docnjoj
1 GW
I need my OSHA earplugs immediately! 
otherDoc
otherDoc
Discharge Curve: Headway 38120S (screw terminal) 10ah cell
- Thread starter oatnet
- Start date
Doctorbass
100 GW
I have Accurate results for you guys!
At least for 0.1 to 3C from now!
After taking an entire week, i finally found the way to work with the CBA without loosing all curves results after re-opening the program... I KEEP IT OPEN 24h/24!!
Test condition:
-cell charged at 0.2C (2A) to 3.700V
-cell charge stop when current reach 100mA (0.01C)
-Cell left alone for 2h before the next discharge to let is stabilize
-Ambient temp 21.3degree C
-cell mounted at 3inch from the bench to facilitate natural air convection
-All discharge stop at 2.0V
-Constant current discharge for 0.1 to 3.5C and constant resistance for higher current.
-Cell have been cycled at many different current 8 times before this test
Please note that i attached the Wh and temp to every curve to let you know the electric energy out of the cell
(next high current dishcharge higher than 3C to come)
the main observation here is the cell heat loss between 0.1C and 3C
so the cell is loosing 5.85Wh (21kilojoules) for a temp rise from 21 to 42.5Celsius in heat in the 3C constant discharge that's 17% lost in heat.
34.2Wh electric energy at 0.1C (the ideal condition for a cell) and 28.3Wh at 3C.
Doc
At least for 0.1 to 3C from now!
After taking an entire week, i finally found the way to work with the CBA without loosing all curves results after re-opening the program... I KEEP IT OPEN 24h/24!!
Test condition:
-cell charged at 0.2C (2A) to 3.700V
-cell charge stop when current reach 100mA (0.01C)
-Cell left alone for 2h before the next discharge to let is stabilize
-Ambient temp 21.3degree C
-cell mounted at 3inch from the bench to facilitate natural air convection
-All discharge stop at 2.0V
-Constant current discharge for 0.1 to 3.5C and constant resistance for higher current.
-Cell have been cycled at many different current 8 times before this test
Please note that i attached the Wh and temp to every curve to let you know the electric energy out of the cell
(next high current dishcharge higher than 3C to come)
the main observation here is the cell heat loss between 0.1C and 3C
so the cell is loosing 5.85Wh (21kilojoules) for a temp rise from 21 to 42.5Celsius in heat in the 3C constant discharge that's 17% lost in heat.
34.2Wh electric energy at 0.1C (the ideal condition for a cell) and 28.3Wh at 3C.
Doc
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pgt400
1 kW
Nice job....does the cell look like it has improved over the paper ones? How would a PSI cell look in comparison at 2c ?
Thanks for sharing your efforts.
Thanks for sharing your efforts.
Ypedal
100 TW
pgt400 said:
Hey doc... i could arrange that !! :wink: Want to borrow a PSI cell ?
Doctorbass
100 GW
Ypedal said:
no prob!.. PM me
dimitrib90
100 W
- Joined
- Oct 8, 2008
- Messages
- 142
Hopefully your power doesnt go out. 
:lol:
EDIT ADD: AWESOME!!! COMPETITION OF PSI CELLS!!!
:lol:EDIT ADD: AWESOME!!! COMPETITION OF PSI CELLS!!!
recumbent
100 kW
pgt400 said:
8) That would be so sweet to have a direct comparison to PSI cells.
Doctorbass
100 GW
Kurt
10 kW
+1 on a direct comparison to PSI cell as they were the cells i was going to get but opted for the headways because of price.
kurt.
kurt.
dimitrib90
100 W
- Joined
- Oct 8, 2008
- Messages
- 142
So far I am impressed with these cells. I am hoping that Headways new BMS is as good as promised.
pgt400
1 kW
Victoria quoted $16.50 per cell for qty 96. Good price on the cells, but UPS shipping is $400 to NJ....so about $4 per cell to ship from China. She responds very quickly to emails. I am really interested to see how these newer units compare to the PSI cells.
Doctorbass
100 GW
I should receive PSI cell soon for test. i'll be glad to make tghe test for you guys.. I'm also very curious to compare them!
