LiFePO4 or regular lithium ion cell?

[tmho]

I have some 18625 cells. The voltages are between 3.6V and 3.7V. There is no marking nor label on them. I am not sure if they are LiFePO4 cells or the regular lithium ion cells. I understand that the nomial voltage for LiFePO4 is 3.2V and the maximum voltage is 3.7V. For lithium ion cells, the nomial voltage is 3.7/3.6V and the maximum voltage is 4.2V. Is there a simple and safe way that I can find out what they are? (If I charge them to 4.2V, I am afraid that they will explode if they are LiFePO4 cells).

 

[mushymelon]

I have some 18625 cells. The voltages are between 3.6V and 3.7V. There is no marking nor label on them. I am not sure if they are LiFePO4 cells or the regular lithium ion cells. I understand that the nomial voltage for LiFePO4 is 3.2V and the maximum voltage is 3.7V. For lithium ion cells, the nomial voltage is 3.7/3.6V and the maximum voltage is 4.2V. Is there a simple and safe way that I can find out what they are? (If I charge them to 4.2V, I am afraid that they will explode if they are LiFePO4 cells).

If the health of the batteries are unknown it may be harder to tell what chemistry you have.
You may be able to determine your battery type by monitoring the voltage of the battery under load until it drops of the cliff.
lifep04 and lipo will have different characteristics but again if the batteries are of unknown health and if you don't have a shit pile of them. Use them in 18650 flashlights and charge them to 3.6 3.7.

Cheers

Mushy

 

[tmho]

I have some 18625 cells. The voltages are between 3.6V and 3.7V. There is no marking nor label on them. I am not sure if they are LiFePO4 cells or the regular lithium ion cells. I understand that the nomial voltage for LiFePO4 is 3.2V and the maximum voltage is 3.7V. For lithium ion cells, the nomial voltage is 3.7/3.6V and the maximum voltage is 4.2V. Is there a simple and safe way that I can find out what they are? (If I charge them to 4.2V, I am afraid that they will explode if they are LiFePO4 cells).

If the health of the batteries are unknown it may be harder to tell what chemistry you have.
You may be able to determine your battery type by monitoring the voltage of the battery under load until it drops of the cliff.
lifep04 and lipo will have different characteristics but again if the batteries are of unknown health and if you don't have a shit pile of them. Use them in 18650 flashlights and charge them to 3.6 3.7.

Cheers

Mushy

Hi Mushy, thanks for your reply. The cells are in a battery pack. It should be at least 6 or 7 years old. Do you know if LiFePO4 cells were popular in the form of 18625 6 or 7 years ago?

 

[mushymelon]

Hi Mushy, thanks for your reply. The cells are in a battery pack. It should be at least 6 or 7 years old. Do you know if LiFePO4 cells were popular in the form of 18625 6 or 7 years ago?

18625 is not a standard i'm familiar with. 18650 is more likely the battery you have.

Where did you get them?

How many packs / how many cells in a pack?

What type of battery pack?

-ebike
-laptop
-backup battery
-unknown

 

[tmho]

Hi Mushy, thanks for your reply. The cells are in a battery pack. It should be at least 6 or 7 years old. Do you know if LiFePO4 cells were popular in the form of 18625 6 or 7 years ago?

18625 is not a standard i'm familiar with. 18650 is more likely the battery you have.

Where did you get them?

How many packs / how many cells in a pack?

What type of battery pack?

-ebike
-laptop
-backup battery
-unknown

Sorry I made a mistake. It should be 18650 instead of 18625.
I got it from someone. It should be from a ebike. Totally, there are 40 cells, 4 cells in parallel in a group and totally 10 group in series.

 

[Spacey]

10 in series sound like li-on and not lifepo4. Usually 12 cells in Lifepo4 if they are a decent supplier...some battery makers cheat you by only using 10 or 11 cells to just make 36v. 43v is usually 12 cell lifepo4....li-ion is usually 10 cell as the cells are over 4v as opposed to lifepo4 3.6v

 

[mushymelon]

Ok so now were talking about a complete pack.
Possible ebike pack.

Is there a bms onboard this pack ?

Do you have the original charger?

Are you planning on using the pack the way it is or reclaiming good cells and rebuilding the pack?

Pictures?

 

[999zip999]

Info please.

 

[tmho]

Thanks for the reply. But sorry I am busy right now. Will provide the information and photos tomorrow evening hopefully.

 

[tmho]

Ok so now were talking about a complete pack.
Possible ebike pack.

Is there a bms onboard this pack ?

Do you have the original charger?

