How long should a new pack keep full voltage?

O

oobagooba

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Sep 16, 2014
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I have a pack under 2 months old it has lost .6 of a volt. 14s4p under 20 charge cycles on it, once the charger shuts down the voltage drops to 58.2.
If i leave the charger on overnight it drops even more, a 10 hour charge drops it to 57.8. I'm losing a full volt on a brand new pack. The vendor tells me this is "absolutely normal." ???

How long should a new pack stay at 58.8? What is your experience?

BTW I broke this pack in easy, never hammered, normally charge between 80-90%, once a week charge to 100%, no improvement.
 
Depends on bms setting and what cells do you have. The quality of cells is very important. So what cells do you have ? Please don't say just Panasonic or Samsung. Which ones.
 
Have you checked the output of the charger? The voltage may have drifted. Some chargers have a variable resistor to adjust the output and others can be adjusted by changing a resistor(s) on the circuit board.
 
Hard to tell what the true setting of your bms. ? Just watch it over time. Don't do a discharge range test do leave on charger a lot longer.
 
after charging the voltage drops to 4.157 volts.

this is complelty normal behaviour for a lithium cell.
 
IMO, pretty much normal. What's not so normal, is if this continues to degrade towards a resting voltage more like 4v per cell. That might indicate some problem cells in there.

So for the next year or so, you'd hope to see the whole pack fall a volt, maybe even two volts later on, then stop dropping if stored a few days or a week.

If the pack is not balanced, then your end resting voltage will always be lower. Because some of the parallel groups never got to full. Then the bms will of course drain the overcharged groups, resulting in a finished voltage lower than expected.

You might need to do some forced balancing. Charge full, Let the bms drain the high cells, then ride around the block, charge full, ride around the block, charge full. This results in the charger restarting, which it might not do on it's own.

If you can restart the charger just by unplugging and replugging the AC, no need to ride around the block.
 
Charger is putting out 58.9 resting and pushes hard up to 58.8, holds it for a while, then drops off. Once "the light goes green" it does not kick back on so there is no trickle or balance mode. Kinda sucks as i paid more for the most advanced charger that goes with the pack.

I will try dan's idea about force charging. Just leaving it on the charger does no good in fact the longer i leave it on the lower the voltage drops. Down a full volt in less than 2 months and 20 charge cycles seems like a lot of loss on a high end pack. I have seen guys on here claiming they still have full capacity after a lot longer than 2 months and was expecting something similar. I have a year-old bmsb pack that holds more voltage and has been pushed hard in summer and winter for over a year now.



flippy said:
after charging the voltage drops to 4.157 volts.

this is complelty normal behaviour for a lithium cell.
Click to expand...
thanks but that really doesn't answer my question. no offense but it just sounds like marketing hype or a shill, no real experience like what i was asking about
 
It sounding like the charger is not turning back on after the bms draining the high cells. Is Dan's replugging trick working after letting the battery seat and balance ?
 
How hard would it be to get it charged, and then disconnect the BMS and let it sit for a while?

The charge voltage dropping sounds pretty abnormal, despite what that vendor said... have you got access to a different charger to eliminate that as the problem?
 
I can't relate to weather you have a true problem or not. But I'm curious why are you full charging a pack just to let it sit for 2 months? This is a no-no for pack longevity. When the pack is not expected to be used for long periods it should be discharge to around 50%. At least that's my understanding.

Bob
 
Another angle would be to charge let set for bms to balance for a day then replug charger and let set with charger time. To see if it further balance your pack. Or to help find the parasite. If so worried put a set of sense wires for ez checking and logging. As logging voltage on paper is proof.
1. 4.14
2. 4.09
3. 3.95
14. Xxx volt
 
dumbass said:
I can't relate to weather you have a true problem or not. But I'm curious why are you full charging a pack just to let it sit for 2 months? This is a no-no for pack longevity. When the pack is not expected to be used for long periods it should be discharge to around 50%. At least that's my understanding.

Bob
Click to expand...
It doesn't sit, i've been using it. For about 6 weeks now, around 20 charge cycles. I don't let it sit fully charged. I have 3 cheaper packs from less-praised vendors that are older and holding more voltage than this one.

I was hoping people would chime in with facts like "my pack holds full voltage after 6 months and 50 cycles" or "my pack is at 58.6 after a year" or whatever the going rate is. Especially with all the people using hi-power packs from "reputable" vendors on here. This is not a cheap pack from a chinese vendor.

The force balance method got it up to 58.7 at one point. I will continue to try that.
 
oobagooba, your charger is acting like a typical lead 48v charger if it turns off after it hits 58.8v. I am not an expert, but for a 14s lithium charger, it should be around 59v and stay at that voltage until you turn it off so it can balance the pack.

I have several 48v lead acid battery chargers that I use to charge my 48v ping. It gets the pack to 58.8, then turns off and does not turn back on. The BMS quickly drops the voltage down to about 57v because the charger stays off. I hook up one of these to get the pack balanced.

ebay dc step up converter.jpg
I would not worry too much about the drop-off, its probably just the BMS doing its job. I would try playing with the charger. You could open up the battery and take a picture of the BMS if you don't know the model. The experts here can help you then.

