# Lithium Battery Monitor



## Voltswagen (Nov 13, 2008)

Here is a link to a hobby site offering an inexpensive BMS.
Once I receive my TS 160's I may purchase one of these to test.
I would be particularily interested in the High and Low voltage alarm capability.
The hobby industry has many years of experience working with Lithiums.
It may or may not be a viable option.
Whaddya think?



http://www.hobbycity.com/hobbycity/..._Name=Cell-Log_Cell_Voltage_Monitor_2-8S_Lipo


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## dexion (Aug 22, 2009)

Quite a bit of discussion about this on the thundersky yahoo forums (and I thought here but I guess not.) 

This is a variation on my watch the shortest cell theme. Now you get to watch 8 of your shortest cells with alarms and logging etc. I figured I would snag one as well along with the harness in one of the TS yahoo threads available on ebay. This device does not come with a harness or even an adaptor to wire one in. Just the mail side you see on the pic. Not a big deal but something to be aware of.

This one is a real cheapy I cant say for sure fits:

http://cgi.ebay.com/3pcs-8S-Lipo-balancer-cable-22AWG-silicone-wire-20cm_W0QQitemZ150394679474QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item230438b0b2

Aparently they guy that posted this one uses it with his cell logger 8.
http://cgi.ebay.com/Chargery-Power-DB8-8S-40cm-Balance-Charge-Leads_W0QQitemZ270\
470253072QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item3ef9488a10

I like the second one its more turn key but it is more $.

Im just not sure what I want to do with the alarm output. A buzzer I suppose or a divider for my pot input or both. I dont plan to ever get close to 80% dod my pack is two times what I need on a daily drive so I guess aside from a problem (loose connection, bad cell etc) I wont get to the lvc point but its nice to know quickly (pre-smoke stage) theres a problem.


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## Voltswagen (Nov 13, 2008)

Dexion
It appears the item in the second link has been removed. Can you find it anywhere else?


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## dexion (Aug 22, 2009)

odd still works for me but I was there before perhaps its cached.

http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=Chargery

use that its down near the middle its $13

Remember to do something with those bullet connectors you dont need them in this application. Cover them cut them off etc.


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## Voltswagen (Nov 13, 2008)

OK thanks.


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## major (Apr 4, 2008)

Voltswagen said:


> Whaddya think?
> 
> http://www.hobbycity.com/hobbycity/..._Name=Cell-Log_Cell_Voltage_Monitor_2-8S_Lipo


Hey Volts,

I thought it looked interesting so I bought 2. They arrived a few days ago. I just ordered the plugs and wire to make the harness. Intend to wire the 2 units to a 14 cell battery which I will test. I heard that if you use more than a single unit on a series string of cells that you have to unplug them from the cells before connecting to the computer or you create a ground loop. Cheap enough to give it a try. 

Too bad the channel voltage limit is only like 5V. It would be nice to use on 6 or 12V batteries also.

Regards,

major


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## Voltswagen (Nov 13, 2008)

Hey Major
How about the harness Dexion posted?
Let us know your results. Thanks for responding.

Roy


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## major (Apr 4, 2008)

Voltswagen said:


> Hey Major
> How about the harness Dexion posted?
> Let us know your results. Thanks for responding.
> 
> Roy


Hi Roy,

I ordered the plugs, pins and wire from DigiKey to make my own. That way I get the lead length what I want. I think I have a crimp tool that will work. I looked briefly at the eBay things and they appear to use the same JST plug.

Also, making my own wire sets should enable me to install the wires on several batteries and move the CellLogs from one to the other with ease.

Hopefully I can get the things wired next week and do some tests. I don't see that as a big challenge for me, but the data logging, transfer to computer and that side of it will likely give me fits. The manual looks pretty good, but I always seem to fumble up the keystrokes or something on these darn computers. 

Regards,

major


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## tomofreno (Mar 3, 2009)

You can see some results from these on this forum, page 3:
http://www.diyelectriccar.com/forums/showthread.php/using-cell-log-measure-voltage-sag-38938.html

I also ordered a couple to compare discharge of cells in different boxes at different temperatures near end of discharge. But I don't intend to use them as a bms since I don't know anything about the circuit design, so how safe they are to leave connected to your cells. I'll just connect them with clips, data log during a run, disconnect and download data to a PC.


