What voltage is too low ?

Charlycop

Charlycop

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Jan 4, 2019
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Hi,

I just got my first batch of 50 laptop batteries.

As you know, it is very long/slow to test the cells with my Liitokala 500, so I wonder if I can send to recycle bin the batteries without testing them. What I mean is : what is minimum voltage to try to revive them ?

Thanks,

Charly.
 
Minimum voltage is 0V. aka those not taking charge in my world.

I just bounce the cells that are to low to automatically start and then run them through. It doesnt take you any time running them more than you have to wait. And if that takes to long time then get another tester.



Not all will get you good values but it totally depends on the batch you get. In most of the cases those below 1V will be low capacity if I look at my cells here but I still run them to see what happens.
 
daromer said:
Not all will get you good values but it totally depends on the batch you get. In most of the cases those below 1V will be low capacity if I look at my cells here but I still run them to see what happens.
Click to expand...

Great, and I saw a video where the guy explained to charge them full, then wait 1 week and check the voltage. If it is below 4V, it means they cannot keep the charge. What do you think about this method ?
 
I do the test first and then after the test my testers leave them fully charged. This is when i check for self discharge but yes its important to do that.

I consider 4.1 or atleast 4.05 after some weeks to be fine. Below is a diagram I made in the early stages that you see floating around


image_ynbbdb.jpg
 
Yuppers. Agree with daromer. If a cell can take a charge, it's worth testing.
 
By the way, I'm testing some Samsung ICR18650-26C, and the datasheet says :
Discharging:
2.75V Cutoff
520mA Standard
5200mA Maximum

Does "Standard" means "continuous" ? and I want to autorize my appliance to get 4A for a short period of time, how long can I do it ?
 
daromer said:
I do the test first and then after the test my testers leave them fully charged. This is when i check for self discharge but yes its important to do that.

I consider 4.1 or atleast 4.05 after some weeks to be fine. Below is a diagram I made in the early stages that you see floating around


image_ynbbdb.jpg
Click to expand...
Into the faq, please.
Together with the voltages to start with: <1,1 Volt into Thrash, >1.1 Volt slow charging = 50mA up to 3.0V, then slowly 0.1A to 3.6V , then normal charging. Or whatever.

(We had this questions several times now, very detailed answered, but i dont even find the threads)
 
Replying to the question on discharge rate, you should be consistent for discharge. That is rated capacity is not driver. The driver is your planned application. Most here will test at 1 amp. Others will drop that lower.

Something to look into if you are just starting out is internal resistance. Six months back you would charge to full capacity then start the discharge. There will be an initial drop in voltage as soon as load is applied. For me if voltage sag was to a value
Below 3.75 I stopped the test and discarded cell

It Might be good For a low amp application like a flashlight or powerbank, but this is an indicator that remaining life is limited

The latest that is Being exploreted is a dedicated 4 wire tester to give a quick reading on remaining life



Hope this helps
 
Charlycop said:
By the way, I'm testing some Samsung ICR18650-26C, and the datasheet says :
Discharging:
2.75V Cutoff
520mA Standard
5200mA Maximum

Does "Standard" means "continuous" ? and I want to autorize my appliance to get 4A for a short period of time, how long can I do it ?
Click to expand...

Standard rates can be sustained continuous, but they are not the maximum continuous rate. "Continuous" usually implies that highest possible continuous rate is given and above that there are only the peak ratings. The standard rates are used for specification purposes only and are usually far off the actual maximum. Actually they are usually the smallest stated rate.
In case of the ICR18650-26C I think the maximum of 5.2A can be sustained continuous and there is no peak rating given. A peak rating would usually be time limited.
 
A laptop cell Will get dead hot att their max rate. IF you need 4a per cell dont use 2nd hand laptop cells you test att 1a...

I highly recommend not to go above the tested current or crosschecked each cell datasheet.

You can find high Power cells in powertools as example
 
Oh, yes, I forgot to mention that the spec sheet gives valid information for new cells only and it doesn't necessarily apply to used cells. If 4A is needed then you have to test at 4A at least but the cells will most likely not be able to do it.
 
