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The Open Source software/hardware corner => General info => Topic started by: RossW on December 04, 2013, 03:04:38 AM

Title: Cell monitoring
Post by: RossW on December 04, 2013, 03:04:38 AM
Not quite sure WHERE this belongs. I didn't want to further disrupt the "Bad Cell" thread. This isn't (yet? ever?) an open source project so may not fit here either, but several of the forum have expressed interest in it.

Had the last of the bits turn up today, late. I only had about 20 minutes spare - but ... well, yeah, I had to do it!

The "first" board - the one that includes the isolated RS232 interface - is my first concern, so I have done it first.
Yes, I rush. Yes, things are crooked. Yes, it still has flux on it. Yes, I haven't soldered all the pins (incase I have to remove the connector during debugging)... but here's the "more or less" finished prototype:

Component side:
(http://house.albury.net.au/04dec2013/100_6113.JPG)

Solder side:
(http://house.albury.net.au/04dec2013/100_6114.JPG)

For scale:
(http://house.albury.net.au/04dec2013/100_6115.JPG)

In what was left of my 20 mins, I hooked up the lab supply and have cranked the input volts from 3V slowly up, watching the supply to the processor and opamp. (Over 5.5V and I'd cook the processor). Hit 5V and stayed there! 10V in, 5.002V out. Perfect.

Hooked more lab supplies to the other cell inputs and the differential amps seem to be working as designed. Looking good.

With the RS232 connected to my laptop, the programming software could see and identify the processor. That was another hurdle passed. And as the phone rang I quickly squirted a 2-line program up. It programmed, verified. Great. All it did was to turn on and off the LED every half a second. But I have a blinky LED! So all the basic bits seem to be working, now I just need to find some time to write the code!!

Stay tuned!
Title: Re: Cell monitoring
Post by: mtdoc on December 04, 2013, 03:47:35 AM
Very cool Ross!  Maybe I missed it, but what exactly are you planning on doing with the PIC (besides blinking LEDs  ;D)?
Title: Re: Cell monitoring
Post by: RossW on December 04, 2013, 04:30:24 AM
Quote from: mtdoc on December 04, 2013, 03:47:35 AM
Very cool Ross!  Maybe I missed it, but what exactly are you planning on doing with the PIC (besides blinking LEDs  ;D)?

OK, the 20c tour....

A small, inexpensive, cascadable board. I'm aiming for under $10/cell.
Each board can monitor 3 cells in a battery. So 2 boards could monitor each cell in a 12V bank. 4 boards for a 24V and 8 boards for 48V.
The boards talk to each other via a simple two-wire daisy-chain cable.
Each board can monitor cells to around 5mV, and sends the information to every other board.
This lets the entire system know what every OTHER cell is doing, and can alert you to an individual cell that is outside a nominal value of everything else. By sharing the information, it automatically takes account of the state of charge of the bank - if it's charging, floating, discharging, almost flat... without you needing to fiddle with it.
An isolated RS232 interface lets you monitor the system for generating alarms, logging, remote monitoring etc.
Each board has an LED which I intend using to indicate "problem" conditions, like which cell(s) are outside limits.
Additionally, I've provided for individual temperature monitors for each cell. So in a system like mine, I will be able to monitor the voltage and temperature of every cell in the bank.

It's designed for nominal 2V cells (lead-acid), but I expect it to work with other chemistry cells, like 1.2V NiCd, and 3V+ lithium cells etc.

I'm really short on time at the moment, so doubt I'll get much code cut in the next couple of weeks, but who knows... stranger things HAVE happened!
Title: Re: Cell monitoring
Post by: Westbranch on December 04, 2013, 05:54:39 PM
If I got it right, you have to go and look at the boards to see just which cell(s) needs attention..?? but the main board will "ring a bell" letting you know that there is a cell amiss?
Title: Re: Cell monitoring
Post by: RossW on December 04, 2013, 06:15:58 PM
Quote from: Westbranch on December 04, 2013, 05:54:39 PM
If I got it right, you have to go and look at the boards to see just which cell(s) needs attention..?? but the main board will "ring a bell" letting you know that there is a cell amiss?

Well, I haven't written the code yet, so it's still somewhat open to discussion!
Lets take a standard 48V battery bank made of 24, 2V cells. We'll call them cells 1 to 24 inclusive. Lets call cell 1 the one thats on the 0V (negative) end and 24 the "high" end at 48V (nominal).

Board 1 will cover cells 1, 2 and 3.
Board 2 will connect to cells 4, 5 and 6.
An interconnect goes between board 1 and 2.
Lets say all the cells are 2.000V +/- 0.05V except for cell 5 which is at 1.85V.
My current plan is that board 2 will blink its LED twice. Pause. Repeat.
Board 1 will be sending out a stream of voltages and temperatures, for every cell in the battery.
The monitoring/logging computer would be able to send an alarm to you based on whatever criteria you choose.

