Seriously...this looks like it would take many many months to get through a significant number of cells. I applaud the level and attention to detail, but damn.
Just wanted to say, that I ordered a BT-C3100 v2 a little over 1 year ago (straight from china on ebay). I did not have any of the 2 issues you had. My unit was never restarting and the fan, although pretty loud in general, oh yes it is, never gave obnoxious sounds like the one you have. I suspect your unit was simply slightly defective. What I have to mention though, my unit gave up the ghost literally a few days ago (the display went "crazy") and doesn't charge anymore. So under heavy usage (which mine did receive) it lasted 1 year. I still call it a winner, given the price tag (£28 inc shipping last year) and the functionality it provides. Cheers.
Well mine's been testing cells pretty much all day everyday for the last two years. Other than running it on a more powerful power-supply and changing the fan occasionally, it's still working perfectly (KNOCK ON WOOD).
Hello. Your video is very helpful. But when you get a set of batteries(ie harvested. From random sources) are you putting straight in the bank to charge them from your dc constant charger? If so what voltage/ current? And how do you know when they are charged? I am currently charging all with the opus and then putting in a box for a month like you. Then would check if they lost voltage and then would do a capacity check. Does my approach good as well ?
Since this video I've changed my strategy, I charge them in the DC-DC only to about 4v and let the Opus complete the charge. This slows the process a bit but makes for more consistent results. I know when the DC-DC is finished charging when the LED goes from red to green. The DC-DC is set for about 4A and 4V max. I often put the cells straight into the Opus without pre-charging them. However, if the cell is less than about 2.3v I need to charge them a little on the DC-DC otherwise the Opus thinks they are nimh batteries and won't charge them. You strategy seems fine to me, you are checking for self discharge before testing them. The thing is, often times, batteries with high self discharge rate also have low capacity. By checking the capacity first, if the cell is weak, I get rid of them right away, no need to keep them in "storage" for a month.
It depends on how your configuration. If your pack is comprised of single cells in series, they need to be very close in capacity. If your pack is comprised of several cells in parallel, then as long as the total capacity of each group of cells is the same then you have more flexibility. For example a 3s2p pack as follows, each set of cells has the same total capacity: (2.1Ah+1.9Ah)-(2.2Ah+1.8Ah)-(2.6Ah+1,4Ah)
If youre asking what the difference in capacity between the 1A discharge and 2A discharge can be it entirely depends on the max discharge rate of the cell. If the cell is rated for 20A then you won't see a difference bigger than 100mah. If the cell is rated for 4A max then you might see a difference of 300mah or 400mah. Assuming all your cells are rated 4A-8A max discharge when new you probably don't want to see more than a 400mah difference. If they are far apart then your IR has gone up and the cell is only capable of maybe a 3A discharge so the difference between 1A and 2A is 33% of its discharge ability.
I'm planning to test 18650 same way as you do, thank you! Few questions though, when you test battery capacity first time and you got, let's say, 2400 mAh, then you let it sit for a month and then test it with 2a discharge, you expect to see result close to 2400 mAh or all that matters to you at this point is to get more than 2000mAh? Which capacity value (from first capacity testing or second) you then use to combine cells in pack?
When testing at 2A, the mAh obtained will always be less, 300 to 400 less is normal but when it's over 450 mAh it normally means the cell has a high internal resistance.