Are you planning on using the pack the way it is or reclaiming good cells and rebuilding the pack?

Pictures?

Yes, I think there is a bms onboard.
Yes, I am supposed to have the original charger. But please see the long story below if you don't mind.
I plan to find out if there is anything wrong with the pack.
The long story:
My friend got an ebike 6 or 7 years ago. Last year he told me that the ebike could only run a very short distance and asked me to check that for him. Because of the long winter/rainy season here, I did not check it right away. Before this summer, I started to recharge the pack first with the charger (I thought with the charger my friend gave me together with the ebike and battery pack). (According to my friend, it should be 36V). After about a month, I checked the voltage of the battery pack was 40V. Then I took the ebike out for a ride. After riding with battery power for a distance of about 12km, I found that the voltage dropped to 38.3V. I recharged it for about 6 hours and I found the voltage was still 38.3V. Then after a few days, I rode it again and I found that less than 5 minutes, there was no more power, and the voltage dropped to 36.4V. I then recharged the battery again for more than 8 hours. While charging, the voltage of the pack was 35.5V and after charging (unplugged), the voltage was 36.6V. Another ride showed power was down before 1 km was ridden. Then I checked the charger and found that is no label/markings. The output voltage was measured to be 37.2V. But how come I got 40V at the beginning. I think I used the wrong charger at the first recharging. (I have 2 ebikes myself. One is with 48V LiFePO4 pack and so I have a charger for it with an output voltage of 58.3V. Its plug is the same as the charger for my friend's ebike charger. Then I think I had used my charger for 48V pack to charge my friend's 36V pack at the first recharging by mistake. That seems showing that my friend's pack should be Lithium ion which should have a maximum voltage of 10 x 4.2=42V.) But how come my friend got a charger with output voltage of only 37.2V. He only got one ebike and so would not give me another one. He had used it successfully at the beginning. So I am confused what type of cells they are and what had gone wrong. Sorry, if I have not made myself clear.

 

[mushymelon]

The pictures show a 10s battery to me.
As spacey pointed out before thats lipo when advertised as a 36v pack.
6-7 years old helps confirm this.

If you fully charged this pack with a 48v lifep04 charger thats bad likely damaged the battery.
if your lucky the bms saved the batteries. If your unlucky your bms was damaged as well.
The voltage reading your getting are very strange. (possible bad charger)

Does the charger hit hvc? ( high voltage cutoff )

Also test the paralleled groups voltages and report back. You can use the balance taps but I prefer to get the readings directly from the battery. Test all 10 groups

 

[dnmun]

i only see 9 pins and 10 channels so the B- is the negative of the first cell and the B+ is the positive of #10. if you have a BMS it would not overcharge if you used a higher voltage charger. it would shut off for HVC.

you need to find that 42V charger, put the battery on the charger and measure the cell voltages first. measure while the battery is charging and post up here.

measure the first cell between the B- spot and the first pin and measure the top channel between the top pin on the sense wire plug and the red wire from the battery to the BMS.

you need to post a better picture of the BMS too. both sides.

 

[tmho]

The pictures show a 10s battery to me.
As spacey pointed out before thats lipo when advertised as a 36v pack.
6-7 years old helps confirm this.

If you fully charged this pack with a 48v lifep04 charger thats bad likely damaged the battery.
if your lucky the bms saved the batteries. If your unlucky your bms was damaged as well.
The voltage reading your getting are very strange. (possible bad charger)

Does the charger hit hvc? ( high voltage cutoff )

Also test the paralleled groups voltages and report back. You can use the balance taps but I prefer to get the readings directly from the battery. Test all 10 groups

Sorry I am not sure what do you mean by "Does the charger hit hvc?" Do you mean if the pack had reached hvc by its bms when charged by my charger for 48V LiFePO4 pack? If that is the question, then I think yes because otherwise I guess the pack would explode. (I did not monitor the charging process because I thought that I was using the correct charger).
The voltages are 3.79, 3.37, 3.64, 3.76, 3.75, 3.73, 3.72, 3.71, 3.69, & 3.69. For the second group with 3.37V, I have manually charged it up to 3.73V to match with the other group.

 

[tmho]

i only see 9 pins and 10 channels so the B- is the negative of the first cell and the B+ is the positive of #10. if you have a BMS it would not overcharge if you used a higher voltage charger. it would shut off for HVC.

you need to find that 42V charger, put the battery on the charger and measure the cell voltages first. measure while the battery is charging and post up here.

measure the first cell between the B- spot and the first pin and measure the top channel between the top pin on the sense wire plug and the red wire from the battery to the BMS.

you need to post a better picture of the BMS too. both sides.