Good Luck
 
Worth noting is that a Li-ion cell if charged using a 4.200v CC/CV charge profile should actually never be 4.200v off the charger. If its 4.20v+ its being slightly over charged, but not a big deal. The end resting voltage will depend heavily on the CV cutoff current. For example 200mA cutoff vs 20mA will be a difference of maybe 0.03 to 0.04v or so. But never trickle charge Li-ions or that can lead to metallic lithium plating. Most cells will specify a recommended cutoff current generally in the 20-100mA range for 18650s. The lower the cutoff mA the fuller the charge. Cells with more cycles and wear on them will drop more voltage after they are charged and have rested.
 
So i found another problem. The built-in meter displays higher than actual voltage. Charger display reads 58.8 but my dvm says 58.3. Battery displays 58.7 at full but dvm says 58.4. My dvm is tits on, it reads full voltage on 3 other chargers i have.

That makes 3 problems with this battery & charger. 1) It doesn't charge to full. 2) The built-in meters read higher than actual. 3) The longer i leave the charger plugged in the more it drains the pack.

999zip999 said:
Oh so you will tell us where you got the pack.
Click to expand...
Luna. After a few emails they quit talking. Not sure what to do next. As dogman said i am concerned about longevity on this pack not charging to full. It is less than 2 months old.
 
Undercharging ,,, resulting in less balancing won't lower the lifespan per se.

The key thing to figure out here is if your bms is balancing the pack or not. I still suspect it is, which is why the pack lowers voltage.

Explain more to us,,, the pack drains more if you leave it on the charger? It holds its voltage if you take it off? I'm just getting confused what is really going on here. It still sounds more or less normal to me. Nothing is that far off, as far as voltages go.

Sure, you'd like perfect, but the real world is always slightly imperfect. I've owned one battery in my life that acted close to perfect, that was pingbattery number one, in 2008. All others have had some voltage drop once used a few cycles. Some right away.

I'm seeing that your pack dropped .04v per cell average, in the first post. so your cells are at 4.16v overnight. Dude, that's full. If they don't hold 4.2v they don't. that,, again, sounds about normal to me. It's not a gas tank, that always holds 15 gallons no matter how old the car is. It's a battery, and what you get when they are new is what you get.

Maybe I've mis read again,, I do that at times. If your battery is dropping from 58v to 54v,, all by itself, unplugged from everything,, overnight. Then you'd damn sure think something serious was wrong.
 
dogman dan said:
Explain more,,, the pack drains more if you leave it on the charger? It holds its voltage if you take it off? I'm just getting confused what is really going on here.
Maybe I've mis read again,, I do that at times.
Click to expand...

Hmmm, i thought i addressed that issue above but one of my posts seems to have disappeared.

Yes, as I said above, the charger drains the pack the longer it is left on. After 10 hours it drains the pack voltage to 57.8, or possibly 57.3. At this point I may have still been trusting the built-in factory meter. Once I checked the Luna meter I see it is overestimating voltage by .5v.

But the primary problem is the charger isn't putting out the full 58.8. Only 58.3. That is why the pack isn't coming up to full. I am working on getting another charger now.
 
Is this Luna's three mode charger ? Do you have a watt meter or C.A. for wh/hr . What's your capacity ? You can fully charge then unplug bms and wait a day to see if cells are leaking voltage or bms draining the pack.
 
And the pack does not drain any,,,, if you take it off the charger overnight?

That's what I'm fishing for.

And for the last time,, you are shitting bricks over nothing at all, if it only drains a volt. On the charger, off it, one volt is like worrying that you got a penny shorted when the cashier made your change.

Let us know if your pack self discharges enough to care about.

Sure, we'd all love cells that hold 4.2v forever, and sometimes we do get some that do that for a month, maybe even six months. But most of the time, right out of the box they only hold 4.18 or whatever. Get over it unless the pack is self discharging a lot more.

Most likely your bms is also responsible for most of it,, doing exactly what it's supposed to do. Nothing to do with the charger. But you do need a charger that does top off the pack.
 
The way this thread ends is not the way it began. Originally I thought there was a problem with the battery, and the thread title and my first 2 or 3 posts reflect that. Since starting this thread I have determined that the charger is not putting out full voltage, so the pack is not getting full voltage, and probably never has.

Once someone above asked what the charger was putting out... only then did I test the charger output separately. Up to that point I was trusting the charger's built-in voltage display (as well as the battery's; both are not displaying the actual output voltage). For some reason the display is .5 volt off from actual output. For some reason the charger is only putting out 58.3, not 58.8.

I am in the process of getting a new charger. Until I get a charger that puts out the full 58.8 volts, any speculation on the state of battery is moot.

Again, this thread has been a learning process, and once I determined that the charger is the primary problem, the title and my first couple of posts about the battery are no longer of direct pertinence to the actual issue. I will follow up once I get a charger that puts out the full advertised voltage.
 
I experience the same thing.. Try and unplug the charger from the socket but leave it plugged to your battery pack, in my case the red light indicating that the charger is on is still lit even after unplugging from the outlet meaning it gets its power somewhere, probably the battery.

Just spit balling here, but maybe the charger once it hits the target voltage stops charging and as long as you leave it plugged on the battery it will draw power from the battery. I have a socket with a timer so it goes off automatically, I'm almost always is spot on with the time it takes to charge my battery since i have a watt meter and i get to see how much i consume, from that i adjust the socket timer.

Sent from my SM-N9005 using Tapatalk
 
all chargers have a load on the output. if no power is suppllied that load will drain a pack. this is the case for all non-linear power supplies.

if you have a onboard charger you can use a relay that disconnects the charger from the pack when no main AC is supplied.
 
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