The difference you see between the 1A discharge test and ~2A discharge test (the resistors don't provide a constant current but a value of 2 ohms will give you 2.1A down to 1.5A) is dependent on the cells internal resistance. If the cell has a higher discharge rate/lower internal resistance it will be less impacted by the 2A discharge and will come out closer to the 1A rate. The highest discharge rated cells wouldn't be fazed by a 1A or 2A discharge and the numbers would be nearly identical but this was 2016, if you wanted high capacity you weren't going to get high discharge rates so a lot of the 2600mah cells had a max discharge rate of 5A. For example the red cells here are likely Sanyo UR18650ZY with a recommended discharge rate of 2.5A and a max of 5A. Speaking in very very broad terms, a new cell will only pull 75% capacity when discharged at its max rated discharge current. When it comes to used cells there are other variables, as internal resistance begins to spike when the cell has seen a few hundred cycles. This directly correlates to voltage drop and you can kind of cheat and figure out which cells have seen a big rise in internal resistance by applying a 1 ohm load when they are fully charged so they are discharging at 4.1A to 4.2A. You'll want to have a voltmeter connected directly to the cell terminals, any wires carrying current will give you an incorrect voltage reading. Using very thick wires can reduce the error of the voltage reading but its best to just attach a voltmeter by itself to the terminals. The moment you apply the load, make note of how low the voltage drops from its charged voltage and determine what the voltage drop is. Very broadly speaking, a new cell dropping more than 0.6V at 4.2A either has high internal resistance or isn't rated to be discharged at 4.2A. You can Google Mooch and HKJ's results to see their discharge graphs and what you should expect. Again, used cells will fare a bit worse but they shouldn't do too bad. If the voltage just bottoms out to 2.7V then that is not a cell you want to use. Also keep in mind the Opus has a known problem that was partially mentioned here, the fan. People were always saying the Opus tested about 10% higher than other chargers and there's a reason why. When a cell is heated up to 35 Celsius it actually performs at its best and will discharge 105% capacity or a bit better if its new. Also, if your charger starts and stops the voltage is rebounding every time it does that which is equivalent to doing a discharge to 2.5V, watching it rebound up to 3V, restarting the test and getting another 5-10% out of the cell which is NOT the way it should be done. Once the low voltage cutoff under load is hit, that's it. Do not restart it. Well the fan on the Opus cant keep up so the charger gets quite hot during charge and discharge for some cells. The Opus will stop the discharge several times throughout the test and that's why it will take 4 hours to discharge a 2.5Ah cell at 1A. So those two factors are giving an inflated capacity result compared to the ZB2L3 which ends its discharge at 3V (though you can adjust it lower). The v2.2 Opus discharges to 2.8V and the v3.1 discharges to 3.1V so there will also be a small discrepancy there but not enough that leaving the ZB2L3 at 3V is ruining your comparison. Below 3V there is very little capacity so you might only get 100mah between 3.0V and 2.8V.
Hey I was wondering how long you let your 18650 batteries sit on the shelf to test the self discharge. Also how much of a drop in voltage you allow before calling a cell bad. For example I had a batch of cells tested and charged to 4.2 volts. They were left for a week and after that week they had all dropped by a bout 2 to 3 10ths of a volt. would you still keep these cells?
When batteries come off the Opus, I let them sit for several hours and they usually settle to about 4.15v. If they are lower, I top them up using a dc-dc converter so that they are all at 4.15v. I let them sit for a month and if they drop below 4.1v I consider them bad. The thing to remember is that the cell's voltage will drop right after it comes off the charger so your best bet would be to check the voltage after 24 hours and record that. Then re-check the voltage after a month. It should not drop by more than 0.05v. Also, I have noticed that some times, if you re-test the cells with a high self-discharge, they will some times be ok the second time. I figure it`s probably because they had been sitting unused for many years and need to be "refreshed".
You need to let the cells sit for a while to see if they exhibit a high self discharge. If the cell voltage drops, that probably means they are starting to develop an internal short which will most likely get worse over time. Also, if you build a pack with even one cell that exhibits a high rate of self discharge, then your pack will become imbalanced fairly quickly.
Its either let them sit and check the discharge rate or buy a YR-1035+ and check AC impedance. Otherwise, like Leaf Xpack said, you're going to be putting cells in your pack that are already developing internal shorts and your pack is going to be a) a huge liability to have in your car or in your home b) greatly decreased in usable capacity
Very thorough testing methods, good job.
Seriously...this looks like it would take many many months to get through a significant number of cells. I applaud the level and attention to detail, but damn.