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## Voltswagen (Nov 13, 2008)

OK Major
Let us know your results.


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## dexion (Aug 22, 2009)

I am abit worried about that myself. What happens if it fails. Can it short 2 or more cells...fire... what about 10F to 70F in 10 minutes (from garage to driving with the heat on etc.) I dont plan to have it connected all the time just run with it on the weekends or something if I want an idea what the cells are doing when i go get freetos or something.


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## major (Apr 4, 2008)

dexion said:


> I am abit worried about that myself. What happens if it fails. Can it short 2 or more cells...fire...


Obviously you can use it as you want. But with 22 ga wire and that little thing, if it failed short on a channel, it would be a small fast fire. I guess you could fuse each lead. Or maybe stick it in a liposack (fire proof bag).

From the size of it and the fact that it is sold at hobby shops, I think it is designed to stay aboard model airplanes. Which is a vehicle application. And may in fact be a worse environment than a car.

But for the price of the units, if they can help you save a single Li cell, money well spent.

Oh yeah, I would rather see this little bugger go up in flames than a Li cell 

major


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## Guest (Dec 24, 2009)

I got some of these and have looked them over. Haven't used them on a car yet, but they look very interesting.

At $28.95 they are certainly interesting. They will monitor 8 cells and log the data to memory. It comes with LogView software, and you can connect the device to a Windows PC to download the data and actually graph it. You can set it to log cell voltages at 1/2 sec, 1 sec, or 2 sec and it has enough memory to do a couple of days worth of cell logging at 2 sec - more than enough for a test drive.

This would be a good way to see if you have an errant cell. Absolute values are very difficult as they change with acceleration, temperature, etc.  But by seeing 8 cells at a time on a graph, you can really see if any cell is RELATIVELY out with the others.

The other interesting thing about these devices is the little open collector alarm function. Yes, you can set it to trigger on high voltage or low voltage, but as I've said many times, and monitor for WHAT. But you can also set it to alarm for DIFFERENCE voltage - and now you have something.

Same thing as above, difficult to say what to alarm for, but you know that there shouldn't be any significant difference from one cell to another in a RELATIVE sense. If you set this for say a difference of 0.2v, and under acceleration, you have one cell diving for the dirt differently than the others, it would set the alarm.

The alarms are open collector and not isolated. But I found some cool, though vey expensive, relays on Digikey. These are 5v relays that are normally closed and quite heavy. You connect the alarm battery lead to the negative of the first cell monitored. You connect the alarm red lead to one of the relay coil terminations. You connect the other relay coil lead to the positive lead of the next cell up. When the alarm goes off, the open collector transistor in the device turns on, actuating the relay.

The relay contacts are 10kv isolated. So you can string the normally closed contacts of the relays in a string. This will form a loop through your battery pack that provides an isolated current path for anything you like. If any cell gets 0.2v out from the other cells, this path will open. 

You could connect this to any 12v relay for example. And connect an LED for example across the normally closed contacts. The relay would then be always ON and the light OFF. But in the event of an alarm, the relay shuts off, turning the light ON. You could do this just as easily with a buzzer. Or the coil of your contactor, disabling your car.

Really any relay could be used with the Cell Log. I picked this $37 one because it was 5v, NC, and had a very high isolation resistance. It's a heavy duty, well made relay and unlikely to fail used this way. In fact, it's unlikely to ever ENERGIZE when used this way. 

These cell logs are VERY unlikely to damage a battery. They do NO current shunting of any kind. They use very light wiring to simply measure voltages with VERY high input impedance, much like a multimeter. The alarms can carry up to 500 ma on VERY light wiring provided. But the relay doesn't need much current to actuate, and the worst that could happen is the little 30 gauge wires burn up. I cannot imagine a failure scenario where these devices would hurt a battery pack.

Jack Rickard
http://evtv.me


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## O'Zeeke (Mar 9, 2008)

jrickard said:


> I got some of these and have looked them over. Haven't used them on a car yet, but they look very interesting.
> 
> At $28.95 they are certainly interesting. They will monitor 8 cells
> 
> ...


