Can a battery have different cut off voltages?

[Nvreloader]

I have 2 different sets of OEM batteries, both the same as far as battery types, 21700 cells,
one has a cutoff voltage of 43.5V = 29.0% v of charge and,
the other has this reading of 46.6v = 49% of charge, as I have just found out.

Can either of these voltages be changed and via what method?
I don't like the 46.6 cutoff set point.

Thanks,
Don

 

[harryS]

There are two ways for a battery to shutdown.
,
The first is the low voltage circuit in the controller, which checks total voltage. For a 48V battery, this is usually set at 40V. It would not be unusual if the battery were at 43V and full throttle or heavy pedal assist pulled enough current to cause the battery to briefly sag to 40V. It's more prevalent with smaller or weaker batteries. Some controller displays allow you to adjust the cutoff _/- a volt or two.
.
The second is the battery BMS shutting off the battery. The BMS is looking at the individual cell group voltages. There are thirteen series groups in a 48V battery, and if any of them go under about 3 Volts, the BMS shuts off the battery.. If the groups are all balanced, shutdown happens around 39 volts. Again, voltage sag may cause an early shutdown. A more trickier issue is unbalanced cells groups. If one or more groups are significantly lower than the the others, they will reach the low voltage point sooner and trigger a shutdown. If you have a balance BMS, this situation shouldn't happen.

 

[6zfshdb]

For the reasons mentioned by @harryS above, I've seen this happen with batteries that are routinely charged to 80% or so. Charging to 100% usually forces the BMS in most batteries to balance cells. Charging to 80% is fine and may improve battery life. Charging to 100% occasionally is a good idea though and may prevent the problem you describe.

It may not be the cause in your case but I thought it worth mentioning.

 

[PCeBiker]

Charging to 100% usually forces the BMS in most batteries to balance cells. Charging to 80% is fine and may improve battery life. Charging to 100% occasionally is a good idea though and may prevent the problem you describe.

Thanks.
I was wondering about that.
I just bought a battery without a smart BMS, so hopefully an occasional full charge will balance the cells.

Can I check my battery's output voltage during and after charging to see if my BMS is forcing the cells to balance?

 

[6zfshdb]

Thanks.
I was wondering about that.
I just bought a battery without a smart BMS, so hopefully an occasional full charge will balance the cells.

Can I check my battery's output voltage during and after charging to see if my BMS is forcing the cells to balance?

Probably not. There wouldn't be much difference between those two readings. You would need to apply a load and see how quickly the voltage drops. A rapid drop usually indicates one or more bad cells.

 

[PCeBiker]

Probably not. There wouldn't be much difference between those two readings. You would need to apply a load and see how quickly the voltage drops. A rapid drop usually indicates one or more bad cells.

OK Thanks.
It's a brand new battery so I guess that I should take some range/capacity/voltage measurements as soon as it arrives for reference in the future.

 

[Slaphappygamer]

I’ve installed one of these between my controller and my display. I can read the voltage as I ride. I can also “lock” the system with the key.

US $14.71 15％ Off | 12-120v Digital Voltmeter Battery Voltage Display+Lock/Key/3gears/Cruise Switch For Electric Scooter Bike Accessory Tricycle ATV

https://a.aliexpress.com/_mKUe2ES

It’s neat to see how many volts are drained on my way to work. I know when I have to charge and when I don’t have enough juice to make it there.

 

[PCeBiker]

I'm in the process of installing a 25 amp KT controller with a KT-LCD8H display on my ebike.



It shows Voltage and Watts but I don't think it calculates total Watt hours used in a given time?
That would be difficult to calculate.

 

[PCeBiker]

I’ve installed one of these between my controller and my display. I can read the voltage as I ride. I can also “lock” the system with the key.

I do like the key lock though.
Right now my theft protection is to simply never let the e-bike out of my sight.
I don't even carry a lock.

I will probably invest in a quality lock eventually and that key lock would be a great addition.

I do have an alarm for it but haven't installed it yet.

 

[Slaphappygamer]

I have the same LCD8H. It does not calculate watt hours. I have found that that voltage displayed is same as my volt meter with the key. Kind of redundant, for me, but I added the display more recently.

 

[PCeBiker]

I have the same LCD8H. It does not calculate watt hours. I have found that that voltage displayed is same as my volt meter with the key. Kind of redundant, for me, but I added the display more recently.

I'm replacing my Das-Kit Controller and C7 Display with KT.

Apparently the volt meter on the C7 Display isn't accurate, and that's a big deal as far as I'm concerned. (I never did check the readings with my voltmeter)

The KT voltage reading is accurate.

 

[Nvreloader]

I found these cutoff set points when using only the throttle,
with the cruse control set to/at around 15mph,
until the battery had a noticeable lack of power,
(which I could suddenly feel),
and then I would stop and test/check the battery with a VM,
to obtain the voltage readings.

My test road is over 50+ miles long and fairly flat,
with a combo of pavement and good bladed gravel road.

Both sets of battery's, original and newly bought (different Brand name)
were tested in the same way over the same course.