I'm asking this, because I will mainly use my powerbank to light up my parking box with 12V LEDs, but I want to be able to use some electric appliance 230V at around 1200W, but it will be quick, like 10seconds, or 20 seconds. Even if my battery pack doesn't last long.

So I'm trying to figure what would be the minimum cells number I need. If I understand well, more the cells are able to output Amps, the less I need cells. After that, it is just a matter of capacity/time in use.

Anyway, if I understand what you are saying guys, you recommend to limit my amps output at 500mA per cells in series for laptop cells.

And you recommend to build a 48V battery minimum for efficiency/inverter cost.

Which means for example, if I want to use one 1200W 230V appliance, I need 48V 1200W (let's assume it is 100% efficiency inverter and no loss by heat), which means 25A, which means 14s50p and 700 CELLS.

if I'm right, that is why I would prefer to use more amps output per cells in series ; if I use 14s25p, 350 CELLS, the cost if cut by half :)

Are my calculations right ?
 
Limit the number of amps/cells in parallel, not series. Parallel adds amps, series adds volts. 500mA per cell is pretty much the goal for reclaimed cells. It keeps them from being stressed too much under heavy loads.

The cell count calcs are right, yes. But the savings over 25p and 50p are negligible. If you're using reclaimed, then that's going to be <$100USD, or even probably <$50USD difference.
I suppose if you buy the laptop packs individually and not by weight, that could have an effect on overall costs.
 
Korishan said:
Limit the number of amps/cells in parallel, not series. Parallel adds amps, series adds volts. 500mA per cell is pretty much the goal for reclaimed cells. It keeps them from being stressed too much under heavy loads.

The cell count calcs are right, yes. But the savings over 25p and 50p are negligible. If you're using reclaimed, then that's going to be <$100USD, or even probably <$50USD difference.
I suppose if you buy the laptop packs individually and not by weight, that could have an effect on overall costs.
Click to expand...

What I meant by "series", is "series pack", which are in parallel (in my example 50 series pack in parallel), anyway, we speak about the same thing.

You are funny, but no matter the cost, if you double the number of cells will, the price will increase by 100%, but your point is valid about the cost, thanks :)
 
Continues max i would say is 1A for laptop cells IF you test at 1A. I have 1A on my system.

Laptop can easy do 5A during 10 seconds or even 2 minutes. So for your load 5A is not a problem if you make sure to limit the max time and design by that.

Temperature sensor in the BMS will help you in that matter to make sure you are safe.

My kids ATV run motors that use up towards 8A per cell easy and they still rolll. The pack on other hand get hot and only run for 20-30min at a time before i swap the pack out........ different application and its out house
 
daromer said:
Temperature sensor in the BMS will help you in that matter to make sure you are safe.
Click to expand...
OK, I understand now.

Speaking of BMS, what is the minimum model you recommend for 14S ?

Is something like this enough (granted there is no heat sensor) ?
 
Charlycop said:
Which means for example, if I want to use one 1200W 230V appliance, I need 48V 1200W (let's assume it is 100% efficiency inverter and no loss by heat), which means 25A, which means 14s50p and 700 CELLS.
Click to expand...

You usually do it the other way round and assume the worst case scenario to leave some room in your calculations :)
I always use 80% inverter efficiency in calculations even though most decent ones are closer to 85% or 90% in reality.

There is no strictneed to build a 48V battery, it could very well be 24V as well. For 1200W output you need about 1500W input, so 31.25A or 62.5A at 24V or 48V respectively. That's manageable. The problem is that laptop cells aren't the most powerful to start with. For laptops the capacity is much more important than high currents. And over time this is just going to be worse.

Depending on available space and budget, and runtime, it might be worth it to look at new cells. It's possible to make a suitable battery that is very small.
 
DarkRaven said:
For 1200W output you need about 1500W input, so 31.25A or 62.5A at 24V or 48V respectively.
Click to expand...

I think this is backwards
48V and 24V, respectively. ;)
 
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