diy solar

diy solar

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

It's not like they are written in stone. If I felt I needed to change them because of a situation I was in, then it's only a few clicks away.. That is the beauty of building my own battery and the smart Bluetooth BMS, I have complete control over it.

I totally agree. But I jumped the gun anyways. Those are the settings I am going to use for my inverter. The BMS will have higher and lower cut off settings.
 
The resistance on 7 cells was .11-.12 then 1 cell was .15

That's still close. It would be interesting to know if cell 7 was the one that measured .15. I don't know that would make any difference. Perhaps someone else would know.
 
That's still close. It would be interesting to know if cell 7 was the one that measured .15. I don't know that would make any difference. Perhaps someone else would know.
Thats what im keen to find out.
I understand 1 cell will always hit bottom first but there was just such a big gap at the end of 320mv which just happened to be #7
 
OK, let's step back a second.
320mv is not significant... please, too many get hung up on such MINUTIA, really, it is almost nitpicking and really serves little purpose. Even perfect matched cells wobble voltage wise at the top. All LFP will settle from 3.65 down a bit while they rest, often unevenly making one or two cells standout, not unusual. A reminder, that these cells are Within the Grade-A Spec of the manufacturer but thee are not Voltage & IR Matched and batched cells and so such deviations is not unusual. This is one reason the Top & Bottom Balancing is mentioned so often.

Assume a generalized rule of 1mv per amp hour capacity is not unusual. Often a Passive balancer (which burns off hi volts only from hi cells) can address such small deviation but Passive is very slow. Larger Capacity cells are often too big for passive to be efficient due to it's slow process.

Longevity practices dictate that we stop the cells at 10% from bottom & 10% from top providing 80% of their capacity for use. 2.75 & 3.28 respectively per cell.

Here is some Excellent Information from Orion BMS Folks (a pretty darn credible BMS Company who knows their stuff. The BMS specific stuff is moot as it depends on what your BMS is, but the battery info is what we want anyway.

High Resistance Cells : Again Orion hs some helpful info.

Something from Battery U:

Hope the info helps.
 
OK, let's step back a second.
320mv is not significant... please, too many get hung up on such MINUTIA, really, it is almost nitpicking and really serves little purpose. Even perfect matched cells wobble voltage wise at the top. All LFP will settle from 3.65 down a bit while they rest, often unevenly making one or two cells standout, not unusual. A reminder, that these cells are Within the Grade-A Spec of the manufacturer but thee are not Voltage & IR Matched and batched cells and so such deviations is not unusual. This is one reason the Top & Bottom Balancing is mentioned so often.

Assume a generalized rule of 1mv per amp hour capacity is not unusual. Often a Passive balancer (which burns off hi volts only from hi cells) can address such small deviation but Passive is very slow. Larger Capacity cells are often too big for passive to be efficient due to it's slow process.

Longevity practices dictate that we stop the cells at 10% from bottom & 10% from top providing 80% of their capacity for use. 2.75 & 3.28 respectively per cell.

Here is some Excellent Information from Orion BMS Folks (a pretty darn credible BMS Company who knows their stuff. The BMS specific stuff is moot as it depends on what your BMS is, but the battery info is what we want anyway.

High Resistance Cells : Again Orion hs some helpful info.

Something from Battery U:

Hope the info helps.
Thank you for that info Steve cheers.
 
FYI GENERAL re XUBA & LUYUAN (their sister company)

They are presently trying to work out how to offer Fully Matched & Batched Cells and they have run into a learning curve about the process and it's costs. Bottom line, this requires serious Test Rigs and Equipment and it is not cheap. Then there is the time factor as it is Time Consuming running cells through complete cycles. The realization that this is a long & tedious process which adds cost per cell hit home. This would add cost per cell / bundle but now that would provide for better pack builds and more performance.

Here is a USA Vendor that offers a Cell Matching Service and they outline (very basically) the extra cost & process. I think it helps explain it just a little.

Here is a concern which will arise from such a service being offered as well, POSSIBLY. The cells must be connected/mounted to the test rig, meaning the terminals will get scratches and I know that some Derwood would run of claiming "the are used cells". It DOES happen, there always has to be a few that just have to go "Chicken Little - The Sky is Falling" mode.

This Service may be offered starting in October or so, depending on what they sort out and if they can make arrangements with a test facility.|
 
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FYI GENERAL re XUBA & LUYUAN (their sister company)

They are presently trying to work out how to offer Fully Matched & Batched Cells and they have run into a learning curve about the process and it's costs. Bottom line, this requires serious Test Rigs and E
I would imagine that to a be substantial outlay for the company not only in the set-up costs but also the operational and maintenance cost also.
There must be a demand for the service though.
 
