how much regen is too much for the battery

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Hummina Shadeeba

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im assuming the charge rate on a cell is a continuous rating but how about very short in time but high SURGES in current when braking? How high can i set the regen and not damage the battery?
 
wow very counter intuitive. but with this study being done with a lithium sulfur cell how similar would it be to ion?

it seems sulfur is the next big thing and its not just hype, or maybe im suffering from the hype.


surely some easy testing of ion cells could be done with a good power supply and registering the energy density of the cell between voltages over repeated cycles. but i suck at math and what current would be appropriate for a single ion cell and they said the transition from detrimental to beneficial happened above ~9 milliamperes
per square centimeter.
 
^^ Hehe... First looked up "dendrites" when rolling "back in the daze" w/sealed lead-acid batteries (24V aka 2x12VDC in series and 10Ah...) AFAIK, NO battery chemistry is immune to "sulfation"... with about the WORST one can do is to leave any cells as partly discharged. Used to be "Charge Early and Charge Often". :) BUT ANY "fast charge" was "BAD" - see regenerative braking. So again, for many/most chemistries, suggest saving any regen for saving brake pads. And to minimize any braking that you DO "need to do". I used to "specialize" in using built-in kinetic energy to coast up to any stops, just to save brake pads AND any save energy stored in my batteries. Kinds hoping one here more knowledgeable will jump into this thread. :D
 
i dont know if you can see this long version of the study:

file:///C:/Users/me%20john%20murphy/Downloads/Self-heatinginducedhealingoflithiumdendrites.pdf


but what would be 9 mA cm^-2 current density?
and how applicable are the results here to ion cells?

(same questions but more concisely written)
 
Managing dendrites with bursts of high current is counterintuitive to the idea that higher current densities increase dendrite formation, says Amartya Mukhopadhyay at the Indian Institute of Technology Bombay. Since dendrite formation cannot be prevented, flattening them with periodic pulses of current is a fantastic way to manage them because it does not allow them to grow too long and it does not require extra materials inside a cell, he says. While the researchers tested this approach in a lithium–sulfur cell, in principle, it could be used with any battery chemistry that uses a lithium metal anode, he says.
Click to expand...

Betcha the Professor is a "busy guy"... wanna ask him?
http://www.iitb.ac.in/en/employee/prof-amartya-mukhopadhyay
Email: amartya_mukhopadhyay@iitb.ac.in

amukhopadhyay.jpg


:mrgreen:
 
Capture.JPG here's from the research gate study I posted above.




nice find! I'll take it at just the quote from the professor as enough go-ahead to try something (safely).


the term "periodic pulses" though doesnt seem to be the short bursts of regen and instead a complete charge cycle at the higher current done periodically, different than regen's time period at least.

how high that current would be still needs probably easy math but I know a guy and will post it up.

I'd assume if I were to put something like 20amps into a 30Q cell it will get really hot and deteriorate. I didnt read a size restriction and there's that unknown ideal current value based on volume (9mA cm^-2) which leads one to believe it could be any size cell but in my mind...how the hell is the cell not going to get hot, and if it gets hot i thought that was across the board bad.
 
exploding isnt the intention! according to the study you posted as well as the screenshot i posted i should be getting further away from potential fire or explosion..ironically by charging with a huge current. if i can just figure out what that current would be.
 
Thinking HIGH amps... but as an "intermittent healing treatment" aka PULSED "high" currents watt go on/off. Can be done w/electronics, but maybe with thermal imaging reporting "funny" colours and causing cutoffs as a "backup". :)

And that "regen" needed to be applied at more frequent intervals for longest-lasting cells... somehow. "Regen" as a battery discharging at stops to "healing treat" the main battery cells? :)
 
this "healing treatment" isn't really pulsed though and a continuous charge cycle at the higher current i believe. i was going to try cycling cells through similarly to the graph i posted above but cant convert the math to figure what current is appropriate for an 18650 sized cell. so forgetting regen for the moment. (although it does make it seem worrying about a pulsed high current with high regen settings isnt such a concern in light of this healing treatment would be for a whole charge cycle)
 
If you have to ask, then the battery will tolerate whatever your regen can provide, for short periods anyway. But you will do damage to the pack that way. It's better to stick to recommended charge rate if you are very excited about longevity.
 
