Ypedal
100 TW
3.5v is fine, it's like 97% charged....
48 volt lifepo4 battery cutting out prematurely
- Thread starter johnnyz383
- Start date
johnnyz383
100 W
Well...i took the trike out for a spin and viola!..all back to normal...i only went out for a 10 min hard drive, because its -8 here...and when i returned the standing voltage is at 52.7...under hard load, voltage sag was 44.5 and cruising was about 49-50 volts, which is normal for my equipment ( Crystalyte 3540 hub motor, Lyen 16 fet 65 amp controller). So letting lifepo4 18650 cells get discharged to 1/2 volt doesnt necessarily mean that the cell is damaged permanently.
John
John
johnnyz383
100 W
As a matter of fact i measure all 16 groups of cells...almost all were 3.333 +/- .01 or .02. Thats the best ive ever had the pack balanced.
John
John
dnmun
1 PW
balance has nothing to do with the resting voltage. a balanced pack has equal amounts of charge stored in each cell, not equal resting voltage.
izeman
1 GW
johnnyz383 said:
as dnmun said: that's nothing special for lifepo4 batteries. they stay around 3.33v for a long time. that's why it's so hard to say from the cell's voltage if it almost full or almost empty.
dogman dan
1 PW
No, they came back, at least for a few ah worth anyway.
But you do know it's battery murder using that 65 amps controller right? I'm making some assumptions of course, about the size of the pack and the quality of the cells. You called it a duct tape pack, so I assume its the cheap cells best used at 1 c max. Generally rated rather optimistically at 2c.
In addition, the pack must be shorting someplace, if cells are draining like that sitting. It could be the bms still draining them, or if this is the vpower type pack, Dnmun often says they short out at the tabs when vibration chafes through the shrink on the cells. Or one cell could be shorted internally. How could that have happened? You only have a 65 amp controller on it.
Start saving for the real battery you need.
But you do know it's battery murder using that 65 amps controller right? I'm making some assumptions of course, about the size of the pack and the quality of the cells. You called it a duct tape pack, so I assume its the cheap cells best used at 1 c max. Generally rated rather optimistically at 2c.
In addition, the pack must be shorting someplace, if cells are draining like that sitting. It could be the bms still draining them, or if this is the vpower type pack, Dnmun often says they short out at the tabs when vibration chafes through the shrink on the cells. Or one cell could be shorted internally. How could that have happened? You only have a 65 amp controller on it.
Start saving for the real battery you need.
dnmun
1 PW
if he has high current discharges then the anode could be growing dendrites that push through the separator and short it internally enuff to drain it down. but without capacity or internal resistance data there is little info to work from.
dogman dan
1 PW
He may have a 65 amps controller, but not be pulling 65 amps. Maybe he's got 40 ah and could handle it at 1.5c. But my guess is he's been hammering that thing to death.
johnnyz383
100 W
Well i appreciate all the comments but you know what they say about assumptions....
.firstly, i have a 65 amp Controller but maxed out at about 45 amps. This being pulled for very short periods of time trailing off rapidly as the speed increases. I have had lifepo4 18650 batteries( total 50 volt, 20 amp) pull 65 amps and went 900 cycles so please give me a break and dont tell me that your killing them by pulling this kind of amperage as, again your not putting this load for any more than a few seconds. Secondly the short occured because the outside batterie's plastic cover wore enough to contact the other battery beside it causing it to short. And the battery pack that went at least 900 cycles would still maintain a surface charge after fully charging. In fact these batteries are extremely durable and hold up to many differing conditions. My next pack will be built using the headway 15 amp cells, and these can certainly take more than 65 amp burst ( in a 72 volt 15 amp configuration)
John
.firstly, i have a 65 amp Controller but maxed out at about 45 amps. This being pulled for very short periods of time trailing off rapidly as the speed increases. I have had lifepo4 18650 batteries( total 50 volt, 20 amp) pull 65 amps and went 900 cycles so please give me a break and dont tell me that your killing them by pulling this kind of amperage as, again your not putting this load for any more than a few seconds. Secondly the short occured because the outside batterie's plastic cover wore enough to contact the other battery beside it causing it to short. And the battery pack that went at least 900 cycles would still maintain a surface charge after fully charging. In fact these batteries are extremely durable and hold up to many differing conditions. My next pack will be built using the headway 15 amp cells, and these can certainly take more than 65 amp burst ( in a 72 volt 15 amp configuration)
John
johnnyz383
100 W
Oh by the way, as for internal resistance as far as the pack is concerned, please re-read the posts. At full throttle, and with a resting voltage of 52 volts, it will sag about 43 volts at 60 f. On the ebike.ca hub motor simulator ( which is remarkable accurate) that equates to about 0.03 ohms, nothing remotely indicative of a worn out battery thats been "hammered to death"
John
John
Hillhater
100 TW
johnnyz383 said:
?? In order to have .03 ohm IR with a 9 volt sag, you would need to be drawing 300 amps !
if that 9 volt sag is at your max amperage of 45 amps, that suggests a pack IR of 0.2 ohms !
..and 9 volt sag is pretty high !
But "PACK" IR doesnt tell you a lot, you could have a near dead short in one parallel group.
You need to check the IR of each group.
Until you do, you wont know if you still have some dud cells lurking in there.
Also , you have never actually said exactly what this pack is ?
I have deduced its a 16S, 16P pack of 18650s , but what Ahr capacity is it ? ... any idea what cells are in it ?
johnnyz383
100 W
Hillhater said:johnnyz383 said:
?? In order to have .03 ohm IR with a 9 volt sag, you would need to be drawing 300 amps !
if that 9 volt sag is at your max amperage of 45 amps, that suggests a pack IR of 0.2 ohms !
..and 9 volt sag is pretty high !
But "PACK" IR doesnt tell you a lot, you could have a near dead short in one parallel group.
You need to check the IR of each group.
Until you do, you wont know if you still have some dud cells lurking in there.
Also , you have never actually said exactly what this pack is ?
I have deduced its a 16S, 16P pack of 18650s , but what Ahr capacity is it ? ... any idea what cells are in it ?
Thanks for the reply...
I suppose you could be right. Given the time i certainly can check this to be true or not. When i checked the ebike calculator i came up with the following;
1st, the simulator says that a 48 volt life battery with a semi recumbent ( mine is a recumbent trike ..Arctrike.com) should go 51 kph. On a level ground, it does 50 kph. This equates to a voltage sag of 45 volts. Ok mine sags to about 44 volts, so it does look like i have more resistance than i should. Yes you are right it is a 16 s 16 p pack of 18650 cells at 20 amps. but however i really only get about 750 watt hours out of it. How do you propose i check the IR of each of the 16 cell groups??
John