That said, your idea of a beeper/bell/klaxon/whatever to say "SOMETHING needs attention, come look!" is probably worth including and I will contemplate the best way to achieve that. (I do have one spare pin on the processor, but no space to do anything with it! Actually, thats a lie... on the "master" board, I might be able to manage it...)
Title: Re: Cell monitoring
Post by: Westbranch on December 04, 2013, 06:43:46 PM
Ross thanks for the clarification. 

Now know that a monitor CPU is also needed to complete the  "Cell Monitoring System".
Wasn't thinking about the BBP in this app.

Eric
Title: Re: Cell monitoring
Post by: RossW on December 05, 2013, 12:13:27 AM
Quote from: Westbranch on December 04, 2013, 06:43:46 PM
Ross thanks for the clarification. 

Now know that a monitor CPU is also needed to complete the  "Cell Monitoring System".
Wasn't thinking about the BBP in this app.

Eric

Eric: the monitoring machine is intended for *logging*.
The system is intended to "monitor and alarm" by itself.
I'm hoping to get an hour to think about some code later today and have penciled in a "system alarm" mode for the protocol, although I will need a revision-2 board to realise it in operation.
Title: Re: Cell monitoring
Post by: Westbranch on December 05, 2013, 12:26:58 AM
sorry, bad choice of words.

I was thinking it should be a CPU that listens and logs the CMS data stream (broadcast?) at a pre-determined rate, eg. every 30 minutes?. 

Does that make sense?

ps I guess the BBP would work here?
Title: Re: Cell monitoring
Post by: RossW on December 05, 2013, 01:33:16 AM
Quote from: Westbranch on December 05, 2013, 12:26:58 AM
sorry, bad choice of words.

I was thinking it should be a CPU that listens and logs the CMS data stream (broadcast?) at a pre-determined rate, eg. every 30 minutes?. 

Does that make sense?

ps I guess the BBP would work here?

Ahh, yes.  I think you're right.
But I also want it to be useful in its own right as a stand-alone system that could just draw your attention to a sick cell.
In this case, either a beeper or something that can alert you to come look more closely, and each board able to advise you of its own status to drill down to the cell(s) - WITHOUT a computer, is my aim.
Title: Re: Cell monitoring
Post by: vtmaps on December 05, 2013, 02:42:31 AM
Sorry, I may have missed it in the other thread... how do you connect the board to the three cells... does this work only for 2 volt batteries or batteries where the cell interconnects are exposed?

Does the wire from each cell to the board have a fuse?

--vtMaps
Title: Re: Cell monitoring
Post by: RossW on December 05, 2013, 04:30:26 AM
Quote from: vtmaps on December 05, 2013, 02:42:31 AM
Sorry, I may have missed it in the other thread... how do you connect the board to the three cells... does this work only for 2 volt batteries or batteries where the cell interconnects are exposed?

Does the wire from each cell to the board have a fuse?

It's intended for 1.2V (NiCd), 2V (lead-acid) and perhaps 3+V (lithium etc) cells.
Each board has 4 terminals for the batteries. A "0V", "2V", "4V" and "6V" nominal. The absolute maximum is 5V per cell.
I have not included fuses on board but you could easily add them inline. The wires can be almost microscopic. Phone cable is overkill. The device shouldn't take more than a few milliamps at most (when flashing the LED), and some tens of microamps the rest of the time. Inputs drive to a 10K resistor (and then to a differential amplifier), so input current is almost nothing.
Title: Re: Cell monitoring
Post by: atop8918 on December 05, 2013, 05:22:57 AM
That is a sweet little thing, Ross. Excellent work. Congrats!
Title: Re: Cell monitoring
Post by: vtmaps on December 05, 2013, 08:10:50 AM
Quote from: RossW on December 05, 2013, 04:30:26 AM
Quote from: vtmaps on December 05, 2013, 02:42:31 AM
Does the wire from each cell to the board have a fuse?
I have not included fuses on board but you could easily add them inline. The wires can be almost microscopic. Phone cable is overkill. The device shouldn't take more than a few milliamps at most (when flashing the LED), and some tens of microamps the rest of the time. Inputs drive to a 10K resistor (and then to a differential amplifier), so input current is almost nothing.

I understood that (about small wires and low current)... where I was going: Code

I struggle to understand code... are electronics allowed in a battery box?  If not, do the wires to your board run through conduit to a fuse box? etc.  I realize that you are prototyping this for DIY types, and may not attempt to have this be listed equipment.... But I'm extremely inexperienced with (and afraid of) melting wires... what happens to phone cable shorting a battery?  How unsafe is it?

--vtMaps
Title: Re: Cell monitoring
Post by: zoneblue on December 05, 2013, 03:13:08 PM
Nice work Ross.

I too would encourge you to consider how this will connnect to blackbox. I see less value in a LED flashing in a battery room, that you rarely visit. (actually my agms i never visit). Blackbox is where this data belongs.

