cells in parallel, I haven't read it in detail as yet, but intend to
will do a synopsis if I have time

https://www.researchgate.net/publication/318308308_Current_Distribution_Measurements_in_Parallel-Connected_Lithium-Ion_Cylindrical_Cells_under_Non-Uniform_Temperature_Conditions