# charging Li-ion batteries



## bblocher (Jul 30, 2008)

300zxev said:


> This may sound like a silly question ... but how do you go about wiring up and charging those small Li-ion (laptop style) batteries.
> Is the BMS really a Battery balancing and charging system in one ?


A BMS, sadly, can mean two things. Battery Monitoring System, and Battery Management System. If the system only reads voltages and currents and reports without taking action to prevent the batteries from being ruined then it's just a monitoring system. A management system will be able to take action on these values. A true management system should also be able to balance the cells.

From my understanding, laptop batteries have a managment system built into them to prevent over and under voltage. They probably don't all balance. For example if you get a Dell laptop battery it probably does, but some cheap replacement might have limited BMS to save money. Just some guesses but certainly brands could differ here.


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## Technologic (Jul 20, 2008)

bblocher said:


> A BMS, sadly, can mean two things. Battery Monitoring System, and Battery Management System. If the system only reads voltages and currents and reports without taking action to prevent the batteries from being ruined then it's just a monitoring system. A management system will be able to take action on these values. A true management system should also be able to balance the cells.
> 
> From my understanding, laptop batteries have a managment system built into them to prevent over and under voltage. They probably don't all balance. For example if you get a Dell laptop battery it probably does, but some cheap replacement might have limited BMS to save money. Just some guesses but certainly brands could differ here.


My guess is laptop batteries have no BMS's of either type outside of voltage monitors and the charger itself also probably has a form of Battery monitoring to cut off charging.


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## 300zxev (Dec 5, 2008)

So how does one use these cells to create an EV pack ?
you would need hundred of these cells ... but if that wasn't a problem ... do you need to put a bms between each of the cells ???


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## bblocher (Jul 30, 2008)

300zxev said:


> So how does one use these cells to create an EV pack ?
> you would need hundred of these cells ... but if that wasn't a problem ... do you need to put a bms between each of the cells ???


Yes all cells would need to be managed. All series packs should have a BMS system. All lithium series packs must have a BMS system. Lithium cells must be kept within their voltage / current specs to last.


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## CroDriver (Jan 8, 2009)

Did anyone made such a li-ion pack? I know that the KillaCycle has one but there are no further information about it.

This batterys look promising to me: *http://yhst-65588400267125.stores.yahoo.net/prdeki.html

*I'm am thinking of making my battery pack out of these.


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## Technologic (Jul 20, 2008)

CroDriver said:


> Did anyone made such a li-ion pack? I know that the KillaCycle has one but there are no further information about it.
> 
> This batterys look promising to me: *http://yhst-65588400267125.stores.yahoo.net/prdeki.html*
> 
> I'm am thinking of making my battery pack out of these.


There are better, cheaper and safer batteries than this sort of system (lifepo appears to be about 35-40 cents/watt hour now).


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## bblocher (Jul 30, 2008)

CroDriver said:


> Did anyone made such a li-ion pack? I know that the KillaCycle has one but there are no further information about it.
> 
> This batterys look promising to me: *http://yhst-65588400267125.stores.yahoo.net/prdeki.html*
> 
> I'm am thinking of making my battery pack out of these.


Unless you're doing a small pack these are going to be unreasonable for cost. Not to mentioned the greatly added complexity of managing thousands of cells for an EV pack.


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## CroDriver (Jan 8, 2009)

So it isn't even possible to make a battery pack for a long range out of li-ion batterys?


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## bblocher (Jul 30, 2008)

CroDriver said:


> So it isn't even possible to make a battery pack for a long range out of li-ion batterys?


Oh no, it's very possible. You're just looking at more work and more money for those small format cells. The A123 cells are great from what I hear and have read on the specs. However you'll end up spending 2x-4x as much as you would with same the Thunder Sky large format cells. As I mentioned earlier you're looking at needing to create a battery management system, or buy one, for hundreds and probably more like thousands of small format cells (depending on the size of traction pack) vs only dozens of large format cells.

Lets compare what two equal traction packs would look like. I'll use the pack I've create in my car as the example. We want to build a 144 volt pack with 160Ah capacity. 

Large format cells:
Building a pack with Thunder Sky or equiv. Each cell is 3.2 volts nominal with a capacity of 160Ah. This takes 45 TS-160LFP cells in series to create 144 volts.. I paid $1.60 (I think, maybe more) per AH. 45 cells x 160Ah = 7200 Ah. So that's $11,520 for the pack.

Small format cells:
Now lets build that same pack with A123 cells. Each cell is 3.3 volts nominal with a capacity of 2.3Ah. This takes (rounding up) 44 cells to create 144+ volts. Now we need to parallel these series packs to create the capacity we are looking for. To get 160Ah we will need (again rounding up) 70 parallel packs. 70 parallel packs with 44 cells each is 3080 total cells. In the developer kit, which is the only way to get those cells currently, unless you can buy enough of them for OEM, is $18.33 per cell or nearly $8 per Ah. This traction pack would cost you approx $56,500. Granted, it's a better battery from the claims in the spec sheet. If you can afford it and build it, awesome!

Just making all the connections of these cells would be a nightmare in my opinion and then to worry about how manage and monitor those cells. Scary to me.


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## jbrecher (Jul 26, 2007)

First thing folks need to know about BMS as the Chinese think it is only needed on the discharge cycle. That is why laptop batteries die is due to over-charging. You leave your computer on A/C charging all the time. Lithium doesn't like trickle charging. 
I don't understand trying to connect hundreds or thousands of small cells to get an EV pack. How many possible failures is that? There are 100 and 200 AH cells out there. Sometimes you just need to pay to play. You may end up spending more with the search for a 10 cent answer rather than getting the right product for the job. Everyone is obsessed with doing it on the "cheap". Yugo's are cheap, but not many lived very long. 
I have a lithium powered Fiero with 100 AH cells. It does just fine. I have two Corbin Sparrows and they do just fine. They were not "cheap" but are very reliable. 
Research is fine. I'm doing that with the Fiero, but don't get carried away with cost. It may cost you in the end.


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