Just wanted to say, that I ordered a BT-C3100 v2 a little over 1 year ago (straight from china on ebay). I did not have any of the 2 issues you had. My unit was never restarting and the fan, although pretty loud in general, oh yes it is, never gave obnoxious sounds like the one you have. I suspect your unit was simply slightly defective. What I have to mention though, my unit gave up the ghost literally a few days ago (the display went "crazy") and doesn't charge anymore. So under heavy usage (which mine did receive) it lasted 1 year. I still call it a winner, given the price tag (£28 inc shipping last year) and the functionality it provides. Cheers.
Well mine's been testing cells pretty much all day everyday for the last two years. Other than running it on a more powerful power-supply and changing the fan occasionally, it's still working perfectly (KNOCK ON WOOD).
Fan failure is more common than nitrogen in the air.
what did you used for 2amp discharge ?
Hello. Your video is very helpful.
But when you get a set of batteries(ie harvested. From random sources) are you putting straight in the bank to charge them from your dc constant charger? If so what voltage/ current? And how do you know when they are charged?
I am currently charging all with the opus and then putting in a box for a month like you. Then would check if they lost voltage and then would do a capacity check. Does my approach good as well ?
Since this video I've changed my strategy, I charge them in the DC-DC only to about 4v and let the Opus complete the charge. This slows the process a bit but makes for more consistent results. I know when the DC-DC is finished charging when the LED goes from red to green. The DC-DC is set for about 4A and 4V max.
I often put the cells straight into the Opus without pre-charging them. However, if the cell is less than about 2.3v I need to charge them a little on the DC-DC otherwise the Opus thinks they are nimh batteries and won't charge them.
You strategy seems fine to me, you are checking for self discharge before testing them. The thing is, often times, batteries with high self discharge rate also have low capacity. By checking the capacity first, if the cell is weak, I get rid of them right away, no need to keep them in "storage" for a month.
could you be able to link in the description of this video the dc-dc constant power devices and equipment you used in this video. Thank you. :)
Could you please tell me what is the maximum difference in capacity of the cells we can put in a pack?
It depends on how your configuration. If your pack is comprised of single cells in series, they need to be very close in capacity. If your pack is comprised of several cells in parallel, then as long as the total capacity of each group of cells is the same then you have more flexibility.
For example a 3s2p pack as follows, each set of cells has the same total capacity:
(2.1Ah+1.9Ah)-(2.2Ah+1.8Ah)-(2.6Ah+1,4Ah)
If youre asking what the difference in capacity between the 1A discharge and 2A discharge can be it entirely depends on the max discharge rate of the cell. If the cell is rated for 20A then you won't see a difference bigger than 100mah. If the cell is rated for 4A max then you might see a difference of 300mah or 400mah. Assuming all your cells are rated 4A-8A max discharge when new you probably don't want to see more than a 400mah difference. If they are far apart then your IR has gone up and the cell is only capable of maybe a 3A discharge so the difference between 1A and 2A is 33% of its discharge ability.
I'm planning to test 18650 same way as you do, thank you! Few questions though, when you test battery capacity first time and you got, let's say, 2400 mAh, then you let it sit for a month and then test it with 2a discharge, you expect to see result close to 2400 mAh or all that matters to you at this point is to get more than 2000mAh? Which capacity value (from first capacity testing or second) you then use to combine cells in pack?
When testing at 2A, the mAh obtained will always be less, 300 to 400 less is normal but when it's over 450 mAh it normally means the cell has a high internal resistance.
