Wet battery

Batteries, Chargers, and Battery Management Systems.
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Monti   1 µW

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Wet battery

Post by Monti » Jun 20 2018 12:26pm

Hi

I have 52v shark battery. The case broke and it got wet inside and then the bike would shut down after a few minutes of load. I took it all apart and found 2 blocks of 5 cells that were showing 3volts the others all showed 4.3 or 4.4
So I have changed the cells but when I charge it up the new blocks don’t get charged up which I assume is correct since 12 cells at 4.4 is already getting me close to the 58v cut off

Because of this when I put load on the bike shuts down after a minute or two.

I am guessing this means the bms can’t balance such a big difference in voltage between the blocks- does that make sense

If so I am planning on bypassing the bms to be able to run the other cells down and hopefully then when the bms is reattached it will be able to balance them as they should be closer together. Does that make sense or should abms be able to balance it anayway and it just needs a new bms?

Thanks for any help

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flippy   10 kW

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Re: Wet battery

Post by flippy » Jun 20 2018 4:24pm

Just charge the all cells manually. If you got a unused powerbank in a drawer you can remove the board and connect that to the cells and charge each group individually with a usb cable. Not fast but works and you are automatically perfectly balanced again. But keep checking the cells, i expect they have lost capacity or might start leaking. Cells dont like water usually.
Lithium beats liquid dinosaurs.

flat tire   10 kW

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Re: Wet battery

Post by flat tire » Jun 20 2018 4:27pm

4.4 volts is way too much I'd consider those batteries to be ruined as well. Sounds like they all took the charge the two low groups should have taken.

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amberwolf   100 GW

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Re: Wet battery

Post by amberwolf » Jun 21 2018 12:38am

Sounds like the BMS got wet and was damaged, causing ssome cells to be drained, and the rest to no longer be drained during balancing/charging.


I would guess that the cells were damaged by overcharging (well, all the ones over 4.2v; the 3v cells might be the only ones still ok). You could test the various groups once you drain the high ones down to 4.2v or lower, and you manually charge up the low ones to equal those.

But I wouldn't leave the BMS connected; it's probably causing the problems you see.

Might be safer to replace the whole battery pack.

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methods   10 GW

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Re: Wet battery

Post by methods » Jun 21 2018 4:39pm

I would junk the BMS
I would hand-charge the remaining cells up to 4.2V
I would discharge the entire pack at a low C rate such that the 4.4V cells dropped to 4.2
I would bump-charge the low riding cells up to 4.2 to bring them all up to balance

I would then loosely attach the pack to the bike (such that it can be jettisoned)
I would hammer the pack hard - for about 1/2 your usual range (watch your CA)
I would hand-feel the cell groups

Do the 4.4V cells get hot?
Do the 3.0V cells get hot?

If nothing is getting super hot... go ahead and cycle the pack until the first cells reach LVC

Did they "come out of balance"?
(meaning do the cells now have different capacity?

...

Dry things out well using a house heater and a box fan in a cardboard box (OUTSIDE)

Look for rust

Be careful with it.

...

I have run every sort of shit-cell duct taped together ...
For me - not charging to over 4.2V PER CELL
Not discharging to under 3.0V PER CELL
Not Charging over a C or two
Not Discharging beyond rated or able (so ... not getting them hot is all that means)
And... taking basic precautions...
No Fires

BUT

I watch my cell levels*
I watch my temperature*
I am careful about short circuit*

Boiling the "juices" inside is what has resulted in most fires I have seen... that and punctures.

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

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methods   10 GW

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Re: Wet battery

Post by methods » Jun 21 2018 4:45pm

P.S. And yea... I have charged a lot of cells to 4.4V

Best thing you can do for yourself...
Is get a representative sample (10pcs of the same)

Take it out to the middle of a parking lot
Hook it up to a power supply
Start trying to brake them

See what happens :idea:

There is Testing and D-Testing

For testing... look for diminished capacity
Look for increased internal resistance (increased heating due to I2R losses)

For D-Testing.... on both fresh and abused cells
Find out what it takes to make them outgas
See what it takes to melt the insulators ****
See what it takes to make a fire

From that -
You can make an informed decision based on measurable data

eh?
(Remember we are still celebrating Canada's decision to take a step back from the war on drugs)

so... eh? :P

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

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LockH   100 GW

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Re: Wet battery

Post by LockH » Jun 21 2018 6:02pm

^^ Watt these guys suggest. Bottom line (or not) have a single, per cell charger handy. :wink:
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Eff. June, 2014 Phoenix Ebike Promotions

(Current ride? High speed lawn chair.)
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Phoenix Ebike Promotions conversion kit (work in progress. More drink holders, etc etc)
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Joined yer local chapter of EA yet?
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methods   10 GW

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Re: Wet battery

Post by methods » Jun 22 2018 6:38pm

For single cell charging I have tried many things...

In the end
If you want to succeed as a hobbyist in anything remotely related to Electrical - you will - require a variable power supply.

AKA - Lab Supply

At a minimum this device has a power switch and 2 dials
One dial sets the max voltage limit
One dial sets the max current limit

At any given time
The supply will attempt to "rail"
First the voltage...