Jack, would you please explain your loop wiring and relay set up once more? I follow the isolation concept but the NC relay part I don't quite get it. I have some of these cell loggers too and would like to try them.
Thanks


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## Guest (Dec 28, 2009)

O'Zeeke said:


> Jack, would you please explain your loop wiring and relay set up once more? I follow the isolation concept but the NC relay part I don't quite get it. I have some of these cell loggers too and would like to try them.
> Thanks



If you notice on the Cell Logger, there is a tiny white connector with two wires, black and red. If you connect the black wire to the most negative terminal, and the red wire to any of the other more positive terminals, nothing happens. There is a transistor in the unit that only turns ON when the alarm goes off.

So if you connect the red wire to one contact of a relay coil, and the other contact to a more positive terminal, nothing happens again.

But if the alarm then goes off, you have a current path from the positive terminal, through the relay coil, through the transistor in the Cell Log, to the negative terminal. This "closes" the relay or energizes it.

Relays quite commonly are normally open, and when you energize it, this closes the two "contacts" which are isolated from the coil. But there are also relays that are normally CLOSED, and that OPEN when the relay energizes.

If you connected a series of these relays together, it would form a wire loop through all the Cell Loggers. It would normally be zero resistance through this loop. You could use this, for example, to apply 12vdc to ANOTHER separate relay coil. 

And that relay would be "energized" all the time. But if ANY of the Cell Loggers, set an alarm, THAT cell loggers relay would energize, it's NC contacts would OPEN, the loop would be open, and the master relay then would de-energize. You could do anything with that, have it light an LED, disconnect the voltage from your contactor, switch in resistance with your pedal/throttle assembly, or serve as a digital input to a small computer system.

In this way, the Cell Loggers do all the voltage monitoring and simply set a condition if any cell varies from the others, or hits a high limit, or hits a low limit, etc. 

Then you can go in, REMOVE the Cell loggers, take them to the bench and hook them up to the laptop and offload the logged data, graph it, and the problem cell should become apparent rather quickly.


Jack Rickard


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## major (Apr 4, 2008)

Voltswagen said:


> OK Major
> Let us know your results.


Hey guys,

It has been a while on this thread, but I've been using these things for a few weeks. I had two which are wired for 7 cells each. I have been using them on my 14 cell LiPo battery on constant current discharge tests. I attached a 5C chart for 7 cells. That is 200 amps.

For some reason, one of the Celllogs blew the USB port when we tried to connect to the computer while it was still on the battery. Although the instructions said this was permissible. We always unplug the loggers now before plugging into the computer to dump data. I ordered a few more cellLog8s.

Anyway, I like the little things. I know Tomo has been using his. Anyone else?

Regards,

major

Opps. Error on the chart. Should read 11.4 minutes, 38 Ahr and 1.81 kWhr. (they are 40 Ahr rated cells)


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## tomofreno (Mar 3, 2009)

Major,

What did you use for a load for the test? 
Why do you estimate resistance by the voltage difference 4.1 - 3.4?
What is the rest voltage of the Kokam cells after full charge? I am not used to seeing 4.1V under 200 A load. Different beast.


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## major (Apr 4, 2008)

tomofreno said:


> Major,
> 
> What did you use for a load for the test?
> Why do you estimate resistance by the voltage difference 4.1 - 3.4?
> What is the rest voltage of the Kokam cells after full charge? I am not used to seeing 4.1V under 200 A load. Different beast.


Hi tom,

I have a rather large bank of resistors with a homemade IGBT chopper to adjust current. I'll post a picture when I get back to the lab.

4.1 volts was the open circuit voltage. It dropped down to 3.4 volts under the 200 amp load. Looking back, I think some of that drop is due to charge removal, not resistance. Resistance is more of a step change in voltage. I am going to do some looking into that. Maybe try a step change from 100 to 200 amps and see what that yields. I suspect the resistance is lower.

As far as rest voltage, they seem to stay right where I leave them. I have been trying to charge to 4.2 V/c. They usually get pretty close, like 4.15, when one or two of them hit 4.2. Even a day or two later, they are all above 4.1. I usually leave a few seconds at zero current at the start of the test. I'll see if I have that on a chart and post it.

major


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## major (Apr 4, 2008)

major said:


> I have a rather large bank of resistors with a homemade IGBT chopper to adjust current. I'll post a picture when I get back to the lab.