Thanks for the reply.
There is no 42V charger. Mine is for 48V LiFePO4 pack. My friend's charger is with an output voltage of 37.2V. He got only one charger.
Below are the picture of the BMS. Hope this time is better.

 

[dnmun]

ok, so this is considered a '36V' lifepo4 pack and you use that 37V charger to charge it. looks like it is balanced too so it should work.

your problem is that it won't charge or is there no output current? if there is no output current you can measure the voltage on the gate of those three mosfets.

the mosfet legs, from left to right, are gate drain source. the gate turns on the mosfet when the voltage on the gate is raised to 10V. the current flows from the drain to the source and the source is connected to the negative terminal of the battery.

use the 20V DC scale on your meter, put the black probe on the source and red probe on the gate. measure that voltage. the gate will be the far right leg in your picture since the mosfet is upside down. the two on the right are the output mosfets.

you can do the same for the other mosfet on the left which is the charging mosfet if it is not charging.

 

[tmho]

ok, so this is considered a '36V' lifepo4 pack and you use that 37V charger to charge it. looks like it is balanced too so it should work.

your problem is that it won't charge or is there no output current? if there is no output current you can measure the voltage on the gate of those three mosfets.

the mosfet legs, from left to right, are gate drain source. the gate turns on the mosfet when the voltage on the gate is raised to 10V. the current flows from the drain to the source and the source is connected to the negative terminal of the battery.

use the 20V DC scale on your meter, put the black probe on the source and red probe on the gate. measure that voltage. the gate will be the far right leg in your picture since the mosfet is upside down. the two on the right are the output mosfets.

you can do the same for the other mosfet on the left which is the charging mosfet if it is not charging.

My problem is I am not sure if the cells are LiFePO4 (max voltage 3.7V) or Lithium ion (max voltage 4.2V). Also, it seems that I do not have the proper charger for it.

 

[mushymelon]

I'm a little confused too because dnmun knows his stuff.

You could attach your multimeter to your lowest cell group and run a load on your battery until you reach lvc (low voltage cut-off).

depending how your bms is setup.

lifep04 2.0- 2.3v

lipo 2.5 - 2.7v

The cells will bounce back up quickly after the load is removed so you need to record the lowest cell v immediately after lvc.
If the bms is working properly you should be able to use it to identify your chemistry type.

Then we can trouble shoot your problems.

 

[tmho]

I'm a little confused too because dnmun knows his stuff.

You could attach your multimeter to your lowest cell group and run a load on your battery until you reach lvc (low voltage cut-off).

depending how your bms is setup.

lifep04 2.0- 2.3v

lipo 2.5 - 2.7v

The cells will bounce back up quickly after the load is removed so you need to record the lowest cell v immediately after lvc.
If the bms is working properly you should be able to use it to identify your chemistry type.

Then we can trouble shoot your problems.

Thanks for the reply. Will try that when I have found a suitable load. At this moment, I cannot think of any suitable load I have on hand other than the e-bike. May be I need to create a connection between the pack and the e-bike while the pack is opened.

 

[dnmun]

the BMS is trying to balance the pack to 3.6V so that is why i said it is a lifepo4 imo.

you can try raising the charger voltage up by several volts and watch to see where the shunt transistor turn on so you will know for certain then.

lifepo4 drops to 3.37V and lipo to 3.8V.

in the past a 36V lifepo4 pack was 12S but they decided they could make this one 10S and still call it 36V battery. jmho.

 

[tmho]

I'm a little confused too because dnmun knows his stuff.

You could attach your multimeter to your lowest cell group and run a load on your battery until you reach lvc (low voltage cut-off).

depending how your bms is setup.

lifep04 2.0- 2.3v

lipo 2.5 - 2.7v

The cells will bounce back up quickly after the load is removed so you need to record the lowest cell v immediately after lvc.
If the bms is working properly you should be able to use it to identify your chemistry type.

Then we can trouble shoot your problems.

Thanks for the reply. Will try that when I have found a suitable load. At this moment, I cannot think of any suitable load I have on hand other than the e-bike. May be I need to create a connection between the pack and the e-bike while the pack is opened.