Ive been thinking about this and have more or less concluded that a arduino type of board paired with an arm board is the best solution. The arduino with its i2c spi, buses  can talk to as many connected devices as we can dream up. Isnt DB9 serial going to limit the number of conections to the number of free uarts ports? Or do you have a some tricky plan in mind?

While rpi, Beaglebone etc have these buses, my thinking is that the arm board focuses on webserver, and the arduino can then use its tiny cpu for realtime bus related stauff, without being bogged by database calls and whatnot.
Title: Re: Cell monitoring
Post by: Westbranch on December 05, 2013, 03:27:10 PM
Ross,  I concur with ZB about a flashing light  not getting observed, often, but also concur about it being a stand alone unit as well.

But I also want it to be useful in its own right as a stand-alone system that could just draw your attention to a sick cell.

It probably depends on what level of Data Junky you are!  A Black Belt wants it all! Everywhere!

Personally I would want a remote beeper and light to annoy me when I am hunkered down in the computer den... ::)
Title: Re: Cell monitoring
Post by: RossW on December 05, 2013, 06:25:52 PM
Quote from: zoneblue on December 05, 2013, 03:13:08 PM
Nice work Ross.

I too would encourge you to consider how this will connnect to blackbox. I see less value in a LED flashing in a battery room, that you rarely visit. (actually my agms i never visit). Blackbox is where this data belongs.

Ive been thinking about this and have more or less concluded that a arduino type of board paired with an arm board is the best solution. The arduino with its i2c spi, buses  can talk to as many connected devices as we can dream up. Isnt DB9 serial going to limit the number of conections to the number of free uarts ports? Or do you have a some tricky plan in mind?

While rpi, Beaglebone etc have these buses, my thinking is that the arm board focuses on webserver, and the arduino can then use its tiny cpu for realtime bus related stauff, without being bogged by database calls and whatnot.

The biggest single issue is that in order to monitor a (lets say) 48V nominal array with lets say, 5mV resolution per cell requires a very significant ADC (being able to measure down to at least 5mV in about 60V). Using a 24 channel MUX puts a lot of demands on it too. And then there's a giant wiring loom and all the problems previously raised.

The next option, using SPI or I2C to talk to a bunch of boards in this application poses problems because all the boards are at different potentials.

Creating a "bigger" system to do it all means each one is specifically for a particular battery configuration. For a 12V bank, you wouldn't use a 24/36/48V system because you'd be wasting most of it. So there would need to be lots of different versions. And if you upgraded from 12 to 24V, or 24 to 48, your old device is rendered useless.

The way I'm doing it, it's stackable and expandable. You only need one point to "talk". At the moment I've chosen to do that via RS232, but it could be via other forms and would be readily connected to the BB project. Remote display heads would also be "trivial" because of the RS232 comms, and because of the isolation very little chance of nasties, ground loops etc.

Lets see if I can get the prototype to do what I want first before we get too anxious!
Title: Re: Cell monitoring
Post by: zoneblue on December 05, 2013, 08:22:57 PM
Quote from: zoneblue on December 05, 2013, 03:13:08 PM
Ive been thinking about this and have more or less concluded that a arduino type of board paired with an arm board is the best solution. The arduino with its i2c spi, buses  can talk to as many connected devices as we can dream up. Isnt DB9 serial going to limit the number of conections to the number of free uarts ports? Or do you have a some tricky plan in mind?

Quote from: RossW on December 05, 2013, 06:25:52 PM
The biggest single issue is that in order to monitor a (lets say) 48V nominal array with lets say, 5mV resolution per cell requires a very significant ADC (being able to measure down to at least 5mV in about 60V). Using a 24 channel MUX puts a lot of demands on it too. And then there's a giant wiring loom and all the problems previously raised.

I Think we are at cross purposes there. I wasnt suggesting that the arduino does the job of your monitor. I see the arduino is a comunications hub of sorts, that talks to various other boards like your battery monitor. An arduino or something built with its processor, is in a better position to do these tasks than {insert random} arm board is. To my mind though it needs to be EASY, a standard conector, and common protocol for all remote devices. We cant have some talking uart, some i2c some spi, or else about 5 of us are the only people that will ever use it.

Will you be able to get all the cell voltages out on serial?
Title: Re: Cell monitoring
Post by: RossW on December 05, 2013, 08:31:34 PM
Quote from: zoneblue on December 05, 2013, 08:22:57 PM
Will you be able to get all the cell voltages out on serial?

My expectation (and what I'm still mulling over in the back of my head) is that you will see a series of lines via RS232, something like this:

V1 2.005
T1 21.2
V2 2.050
T2 21.3
V3 1.990
T3 21.2
.... (repeated with incrementing cell numbers appropriate to bank size)
V24 1.805
T24 21.1
A24
!

