So your meter indicates 3.54V as 3.56 or 3.57 which is less than 1% error.
For Lithium the nominal voltage is not when pretty much dead as Lead,
but closer to the halfway point.
Since your pack is pretty low in charge, below 20% I am guessing, the total
pack voltage is well below the nominal voltage, which is 12 x 3.8 = 45.6V
Max charge voltage of each cell is 4.2 but I would suggest to keep it under
4.1 if you are not required to get the absolute max out of the pack at all 
If you are doing a race for max distance then go ahead and aim for 4.2 or 
but in daily operation if you want longevity, then I suggest you charge to 4.1V.

You will need a (simple) BMS to tell you when a cell goes over 4.2V or under 
and preferably does some low-current balancing for you, for example the Leaf
BMS has 10mA balance current and runs 24/7.
You definitely want to get a signal from the BMS when any cell is hitting its 
so you can either drop a contactor (to stop charging or driving) or at minimum 
a very noticeable warning that something is going out of spec, so you can 
respond to it
(especially while driving, since during charging you are likely asleep).

12 x 4.1V is 49.2V which is a convenient voltage that most 48V power supplies 
can easily be trimmed up to using the trimpot on the supply.
I have very many 48V power supplies, so let me know if you like to talk about 
getting one.

In fact, last week I disassembled an Enginer unit, which is a 48V Lithium 
battery pack for a Prius
with a charger and a DC/DC converter to the Prius's Hybrid packs ~200V, 5kW.
I do not trust the BMS that came with it as most batteries were toast, but you 
are welcome
to experiment with it if you like.

-----Original Message-----
From: EV [] On Behalf Of fred via EV
Sent: Tuesday, January 30, 2018 3:15 PM
To: via EV
Cc: fred
Subject: [EVDL] Leaf module charging recommendations

Thanks to Jerry Dycus for selling me a great looking clean Volt battery module. 
My still-working Radio Shack (top of the line) digital multimeter tells me all 
the cells are within 0.01 at 3.56 or 3.57 volts.
I've found this useful bit of data:
Number of cells        36
Construction            12 in-series x 3 in parallel Length                     
Width                        9.5"
Height                      10.5
Weight                     45 lbs
Output terminal        M6 nut
Amp Hour                47
Total Voltage           48vdc


Cell type                        Laminate type Cathode material           
LiMn2O4 with LiNiO2 Anode material              Graphite Rated capacity (0.3C)  
 17 Ah Average voltage            3.8 VDC Maximum Voltage         4.2VDC 
Minimum Voltage          3.0VDC I measured 42.5vdc across each 12 cell block 
and the math says it should be 42.72vdc, which is close enough for my meter. 
It's not 48vdc and from an earlier discussion I expected that to be the case.
When it comes to charging this battery, I would like to ensure to get the right 
stuff. My experience with other lithium based batteries is that the nominal 
voltage of the charger is referenced to the battery and in all cases, the 
battery voltage is higher than the nominal voltage "listed." That is to say, a 
36v battery charges to 42vdc and rarely drops to the 36v reference figure in 
regular use. The charger, of course, pushes electrons into the battery at those 
higher levels.
In the case of the Volt battery, I believe I would not want to use an 
off-the-shelf charger rated for a 48v battery. My search results have all been 
ending in devices with excessive top-end termination.

I would like to have an off-the-shelf solution, however, if such a charger 
exists. My current collection of chargers are plug-in and go type, in that they 
have appropriate profiles for charging to a specific level and tapering off as 
appropriate for the pack.
As an additional consideration, this battery does not need to be charged in an 
hour or even two or three. I'm amenable to a configuration that requires a ten 
hour or longer charge period, especially if cost is lower.
I welcome corrections to my train of thought, even to the point of derailment 
as appropriate. I'm hoping for an off-the-shelf solution that works 
out-of-the-box or works with appropriate adjustments on the panel or equivalent.

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