Max. safe discharge current for unknown cells (18650 6P)

[sleepless]

Hi all,

today I got a Phaserunner because my BBSHD stock controller died (again). Without doubt I want to increase the power now that I got this powerful controller. The only way to do this (without buying a new battery) is to set up the max. current to be drawn from the pack.

Well, I have a battery pack with unknown cells and no BMS, 14S6P. To be honest: it's in a heat shrinked sleeve and I don't want to open it up to check the brand / model of the cells. So theoretically: what could be the lowest rated continuous safe discharge current of a cell? I mean there are crazy cells like the Muratas which are capable of a constant 30A disscharge which would lead to a max. of 180A for the 6P pack. But what if I got the badest possible cells? Can they handle 10A? They can handle 5A for sure because I used them with the stock controller with 30A.

I'm just considering how risky it is to draw 40, 50 or 60A from the pack. Especially if I do it just while accelerating (I mean it's impossible to ride with >3kW for a long time, isn't it? )

I appreciate any answer!

 

[spinningmagnets]

Perhaps attach a surface contact probe from a temp sensor (digital barbecue thermometer?).

Slowly raise the amps being drawn from the cell until the cell reaches about 110F. Temporary peak amps might be 50% more, but those are very rough numbers...

 

[john61ct]

And realize you may be reducing lifetime cycles by a lot.

Start saving now for the next pack, adding an extra string and using top-rated cells from a quality source.

 

[dustNbone]

I envy you. Not knowing what cells were in my pack would keep me awake at night.

 

[docware]

Hi all,

Well, I have a battery pack with unknown cells and no BMS, 14S6P. To be honest: it's in a heat shrinked sleeve and I don't want to open it up to check the brand / model of the cells. So theoretically: what could be the lowest rated continuous safe discharge current of a cell?

Don´t be silly and open the pack. Then again put it in the heat shrinked sleeve or something similar.

 

[Dui ni shuo de dui]

Yeah....
While I can understand that we sometimes get lazy, you really shouldn't in this case.

Running lithium batteries without a BMS is only barely acceptable whenever you know all your cells specs very well, which apparently you don't. So first thing will be to install one asap.

And while you'll be installing the BMS that will leave you plenty of time to check the cells specifications.

Either that or buy a proper new pack, adapted to your new setup.
Guessing these kind of things doesn't make any sense and can end up horribly.

 

[amberwolf]

With no protection, no monitoring, and completely unknown cells (could be garbage recycled scrap!), I would stick with 1C max continous, and 2C peak for a few seconds at a time.

Meaning, if the pack is 10Ah, I'd stick with 10A max continous, so a 10A limit on the controller.


Was the pack really expensive? If not, it's probably not "badass" cells.

The cheaper it was, the more likely it's just lowend cells, and possibly even recycled scrap cells that don't even stay in balance.

The worse quality the pack is, and the more you draw from it, especially the faster you draw it out, the more likely some form of dramatic failure would be. A fire is one common form of such a failure. Dead cells is another.

At best, the more current you draw, the faster teh pack will degrade, and the sooner you'll have to buy a new one.



You might also ask yourself *why* the controllers keep failing. Are they overheating from too much load (being in the wrong gear for the speed and load)? Environmental (rain, water, heat etc)?

If its' a heat thing, then maybe the whole system you have isn't quite up to the loads you're putting it thru, and you might consider a more complete upgrade.

 

[sleepless]

Thanks guys. You are all right and I opened it up to check them. Thankfully it are Panasonic NCR18650PF :thumb: I knew it weren't bad cells, I just wanted to assume the worst case scenario :wink: so I think I can set 60A

I don't need a BMS since I'm monitoring each cell group by myself and keep them balanced.

You might also ask yourself *why* the controllers keep failing. Are they overheating from too much load (being in the wrong gear for the speed and load)? Environmental (rain, water, heat etc)?

The first controller failed after just two months. Bafang repaired it and even though I treated it very carefully, it showed error codes after another two months or so. But it worked with error 12 for about 8 months until failing completely. I think it was just a bad controller and the repair from bafang didn't help much. But why should I buy a new stock controller if I can get a more powerful (and hopefulyl reliable) one now?