escooter not lasting as expected SLA battery

Returnformer · Apr 11, 2019

hi. i purchased a used scooter style ebike from someone, and its not lasting as well as i thought it would. i was able to ride it home, a distance of about 4.5 miles, and it started out good, at maybe 25 mph, and made it up a fairly steep hill, but about halfway home or so it started slowing down, until it was barely crawling along at maybe 4-5 mph for the last mile or so. i dont have a charger yet (on the way) so im not sure charged voltage, but it currently reads about 48.5 volts. i know my lithium ion battery on my regular ebike only cuts out at 36 volts or so, so i would expect it to stilll work good at that voltage. unless maybe lead acid batteries are different...?

does this sound like its just an old battery without much capacity left? or might it be a problem with the scooter itself?

thanks.

amberwolf · Apr 12, 2019

A 48v battery (your scooter) and a 36v battery (your bike) are completely different cutoff voltages (LVC), dependent on both the chemistry (lead vs ltihium) and hte number of cells (24 vs 10) in series. (and also the controller, and/or the BMS, which only your bike's battery has)

SLA are saggy, and don't last very long--100 cycles (charging then discharging) or less is not uncommon. So used SLAs could have any number of problems. They may even have been left sitting discharged at some point (more than once), which sulfates (damages) them.

Anyway...your batteries are basically "dead" (discharged) when the speed starts to drop significantly (even though when you let off the throttle the voltage bounces back up). Recharging immediately at that point is the best option. Letting them sit any length of time after that without recharging damages them.

You could buy new SLA to verify, but my guess is that even brand new SLA won't get you much (if any) better than what you've already got. Typically you don't even get half the capacity of SLA as usable range. May take 2-3Ah per mile of "labelled" capacity.

You'd probably have to replace with a good lithium pack to get the more typical 1/2 to 1 Ah per mile range.

So if you have 4 x 12Ah SLA in series right now, then a quality 48v 12Ah lithium pack would weigh most likley less than half what your SLA does, have at least twice the recharging lifetime, and most likely more than twice the range (possibly several times the range.

What I would do first, is buy a wattmeter (tehre's a lot of threads about differnet kinds), to monitor actual power usage, peak and sustained currents, etc. I've used several kinds, and prefer the Cycle Analyst from http://ebikes.ca , but it does cost a lot more (has more functions though, which you may or may not have a use for).

possible searches
https://endless-sphere.com/forums/search.php?keywords=wattmeter&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

https://endless-sphere.com/forums/search.php?keywords=watt+meter&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Returnformer · Apr 13, 2019

amberwolf said:
A 48v battery (your scooter) and a 36v battery (your bike) are completely different cutoff voltages (LVC), dependent on both the chemistry (lead vs ltihium) and hte number of cells (24 vs 10) in series. (and also the controller, and/or the BMS, which only your bike's battery has)

SLA are saggy, and don't last very long--100 cycles (charging then discharging) or less is not uncommon. So used SLAs could have any number of problems. They may even have been left sitting discharged at some point (more than once), which sulfates (damages) them.

Anyway...your batteries are basically "dead" (discharged) when the speed starts to drop significantly (even though when you let off the throttle the voltage bounces back up). Recharging immediately at that point is the best option. Letting them sit any length of time after that without recharging damages them.

You could buy new SLA to verify, but my guess is that even brand new SLA won't get you much (if any) better than what you've already got. Typically you don't even get half the capacity of SLA as usable range. May take 2-3Ah per mile of "labelled" capacity.

You'd probably have to replace with a good lithium pack to get the more typical 1/2 to 1 Ah per mile range.

So if you have 4 x 12Ah SLA in series right now, then a quality 48v 12Ah lithium pack would weigh most likley less than half what your SLA does, have at least twice the recharging lifetime, and most likely more than twice the range (possibly several times the range.

What I would do first, is buy a wattmeter (tehre's a lot of threads about differnet kinds), to monitor actual power usage, peak and sustained currents, etc. I've used several kinds, and prefer the Cycle Analyst from http://ebikes.ca , but it does cost a lot more (has more functions though, which you may or may not have a use for).

possible searches
https://endless-sphere.com/forums/search.php?keywords=wattmeter&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

https://endless-sphere.com/forums/search.php?keywords=watt+meter&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

oh, oops. ive probably screwed the battery up even worse, then, as its been sitting a week already without being charged since i dont have the charger yet. its supposed to come tuesday, though.

my bike is also a 48v battery, 52 cell lithium ion, i think, otherwise, yeah, itd obviously be different cutoffs.

so it doesnt sound like anythings wrong with the bike itself, then? just needs a new battery, not that itll get a ton more range with one?

thanks.

amberwolf · Apr 13, 2019

Returnformer said:
my bike is also a 48v battery, 52 cell lithium ion, i think, otherwise, yeah, itd obviously be different cutoffs.