The "A24" on the penultimate line is indicative, but says "Cell 24 is in Alarm state". There may be no "A" lines, or multiples.
Title: Re: Cell monitoring
Post by: RossW on December 07, 2013, 02:18:36 AM
Well, the I managed an hour or so today to have a crack at the first rough pass of the code.
Here's the first board with real data out of it. (Connected to a nearly flat 9V transistor battery with a divider string of 1K, 1K2 and 1K to synthesise some sort of cells).

Voltages measured (they were fluctuating) on V1, V2, V3 inputs were:
2.336 V 
5.085 V  (2.749)
7.760 V  (2.675)

Here's the actual display, cut and pasted from the terminal window:


*V01 2.314
T01 23.9
V02 2.761
T02 24.1
V03 2.698
T03 24.1


The bulk of the rest of the code is done and I've so far used 25% of the codespace available to me, so any particular feature requests for me to think about for when I get another hour on it??

Next stop: burn the code into board #2 and cascade them!
Title: Re: Cell monitoring
Post by: boB on December 07, 2013, 06:47:58 PM

Ross, looks like you have one cell that is a bit low ?

boB
Title: Re: Cell monitoring
Post by: RossW on December 07, 2013, 08:12:01 PM
Quote from: boB on December 07, 2013, 06:47:58 PM

Ross, looks like you have one cell that is a bit low ?

Since I was synthesising the cells (as mentioned, by 1K + 1K2 + 1K in series across the inputs), I was AIMING to have an imbalance - you know what testing is like? Three identical readings could be caused by a short on the board, or software reading or writing the same variable etc.

I've just finished populating the first "slave" board and hooked it up. Dumped the code into it and cascaded them, and woot! They're talking!
Title: Re: Cell monitoring
Post by: boB on December 07, 2013, 10:00:51 PM
Quote from: RossW on December 07, 2013, 08:12:01 PM
I was AIMING to have an imbalance - you know what testing is like?


Oh.  OK.  Yes, I do.
Title: Re: Cell monitoring
Post by: RossW on December 12, 2013, 03:49:37 AM
Been working interstate for a few days, but got a couple of hours to work on it again today.
Had a perplexing problem that turned out to be a timing issue. I'm running the processor at its minimum speed of 4MHz (it can go up to 32MHz) - but trying to keep consumption down. In my test configuration of 2 boards, the data was whistling around the ring quicker than the processor could work out what to do with it. Once identified, easily fixed.

So, here's a raw data dump of it running. Still only with "synthesised" inputs of a resistive divider on each of the two boards (two boards is the "worst case" scenario, any more than this just gets easier)


S150
*V01 2.296
T01 0.0
V02 2.728
T02 0.0
V03 2.681
T03 0.0
A01 7.705 2.568 .150
#V04 2.312
T04 0.0
V05 2.697
T05 0.0
V06 2.682
T06 0.0
A04 15.396 2.566 .150
E01
E02
!E04
S101
*V01 2.289
T01 0.0
V02 2.720
T02 0.0
V03 2.672
T03 0.0
A01 7.681 2.560 .101
#V04 2.302
T04 0.0
V05 2.687
T05 0.0
V06 2.672
T06 0.0
A04 15.342 2.557 .101
E01
E02
E03
!E04
E05
E06
S210
V01 2.280
T01 0.0
V02 2.708
T02 0.0
V03 2.663
T03 0.0
A01 7.651 2.550 .210
#V04 2.288
T04 0.0
V05 2.668
T05 0.0
V06 2.653
T06 0.0
A04 15.260 2.543 .210
E01
!E04


You can completely ignore *, # and ! characters. They're just used as flags to identify data phases in the ring.
Basically, I've turned the board on and immediately sent it a "SENSITIVITY 150mV" command.
(I stupidly left unplugged the temperature sensors - they're working perfectly, just not shown here)
The first board has spat out voltages for cell 1, 2 and 3.
The  "A" line is currently a diagnostic line. Says the total of all cells up to the board starting with cell 1, was 7.705V, the average cell voltage is 2.568V, and the sensitivity (from non-volatile memory) is 150mV
The second board then kicked in its offering, with voltages for cell 4, 5 and 6.
Another diagnostic displayed, board starting with cell 4 and we're up to 15.396V, average now of 2.566V per cell.
We have ERROR conditions on cells 1, 2 and 4.  (they are more than 150mV from the system average)

I then changed the threshold to 101mV. This time it's errored on all 6 cells.

Then changed the threshold to 210mV and cells 1 and 4 have errored.

I'm oversampling (reading each A/D channel 16 times, and averaging).
The only code I need to write now is to make each board lampen-blinken to display its alarm/error condition and some overall tidyup. Adding some timeouts so the system can't get hung up in a state waiting for something etc.

I'll be away again over the weekend, but hopefully get a chance to build up some more boards and connect it to my bank and get some real live data.

I also found a source of inexpensive 1% resistors, they should be here tomorrow, and I'll replace the 5% networks with these.