Hey tom,

Here's what it looks like. The tower has 24 one kilowatt braking resistors. However we can run 50 kW easily with the fans going and even up to 100 kW for shorter durations. Have tested 168V battery packs up to 300 amps. Resistors can be configured in many combinations of series/parallel. 

The gray box hanging on the side houses an IGBT chopper. At those voltages and currents, you just can't switch it on and off with a contactor. This also gives the capability to set the resistance lower than needed and adjust the duty cycle during the test to keep the current constant.

I actually have a couple of the resistor towers with 14 resistors each for sale. Contact me PM if interested.

Regards,

major


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## major (Apr 4, 2008)

tomofreno said:


> What is the rest voltage of the Kokam cells after full charge?


Hi tom,

Here is another test chart. Same battery run at 6C (240 amps). Current started at approx 30 seconds. So prior to that you can see the open circuit cell voltages. Notice the step change at 30 seconds when the current is applied. The top cell drops from 4.12 to 3.68 volts. Or 0.44 volts for 240 amps. This gives an internal resistance of 0.00183 ohms for that cell. A better number to use than I posted before.

At this higher current, notice the wider spread in cell voltage. Small bumps in the curves are where we adjust the PWM to keep a constant current. Trying to get a "set it and forget it" current limit circuit installed. But by hand adjust, we keep +/- 2% pretty well.

These cells are rated for 5C continuous, which we ran, no problem. And they are rated 10C pulse, whatever that means. So at above 5C, we keep an eye on the temperature and shut down before full discharge. For this test, we stopped at maybe 40% SOC.

We're getting some nice results, but these charts I post are preliminary. Not to be taken to the bank. I need to do some further calibration and work on getting better data into the computer, like current and temperature. Not to mention the other 7 cells. Man, it takes a long time to get those CellLogs from half way round the world 

Regards,

major


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## tomofreno (Mar 3, 2009)

> Here's what it looks like.


 Whoa! Nice setup major!


> The top cell drops from 4.12 to 3.68 volts. Or 0.44 volts for 240 amps. This gives an internal resistance of 0.00183 ohms for that cell.


 Impressive. What is considered "low voltage" for these cells?


> These cells are rated for 5C continuous, which we ran, no problem.


 So they did not overheat at 5C, but did in about 5 minutes at 6C? How long did you run them at 5C and what temperature rise did you see? What is the high temperature limit? Great data! I guess you plan on doing this regularly to test different cells (lot of work/expense for test of one pack)?


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## JRP3 (Mar 7, 2008)

major said:


> Man, it takes a long time to get those CellLogs from half way round the world


The website is showing "-1" in stock, it might be a while


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## EVMAN (Jul 26, 2007)

I'd like to mention that "BMS" has come to mean:
"Battery Management System" which is a Battery Voltage Monitor PLUS a Controller to "do things" to, usually, the controller/inverter(output) and the charger(input). Basically controlling current in and out.
"Battery Monitors" (BM) just read the voltage.

"Newer" battery chemistry requires careful monitoring to prevent catastrophic failures. Things that did not occur with NiCads or PbAcid.

Equalization is a popular term and seems to be necessary for EVen floodies.
I've been working on a Battery Monitor for a while now to read the Voltages
on my 18 floodies in my EV. I'd like to know which battery in my pack is going
south before it truly bites the dust. This BM looks VERY cool!! I wish they made a version for 6V floodies 

Here's another BM, for a E-trike.
http://ev.higgsnet.com/BatteryMonitors/BatMon.htm 
Has schematic. It's a PIC16F676. No code though


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## major (Apr 4, 2008)

JRP3 said:


> The website is showing "-1" in stock, it might be a while


I got notice they were in fact shipped and I would receive them within the next the 45 days  That was like 2 or 3 weeks ago.


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## JRP3 (Mar 7, 2008)

major said:


> within the next the 45 days


45 days? Was that a typo?


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## PTCruisin (Nov 19, 2009)

JRP3 said:


> 45 days? Was that a typo?


I just got the same email for a cell-log I ordered last week:

YOUR ORDER MAY TAKE UP TO 45 DAYS TO ARRIVE.