If it shuts off at 36v, then something is wrong with the system. A 48v lithium battery uses 13 cells in series to get the 48v (nominal), which is about 54v fully charged (4.2v per cell), and around 42v empty (about 3.2v per cell). (yours would be "4p" or four cells in parallel in each of the 13 groups, to get 52 cells).

Technically they may be able to discharge down to 2.8v per cell to totally dead, which would be about 36v but that's really not good for them, and repeatedly doing that will shorten their lifespan. It's pretty much just an emergency cutoff voltage, below which permanent damage to the cell can result (some of which can cause a fire, if not during discharge then during the subsequent recharge).

So it sounds like you have a controller that does not have it's own LVC, or it is set wrong, perhaps for a 36v battery instead of a 48v, so it is allowing discharge below about 42v, which it shouldn't.

I'd recommend putting a wattmeter on there, so you can stop discharging manually once it reaches 42v or so. Then you can look at how many Ah / Wh that is, and then keep track of your Ah / Wh usage. That will let you know about how much range you have left, as the battery ages it'll get less and less.

A simple voltmeter could also be used, but it will not give you the other useful information.

so it doesnt sound like anythings wrong with the bike itself, then? just needs a new battery, not that itll get a ton more range with one?

Probably nothing wrong with it based on what's been posted so far, other than an old SLA battery. More range will depend on the size of battery (watt-hours) vs the power demands of the scooter.

You may be able to use your ebike's battery to test the scooter with, if the bike's battery can handle the power output the scooter requires. (you can check the A rating of the controller on the scooter, if it's marked, with the A rating of the controller on teh bike, if it's marked. If the ratings are the same, or the bike's is higher than the scooter, then it should be safe to test. If the ratings on the scooter are higher than teh bike, then the scooter may need more power than the bike battery can supply safely (assuming the bike battery is rated to match the bike's controller).

LeftieBiker · Apr 13, 2019

Now you know what happens when an SLA battery is repeatedly run too low and then left undercharged (it's too common, so the first owner also likely did it). When you get new batteries, remember:

* Stop IMMEDIATELY when the scooter starts to slow down. A voltmeter will give you some warning, by dipping into the red zone under any load. If you have to run it a ways with a low charge, connect the charger the minute you get home. Even a couple of hours is too long to wait.

* ALWAYS recharge right after use. Even when you only ride a few minutes, recharge immediately. SLA batteries HATE to be below 100% charge, and will deteriorate fast if left undercharged - especially below 80%.

* If you leave the scooter for more than a couple of days, "pre-charge" it BEFORE using it. This will extend the range a bit, and may remove a little sulfation from the plates.

* SLA batteries have, as already mentioned, a limited life span. The more you stop well before that slowdown, the longer they will last.

Returnformer · Apr 13, 2019

amberwolf said:
If it shuts off at 36v, then something is wrong with the system. A 48v lithium battery uses 13 cells in series to get the 48v (nominal), which is about 54v fully charged (4.2v per cell), and around 42v empty (about 3.2v per cell). (yours would be "4p" or four cells in parallel in each of the 13 groups, to get 52 cells).

oh, well, that was actually just a guess to illustrate that it goes below rated voltage. ive never actually run it down to the point where it shut off. (unlike my old 36v bike.) i tracked the voltages before and after use for a couple days; looking at that, the lowest it went was 44.6. being that it was still working good at that voltage, i wouldve thought that the scooter should still work good at 48v.

amberwolf · Apr 13, 2019

Returnformer said:
oh, well, that was actually just a guess to illustrate that it goes below rated voltage. ive never actually run it down to the point where it shut off.

Well, garbage in, garbage out: Inaccurate data gets you inaccurate help; answers based on data that is only a guess is not necessarily reliable, so I'd recommend noting whenever you're posting guesses, and when you're stating measured data.

being that it was still working good at that voltage, i wouldve thought that the scooter should still work good at 48v.