No, I haven't worked out a price yet, still a little early for that - but will be interested in "expressions of interest"!
Who else "can't live without one"?
Title: Re: Cell monitoring
Post by: RossW on December 16, 2013, 05:15:26 AM
Well, it's been a busy week (or however long its been!), but today someone (naughty man!) started throwing money at me, so I've had to make a little time to get some more work done.

I've made up interconnect cables and battery cables for 4 boards and taken 4 of the prototypes out to one of my 48V strings. I've connected cells 1-3, 4-6, 19-21 and 22-24 (being both ends of a 48V string). No magic smoke. All just worked perfectly!

Connected a laptop and there was all the data, just as expected!

I've got some tweeking to do. Mostly in terms of timeouts so it'll recover nicely from one board being disconnected, and although all 12 channels are reporting voltages "pretty close" to actual voltages, I'm going to add an additional function to calibrate them. (I think the only one that was more than 20mV in error was the one using 5% resistors, all the others have 1%) - but still, a calibration pass should make them read pretty much bang on.

Boards are taking slightly more current than I expected at about 2.2mA, so I will be investigating where that's going and what (if anything) I can do to reduce it.

I've left these 4 boards running a "ring test" - basically each board gets the "ring test" token - turns its LED on for 500ms, then turns it off and passes the token on. This will go until either a board resets for some reason, or I  break the ring connection (unplug a cable). It's been going for 3 hrs now and still running, so thats a good sign!

The local store hopes to have more connectors for me by the end of the week, so I can get another 4 boards online and running. Tomorrow, time permitting, I'll at least get these boards logging and see how they trend over time. That could be quite interesting!
Title: Re: Cell monitoring
Post by: Westbranch on December 16, 2013, 12:46:34 PM
Hi Ross, do you have any pics of the boards and connectors, showing a size reference also?  tks
Title: Re: Cell monitoring
Post by: TomW on December 16, 2013, 02:31:46 PM
Quote from: Westbranch on December 16, 2013, 12:46:34 PM
Hi Ross, do you have any pics of the boards and connectors, showing a size reference also?  tks

He posted a few links to such photos over on IRC but I did not bookmark them.

Ahh, found one in my history.

Pretty sure he won't mind if I post it here:

(http://house.albury.net.au/13dec2013/100_6123.JPG)

Tom
Title: Re: Cell monitoring
Post by: Westbranch on December 16, 2013, 03:55:59 PM
didn't see those pics .  I think that is a O zzie  10 cent piece.  think I have one , will check. Nope can't find it...
Title: Re: Cell monitoring
Post by: RossW on December 16, 2013, 04:51:00 PM
Quote from: Westbranch on December 16, 2013, 03:55:59 PM
didn't see those pics .  I think that is a O zzie  10 cent piece.  think I have one , will check. Nope can't find it...

It is, but here's another pic of incomplete boards - purely for scale!

(http://house.albury.net.au/28nov2013/100_6104.JPG)

And the board with isolated RS232 when populated is like this:
(http://house.albury.net.au/04dec2013/100_6115.JPG)
Title: Re: Cell monitoring
Post by: Westbranch on December 16, 2013, 09:00:12 PM
Boy they are tiny... what will you house them in?
Title: Re: Cell monitoring
Post by: RossW on December 16, 2013, 09:18:22 PM
Quote from: Westbranch on December 16, 2013, 09:00:12 PM
Boy they are tiny... what will you house them in?

Matchboxes? :)

I'm not sure. One of my plans was to pot them in epoxy which would make them tough and durable, insulated, and be the case all in one. But I remember my last grand plans for pouring cases and the time it took and the mess the black stuff made!

This morning I was thinking that if I get enough people wanting them, I should go to the "minister of finances" with a business case for a 3D printer  <grin>. Do you think it'd work?
Title: Re: Cell monitoring
Post by: Westbranch on December 16, 2013, 10:25:13 PM
From what I hears on CBC radio today, 3-D printers are about to 'make' the world overnight, again...
http://www.cbc.ca/ideas/episodes/2013/12/06/the-revolution-will-be-extruded/

Very interesting outlook.
Title: Re: Cell monitoring
Post by: RossW on December 22, 2013, 12:42:40 AM
So, I got 8 of these boards connected, finally.
The fact I have a failed cell was the final push - wanted to get some actual data to see what it tells me!

Like many here, I record the battery volts via the classic.
It's useful and told me quite a bit about what was going on.
Looks like this:
(http://general.rossw.net/batterymonitor/bm2.gif)

Clearly, battery volts died quickly around 12:30am resulting in the generator autorunning.

But wouldn't it have been nice to know just what was happening??

Well! Here it is!
(http://general.rossw.net/batterymonitor/bm1.gif)

And here's just the (worst) cell, split out to see:
(http://general.rossw.net/batterymonitor/bm4.gif)
Title: Re: Cell monitoring
Post by: Westbranch on December 22, 2013, 01:03:40 AM
Ross, am I reading things right and see that cell 25 is going bad too? :-[

What happened to cells 8 -24  with min of 0.00?
Title: Re: Cell monitoring
Post by: RossW on December 22, 2013, 01:47:50 AM
Quote from: Westbranch on December 22, 2013, 01:03:40 AM
Ross, am I reading things right and see that cell 25 is going bad too? :-[

Which is cell 25? (I only have 1-24!)