Hummina Shadeeba said:
im assuming the charge rate on a cell is a continuous rating but how about very short in time but high SURGES in current when braking? How high can i set the regen and not damage the battery?
Click to expand...
This depends a lot on what kind of battery it is and for how long you are charging at a high rate and what the state of charge is.

Most electric cars charge during regenerative braking at very high rates. On my bike, it would be hard to over charge the battery with regen. I think the wheel would lock up before the battery current got too high. One thing to watch out for is having the pack voltage go too high during regen (reverse sag).
 
from what i read it seems if the cell is less than 50% state of charge it could take a lot more than the stated charge rate but forget regen....how about this weird high current "healing" cycling? what current would it be?

why would your wheel lock up if the regen was too high a current?
 
Hummina Shadeeba said:
following this high current healing regime would not be sticking to the recommended charge rate and is shown to end up with safer cells.
Click to expand...

Oh oh... "the recommended charge rate"... :wink:
 
Hummina Shadeeba said:
from what i read it seems if the cell is less than 50% state of charge it could take a lot more than the stated charge rate but forget regen....how about this weird high current "healing" cycling? what current would it be?

why would your wheel lock up if the regen was too high a current?
Click to expand...

I have no experience with lithium sulfur batteries and I don't think they are really available yet. But dendrites have been around for ages and were commonly a failure mode for nickel cadmium batteries. You could "burn off" the dendrites with a high current pulse. The pulse was very short but hundreds of amps. As long as nothing (other than the dendrites) gets hot, I don't think there is any limit on the current.

With regen, the kinetic energy of the bike is being converted to electrical energy and absorbed by the battery. The higher the regen current, the higher the braking force on the wheel gets. If I set the regen too high, either the wheel starts skidding or the drive belt slips. It never really "locks up" but the wheel skids and you can crash as a result.
 
ok i see what youre saying ...if you set regen so high it would just be increasing the braking force as well. i though something else.

but about charging with high current as described in the study above and the screen shot I posted, it would be a full charge cycle at at least 9mA cm ^-2, infact up to 15mA cm ^-2. whatever that current level would be i cant figure the math. so not pulses and and many full charge cycles in a row at this current.

how much would that current be for an 18650?
 
Hehe ^^ "One test is worth a thousand opinions". :mrgreen:
 
if only i had a clue on the math. For a test all i would do would be following the charge schedule above and blasting my stuff with super high current for the right ratio of cycles and seeing what the overall mah shows going from 3.5 to 4.1.

so many people are worried about going over the manufacturers max charge rate while doing regen and judging from the amount of high charge-rate healing going on, either pulsed or continuous, it seems not worth worrying about at all. wish there was more info or maybe no one wants to be the one saying its ok to charge much faster.

all i need is a current value based on the formula above for an 18650 size cell.
 
One important thing to mention, that I don't think has been said, is that if you want regen thru the moon, and ultra fast charges...


...get RC lipo. The fancier ones support several C charge rate, which means you can burst ridiculous amounts of regen power.
 
yea lipo would be probably be a safer bet but the math seems to be missing something as its a volume to current conversion but the volume is based on a 2 dimensional surface it seems as if you were supposed to unroll an 18650 to figure out maybe. im more so just trying to figure out this math and see what current they were actually using in the study
 
flat tire said:
One important thing to mention, that I don't think has been said, is that if you want regen thru the moon, and ultra fast charges...

...get RC lipo. The fancier ones support several C charge rate, which means you can burst ridiculous amounts of regen power.
Click to expand...

Oddly, on the `Sphere "Search found 5608 matches: lipo fire"... :wink:

Per OP "How high can i set the regen and not damage the battery?"... where "lipo" and "fire" doesn't sound like a great combo. :mrgreen:
 
i have a 4.1Kwh battery pack on my "if he dies, he dies" scooter with a 4kW motor and 300A controller and i have not noticed any ill effects from having the regen set to 100A (at 60v). usually the regen only lasts for 1~2 seconds at that rating before tapering off to zero when standing still. under full regen i can go from 30mph to 0 in about 5~7 seconds. the main reason for not having more regen is that the back tire simply does not have the grip. it barely clings on at those heavy regen levels.
 
^^ Watt battery chemistry, may I ask?
 
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