I'm assuming the "48v" was after you stopped and got off and went to get the meter and then measured it. So the battery would have time to "recover" from whatever voltage it actually dropped to under load.

This is where a wattmeter is useful, because most of them monitor the minimum voltage a system drops to, and the peak current and watts, as well as watt hours and amp hours, and realtime voltage and current.

FWIW, an SLA battery at 12v is closer to dead than full; 10v is pretty dead. 13-14v is about full.

Returnformer · Apr 13, 2019

amberwolf said:
Well, garbage in, garbage out: Inaccurate data gets you inaccurate help; answers based on data that is only a guess is not necessarily reliable, so I'd recommend noting whenever you're posting guesses, and when you're stating measured data.

yes, definitely true, i shouldve specified...

amberwolf said:
I'm assuming the "48v" was after you stopped and got off and went to get the meter and then measured it. So the battery would have time to "recover" from whatever voltage it actually dropped to under load.

This is where a wattmeter is useful, because most of them monitor the minimum voltage a system drops to, and the peak current and watts, as well as watt hours and amp hours, and realtime voltage and current.

yes, it would have recovered from the load by then, but the same applies to my other measurements of my li-ion battery.

amberwolf said:
FWIW, an SLA battery at 12v is closer to dead than full; 10v is pretty dead. 13-14v is about full.

ah, so yeah, thats what i was wondering and kinda figured based off what i was seeing. the sla seemed pretty dead by 48 but my li-ion goes down to at least 44 or so.

amberwolf · Apr 13, 2019

Returnformer said:
ah, so yeah, thats what i was wondering and kinda figured based off what i was seeing. the sla seemed pretty dead by 48 but my li-ion goes down to at least 44 or so.

Different chemistries have different SoC (state of charge) curves.

Not everything on this site
https://batteryuniversity.com/learn/
is useful, but there is a lot of stuff there if you're interested in knowing more about how different kinds of batteries work.

Returnformer · Apr 13, 2019

amberwolf said:
Returnformer said:

ah, so yeah, thats what i was wondering and kinda figured based off what i was seeing. the sla seemed pretty dead by 48 but my li-ion goes down to at least 44 or so.

Click to expand...

Different chemistries have different SoC (state of charge) curves.

Not everything on this site
https://batteryuniversity.com/learn/
is useful, but there is a lot of stuff there if you're interested in knowing more about how different kinds of batteries work.

cool, thanks!

Dui ni shuo de dui · Apr 14, 2019

amberwolf said:
Returnformer said:

my bike is also a 48v battery, 52 cell lithium ion, i think, otherwise, yeah, itd obviously be different cutoffs.

Click to expand...

If it shuts off at 36v, then something is wrong with the system. A 48v lithium battery uses 13 cells in series to get the 48v (nominal), which is about 54v fully charged (4.2v per cell), and around 42v empty (about 3.2v per cell). (yours would be "4p" or four cells in parallel in each of the 13 groups, to get 52 cells).

Technically they may be able to discharge down to 2.8v per cell to totally dead, which would be about 36v but that's really not good for them, and repeatedly doing that will shorten their lifespan. It's pretty much just an emergency cutoff voltage, below which permanent damage to the cell can result (some of which can cause a fire, if not during discharge then during the subsequent recharge).

So it sounds like you have a controller that does not have it's own LVC, or it is set wrong, perhaps for a 36v battery instead of a 48v, so it is allowing discharge below about 42v, which it shouldn't.

Just a little remark:
You can set a lower cutoff voltage than the usual recommended voltage per cell, because of voltage sag under load.
Basically, when you accelerate your voltage will go down and if you set the cutoff too high then you just lose a bit of capacity because you will reach this value while you still have capacity left. It's not that much capacity, but in some case it can be the difference between riding and pushing

I agree that 36V might be a little bit too low, maybe 38V would be more appropriate, but it's not far off.
Reason being, after the cut off, the cells voltage will rise again and sit at a much higher value than under load, so they can remain like that for a while waiting to be charged again.
That depends a bit of how powerful your bike is though,if it isn't powerful then the lag will be low, in which case it's indeed better to go up.

So first thing, you need to determine your voltage sag (is it 1V under max load? 2V? 3V?), and then set your BMS limit accordingly.

escooter not lasting as expected SLA battery

Returnformer

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