Contrary to popular belief charging a Lithium Ion battery as little to do with 
the voltage of the charger.

Charging Lithium Ion batteries is a procedure when one holds the current 
constant until a voltage is reached and then holding the voltage constant 
letting current drop to a current cutoff value. 

You can use any voltage over the max voltage of the cell while in constant 
current mode. 

Any charger or power supply can do this the part it may not do is the constant 
voltage phase of the charge. 

You could just skip the constant voltage phase and shutoff the charger when the 
voltage is reached. You will be over 90% charged at this point especially if 
you are using a low current.



Sent from my iPhone

> On Mar 12, 2019, at 9:59 AM, Dan Baker via EV <ev@lists.evdl.org> wrote:
> 
> Thank you again for the great info Jay.  Fire is never a good thing with
> any vehicle and fires on boats are much worse than land vehicles, you
> likely won't drown or your car wont sink if it catches fire.  Perhaps I can
> install a trapdoor below my batts and eject them like a warp core on a Star
> trek episode in a worse case scenario lol.   I do carry an extinguisher at
> all times as per safe boating regulations, mine is 2x the min. size
> required just in case.  I see a lot of these lithium batteries come with
> chargers that are only 2 pin so I suspect they are a fixed top voltage and
> an internal BMS to limit?   My Sevcons are isolated I know that, what I
> don't know is if the top voltage can be changed.  They have an interface on
> them which allows some settings but I could not find any documentation
> online about them, Sevcon's website has nothing on them, may have to give
> them a call.   I got them on a ebay deal clear out at a really good price.
> If I don't charge with my Sevcons and use the included individual 12v
> chargers, would there still be worry of connecting too many in series?  Is
> it charging,discharging or both the issue when connecting in series?
> 
> Cheers
> Dan
> 
>> On Mon, Mar 11, 2019 at 9:18 PM Jay Summet via EV <ev@lists.evdl.org> wrote:
>> 
>> 
>> 
>>> On 3/11/19 7:40 PM, Dan Baker via EV wrote:
>>> 
>>> I have two really nice 17amp 48v Sevcon lead acid chargers,  would I be
>>> able to use them with these Lithium packs (connected to match 48v of
>> batts
>>> of course)?
>>> 
>> 
>> You can certainly hook up a Lead Acid battery charger to a Lithium
>> battery bank, and it will charge the cells as long as it's voltage is
>> above the battery bank voltage. Doing so is probably not safe however.
>> 
>> The trick is stopping the charge right when the cells are full, but not
>> overcharging them.  If you overcharge a flooded Lead Acid battery, it
>> bubbles a bit of Hydrogen out and the next time you top it up with
>> distilled water everything is good. (This is how they equalize all the
>> cells in a Lead Acid battery...they overcharge them all until they all
>> bubble....)
>> 
>> If you did the same to a lithium ion battery, it may burst into flames
>> very energetically, so your charger must be able to detect the voltage
>> level of every cell and stop charging the pack as soon as any cell
>> reaches it's "maximum" voltage.
>> 
>> Typically a "12 volt" charger will go up to 14.6 volts for a while to
>> equalize all six of the 2 volt cells in a lead acid battery, and then
>> drop down to 13.6 volts to maintain (float) the charge.)  In the same
>> way, a "48 volt" charger may actually go up to 58.4 volts.
>> 
>> 
>> You need to make sure that your "48 volt" lithium ion batteries can
>> safely be charged up to 58.4 volts (and that there is some way to make
>> sure that none of the cells are out of balance, because if even one cell
>> is too high, it may burst into flames....igniting other cells.....)
>> 
>> So, if you have a BMS that can turn a relay to turn off your
>> chargers...you probably could use those chargers to charge your
>> batteries safely. As long as the relay/bms worked every time.
>> 
>> Typically, a charger dedicated for LiIon batteries allows you to program
>> a specific stopping voltage (or comes pre-programmed for the appropriate
>> voltage of your pack.) They sometimes also have other safety features
>> such as automatically stopping after a set time limit, or a set number
>> of amp hours, or watt hours have been delivered, even if the voltage
>> hasn't reached the stopping point. They also usually have some way to
>> interact with a BMS (or a built in BMS) that allows them to stop
>> charging if any single cell within the pack goes above the max voltage
>> per cell.
>> 
>> Jay
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