Quote
What happened to cells 8 -24  with min of 0.00?

I built the first two boards (one with the RS232 interface, one without) to work out the code.
I built up two more boards (4, total) and put them on a real live battery string to make sure they did actually work in the environment. 4 boards, monitored 12 cells.
Of course, I did the "top" and "bottom" 12 cells. (1-6 and 18-24). Then, when more connectors came and I was able to complete the last 4 boards I put them in service.
All of the data has intermittent holes in it from where I've been either playing with stuff, or testing various things.
This is what "prototyping" is about <grin>

I also have only 6 temperature sensors connected (3 sensors on each of two boards). It's exactly the same code in each board, so if one works, they should all work.

I'm still adding some software features, so it'll be a bit on and off for a while, but it's basically a working gizmo.

Don't laugh... but here's a picture of how I've set up these test ones. In real use, they'll have lugs to go under the battery terminals - but I didn't want to disturb my setup just to add wires. Hence the clip-leads.
(http://house.albury.net.au/21dec2013/100_6135.JPG)

A possy of 'em!
(http://house.albury.net.au/21dec2013/100_6134.JPG)
Title: Re: Cell monitoring
Post by: Westbranch on December 22, 2013, 01:06:43 PM
Damn bumble fingers, SHB  22

In real use, they'll have lugs to go under the battery terminals

Ya, I had thought about that little issue, lots of dis/re-connecting to do...  do they make lugs that will fit larger bolts and small wire?  18ga?
Title: Re: Cell monitoring
Post by: RossW on December 22, 2013, 02:48:57 PM
Quote from: Westbranch on December 22, 2013, 01:06:43 PM
Damn bumble fingers, SHB  22

In real use, they'll have lugs to go under the battery terminals

Ya, I had thought about that little issue, lots of dis/re-connecting to do...  do they make lugs that will fit larger bolts and small wire?  18ga?

My current thought is that I will use a larger lug and actually put the temperature sensor in it, then fill with thermal epoxy. That way, it'll be one wire for temperature sensing and voltage sensing, overcomes several things in one hit.

But I guess it will depend on what people want or need!
Title: Re: Cell monitoring
Post by: Westbranch on December 22, 2013, 04:40:52 PM
great idea!  ;D

will it matter which post it's on  + or -?
Title: Re: Cell monitoring
Post by: dgd on December 22, 2013, 05:35:41 PM
Quote from: Westbranch on December 05, 2013, 03:27:10 PM
Ross,  I concur with ZB about a flashing light  not getting observed, often, but also concur about it being a stand alone unit as well.

But I also want it to be useful in its own right as a stand-alone system that could just draw your attention to a sick cell.

It probably depends on what level of Data Junky you are!  A Black Belt wants it all! Everywhere!

Personally I would want a remote beeper and light to annoy me when I am hunkered down in the computer den... ::)

Wb,
Hmmm, interesting usage.

I see this monitoring system as just an early warning to prepare for some serious depletion of the bank account. Since there is probably almost nothing one can do to FIX or cure a sick cell no matter how soon you detect its ailing.
Its will die anyway and getting it away from the other cells will hopefully prevent the 'bad apple in a barrel' syndrome.
Leds, lights, bells, whistles, warnings, electric shocks etc not necessary. Happy if it just sent me a soothing email apologising for impending financial poverty.   :)

dgd
Title: Re: Cell monitoring
Post by: RossW on December 22, 2013, 05:56:43 PM
Quote from: dgd on December 22, 2013, 05:35:41 PM
I see this monitoring system as just an early warning to prepare for some serious depletion of the bank account. Since there is probably almost nothing one can do to FIX or cure a sick cell no matter how soon you detect its ailing.
Its will die anyway and getting it away from the other cells will hopefully prevent the 'bad apple is a barrel' syndrome.
Leds, lights, bells, whistles, warnings, electric shocks etc not necessary. Happy if it just sent me a soothing email apologising for impending financial poverty.   :)

I actually disagree. We've been talking this to death in IRC. What it's telling us, what it proves (and disproves) etc.
Since I have AGM cells, the idea of just cooking them hard to equalize like you might FLA isn't an option. But it DOES suggest that a charge-sharing system MIGHT help. Early indications that a cell is getting over (or under) charged - ie, OUT OF BALANCE - means you might be able to give it some remedial attention while it's only "slightly out of balance" before you kill it.
Title: Re: Cell monitoring
Post by: dgd on December 22, 2013, 06:13:50 PM
Quote from: RossW on December 22, 2013, 05:56:43 PM

I actually disagree. We've been talking this to death in IRC. What it's telling us, what it proves (and disproves) etc.
Since I have AGM cells, the idea of just cooking them hard to equalize like you might FLA isn't an option. But it DOES suggest that a charge-sharing system MIGHT help. Early indications that a cell is getting over (or under) charged - ie, OUT OF BALANCE - means you might be able to give it some remedial attention while it's only "slightly out of balance" before you kill it.

