yopappamon

You don't have to disconnect the BMS to measure the cells. You just need access to the balance leads. They are smaller wires, one per cell. Just measure between one wire and the next. Start with the battery negative and find the balance lead that gives you 3ish volts and go from there.

sunnyday

im getting EXACTLY..3.35 volts on each cell...which puts me in the 53.3- 53.6 total voltage im getting out of the whole pack.

so this tells me all 16 cells are in balance...but are not taking and holding 3.65 volts each cell

so either this is how the battery is suppose to be...or my charger just isnt gonna put enough volts into the pack to get it to 58.4 volts and allow the pack to stay there after taking it off charge...

at least I know that none of my cells are bad.

maybe its possible that these are cheaper cells, and are not gonna take 3.65 volts each > ?

yopappamon

It's possible that the BMS is balancing the cells to a lower voltage than you are expecting. Is the BMS getting warm after you have disconnected the charger?

sunnyday

my BMS gets warm..but not hot...

im thinking that maybe my battery is meant to only hold a max of 3.35 volts per cell

or my battery charger is only gonna be able to pump enough voltage in my battery to get each cell to hold 3.35 volts constnat no load.

sunnyday

do you think I should discconnect the BMS and hook my charger up to the battery and see if the indivdual cell voltage will take and hold more then 3.35 volts each ? My charger only puts out about 58 volts max..so it cant overcharge the battery pack.

sunnyday

Im waiting for a special lightweight aluminum seat post rear rack to come in...once that does arrive..I will hook everyhting up and post some more pictures of the completed bike....

then I plan on making a aerodynamic plexglass windshield to reduce wind resistance against my body...

sunnyday

it seems that aerodynamics is very important also...something as simple as a large water bottle will add unecessary wind resistance...

so I am gonna have a clear plexiglass windshield in the front at about a 60-90 angle, which will cut thru the wind , along with making sure my square battery will have a arrow shaped front to it, so the wind does not hit the flat surface of the battery body....etc...

sunnyday

I also plan on cutting down the length of my wires ....for example...the battery wire that hooks to the hub wire , is about 3 -4 foot to long...so instead of wrapping all that extra wire around the bicycle frame...im gonna cut it out, resolder all connections...this will look alot neater and also help a bit with efficiency by doing away with the added resistance created by having 4 foot of uneeded wire connection...

every little bit adds up in the end.

yopappamon

If it was me I'd stop worrying until I tried it out and found that there really was or wasn't a problem. You might end up creating a problem where there was none.

morph999 

3.35v is the normal operating voltage for most lifepo4. Mine hold at about 3.50v and don't go down much more after that. It's possible that your BMS is bleeding the cells down to 3.35v automatically. From 3.50v to 3.35v is not much at all.....after about 30 seconds on my bike, my cells bleed down to 3.35v as do all other brands of cells. Look at any lifepo4 curve and you'll see that the higher the voltage, the steeper the curve. The only thing your cells are missing (possibly ??) is the surface charge. The only way that I know that my cells are charged is by the surface charge, though and if your cells are always 3.35v per cell then it's difficult to tell when they are fully charged and when they aren't. Is this an ebay battery? I advise people not to buy ebay batteries. Your cells might be fine, though. I don't know. I had one cell that would never go above 3.38v and it turned out that there was something wrong with it and it eventually blew up from too much charging. Good luck. Could be that your cells are fine. I don't know. Each brand is slightly different. Anyone who wants to buy lifepo4, I advise them to do heavy research here and also at endless-sphere.com. Look up on Google what people say about ebay lifepo4.



My suggestion is to sit and watch your cells charge the next time around. Sit there with a multi-meter and watch what the voltage does. If the cells go up to about 3.60v or more and then bleed down, then your cells are fine. I don't know how your bms works, though. Maybe you could disconnect the bms and charge each cell by itself and see if they go up to 3.65v. 3.65v is the standard top voltage for all lifepo4. You can go up to about 3.8v without hurting the cells.