*IMPORTANT*
1) To check on the status of your order please log into your account on our website.
It can take up to 48hrs for the tracking details to become active within the postal system.
2) If you are unsure of the location of your parcel please contact the *postal office* in your country.
3) If your parcel arrives damaged or opened, DO NOT accept it unless you open the parcel in front of the courier/postman to check and count contents, or reject the parcel as being damaged and have it *returned to sender* and notify us straight away.

Regards
www.hobbyking.com. 

I think it's a CYA bot mail message. At least I hope it is.


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## JRP3 (Mar 7, 2008)

I guess that includes the time needed to build the units first. I think they may have been swamped with the recent interest in the product.


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## PTCruisin (Nov 19, 2009)

JRP3 said:


> I guess that includes the time needed to build the units first. I think they may have been swamped with the recent interest in the product.


They showed a positive inventory when I ordered and I received this email yesterday:

Dear Ralph
This is an email from hobbyking's product checker #7.
I would like to inform you that your product(s) have been double checked and are now packed in their box and sent to the dispatch area. Please allow 48hrs for any tracking information to be displayed/updated.

Thanks for your support!
Hobbyking.com

So I think they just say 45 days to cover any delays in transit. They do seem to sell a lot of them as I've noticed the inventory going negative more than once.


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## major (Apr 4, 2008)

tomofreno said:


> What is considered "low voltage" for these cells?
> So they did not overheat at 5C, but did in about 5 minutes at 6C? How long did you run them at 5C and what temperature rise did you see? What is the high temperature limit? Great data! I guess you plan on doing this regularly to test different cells (lot of work/expense for test of one pack)?


Hi tom,

We try to not go below 2.5V on any cell. At high current, once they get to the knee, they go south in a hurry. We have the alarms set on the CellLogs. And what you see on the charts is only half the cells. The other logger still works to monitor during the test, we just can't get the data from it.

Like I said, these are preliminary results. I still have a ways to go with the data system. We've just been using thermometers. I will have thermocouples next week, I hope. So for now, when above 5C, we stop if we see anything looking "very warm", maybe in the 140 to 150 F range. And on the 6C test, I have a suspicion that the clamp-on ammeter was reading low. Here again, we will be using a current sensor fed to the computer.

I built the test equipment about 10 years ago for lead-acid packs. It is mostly from surplus parts. Got banged around and stored away. Then I pulled it out a few months ago when I happened across some of these LiPo cells. Just trying to figure out these things. Looks like I will have some other Li batteries to test for a client. Just trying to work out the bugs. 

Posting up here to get feedback and see what others are doing. Comments and advice welcome.

major


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## GerhardRP (Nov 17, 2009)

major said:


> Posting up here to get feedback and see what others are doing. Comments and advice welcome.
> 
> major


Nice setup and data
The sort of measurement I would like to see would simulate stop-and-go driving on a vehicle with a two hour "range"... maybe this test..
Start fully charged, then [run, say, 15 seconds at 5C (or more) then 10 minutes at 0.5C followed by 1 minute unloaded]...repeat until dead.

Gerhard


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## Posthumane (Feb 21, 2010)

Great test results major. These are the Kokam "high power" cells correct? I'm curious where you got them, and if purchased normally, what the price was. I've been getting a pretty wide range of quotes on their 100 Ah cells from distributors, and Kokam doesn't seem to be responding recently to direct quote requests. That may be because of the Dow merger, so I will try again soon, but I really like these batteries for their energy density. I'd love to see some tests of their "high energy density" cells which are rated at 1C continuous, 3C pulse.


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## major (Apr 4, 2008)

Posthumane said:


> These are the Kokam "high power" cells correct? I'm curious where you got them, and if purchased normally, what the price was.


Sorry Pos,

I can't get into that due to some confidentiality issues. And can't help you on price or availability either. But I think these are very pricey cells. And yes, the ones I have are 40 Ahr high power.

The subject here was more about the monitor and testing of it rather than the cells. I should have some more tests later in the week as I finally got my replacement CellLog8. Now to figure how to plot 14 cells 

Regards,

major


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## JRP3 (Mar 7, 2008)

Posthumane said:


> I'd love to see some tests of their "high energy density" cells which are rated at 1C continuous, 3C pulse.


That's a fairly poor C rating compared to TS or SE.