Doc
Doc
dnmun
1 PW
IR(5,35A)=12.7mohm, and IR(10,20)=12mohm at 3.51Wh discharge, and from RLT's graph on the old drbass headway thread i got 17mohms or so http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=3374&st=0&sk=t&sd=a&start=240
from RLT's graph i estimated 2.50V@35A, and this new blue screw cap is pretty flat at 2.90V, and biggs also had 16mohm from the old brown paper tabbed cells with his RIM100, and got something around 8mohms for his first batch of these blue screw tab cells. back in september.
as i remember.
i still think the RIM unit was measuring input impedance and not output impedance, which may account for the difference. the other consideration is that the batch that biggs got and this batch were mixed by headway at the same time and we are seeing the aging of the cathode as an increase in the IR itself from this aging process.
thanks so much doc.
from RLT's graph i estimated 2.50V@35A, and this new blue screw cap is pretty flat at 2.90V, and biggs also had 16mohm from the old brown paper tabbed cells with his RIM100, and got something around 8mohms for his first batch of these blue screw tab cells. back in september.
as i remember.
i still think the RIM unit was measuring input impedance and not output impedance, which may account for the difference. the other consideration is that the batch that biggs got and this batch were mixed by headway at the same time and we are seeing the aging of the cathode as an increase in the IR itself from this aging process.
thanks so much doc.
pgt400
1 kW
pico1 said:
There are new BMI's on ebay for $47.00 each...OUCH!!
Doctorbass
100 GW
I repeat again:
Please be carefull when evaluating cell voltage at high current such as 35A...
MY CBA use the "pro" (i prefer using bug corrected) version that compensate for the resiatance of the probe wires..
That mean that with the non corrected version CBA soft and the problem of resistance in wire.. like if using it at 35A with the OEM 13AWG silicone wires, the voltage reading at 35A may be around 2.7 to 2.5V... so that could introduce some interpretation error..!!!
My CBA is corrected!.. and calibrated.. So the voltage you see on the graph IS THE SAME AS the one measured directly on the cell tab/screw attachement while drawing current on it...
I mean some CBA without this compensation/error correction of voltage will make you think that the 2.5V on the graph is the same as on the cell tab.. AND IT'S NOT..
Then when comparing differences of my cell tests with other tests, ensure that these tests have the error compensation!
Doc
Please be carefull when evaluating cell voltage at high current such as 35A...
MY CBA use the "pro" (i prefer using bug corrected) version that compensate for the resiatance of the probe wires..
That mean that with the non corrected version CBA soft and the problem of resistance in wire.. like if using it at 35A with the OEM 13AWG silicone wires, the voltage reading at 35A may be around 2.7 to 2.5V... so that could introduce some interpretation error..!!!
My CBA is corrected!.. and calibrated.. So the voltage you see on the graph IS THE SAME AS the one measured directly on the cell tab/screw attachement while drawing current on it...
I mean some CBA without this compensation/error correction of voltage will make you think that the 2.5V on the graph is the same as on the cell tab.. AND IT'S NOT..
Then when comparing differences of my cell tests with other tests, ensure that these tests have the error compensation!
Doc
Doctorbass
100 GW
UPDATE INCLUDING REAL RI MEASUREMENT
PLEASE NOTE: that this cell that i use for the test is the first out of two that i have to test. I already began the 0.1C discharge on the second cell and it look good.
The first cell (the one on the graph results) have been cycled 10 times with different currents, temp and the 9mOhms IR i measured seems stable. I also measured it at 0.1C (1A) and it is still 9mohm so that confirm that the method is constant and the cell too!
That first cell reached temp around 45-50 degree C during more than 1h before these tests when i cycled it to 35A disch, like 6 times.
I'm impatient to know discover the second cell performances!!
Doc
PLEASE NOTE: that this cell that i use for the test is the first out of two that i have to test. I already began the 0.1C discharge on the second cell and it look good.
The first cell (the one on the graph results) have been cycled 10 times with different currents, temp and the 9mOhms IR i measured seems stable. I also measured it at 0.1C (1A) and it is still 9mohm so that confirm that the method is constant and the cell too!