Ok, perhaps I'm just too cynical. Having spent too long and been optimistic about recovering 'going bad' cells, just to always be disappointed, I sort of thought that recovery was wishful thinking.
But I defer to your logic as 'out of balance'  and 'remedial attention' before it topples over looks a useful approach to prolonging battery life (in theory!).
And this monitor possibly coupled with a charge sharing system, I assume such as a BMS on LiFePO cells,
looks like a useful tool.
I suppose the trick will be deciding how far the deviation in voltage means starting to need this remedial action.

dgd
Title: Re: Cell monitoring
Post by: RossW on December 22, 2013, 06:26:38 PM
Quote from: dgd on December 22, 2013, 06:13:50 PM
Ok, perhaps I'm just too cynical. Having spent too long and been optimistic about recovering 'going bad' cells, just to always be disappointed, I sort of thought that recovery was wishful thinking.

I agree, once VRLA (SLA, AGM etc) are dead, I don't think you can do anything to bring 'em back.


Quote
But I defer to your logic as 'out of balance'  and 'remedial attention' before it topples over looks a useful approach to prolonging battery life (in theory!).
And this monitor possibly coupled with a charge sharing system, I assume such as a BMS on LiFePO cells,
looks like a useful tool.

That's what we've been talking about (again, in IRC) - ways and means to detect the early signs of imbalance, and then shunt some power around charged cells to give undercharged cells a bit of a lift.

My personal opinion is that LFP (LiFePO4) will explode and catch fire if they're let go too badly out of balance, so everyone uses a BMS because it's mandatory to do so, whereas lead-acid (usually FLA) doesn't do that, and just overcharging (ok, lets give it a funky name 'equalizing') has been the accepted practice. It works well enough, it just became the defacto "standard way to do it". Doesn't mean it's the RIGHT way. But it's largely non-destructive, and certainly cheaper than additional bits.

BUT it doesn't work with sealed cells. I reckon if we payed the same attention to balancing AGM as we are forced to with LFP, then AGM would probably last far far longer and be far less finniky than we're used to.


Quote
I suppose the trick will be deciding how far the deviation in voltage means starting to need this remedial action.

Not enough data (yet) to know, but this project just may be the one to change all that.

Out of curiosity yesterday, I looked at some 16-bit ADC. (that would give around 2mV/cell resolution on a 48V bank).
At over $400 for a 6-channel board, you'd need 4 of them for a 48V bank. Plus a computer. Plus someone to write the software to collect the data and do things with it. I don't see anyone but the real die-hards doing that!

However, if you could monitor every cell in your battery for (lets say) $10/cell, would you? (I reckon lots would)
Title: Re: Cell monitoring
Post by: zoneblue on December 23, 2013, 12:47:55 AM
Cool, great progress Ross. How are you getting the serial data stream out to your network? Or is this still laptop out in shed prototype?
Title: Re: Cell monitoring
Post by: RossW on December 23, 2013, 05:10:20 AM
Quote from: zoneblue on December 23, 2013, 12:47:55 AM
Cool, great progress Ross. How are you getting the serial data stream out to your network? Or is this still laptop out in shed prototype?

An old single-port terminal-server. (Argus TS-1). There are thousands of these sorts of things out gathering dust. Lots don't immediately "look" like they're useful, but they are. Even UPS serial interfaces.
Title: Re: Cell monitoring
Post by: RossW on December 23, 2013, 05:27:48 AM
Quote from: zoneblue on December 23, 2013, 12:47:55 AM
great progress Ross.

Just a quick shot from last night. Ran the genset because we'd had very little sun during the day.
Overnight discharge curve is VERY different... in no small part because I was able to actually see which cell(s) were going to be trouble!

(this is also with now just one, 500AH bank instead of two)
Title: Re: Cell monitoring
Post by: Westbranch on December 23, 2013, 02:23:44 PM
presumably the one with all 12 good cells??  Looks like one could almost identify this set within the other one...
Title: Re: Cell monitoring
Post by: RossW on December 23, 2013, 02:34:49 PM
Quote from: Westbranch on December 23, 2013, 02:23:44 PM
presumably the one with all 12 good cells??  Looks like one could almost identify this set within the other one...