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## Matthijs (Jun 19, 2009)

major said:


> Sorry Pos,
> 
> I can't get into that due to some confidentiality issues. And can't help you on price or availability either. But I think these are very pricey cells. And yes, the ones I have are 40 Ahr high power.
> 
> ...


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## major (Apr 4, 2008)

Nice work with photoshop, Matthijs 

Here is another test plot, both the same, just an expanded scale on #2. We were a little slow shutting down. But I thought some might be interested in how fast these tank after the knee.

0pps, 2nd cell 5 is cell 6.


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## racunniff (Jan 14, 2009)

major said:


> Nice work with photoshop, Matthijs
> 
> Here is another test plot, both the same, just an expanded scale on #2. We were a little slow shutting down. But I thought some might be interested in how fast these tank after the knee.
> 
> 0pps, 2nd cell 5 is cell 6.


Wow. Argues that LVC should be 3.0V or so instead of 2.7V. Or, at least, you should consider 3.2V "empty"


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## dimitri (May 16, 2008)

Lesson learned Major, do not take coffee breaks during 5C testing 

Nice data, thanks for sharing!

I don't see why anyone would be using these cells unless they have well funded racing application.


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## Matthijs (Jun 19, 2009)

major said:


> Nice work with photoshop, Matthijs
> 
> Here is another test plot, both the same, just an expanded scale on #2. We were a little slow shutting down. But I thought some might be interested in how fast these tank after the knee.
> 
> 0pps, 2nd cell 5 is cell 6.


Well it was not mine but it seems Doctorbass was contacting the company for this kind of CellLog and they agreed to make an production run but only in a volume of a 1000 pieces minimal. 

http://www.endless-sphere.com/forums/viewtopic.php?p=228365#p228365
http://endless-sphere.com/forums/viewtopic.php?p=225074#p225074


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## tomofreno (Mar 3, 2009)

> Well it was not mine but it seems Doctorbass was contacting the company for this kind of CellLog and they agreed to make an production run but only in a volume of a 1000 pieces minimal.
> 
> http://www.endless-sphere.com/forums...228365#p228365


 The large screen Cycle Analyst (link within this link) looks very interesting. Gives both Ah and Wh (TBS only gives Ah), and gives these separately for regen so you can see how much energy you add to the pack. Also pack voltage, min voltage due to sag... and they plan to release a datalogger board for it this May.


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## whiteggs (May 21, 2010)

I'm planning to use 3 CellLogs, can I use a single power supply(9-12v) for the red alarm output wires and only use 1 buzzer/led(for all 3 relays) that are also powered by the same mentioned power supply?


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## major (Apr 4, 2008)

whiteggs said:


> I'm planning to use 3 CellLogs, can I use a single power supply(9-12v) for the red alarm output wires and only use 1 buzzer/led(for all 3 relays) that are also powered by the same mentioned power supply?


Hi eggs,

As far as I can tell (from reading the manual and web posts), the alarm output on the CellLog8s is an open collector circuit with ground common to cell #1 being monitored by the device.

This means you cannot connect multiple CellLog8s alarm circuits directly together or you will create a short circuit of cells being monitored. You need to connect each CellLog alarm to an optocoupler or separate isolation relay if you want any single alarm from multiple CellLogs to trigger an action for your set up.

I have plans to do this, but have not yet attempted it. If you get to it before me, please post it and share.

Regards,

major


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## Guest (May 23, 2010)

tomofreno said:


> The large screen Cycle Analyst (link within this link) looks very interesting. Gives both Ah and Wh (TBS only gives Ah), and gives these separately for regen so you can see how much energy you add to the pack. Also pack voltage, min voltage due to sag... and they plan to release a datalogger board for it this May.


I loved the idea. And I bought one. The current measurement is very poor in accuracy. The switch that you use to select menu items is not debounced. This is a good idea poorly executed. But the fatality here is it just doesn't measure currrent very well. Not nearly on par with the TBS or Xantrex.

Jack Rickard


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## Guest (May 23, 2010)

major said:


> Hi eggs,
> 
> As far as I can tell (from reading the manual and web posts), the alarm output on the CellLog8s is an open collector circuit with ground common to cell #1 being monitored by the device.
> 
> ...