The OEM battery's #1-2 have been charged 8 times,
from 43.5v up to 53.8v average voltage range,
and this is the first charge of the new bought #3-#4 battery's,
from 39.5/40.4v up to 53.8v (both the same).

This first test of 3-4 battery's went from 53.8v to 46.6v,
I am hoping a couple of more charges will produced better readings,
(closer to the OEM battery's 1-2 readings)
while the 3-4 battery's get settled in etc.

Just waiting for some "NO" wind days, less than 5-10 mph.
Your thoughts and suggestions........
Tia,
Don

 

[6zfshdb]

I do have an alarm for it but haven't installed it yet.

View attachment 148774

I have the same WSDCAM alarm. I wasn't expecting much for $18 but I was pleasantly surprised at how well it works.

The trick is to secure it to the bike so it isn't easily taken off and the battery removed.

 

[PCeBiker]

I found these cutoff set points when using only the throttle,
with the cruse control set to/at around 15mph,
until the battery had a noticeable lack of power,
(which I could suddenly feel),

I'm thinking this,..

The first is the low voltage circuit in the controller, which checks total voltage. For a 48V battery, this is usually set at 40V. It would not be unusual if the battery were at 43V and full throttle or heavy pedal assist pulled enough current to cause the battery to briefly sag to 40V. It's more prevalent with smaller or weaker batteries. Some controller displays allow you to adjust the cutoff _/- a volt or two.

Is there any way for you to monitor the voltage as your bike is having that lack of power?

How big are your batteries?
Does your ebike draw from both batteries at the same time?

You've got a big heavy ebike. It probably draws a lot of power.
Have you got a Watt meter or current meter on your bike?

 

[PCeBiker]

I found these cutoff set points when using only the throttle,

Those cutoff points are probably the voltage after it bounced back from low voltage cutoff at ~40V

It's like starting a car.
The battery voltage drops to around 10V while the starter motor is drawing huge current.

The voltage jumps back up to 12 volts instantly after you stop cranking the engine.

It's the voltage under load that is important.

 

[Nvreloader]

Is there any way for you to monitor the voltage as your bike is having that lack of power?

There is a voltage reading section on the display, when the bike is turned on.

How big are your batteries?

The battery's 21700 battery's, 48v-15ah-720wh dual battery's

Does your ebike draw from both batteries at the same time?

Yes, This bike uses both batteries at the same time,
the bike weighs in at 90#'s with all the gear loaded on, plus my fat butt @ 200#'s

You've got a big heavy ebike. It probably draws a lot of power.
Have you got a Watt meter or current meter on your bike?

No, only the v% meter in the display.
I can see that there is a reading around the 250w? section,
just under this reading, where I normally run,
but there is a LOT of variance/jumping around when using,
the throttle, during the road tests.

When I felt the battery lose power,
this v % meter read the same as the reading
I got with the V meter = 46.6V on both battery's.

Tia,
Don

 

[PCeBiker]

Yes, This bike uses both batteries at the same time,

No, only the v% meter in the display.
I can see that there is a reading around the 250w? section,

but there is a LOT of variance/jumping around when using,
the throttle, during the road tests.

When I felt the battery lose power,
this v % meter read the same as the reading
I got with the V meter = 46.6V on both battery's.

My guess is that one of your batteries cut out when the BMS detected a voltage of ~40 Volts, then you were running on only one battery.

That sag in voltage may have happened in a millisecond and it probably wouldn't register on your display, especially if your display is showing the average voltage of your two batteries. Then by the time you checked the voltage, the battery had recovered to 46.6 volts.

On my batteries, the BMS will reset if the load is disconnected or it is charged.

 

[AguassissiM]

One could always install a battery cullometer to monitor your battery.

 

[PCeBiker]

One could always install a battery cullometer to monitor your battery.
View attachment 148858

I think that would be a great idea for @Nvreloader
It's really important for him to know where his batteries are at.
He's out in the middle of nowhere where pushing or pedaling his bike really isn't an option.

 

[Gionnirocket]

Don
I'm sorry but I think you've got some bad batteries... But to know what's going on you can't run two in parallel to test.
1.Run each battery individually to test capacity and voltage range.
2. Full charge should be 54.6v, not 53.8v
3. As others have mentioned LV cut off should be around 40v
4. I know you have an Ultra.. What's you controller LV set to on page 1 of the settings.
5. Check the voltage output of your charger... Should be 54.6v

From the information we have so far I'd guess you have a battery(s) with bad cells. The internal resistance of one group is lower than the rest of the pack causing it to charge and discharge faster than the others in that battery. This is why you're only reaching 53.8v on a full charge.. because the one bad group is reaching HV cut off before the others and the BMS only allows charging until the first group reaches 4.2v. You don't have a balance BMS otherwise this wouldn't be a problem on the charge side of reaching 54.6v.

I'm of the opinion that and no amount of cycle charging to 100% is going to correct this as you can't correct the internal resistance problem of the bad cell group. You may get it to incrementally take a higher charge but be careful as you'll repeatedly be pushing a defective group to its HV limit. In other words don't try to force it by charging repeatedly in the same use cycle... This is how fires start.