diy solar

diy solar

Xuba Electronics: DEAL - 280AH LiFePo4 cells. Purchase & Review

Is anyone worried that the batteries could get overcharged because the reported voltage under load is lower? Example:
1. Batteries are fully charged.
2. Start 1kW load, battery voltage drops to 1.5V which triggers 200A bulk charge current from 2x flexmax 100 charge controllers.
Would this bring the voltage back up, causing the charge controller to stop, but looping back to #1 and looping this cycle?
3. battery gets damaged until voltage increases and the charge controller stops charging the battery.

I see there are various timing options and tests for the various charge steps. It's looking like I'm going to have to get quite comfortable with these.

Maybe a current monitor connected to a raspberry Pi would help. I could detect when the batteries really should stop getting charged.
Unfortunately there seems to be no way to tell the flexmax CC or Radian inverter to stop charging. :-(
 
I am not worried. But i make sure that the voltage settings are correct. Outback has a lot of options. Can you set Absorb time? There is a rebulk setting on my Outback that should prevent that cycling.
 
JIMMY said:
I have been quoted $299 for 50pc to Brisbane.

Seems reasonable to me for 275kg.

There is clearance to pay this end too though.

Jimmy
Click to expand...
Is there import taxes/tariffs to pay at Brisbane.
Do you know much it is or where I can find info on it.
 
One of my XUBA cells keeps going higher than the others in a 12v 280ah setup. Using a chargery set to balance, it is always higher. When charging @ 13amps the high cell (closest to the negative) goes over 3.65 V and trips the BMS.
I believe I have a bad cell, but I haven't paralleled them and top balanced. I did parallel them around 3.25V for a week before this.
What do you y'all think?
 
So is it possible the cells are OK, and if I just buy a power supply and top balance, then I can just run them down and recharge and see if they match at the top again? Question is, why can't the chargery with 1.2A passive balancing keep up? Doesn't that indicate that the cell is bad?
 
bostonbuzz said:
So is it possible the cells are OK, and if I just buy a power supply and top balance, then I can just run them down and recharge and see if they match at the top again?
Click to expand...

Yes, this is possible. I always top-balance any cells I use and never had issues really.

I'm not familiar with chargery, but I guess there are some parameters that need to be set - what are they like? But even then, 1.2A per cell can take a while with 280Ah cells if they're out of balance...
 
It could mean it has slightly less capacity. Technically you equalized the cell voltages at 3.25 but since that cell has a slightly different charge curve than the others, it got to 3.65 v before them. It could also mean the other cells have more than 280 Amphours. If you don't want to take the pack apart you can hook up a high Wattage regular light bulb or big Wattage register and drain it a little. That is all the BMS is doing but doing it slower.
 
bostonbuzz said:
So is it possible the cells are OK, and if I just buy a power supply and top balance, then I can just run them down and recharge and see if they match at the top again? Question is, why can't the chargery with 1.2A passive balancing keep up? Doesn't that indicate that the cell is bad?
Click to expand...
A couple of things you could do. Parallel them to 3.65V. As battery, use a light bulb or resistor to bleed off the one high cell till you can get them all charged up together. On mine I just spent the time to parallel top balance them the first time.
 
bostonbuzz said:
So is it possible the cells are OK, and if I just buy a power supply and top balance, then I can just run them down and recharge and see if they match at the top again? Question is, why can't the chargery with 1.2A passive balancing keep up? Doesn't that indicate that the cell is bad?
Click to expand...

Have you checked your balance settings in the Chargery?
 
Thanks guys I’ll give it a shot putting a load on and then charging and repeating. It’s not making total sense because it was balanced around 14.1v and somehow goes more out of balance as it sits. I checked the parameters. It is set to “on” for charge discharge and storage above 3.2v and accuracy to 8mV.
 
bostonbuzz said:
It’s not making total sense because it was balanced around 14.1v and somehow goes more out of balance as it sits.
Click to expand...
That doesn't make sense. After you check the BMS settings unplug the balance leads and see if you get the same result. I can understand a cell drifting down but drifting up is unlikely unless the BMS is providing Vampire current. I use that term loosely since Vampire loads are more common. :)
 
bostonbuzz said:
Thanks guys I’ll give it a shot putting a load on and then charging and repeating. It’s not making total sense because it was balanced around 14.1v and somehow goes more out of balance as it sits. I checked the parameters. It is set to “on” for charge discharge and storage above 3.2v and accuracy to 8mV.
Click to expand...
I've seen my cells show slightly different voltages, usually during charging or discharging, with one or both end cells in the series. One end cell would show slightly higher, the other end would show slightly lower than the rest.

What I did was number each of my cells and change the order of them in the series moving the end cells in the middle and the middle cells as new end cells. Got similar voltage results with the new end cells suggesting it wasn't a specific bad cell, just the nature of charging/ discharging the pack. Perhaps give that a try and see if the cell in question still stands out from the rest. I'd parallel them out first, though.

Can also compare the voltage readings from a Digitial Mutli-Meter (DMM) with the BMS readings. See if they show similar or different readings from each other. I have 4 different meters with my pack, all show slightly different readings from each other, and periodically I'll see one meter show something more different compared with the others. But, as I use the pack, I check again later and the readings are more in-line with each other again.
 
I think this is pretty universal with packs. The Cell receiving the (+) will end up with a higher / faster charge than the last cell in the string which is (-). The difference should "not be huge" and will settle once charging stops.
 
After reading all 48 pages, I finally took the plunge and ordered a set of my own. Amy was super helpful and the ordering process wasn't nearly as scary as I thought it would be. I did sea freight DDP, so it will be at least a month before I see them.

Thanks to everyone that contributed information here. It has been a huge help and it saved me a lot of money.
 
Sgt Raven said:
I haven't but I have thought of it. Like what the individual cells are wrapped in, but groups of 4.
I think any more than that would get too heavy to easily handle.
Click to expand...
Do you think this affect heat dissipation negatively? If not, any idea where to get some giant shrink tube guys? haha I like the idea.
 
Jeremiah said:
Do you think this affect heat dissipation negatively? If not, any idea where to get some giant shrink tube guys? haha I like the idea.
Click to expand...
My pack has 2 strips of HD double sided tape between the cells and I'm only pulling 6A. I have one window open and a fan going in the room. It's probably 70F air temp in there and the cells are cold to touch. The pack is between 71-73F by my infrared thermometer. The Smart BMS external temp is the same.
 
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