Heaters and long charge times

I was trying out my Opus tester over the weekend using the charge function,and noticed a few cells going over the 60C temp limit and the Opus would drop the current then continuecharging after the cell cools a bit. I checked a few that were up to62 and 63 degrees, and got this photo of one over 60C.

Also notedlong charge times on some of these cells. The specs in the database (excellent resource) say about 3 hrs for full charge for the 3 or 4 cells Ilooked up.

Also Isee a difference in voltage comparing the Opus to my voltmeter... voltmeter is about 40 mv lower than Opus.

My questions are
1) at what temperaturedo you reject a cell for being a heater ? How do you catch heaters if you are not there monitoring in person?

2) doeslong charge times (>3 hrs) indicate issues with cells ? I saw some going 10 hrs, these started charging around 2.3v .

1. When i cant touch them charged at 1A. Then the cell is no good for my application and therefore binned. I catch them by time. I check 2 times per 24hours and since i run charge/discharge/charge they should just be done at 10-12 hours. All still charging are heaters.
Second test is just to let them sit and check self discharge. Most of the heaters will self discharge alot.

2. Yes long charging time is generally an issue. The opus will start charging slowly so it can easily take more than 3 hours. For instance a 3.5Ah cell will take at least 4 hours and with being totally empty it can take 5 hours too. Its all relative but 10 hours for a normal 2.5Ah cell... NO... (This is at 1A charge rate) If you change charge-rate to 0.2A then it will of course take long time. So check that.

Edit: The voltage will differ. You did measure at the cell and the Opus measure inside. At full rate charge that should diff somewhat. Try checking when the battery is kind of fully charged and the values should be closer. With that said the Opus is cheap.... It will vary easy 10% of the readings...

I charge my red Sanyos at 300mA , they take a day to test, but heaters only seem to get to hot to touch rather than burn your skin level, meaning I find them long before they reach deadly angry heater level. 1000mA is asking for trouble on red Sanyo if your not around to check on them.

Be interested to see if someone has had the sanyos catch fire!

You simply can't not monitor the cells while charging. Either you use a device that does it for you or you check them by touching them from time to time.
Long charge times can indicate a problem but it depends on the chosen charging current in relation to the capacity. If the cell has 3Ah and you charge with 0.3A then it is no wonder that it will take forever to charge it. However if it still takes a long time at a reasonable current then there is a problem with the cell. It will probably get hot then as the excess power is turned into heat. That is why the manufacturers state a charging time in the datasheet.

I always monitor the red sanyos and Charge Test at1000mA. I remove the heaters when too hot(my check using asurface temp gage says 55 C and over then)to handle,let them cool, then reinsert them into the opus. Then try again. Many stop heating after one or twotries.

If when charging they getvery close, meaning 4.18v or so and seem to take forever to get to 4.20v then I remove them again from the opus and reinsert them, charging at the 1000mA setting again. This seems to push them over and get to 4.20v and discharge. Not sure if its the initial 1000mA push before it adjusts downward or what? Not sure if this is the right thing to do but it works for me and saves time

If you test at 0.3A I also assume you never will go above 300mA when using the cell?

For testing without being around you can do like this:

I use an IR thermometre (FLIR TG165) and anything that's over 40C is removed right away and set aside. Eventually I'll try them again and if they're still over 40C, i'll bin them.

Thanks for the replies.


I have been doing all my chargingwith 1000ma.

I noticed another thread in this forum where temperature and current and specs and arduino are well documented, so i will spend some more time reviewing that post as well.


@daromer, nice video on the temp sensors for the Opus chargers. I am not kidding when I say that I ordered some thermistors today during lunch break... thinking I had an original idea to retrofit the Opus for temperature and voltage logging. That was before watching your video!

I was thinking of a "sensor disk" that could be inserted with the battery to measure temp, current and voltage. It would have wires also, and not much space to put it and the temperature is much lower at the end of the cell than in the middle, so I like your method expecially with the Graphite and Graphina logging and charting. Seems decades ahead of what I did just 7 yrs ago...


Here is a video I just quickly shot and uploaded to mark the crossover to 18650s and the changes the new projects will bring to the garage.


I like the idea of having automated logging to go along with manual testing. Actually, it would be nice to have automatic testing if it can be safe enough to cut the power or send me a txt when the temp gets too high.Until then,I will be studying more examples of how to implement automatic logging as I build up my test bench (mine will be a test wall to conserve space).

Thanks again for all the advice on this thread.

jestronix said:

I charge my red Sanyos at 300mA , they take a day to test, but heaters only seem to get to hot to touch rather than burn your skin level, meaning I find them long before they reach deadly angry heater level. 1000mA is asking for trouble on red Sanyo if your not around to check on them.

Be interested to see if someone has had the sanyos catch fire!

Click to expand...

I'm test charging some previously very hot red Sanyo's for the second time nowafter the initial wake up charge and I'm finding that those that hold their voltage well over the resting period (about a month) dont heat at all when charged again at 1Amp. Others here have also noticed this I think. So I'm wondering if its a chemistry thing with some of these cells as one user suggested and not (always) internal resistance?
I think in most powerwalls you will ever try and push 1Amp into a cell so its probably not an issue.

50C is my cut off for inclusion when testing.

Jimmy

Many people have seen it. Not sure in long term if it stays cool or if its one-time. I have not personally tested that. I just scrap them currently. (Have not had many at all so no loss)