Not as easy to answer as you might think.spuzzete wrote: to what voltage is safe to discharge those laptop batteries?
Is 3.0 volt too low discharging at 1C or less?
I am building my own recycled pack
My assertion is that ...chilledoutuk wrote:Here is a datasheet i found on sanyo 2600mah 18650 cells
http://www.batteryonestop.com/baotongus ... 0F-26A.pdf
they state that you can discharge to 3.0v on there cells at 1c discharge rate.
If you have a very well balanced pack that you built using a cell matching then going that low would probably be ok however if you don't then going a bit higher should protect your cells from one of the cell banks going too low a voltage before the lvc kicks in.
when i test 18650 cells and discharge to 3.0v at 5 amps they bounce back to 3.5ish afterwards which shows they haven't been overly discharged.
DrkAngel wrote: 1st, every cell type, manufacturer, capacity cell, has different optimal voltages.
In my testing, I have rated optimal depth of discharges at 3.4V, 3.5V, 3.6V 3.7V dependent on the cell type. (static voltage)
I would never recommend dropping to 3V, even under maximum throttle.
The red 18650 cells appear to be 95% discharged at 3.6V, any further discharge will drop voltage precipitously, resulting in unnecessary cell damage.
So ... find your optimal DOD (depth of discharge), then apply a 1C load to determine optimal voltage, under load.
I don't think anyone else on this thread owns a metalized fire suit. Oh well....Ypedal wrote:this entire thread is a trainwreck........ it reeks of " safe " ..
Thanks for the info!DrkAngel wrote:My method of determining optimal voltages - Lithiums - mAh/100th V - Discharge Tests
A low tech alternative.
Full charge - check voltage.
Run lap, (around track? around block? etc.) the shorter the more accurate.
(Maintain consistent laps, same speed or same throttle usage ... etc.)
Measure voltage at stop after each "lap". (Digital meter, highly recommended.)
Voltage will drop sharply till optimal charged voltage is reached.
When voltage begins to drop sharply, again, you have exceeded "optimal" low voltage.
Good methodology!spuzzete wrote: Thanks for the info!
I am testing the 3s2p (10.8v charged at 12.3v - 4Ah) packs using a 12v 50W light bulb. I use the 1-8s voltage alarm (the one that was posted also in this thread) set to 3.6 to each cell and I record the time until it beeps. So far the best pack timed 19.5 minutes to reach 3.6volt, all the cells were discharging with the voltages being very close together.
Battery University.comSamTexas wrote:Those percentages sound impressive. But have you verified their accuracy?DrkAngel wrote: Lithium Cobalt charging, at moderate rate, is 98-99% efficient, a good measure of capacity.
, but lithiums, particularly Lithium Cobalt, at moderate charge rates, attain near 100% efficiency!
spuzzete wrote:Thanks guys for your feedback.
I would like to make a tutorial (pdf) and a video of what I've learned here and my way to build the battery pack once I've finished testing & assembling the batteries.
I think it would be useful for many people, and quicker to read/get to the point. This thread is excellent but is 25 pages long
one thing I'd like some clarity on is what is the xC (like .5C - 4C) that's being talked about so much, and what is the meaning of the things like 14S8P, I'm guessing the configuration of the batteries, but have not found confirmation... would that be 14 series, 8 parallel? so a 51.8 volt pack, then running 8 of these packs in parallel to boost Ah ?
I have an ezip and the battery died in less then a year, bikes been siting 2 years now due to new baby and no time to do anything, so now I have some time and would like to get the bike up and running, but better then it was.
I agree with you.chilledoutuk wrote:The difference in remaining capacity at standing of 3.6 to 3.0v may be minuscule but at 2c its most of the cells capacity.
If your running your cells at even 1c discharge a lvc of 3.6 will still be cutting you off way too early.
Discharging cells at 5A they don't reach the cliff until they are about 3.2 to 3.3 volts.
What I am saying is if your running your 18650 cells at a highish discharge rate 3.6 lvc would be cutting you off way to early.
if you have a huge pack and only run at say 0.5c peak discharge current then maybe 3.6v might work ok.
But however in the same situation that pack would be fine down to say 3.1v if the pack was built properly will cell matching used.
For example when building one of my packs I tested the capacity of every cell and then was able to get all cell rows within 2mah capacity of each other using a cell matching program kindly provided by another ES member.
"C" is Capacityswampjeep wrote: one thing I'd like some clarity on is what is the xC (like .5C - 4C) that's being talked about so much, and what is the meaning of the things like 14S8P, I'm guessing the configuration of the batteries,
This graph is invaluable and should be understood and memorized by anyone using or wanting to use laptop 18650 cells. Continuous discharge above 1C not only reduces the cell capacity, it also raises the cell temperature to unacceptable and potentially dangerous level. That said, it's perfectly okay to reach 2C for a short period of time (60 secs) every 5 minutes or so.DrkAngel wrote:
Not bad at all! Judging from your graph, you could easily go for another 10 to 15 minutes. Under 0.6C load, you can safely go down to 3.00V. Once the load is removed, the voltage would jump back up to around 3.5V.spuzzete wrote: Not bad for batteries worth $0 !!
I just wanted to see how many minutes they would last under load, and I am pretty happy with the results . I did not want to push those batteries too much. I think once they will be on the bike it will be different, as the load will not be constant, and maybe that's a good thing especially when no power is used it will give the battery pack time to "breathe" a little.SamTexas wrote: Not bad at all! Judging from your graph, you could easily go for another 10 to 15 minutes. Under 0.6C load, you can safely go down to 3.00V. Once the load is removed, the voltage would jump back up to around 3.5V.
Voltage sag seems excessive?spuzzete wrote:I put together some data from a test I did last week.
Here is a graph:
I discharged those 3 batteries in series (3s12p 10.8v 24ah) with 3 12v 50w lights bulb in parallel.
Not bad for batteries worth $0 !!