Finally, I did something to check the lvc, but the results are still confusing me.
I only could find the e-bike as the load to the battery pack. At first I open the pack and connected the cell no.2 (supposed to be the lowest cell group) to a meter to monitor the voltage. I also connected the pack to the e-bike. I turn the throttle all the way and let the motor ran in idle (no body sitting on the bike, just let the wheel rotate without touching the floor). After waiting for a while, I started to keep squeezing the brake to slow down the wheel hoping that this would speed up the happening of the lvc. At about 3.12V, the power was cut. But the voltage soon went back to 3.50V after 1 or 2 minutes. Before recharging the pack, the pack voltage was 35.4V. Then I recharged the pack with the original charger (output voltage 37.2V). The voltage of the pack went up gradually to 38.2V and the indicator on the charger was red indicating it was charging. (Then my first confusion is how come a charger with output voltage of 37.2V can charge a pack to 38.2V.) I did not continue the charging because I needed to go out and I did not want to leave the charging unattended. After several hours, I came back home and the pack voltage was found to be 37.4V. When I plugged back the charger, the charging indicator stayed green meaning it was not charging, and there was no change in the pack voltage.
One day later, I checked the lvc again in a different way. I welded 2 wires to the cell no.2 so that I can monitor it voltage while the pack is close/assembled. Then I took the e-bike out and ride it and at the same time monitoring the voltage of cell no. 2. After riding for 9.5km, the power was cut automatically and the voltage of no.2 cell group was about 3.51V. The pack voltage was about 35.5V.
Today, I tried to recharge the pack again. The pack voltage rose gradually in about 2 hours from 35.5V to 40.2V. Then the indicator on the charger changed from red to green and the voltage of the pack came down gradually to 39.3V. For the cell no.2 pack, the highest voltage was 4.04 and came down to 4.02V.
Will these show the pack is regular lithium ion instead of LiFePO4? Is the original charger suitable for this pack? How come the pack can reach a voltage which is higher than the voltage of the charger?

 

[tmho]

Later, I checked the voltages of each cell group with results as follows:
3.95, 3.96, 4.17, 3.91, 3.90, 3.89, 3.90, 3.89, 3.89, 3.89

Then I will say the hvc should be about 4.2V at cell group no.3. But at this moment, the balancing function of the bms is not working properly. Am I correct?

 

[fechter]

I would guess those are Li-Mn cells and should charge to 4.2V, or 42v for the pack. It's possible the charger is not putting out the proper voltage to get a full charge. I've never seen LiFePO4 in 18650 cells from that era.

 

[mushymelon]

Later, I checked the voltages of each cell group with results as follows:
3.95, 3.96, 4.17, 3.91, 3.90, 3.89, 3.90, 3.89, 3.89, 3.89

Then I will say the hvc should be about 4.2V at cell group no.3. But at this moment, the balancing function of the bms is not working properly. Am I correct?

My best guess is that your correct, and the batteries are not balancing.

Please confirm charger and battery voltages with another multimeter first, multimeters go squirrely all the time.

Keep in mind cell #2 may not be the cell thats hitting lvc first bad cells will often charge up faster and drop faster.

My next step would be to find a charger that outputs 42v.

Bring down that high cell first then charge back up.

 

[fechter]

Many chargers will only reach their peak voltage with a load. Once the charger current drops (indicating full charge), many of them will cut the output voltage. There are many flavors though. In other words, if you measure the charger output without the pack attached, you may get a misleading measurement.

With the pack attached, you should see the voltage climb steadily until it reaches some maximum and it generally holds there for a while, then the charger shuts off or goes to float.

With LiFePO4, once they reach around 3.7v, the voltage will start climbing rapidly as they are done charging. LiIon does this around 4.2v.

 

[tmho]

Later, I checked the voltages of each cell group with results as follows:
3.95, 3.96, 4.17, 3.91, 3.90, 3.89, 3.90, 3.89, 3.89, 3.89

Then I will say the hvc should be about 4.2V at cell group no.3. But at this moment, the balancing function of the bms is not working properly. Am I correct?

My best guess is that your correct, and the batteries are not balancing.

Please confirm charger and battery voltages with another multimeter first, multimeters go squirrely all the time.

Keep in mind cell #2 may not be the cell thats hitting lvc first bad cells will often charge up faster and drop faster.

My next step would be to find a charger that outputs 42v.

Bring down that high cell first then charge back up.

Thanks for your suggestion of checking the charger and battery voltages. Before, when I checked the output voltage of the charger, I first plugged the charger to the AC source. Then connected the output of the charger with the probes of the multimeter. This time, I did something different. I first connected the output connectors of the charger to the probes of the multimeter before I plugged to the AC source. To my surprise, I found the reading of the multimeter first showed a reading of 42.5V. But after 0.5 second, the reading changed to 37.2V. This had been confirmed to be the same with another multimeter. Is the charger with problem or it is designed like this? Do I need another charger? (Other voltages had been confirmed to be correct with another multimeter.)