That first cell reached temp around 45-50 degree C during more than 1h before these tests when i cycled it to 35A disch, like 6 times.
I'm impatient to know discover the second cell performances!!
Doc
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dimitrib90
100 W
- Joined
- Oct 8, 2008
- Messages
- 142
pgt400 said:
link?
pgt400
1 kW
http://cgi.ebay.com/10AH-LiFePO4-BMI-battery-3-3V_W0QQitemZ130271429385QQcmdZViewItemQQptZBatteries?hash=item130271429385&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50
Or just search BMI Battery
Or just search BMI Battery
dimitrib90
100 W
- Joined
- Oct 8, 2008
- Messages
- 142
pgt400 said:
You said "new" BMI cells and I thought you were talking about different cells. :wink:
HAL9000v2.0
10 kW
Great work, Doc. Thanks for the results.
If I understod this chart correctly I can count with average 3,0V per cell on 30A?
If I understod this chart correctly I can count with average 3,0V per cell on 30A?
Doctorbass
100 GW
HAL9000v2.0 said:
Not exactly. At 30A, the mean voltage(see the purple curve) is not 3.0V but less than that. This is more like 2.85V for the average voltage over the entire discharge. to hold 3.0V average you would need to use 2p.
Doc
AndyH
10 kW
Doctorbass said:
Hi Doc,
How accurate is the current display on your modded CBA?
Doctorbass
100 GW
AndyH said:
I calibrated it so that my calibrated reference multimeter indicate the same voltage value than the cell tab while dishcarging at 10 to 30A
The error is 0.05V based on the total dynamic of the discharge current due to the non linearity of the error over the current value. from now that is the minimum error i can acheive
Doc
AndyH
10 kW
Hi Doc,
I understand that you have the voltage calibrated. I have the 'pro' version of the CBA V2 software as well. I can get the voltage to ±.02V (better with more trial and error).
What I cannot do is get the current (A) display calibrated. It's displaying 1.5 to 2.0 amps higher than an ampmeter at the cell. The calibration function for 'current' is only for small discharge currents, and only gives 100mA of range. [edit] My error is coming from a damaged amplifier - not from the CBA or software. Eureka! [/edit]
As I see it - Pro/Con for the CBA: Pro: Inexpensive, easy to use, quick to learn, easily allows different people to compare results and thus compare batteries. Con: Known (but consistent) inaccuracies. I don't like the inaccuracies, but this device is only calibrated to the powerpole connections, per the company, and we know that our test leads add error. The device is not designed to be a lab-grade instrument. I think it's useful as a comparison tool provided we know of its weaknesses. In other words - as long as we don't mess with the device, we should all have the same error, and we can be fairly sure we can compare our pictures to compare cells.
Here's a shot of a 2A discharge of a 38120 Headway from my LaMantia BA402. DIsregard the dotted line - the thermocouple was not attached to the cell. Both voltage and current are ±.01 at the cell terminals:
I understand that you have the voltage calibrated. I have the 'pro' version of the CBA V2 software as well. I can get the voltage to ±.02V (better with more trial and error).
What I cannot do is get the current (A) display calibrated. It's displaying 1.5 to 2.0 amps higher than an ampmeter at the cell. The calibration function for 'current' is only for small discharge currents, and only gives 100mA of range. [edit] My error is coming from a damaged amplifier - not from the CBA or software. Eureka! [/edit]
As I see it - Pro/Con for the CBA: Pro: Inexpensive, easy to use, quick to learn, easily allows different people to compare results and thus compare batteries. Con: Known (but consistent) inaccuracies. I don't like the inaccuracies, but this device is only calibrated to the powerpole connections, per the company, and we know that our test leads add error. The device is not designed to be a lab-grade instrument. I think it's useful as a comparison tool provided we know of its weaknesses. In other words - as long as we don't mess with the device, we should all have the same error, and we can be fairly sure we can compare our pictures to compare cells.
Here's a shot of a 2A discharge of a 38120 Headway from my LaMantia BA402. DIsregard the dotted line - the thermocouple was not attached to the cell. Both voltage and current are ±.01 at the cell terminals:
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