The difference you see between the 1A discharge test and ~2A discharge test (the resistors don't provide a constant current but a value of 2 ohms will give you 2.1A down to 1.5A) is dependent on the cells internal resistance. If the cell has a higher discharge rate/lower internal resistance it will be less impacted by the 2A discharge and will come out closer to the 1A rate. The highest discharge rated cells wouldn't be fazed by a 1A or 2A discharge and the numbers would be nearly identical but this was 2016, if you wanted high capacity you weren't going to get high discharge rates so a lot of the 2600mah cells had a max discharge rate of 5A. For example the red cells here are likely Sanyo UR18650ZY with a recommended discharge rate of 2.5A and a max of 5A. Speaking in very very broad terms, a new cell will only pull 75% capacity when discharged at its max rated discharge current. When it comes to used cells there are other variables, as internal resistance begins to spike when the cell has seen a few hundred cycles. This directly correlates to voltage drop and you can kind of cheat and figure out which cells have seen a big rise in internal resistance by applying a 1 ohm load when they are fully charged so they are discharging at 4.1A to 4.2A. You'll want to have a voltmeter connected directly to the cell terminals, any wires carrying current will give you an incorrect voltage reading. Using very thick wires can reduce the error of the voltage reading but its best to just attach a voltmeter by itself to the terminals. The moment you apply the load, make note of how low the voltage drops from its charged voltage and determine what the voltage drop is. Very broadly speaking, a new cell dropping more than 0.6V at 4.2A either has high internal resistance or isn't rated to be discharged at 4.2A. You can Google Mooch and HKJ's results to see their discharge graphs and what you should expect. Again, used cells will fare a bit worse but they shouldn't do too bad. If the voltage just bottoms out to 2.7V then that is not a cell you want to use.
Also keep in mind the Opus has a known problem that was partially mentioned here, the fan. People were always saying the Opus tested about 10% higher than other chargers and there's a reason why. When a cell is heated up to 35 Celsius it actually performs at its best and will discharge 105% capacity or a bit better if its new. Also, if your charger starts and stops the voltage is rebounding every time it does that which is equivalent to doing a discharge to 2.5V, watching it rebound up to 3V, restarting the test and getting another 5-10% out of the cell which is NOT the way it should be done. Once the low voltage cutoff under load is hit, that's it. Do not restart it. Well the fan on the Opus cant keep up so the charger gets quite hot during charge and discharge for some cells. The Opus will stop the discharge several times throughout the test and that's why it will take 4 hours to discharge a 2.5Ah cell at 1A. So those two factors are giving an inflated capacity result compared to the ZB2L3 which ends its discharge at 3V (though you can adjust it lower). The v2.2 Opus discharges to 2.8V and the v3.1 discharges to 3.1V so there will also be a small discrepancy there but not enough that leaving the ZB2L3 at 3V is ruining your comparison. Below 3V there is very little capacity so you might only get 100mah between 3.0V and 2.8V.
Hey I was wondering how long you let your 18650 batteries sit on the shelf to test the self discharge. Also how much of a drop in voltage you allow before calling a cell bad. For example I had a batch of cells tested and charged to 4.2 volts. They were left for a week and after that week they had all dropped by a bout 2 to 3 10ths of a volt. would you still keep these cells?
When batteries come off the Opus, I let them sit for several hours and they usually settle to about 4.15v. If they are lower, I top them up using a dc-dc converter so that they are all at 4.15v. I let them sit for a month and if they drop below 4.1v I consider them bad. The thing to remember is that the cell's voltage will drop right after it comes off the charger so your best bet would be to check the voltage after 24 hours and record that. Then re-check the voltage after a month. It should not drop by more than 0.05v. Also, I have noticed that some times, if you re-test the cells with a high self-discharge, they will some times be ok the second time. I figure it`s probably because they had been sitting unused for many years and need to be "refreshed".
Your opus charger fan is faulty, that sound is not normal, mine doesnt sound like that
Helpful, thanks
About 1 month charge evades me what logicdictates this NONE
You need to let the cells sit for a while to see if they exhibit a high self discharge. If the cell voltage drops, that probably means they are starting to develop an internal short which will most likely get worse over time. Also, if you build a pack with even one cell that exhibits a high rate of self discharge, then your pack will become imbalanced fairly quickly.
Its either let them sit and check the discharge rate or buy a YR-1035+ and check AC impedance. Otherwise, like Leaf Xpack said, you're going to be putting cells in your pack that are already developing internal shorts and your pack is going to be
a) a huge liability to have in your car or in your home
b) greatly decreased in usable capacity