What should be the lower limit be for a battery

[Big Tom]

I hope this question can easily be answered and that it is not that stupid of a question.

How far can one deplete one's battery before the battery will receive damage. I operate a 48 volt 10AH (limn) and my dad has a 60v 20AH (lipo4) on a scooter. I was told that the scooter will not operate at a lower voltage then 63 volts. To me this sounds silly. I also was told that my battery should not be depleted lower then 49 volts. What should I limit these batteries to for a lower voltage limit. I am not sure if these people that told me this is, real knowledgeable, they deal mostly with lead acid.

Thanks Tom

 

[wesnewell]

To preserve life and performance you probably shouldn't take them below a resting voltage of their nominal voltage. That's being real conservative, but it will extend the life of the battery. You can find the nominal voltages for most rechargeable batteries here.
http://en.wikipedia.org/wiki/Rechargeable_battery
Absolute lower ends are a lot lower, but once below nominal, they will fall off a lot quicker.

Assuming your battery is 14s then 49V sounds about perfect under load. And 63V sounds good for a 20s lifepo4 pack, which will charge to ~74V.

 

[dogman dan]

In general, the nominal voltage is just about 100% discharged on all chemistries. So your 48v battery likely should not ever go below about 45v, and idealy would not go much below 48v. It's starting out full charged at a much higher voltage, likely at least 54v, possibly as high as 60v.

 

[Drunkskunk]

Lithium don't work like Alkaline, NiCad, or old Lead acid car batteries. their voltage is all above a certian point, and below that voltage, they are damaged.

Your 48v Limn is a Lipo battery, 3.7 volts per cell nominal. So a 14 cell in series pack would be 51.8 volts (basicly of 48 volts). You can take Limn down to 3 volts per cell, but expect to damage them if you do so more than very occasionaly. some manufacturers cells can handle 2.7v per cell, others are totaly destroyed at 2.99 volts.
But its best to never take them below 3.7 V per cell. they have somewhere around 90%-100% of their total capacity above that point, and after that point, the voltage and power drop off sharply.


(example of Lipo discharge curve)

 

[Big Tom]

For all members that have a Cycle Assist or another device which will limit how far down your battery can be taken in voltage when in use, what do you set your lower limits at. Like if you have a 60 volt (or 48 or 36 v) battery what voltage would you set as your lower limit.

Thanks Tom

 

[wesnewell]

That would depend on battery chemistry and sag. Standard for SLA would be 10.5V per 12V battery. So 42V for 48V sla pack. For lipo, about 3.5-3.6V per cell depending on how much sag your pack has. 3.6V would be safe for all of them. Most lifepo4 packs have a bms to handle protection on a cell level. If you don't have a bms, then I'd go with 3.0-3.2V per cell. I went from sla to lipo and haven't used lifepo4 and don't plan to.

 

[dogman dan]

For a vague question, a vague answer is what you get. In general, two or at most four volts below the nominal voltage is pretty good. So a 48v battery could be set for 46 or 44v. Under load, 44v would get you 46v resting as your stopping point on many ebike batteries.

 

[dnmun]

for 48V lifpo4 pack, 16s, using 2V for the LVC, then you should use 32V for the LVC on the controller, max. so using a 36V controller with 30.5V LVC is fine.

 

[Big Tom]

Thank you for the responses.

I do not know much about my batteries (do not know how many cells, ect) as I bought them in a kit. I figured that the controller would have been set up to limit my batteries and It seems to have been. My CA tells me that my 48 v battery has 54.5v when fully charged but the electric motor will cut out and read 44.5 - 45v (with no drain). When a so called battery expert told me that under no conditions should you drain your battery below the rated 48v, 60v I started to wonder and wanted to learn what was correct.

Thanks again.

 

[dnmun]

we have no info to help you. it sounds like the pack is severely out of balance and you are only getting about 20% of the capacity.

can you provide any info at all so we could help?