Same bank of 24 cells (48V). But 3 identified "weak or suspect" cells removed and replaced with three cells from my now defunct secondary bank. (Yes, it means I'm now having to make do with 500AH until I seal the deal on the new LFP bank)
Title: Re: Cell monitoring
Post by: offgridQLD on March 26, 2014, 08:58:45 PM
What about just using a product like this  for $27.....

https://www.hobbyking.com/hobbyking/store/__9282__Cell_Log_Cell_Voltage_Monitor_2_8S_Lipo.html (https://www.hobbyking.com/hobbyking/store/__9282__Cell_Log_Cell_Voltage_Monitor_2_8S_Lipo.html)

I have a few of them laying around and have been using them on multiple cell batery projects for years. They have provisions for 8 cells each and can log the data via USB I made up some extension leads for the harness wires to make it a more practical length for larger battery projects , They have a audio alarm for under/over voltage. They can be calibrated and a lot of the setting are user adjustable. Great for a quick visual to of what each cell is doing.

Title: Re: Cell monitoring
Post by: zoneblue on March 26, 2014, 10:50:39 PM
We are all wondering how Ross's new lifepos are going too.
Title: Re: Cell monitoring
Post by: Westbranch on January 22, 2015, 11:18:46 PM
You do want to make sure you do NOT overcharge a cell like this one was (destructive test)
http://gwl-power.tumblr.com/post/70017866727/test-the-winston-lifepo4-cell-160ah-short-circuit
Title: Re: Cell monitoring
Post by: RossW on January 23, 2015, 05:00:41 AM
Quote from: zoneblue on March 26, 2014, 10:50:39 PM
We are all wondering how Ross's new lifepos are going too.

I'm madly saving up to double them and ditch the rest of my lead-acid entirely.

I'm really pleased with their ability to soak up current, how stiff they are, their multiple-poor-days charging performance is.
They're small, light and tight. In short, I've nothing bad to say about them at all.
Title: Re: Cell monitoring
Post by: Westbranch on January 23, 2015, 11:33:19 AM
Ross, have you managed to (really) stress test them yet?
Title: Re: Cell monitoring
Post by: RossW on January 23, 2015, 04:45:59 PM
Quote from: Westbranch on January 23, 2015, 11:33:19 AM
Ross, have you managed to (really) stress test them yet?

Oh boy, you had to ask, didn't you?

19 days ago, my old original inverter @*#& itself at 5:25am.
After operating flawlessly for 10 years and 6 days, it just plain gave up.
Not quite sure of the events however. Piecing what I can back together after the event, the day before we had poor sun, but I thought we'd make it. Daughter had just moved back home after 4 years university, so my guess as to how much power we were going to use may have been a little wide of the mark.

Graphs indicate that some (unknown) additional and non-trivial load applied around 1am, volts started to drop quickly with the cells low SoC, and battery volts got "low" (48V) about 5am. Inverter called for the generator. Genset had run - for exactly 5 minutes. Looks like the inverter had failed to sync, reason unknown. Batteries continued to drop. At (near as I can tell) 43V the inverter shut off and/or died.

43V is about 5V below anything I've ever let them get to. That's down to 2.69V/cell for the LFP.

With a dead inverter/charger, I couldn't even just run the genset to put some charge into them. Was several more hours before I had some sunlight and could divert 100% of that power to the LFP bank.

Managed to get them at least into absorb by that afternoon. A couple of weeks on, and they seem to be behaving exactly the same way they were before the event...

There is no sign of any mechanical issue (bulging) and there was no sign of any significant temperature rise at the time.
Title: Re: Cell monitoring
Post by: ClassicCrazy on January 23, 2015, 06:12:15 PM
Here is where the real battery abusers lurk - on the electric bicycle forums - lots of info
http://endless-sphere.com/forums/viewforum.php?f=14
Title: Re: Cell monitoring
Post by: Westbranch on January 23, 2015, 07:18:38 PM
CC, can you narrow the search for some disaster in waiting for us, or similar discussion to what we are covering?

tks
Title: Re: Cell monitoring
Post by: ClassicCrazy on January 24, 2015, 12:28:42 PM
Quote from: Westbranch on January 23, 2015, 07:18:38 PM
CC, can you narrow the search for some disaster in waiting for us, or similar discussion to what we are covering?

tks

You asked about stressing out Lithium batteries - here are some stress tests done on various chemistries including LiFePo4
http://youtu.be/dree0rTr1HM
Title: Re: Cell monitoring
Post by: Westbranch on January 24, 2015, 01:06:04 PM
Wow, determined, they should call him the destroyer!  :o :o
Title: Re: Cell monitoring
Post by: ClassicCrazy on January 24, 2015, 04:30:39 PM
His goal was to really test Lithium batteries to find out what happens in real world possibilities  - high heat, over voltage, punctures, etc.  Obviously those were extremes but make you really understand that caution is always advised with such high energy sources .
Title: Re: Cell monitoring
Post by: fca on September 03, 2016, 11:58:31 AM
Hi Ross . How does this project boards end up I setting up a new battery bank and I want to add cell monitoring.
Can't find anything ready to buy for leadacid cells . I want exactly what you show, measure single cell voltage and temperature .
Did this work for you, did you sell these boards ?
My goal is to have them connected to board like arduino that than will serve that info by modbus/tcp to my scada app.
Please get in touch .
Regards