I played with it a bit. Got some 5v NC relays. Wire the black negative of the cell log to the negative terminal of cell 1. Wire the red wire to coil of NC 5v relay. Wire other end of coil to positive voltage 2 cells up the line.

Do this as many places as you like, then wire all the NC contacts in series. Any Cell Log that alarms will open this closed loop circuit by energizing the relay.

Too much wiring. Too little gain. Not enough time. I've already had a single Cell Log cause a fire by itself.

Jack Rickard


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## Tiger (May 24, 2010)

Hey guys
I came across this by accident, I building ATV, and UTV, 
My BMS system had several minor problems, one being you could never hear it when it was signaling you that your energy was low, 
I added to the program a flashing light to the display, but, when I got down to the critical area I had it cut the power in half, when it dropped further in half
Then it would then flash red, then give 10 seconds and cut off
once the bounce occurred
i could limp home
just some advise


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## Frank (Dec 6, 2008)

jrickard said:


> The current measurement is very poor in accuracy. Jack Rickard


Hi Jack,

How "close" was the current measurement? Do you think it's repeatable i.e. even if not accurate could still be used as a relative measurement of capacity?

thanks


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## Tiger (May 24, 2010)

Hi
There are two methods which will show your capacity, and both are not that good at the present time,


you can have your voltage charge which will show you where you voltage has dropped to, but, as you drive the EV, it is pulling the voltage, so it drops, then you have the bounce back which will show a much higher voltage, This is not that good, because your voltage will vary on acceleration, and your driving habit, so you need to be stopped to see where you stand, and if you use a rabbit start this will deplete your battery very quickly
SOC, state of charge, is a theoretical level of amps in your battery, and it is to measure your voltage and how much current you are pulling, with RPM, this done in your BMS, it will not go up or down as if you where measuring voltage only, but, it will give a little better handle on your AH in your battery


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## MN Driver (Sep 29, 2009)

Tiger, RPM won't matter, you can count the Ah's though and for lithium it's a fairly accurate method of determining state of charge as long as you know your pack capacity.

"If you use a rabbit start this will deplete your battery very quickly" This may be true for lead acid but for the size of lithium batteries being used in EVs to get any decent amount of range, even intermittent 3C will have a minimal affect on the amount of Amp-Hours that can be pulled from a pack, if you were aiming to use 80%(or 70%) of your capacity as is suggested for maximum life for LiFePO4 cells you won't lose 20% of your Ah availability if you keep it under 3C and your pack is capable of a 3C constant discharge without dropping low on voltage. If the battery isn't capable of this, it's possible that it will reach its discharge cutoff voltage which isn't ideal for the operation of the battery pack to be pulling that many amps.


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## JRP3 (Mar 7, 2008)

Check out Dimitri's thread on the Ah/Wh SOC meter he's developing.


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## Tiger (May 24, 2010)

Mn Driver
I am running several systems, now. The SOC is the method I am using, however, I have limited my amps to 1 1/2 c on my batteries
I beginning to do work with supercaps now, and looks very good in giving me much better range, the question will be how much better range then adding more batteries, or setting up a parallel system.


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## JRP3 (Mar 7, 2008)

For the size, weight, and cost of supercaps you're better off using more batteries. Jack Rickard put 36 Maxwell supercaps in his GEM and went about half a block before it ran out of juice.


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## whiteggs (May 21, 2010)

Thanks Major, Jack ...should have read manual first 
I'm trying to simplify the wiring... as each Celllogs output(500ma ) is enough to power a small beeper, can I use diodes for each CellLog instead of relays to isolate - one diode for the black negative wire and another for the red wire.
I'll power the beeper from a separate 12v supply... so the 1.4v voltage drop from the diodes is still negligible.





major said:


> Hi eggs,
> 
> As far as I can tell (from reading the manual and web posts), the alarm output on the CellLog8s is an open collector circuit with ground common to cell #1 being monitored by the device.
> 
> ...





jrickard said:


> I played with it a bit. Got some 5v NC relays. Wire the black negative of the cell log to the negative terminal of cell 1. Wire the red wire to coil of NC 5v relay. Wire other end of coil to positive voltage 2 cells up the line.
> 
> Do this as many places as you like, then wire all the NC contacts in series. Any Cell Log that alarms will open this closed loop circuit by energizing the relay.
> 
> ...


