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On 12/22/2018 at 10:29 AM, bmwking said:

according to that data sheet each cell has a max operating voltage of 4v, meaning he could charge them up and including @ 16v, over that will shorten the life span of the cells.  should be fine in an automotive application.  as far as balancing, it's not really necessary as long as he puts each cell on a trickle charger to make sure theyre topped up before connecting them.  balancing circuitry is really only necessary when running several banks of lithium off the same charging source, and even then we're talking like 4+.  it comes in handy in solar and RV applications.

Dont forget the most important aspect when evaluating lithium batteries: C-rate for both charge and discharge. Its not always listed but thats the most important performance specification.  

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Lithium with a good C rate (10C or more is desired, but less can work if you size everything appropriately) can support 5KW per 40Ah.  I recommend using more Ah/KW, but thats a different argument.

Let's assume you're using this 160Ah battery for 5KW, drawing around 480-500A for discussion purposes.  Also, I'm referencing the spec sheet in the original link: http://voltronixusa.com/wp/wp-content/uploads/Voltronix-160Ah-Battery-Cell2.pdf

First comment: 160Ah at 48A discharge.  This battery's C-rate is 48A, so 480A would be 10C.  A 5K amp would be right at the limit of the battery, ignoring alternator current.  OK, we're fine there.

Second note: 480A max continuous discharge current is shown below nominal capacity... perfect, we sized the 5K at 10C, so this confirms that this battery can acceptably discharge at 10C. 

Super important side note: What happens when a battery is discharged past its C-rate (assuming internal resistance allows that much current flow)?  Voltage dips lower than the low-end cutoff voltage.  These cells list only an operating voltage of 2.8-4.0, so with 4 in series I can only assume 2.8 per cell (11.2V at bank) is the lowest possible voltage before cell damage.  That low-end cutoff is usually somewhere between 8-10V with most lithiums.  If your C-Rate causes these cells to dip lower than 11.2V, then thats the limit of these cells.  In this case, a 480A (10C discharge being pulled by the 5K, and without alternator input) discharge would dip this bank to 11.2-ish volts.  Big side note here.

Finally, lets consider the alternator.  The specs say the maximum charge current is less than 3C (48A x 3 = 144A).  Lets assume you have a 300A alternator, which is an acceptable size for a 5K.  300A is 6.25C.  This is double the amount your batteries can take in.  Either you size down your alternator (not recommended) or you double your bank to prevent cell damage from charging above its C-Rate.  (2) 160Ah banks is way more than necessary for a 5K, but if 2 of those banks is cheaper and lighter weight than AGM, then its a good design choice.

Then again, you could hook em up and see how long til they overheat and catch fire. 

EDIT: just noticed the graphs on page 2.  K2 cell spec sheet show actual discharge current versus voltage drop, surprised this company didnt.  Says something about how the cells are intended to be used... they arent exactly bragging about their high C rate capabilities.  Best of luck sir.  Dont catch fire.

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1 minute ago, BassMunky said:

2 160ah lithium battery and 300alt.

This was an example sir.  Not a recommendation.  Clearly stated in the explanation.

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Fact of the matter, OP's "160Ah @ 48A" cells are probably realistically like "40Ah" or so when used in a car audio application or any with a higher C rate than its used to.  The biggest restriction is the input current limit of 3C.

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  • 2 months later...

I just tried to look at all these posts about lithium and I am pretty lost.

Any good resources you used to learn all this like books and such? @WalledSonic

I'm curious if learning to make my own bank of lithium would be better than going out and buying older tech like limitless.

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On 3/15/2019 at 10:39 PM, Joshdashef said:

I just tried to look at all these posts about lithium and I am pretty lost.

Any good resources you used to learn all this like books and such? @WalledSonic

I'm curious if learning to make my own bank of lithium would be better than going out and buying older tech like limitless.

https://batteryuniversity.com/learn/

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