HeadwayHQ

3.2-3.35V is the operating voltage of the LiFePO4 chemistry.
3.65 +/- 0.5V is the charging voltage of the LiFePO4 chemistry. (This does not mean the cells will keep a 3.65V charge, it is only for the CC/CV charging method during charging ONLY)

From everything that you have explained, the charger is working correctly (charging the 16S pack at 58.4V), the cells bleed back to their normal working voltage after removing from the charger (3.35V per cell or 53.6V for a 16S LiFePO4 battery pack) as the cell chemistry should, you've checked the cells individually and confirmed that their voltages are all balanced, again (just for reinforcement), the 3.65V per cell is the voltage for charging ONLY the cells do not, DO NOT remain at 3.65V after removing from charger

Sangesf, yopappamon, morph999 and others on this thread are giving you the right advice about your battery pack, and like yopappamon said, you may just end up creating a problem when there was none to begin with!

Sangesf

MY LiFePO4 cells (36v pack and BMS) get charged at 44.4v which is 3.7v each. As soon as I pull the charger off they do drop but only to 3.65 each within 5 min and after a couple of hours (on a .03a load) will drop to about 3.3x per.
Your controller (or BMS) MAY be "bleeding" off the extra voltage/current. But if you haven't cycled the battery yet, then that might be what your seeing.
When you start using the battery, go 10miles and then charge it to full and see what they are at.
Also, I would try leaving it on for more then 30min "extra" and leave it on overnight and see what occurs. If the charger is working correctly then it shouldn't harm the battery at all.

SeizeTech

use extreme caution when bypassing a BMS board, because you will run the risk of charging too fast, charging to too high of a voltage, charging at a normal charging current but not backing off when the temperature of the battery gets too high. all of these conditions can cause permanent damage to your battery....and in not so extreme conditions, you might even cause a battery to catch on fire or explode.

In my opinion, it tempting ( and prudent) for me to reccomend that you just dont mess with the BMS. However, its only an expensive battery, and it's yours to play with. Personally, I've bypassed the BMS to manually balance the cells. And, I wouldn't hesitate to bypass it for troubleshooting purposes.....but I would never utilize a system on a regular basis where the BMS is bypassed, I think thats just asking for trouble.

best of luck to you

Sangesf

I received the 36v 20ah battery and accompanying charger today..
After the charger read full charge "green" I read voltage.. It read 45.6 or 3.8 per cell.. A little high.
I pulled the charger off and it dropped immediately to 40.8v or 3.4v per cell..
I plugged the charger back in an watched it cycle red/green for about 15 min..
I then read the voltage immediately drop to 41.4v or 3.45 per cell.
I read each cell group..
Some were at 3.3x, some at 3.4x, one at 3.57v and one at 3.65v..
Showing out of balance... But improvement.
I'm guessing the charger and BMS are working OK and trying to balance all the cells..
I will leave it on the charger for the next 6 hours and see if I get more balanced cells..
Then after I check each cell group (Hopefully a little more balanced) I will range test..
I MAY have to cycle the battery a few more times before the cells get better balanced..
All will be figured out within the next few days..
If after 5 days (a minimum of 10 cycles), they are not balanced by then, I will leave it on the charger for 48 hours. If at that point they are not balanced, I will contact the seller and get a new (hopefully working properly) BMS.

Sangesf

5 hours later and hot OFF the charger, it's at, and held at 42.7v for 20 mins so far or 3.56v per cell...
Put it back on charger and will wait another 2 hours and see what I get, and will check each cell group specifically.

Sangesf

Welp, time for a little update...
After running the battery through it's paces and 10+ cycles of charge and recharge....
Here are the results..
Today, charged to full from almost dead...
Charger stopped at 45.6v (as usual) which is 3.8 per cell...
Pulled it off the battery and the battery read 43.8v or exactly 3.65v per cell.. Perfect!
Waited 20 minutes and it read 43.2v which is ~3.6v per cell and has stayed at that voltage for an hour.
BMS is working PERFECTLY for HVC..
Will test for LVC and actual AH when I get a watt meter.