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## honn1002 (Nov 26, 2008)

I feel like I should share this cell monitoring with LVC and HVC protection that I put together. You can use many cells as you want. I used 40 Thundersky cells (128V nominal) for the diagram. I would put a 1A fuse on each wire close to the battery connection for safety. So total fuses should be 41 for 40 cells. All the parts require to build the cell monitoring system cost about $100. I used PCB type mini relays to turn on/off the cellLogs via the key switch.


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## Frank (Dec 6, 2008)

Thank you for posting that, I will study it sometime in the near future as I've been contemplating something similar. You can't enable both low and high voltage alarms at the same time though can you? Do you change each CellLog depending on charge/discharge situation?

thanks


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## major (Apr 4, 2008)

Frank said:


> You can't enable both low and high voltage alarms at the same time though can you? Do you change each CellLog depending on charge/discharge situation?


Thanks for sharing that honn1002.

Frank,

I think it works this way. The CellLog trips the single alarm output for any of 3 reasons: cell voltage higher than set HV limit, cell voltage lower than LV limit, or cell to cell voltage difference greater than set Delta V. So no matter what you're doing, driving or charging, if any of the 3 fault conditions appear, you need to take action. 

If you're charging, it is unlikely you will see a LV alarm. If you are driving, unlikely to see a HV alarm. So one setting and one circuit works for both. I like it 

honn,

Do you have this system installed and working?

Thanks again,

major


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## Frank (Dec 6, 2008)

For some reason I thought only one alarm function at a time would work...

I'm installing batteries at the present time. Still a couple of weeks out for the CellLogs I think. Too many other projects, lol.


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## dimitri (May 16, 2008)

honn1002 said:


> I feel like I should share this cell monitoring with LVC and HVC protection that I put together. You can use many cells as you want. I used 40 Thundersky cells (128V nominal) for the diagram. I would put a 1A fuse on each wire close to the battery connection for safety. So total fuses should be 41 for 40 cells. All the parts require to build the cell monitoring system cost about $100. I used PCB type mini relays to turn on/off the cellLogs via the key switch.


Honn,

interrupting DC output of the charger is a bad idea. Some chargers can blow up if interrupted during CC stage like this.

You'd be better off interrupting AC power via SSR relay.

Looks like after all said and done this solution would cost about the same as MiniBMS


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## honn1002 (Nov 26, 2008)

You're welcome....

Frank, Major just answered to your questions.

Major, I haven't built the cell monitoring system yet. I ordered all the parts that require to build it. I don't have the lithium batteries yet. 

Dimintri, Thanks for the input about the interrupted charger. Likely it should be occurred during CV stage as the cell voltages reach close to the high voltage limit. 

Anyway it's a great idea to connect it to the AC power line. But the relay needs to be latched or else it would toggle on/off the charger.


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## dimitri (May 16, 2008)

Also, relays and LEDs in series could work, but only if operating currents and voltages are properly matched. If not, you will either burn the LED or relay won't trip.

Just thought I'd point it out


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## honn1002 (Nov 26, 2008)

dimitri said:


> Also, relays and LEDs in series could work, but only if operating currents and voltages are properly matched. If not, you will either burn the LED or relay won't trip.
> 
> Just thought I'd point it out


The relays for the alarm output are small with very low coil current so the LED's should be able to handle.


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## major (Apr 4, 2008)

I thought I'd bump this thread, especially because I could use some help. I've been away from battery testing for a while, but back into it now. I had a friend helping me before who was doing most of the legwork on the computer  He took a job out west and is unwilling to make the 3000 mile commute But now, I can't pull the data file from the cellLog to the computer.

The instructions are poor. Just wondering if someone out there can give me a clue. Also, any links to updated software?

Would be appreciated,

major


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## JRP3 (Mar 7, 2008)

It's been a while since I used one but I remember there is a specific sequence that has to happen. First start the software, then plug in the cell log, or maybe vice versa? Then use the cell log buttons to scroll through the options to transmit the log file, but maybe you have to set up the software to receive first? Something like that. I think, maybe


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## Frank (Dec 6, 2008)

I never had any luck getting the file transfer to work and primarily use the celllogs as end of ride and end of charge monitoring devices.

Please post if you figure it out!


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