Shorai lithium batteries

Bozo wrote:

bountyhunter wrote: I found this plot of a typical CC/CV charge mode for an Li battery. It shows how the charger holds the current constant until the battery voltage reaches the "set point" then it tapers off the current and holds at constant voltage (this plot is for a single 4.2V cell). This is the ideal characteristic for Li charging. A bike's electrical system has nothing to limit the max current during the CC mode.

NOTE: the "1C" charge current refers to the A-hr rating of the battery. A 14 A-hr battery has a C rate of 14 Amps.

Pardon my ignorance, special chargers are mentioned here but on the site I bought the battery off states that no special chargers are required. Any comments??

I recall Shorai highly recommends using their charger. There are definitely some lead acid float chargers that will kill an Li because they don't shut off, they keep "trickling" current in continuously and Li won't tolerate that. The other problem is that the set voltage on a Pb float charger is too low, typically 13V ballpark for keeping a lead acid battery in "standby". The Li needs a higher voltage to get a full charge on board.

Well designed lead acid chargers also have temperature compensation built in. I did one of the IC's that the car makers used back in the 80's and they specified a tempco of about -15 mV/C. That is necessary for a Pb battery sitting outside in your garage: as the temp varies the correct charge voltage has to track the battery. But an Li does not have that characteristic so that type charger would be wrong for it.

I think it's probably smart to use a dedicated Li charger if you spend the big bucks for the battery. As for the charge from the bike's alternator, nothing you can do except watch and see and maybe check the temp of the battery after running it a while. If it's getting hot, that's a bad sign.

NakedFun wrote: This may help explain a bit: batteryuniversity.com/learn/article/char...ithium_ion_batteries

Cory

Good article. I particularly enjoyed their phrasing:

a safety membrane on some Li-ion bursts open at about 3,450kPa (500psi) and the cell might eventually vent with flame.

"Vent with flame" sounds so much more refined than "explode and burst into flames"..... :laugh:

Back in the 90's when we first started working with Li batteries, I coined the phrase "rapid spontaneous disassembly" for published articles rather than say EXPLODE....... :woohoo:


Note that Shorai and all auto Li batteries are Lithium Iron Phosphate (LiFePO4) so this part applies:

Li-phosphate (LiFePO) makes an exception with a nominal cell voltage of 3.20V and charging to 3.65V.

That means max charge voltage should be limited to about (4 x 3.65) = 14.6V. That means MOST bikes will be OK because they are typically in the 13.5 - 14.5V ballpark. Going on the low end just means the bttery is not 100% charged (which won't hurt anything), going too high can kill it as stated in the article.

Thanks for your replies especially the battery article, I believe I can use my voltage limiting (and current limiting) bench top power supply if need be.
Baldy, yours is similar to my heinz variety bike I'm putting together from all the spares I had (I meant the GPZ style not that yours is a hybrid :sick: )
I hope mine looks somewhere like yours when I finish - nice bike.