Testing equipment to quickly and efficiently cycle big batteries is custom, large, and expensive. Especially when data logging is required. Typically 6-7 figures USD.
 
I keep seeing references to "300 kgf" as if it's something odd, but this is a relatively typical way to refer to forces in the metric system although it is not the standard unit.

300 kgf is the force exerted by 300 kilograms of mass at standard earth gravity (9.806 m/s^2 acceleration), or 2942 Newtons. This is the proper SI unit of force.

For us used to degrees Foreignheit and length based on a monarch's thumb, naturally this is equivalent to 20.56 slugs and by multiplying by the 'Merican acceleration due to gravity (a perfect 32.17 ft/s^2) we come to this being the force exerted by about 640 pounds of mass. Naturally this is not the exact answer since we rounded several times in these calculations.

Or you could say 300 kg is 661 lbs, and do that. For us used to one relatively stable gravitational field the line between "force" and "mass" is very blurry...
 
I keep seeing references to "300 kgf" as if it's something odd, but this is a relatively typical way to refer to forces in the metric system although it is not the standard unit.
...
Or you could say 300 kg is 661 lbs, and do that. For us used to one relatively stable gravitational field the line between "force" and "mass" is very blurry...

Though I was unfamiliar with the unit, it wasn't too hard to grasp once I looked into it, and it started being discussed.

Where (I perceive and feel) the uncertainty to be, is how to implement that spec in a design, and when and why it is beneficial.
 
why it is beneficial.

High charge and discharge currents can create voids in the roll/sandwich. Compressive force reduces or prevents these voids. In prismatics it also provides support for the large, but very thin layers. Physical support is also seen in other chemistries with thin layers. For example pure lead AGM batteries make use of a higher density AGM mat between the cells. If memory series, lifeline uses the case to provide some compression when they assemble, which provides some of their legendary lead acid vibration resistance.

Since most of use are not exceeding 0.5C, and 90% of the time we are under 0.2C, its much less of a concern. But with 1C rates? It obviously makes enough difference that the cycle life chart calls it out.
 
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Since most of use are not exceeding 0.5C, and 90% of the time we are under 0.2C, its much less of a concern. But with 1C rates? It obviously makes enough difference that the cycle life chart calls it out.

This was one of the things I have been pondering with no way to answer based on the datasheet alone. Under what conditions is this compression beneficial, I'm sure it won't hurt no matter what, but it would be useful to know whether (like active or passive cooling) it is beneficial at high 1+ C rates or if it is beneficial regardless of C-rate.

It would also be useful to know how they measure it (100% SOC? 50% SOC? etc).
 
I keep seeing references to "300 kgf" as if it's something odd, but this is a relatively typical way to refer to forces in the metric system although it is not the standard unit.

300 kgf is the force exerted by 300 kilograms of mass at standard earth gravity (9.806 m/s^2 acceleration), or 2942 Newtons. This is the proper SI unit of force.

For us used to degrees Foreignheit and length based on a monarch's thumb, naturally this is equivalent to 20.56 slugs and by multiplying by the 'Merican acceleration due to gravity (a perfect 32.17 ft/s^2) we come to this being the force exerted by about 640 pounds of mass. Naturally this is not the exact answer since we rounded several times in these calculations.

Or you could say 300 kg is 661 lbs, and do that. For us used to one relatively stable gravitational field the line between "force" and "mass" is very blurry...
Working in metric units.
Building a compression frame with 2 end plates and 4 threaded rods with nuts, one in each corner.
It would be handy if someone could calculate the torque in newton/meters that would have to be applied on each nut to create a force of 2942 newtons on the cells.
The newton/meter torque on the nuts would have to be converted to tensile force applied to the rod and therefore compression force on the cells.
Other than doing this one wouldn't know what compression weight/force the frame was applying to the cells without using some sort of force gauge.
Any statics engineers here that could help
 
I would worry about there being enough threads in those joining nuts. There are specific nuts used in Unistrut for joining threaded rod that provide much more threads to be used.

Otherwise, that's pretty cool!
 
I would worry about there being enough threads in those joining nuts. There are specific nuts used in Unistrut for joining threaded rod that provide much more threads to be used.

Otherwise, that's pretty cool!
Yeah, imagine that, they are called "coupling" nuts.
 
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