So with the current dial set at an arbitrary value (greater than 0) one will see the voltage rise to the set point.

Upon applying load the current will increase until it hits the current limit
At the current limit and beyond the voltage will begin to sag as a function of Power:

Power = Voltage x Current

Example: Voltage set to 10V, Current set to 10A
Maximum available power = 100W

Should a load of 1 ohm be applied...

Theoretical max is 10V/1ohm = 10A

Should the load be doubled to 1/2 ohm (two 1 ohm resistors in series)
the math works out to 10V / 0.5ohms = 20A
Since the current limit is set to 10A, we use a different formula for power:

Power = current squared * resistance

10A * 10A * 0.5ohms = 50W (which is indeed below the 100W setpoint)

Should the current limit dial be increased to 20A we will see

20^2*0.5= 200W
Where our limit was at 10V * 20A = 200W

The resulting "sag voltage" for a 0.5 ohm load on a 20A current limit with a 10V voltage limit works out to:

Volts = current * resistance (ohms law)
20A * 0.5ohms = 10V
Ah - balance again

...

Lab supplies can be had in many flavors
$50 - $250 is a reasonable range to look at.
You will NOT get anything you love for $50
$250 is where you START (with risk) to look at something awesome.

Your voltage must go as high as your pack (or whatever you want to test to... say 60V)
Your current... well... more is better eh? 20A is a nice spot to charge at yea?

I promote Sorensen DCS Power supplies, the DCS series
Rack mount
https://store.programmablepower.com/pro ... -dc-supply

You can see that they are a couple of kilo-bucks

Look to Ebay (and BE CAREFUL...)
They can be had for under $350 regularly

Most common failure mode is the fan
Second most is overheated internals
I have purchased over 20 used

...

I regularly charge with a power supply as described above.
One can set the supply to 4.2V and 20A
You can average out a pack QUICK like that... just mind your C rates

I calculate as follows:

AH of cell?
# cells in parallel?
Quality of cell (Good or Bad)

I start by assuming 1C
I multiply the AH rating of the cell by the number of cells in parallel
I multiply that by 1 for bad cells and 2 for good cells (super general)

So for 3Ah cells
With 3 in parallel
Assuming good "vaporizor" quality cells...

3*3*2 = 18A

So ... for a 3P pack of good 18650's I crank the supply up to 18A and let it rip to 4.2V

...

These supplies come with many modes of remote control
There are simple switch inputs
Active low inputs...

These are inputs which can be activated by simple "BMS" circuits

I have in the past
Released designs of the SIMPLEST form possibly imaginable
Involving (per series cell) only TWO PARTS

A sensors... and an opto coupler (to gang the outputs and avoid the ladder of potential)

A circuit like this can be very easily verified with a $5 "test circuit" to exercise LVC and HVC
Using a circuit like this one can do aggressive stuff more confidently...
But...

Dont forget cell temperature

Monitoring and dealing with this is beyond the scope of this -
SO...
Just do your charging in a spot that can tolerate a good size lithium fire

And you are set :P

...

Otherwise
Grab a $10 Arduino
Hook to it a $1 temperature probe or 10
And... gang its output to the inhibit line of the charger

...

Charging decomposed

Have fun

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

Monti   1 µW

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Re: Wet battery

Post by Monti » Jun 27 2018 9:04pm

Thanks for all the answers. I managed to charge them all up using a single cell charger. then I discharged them all using a light bulb to get the total down fro 60v to about 57. This meant I could set it all up to use (even if the bms did look pretty bad). Took it for a ride and it cut out but this time after 30 minutes of hard riding so I am going to change out the bms- just need to find a compatible one (just posted a photo on another post showing what I am looking for)

cheers

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methods   10 GW

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Re: Wet battery

Post by methods » Jul 03 2018 1:23pm

Good job Monti

Thanks for closing the loop and keep at the fix + updates!

(you have no idea how many unsuspecting folks are going to be swimming in this sort of work once the axe falls on Big Oil...)

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

999zip999   100 GW

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Re: Wet battery

Post by 999zip999 » Jul 03 2018 3:00pm

Method when you have charged a cell to 4.4v does it self discharge or will hold 4.4v in the barbecue ?

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methods   10 GW

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Re: Wet battery

Post by methods » Jul 09 2018 8:07pm

I never really paid attention ...

I have on many occasions found cells resting at 4.31V, 4.35V....
Only a few rare times at 4.4V.....

But the read dark and dirty truth is... (cover your ears kids :shock: )

MOST OF THE TIME

* I build up a pack out of super sketch packs that I got for free or cheap (already rejected by professionals)
* I balance them
* I charge them at 1C to a sum total of 4.2V * Cells in series
* I dont look
* I feel them from time to time around 3/4 of the charge (looking for obvious hot or future pop/fire)

I dont even monitor :o

BUT

I have spider sense for this
I have been charging lipo since lipo was not "a thing"
Dont try it at home

...

My guess?
They will definitely hold a 4.4V charge (as they eat themselves)
How long? No idea - depends on AH, chemistry, form factor, age of cell....

LFP would be a better one to ask that question

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

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