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Our NEW GO-TO LiFePO4 vendor...09.20.21

I think silicon is cheaper than nichrome or whatever these days.
But you will have to try harder not to burn it up. Good choice of resistor and power dissipation is limited. Transistor turned on too hard would melt. I've used PTC resistor to adjust bias of a transistor, but that thing (and 0805) cost me a buck.
My Docan cells look like they will be fine with the JBD's roughly 200ma passive balancing now that I have increased the setting for the cell voltage at which balancing turns on from the factory default of 3.3v to 3.4v. My problem was that it was balancing the wrong cells when that voltage setting was too low.

But this is a fun intellectual problem, and could be useful for cells that are not so well behaved. If these can be built at $5 per cell in a bus bar form factor that you just put on top of each cell with no additional wires or additional bluetooth links that need to be watched, I like that better than adding a more complicated commercial device that does 2A active balancing. Yes, it's still just passive balancing, but is simple and solves the primary problem of having a few cells run up beyond 3.6v while others are still getting charged. Dump currents could be increased as high as might be needed for some especially problematic grade C cells by adding extra resistors in parallel.

Your earlier suggestion of using a PNP to drive the high power NPN is good, since your PNP's Vce-sat is lower than my NPN driver's Vbe. A little bit more headroom to get the driver's collector current dialed in.

Yes, I would have to try harder for appropriate proportional control of a transistor, switching is easier. Every commercial balancing circuit I have looked at does it with switching. Wirewound through hole resistors of appropriate size don't necessarily need a heatsink, here's a datasheet showing one that works fine at up to 70C ambient air temps before needing to be derated https://www.mouser.com/datasheet/2/303/res_tuw_tum-1228619.pdf Also, that resistor is built to deal with surface temps of 275C, where heat dissipation is much faster than it is for the 120C or so max case temp of a transistor.
 
Hi!
Could you please send me a link to the springs you used in your fixture?
The picture's right battery seems to show them almost bottoming out, or is it just the photo's angle?
Thanks in advance
For what it's worth, post #808 from a couple months ago has a description of how I used four red die springs from Amazon for a 1P16S compression box. I have since moved to a 2P16S configuration using two red die springs down the middle at 150kgf per spring, the four outside rods use yellow die springs at 75kgf per spring. (Edit: Best to use all red springs. See post #884.)

From post #808 in this thread of July 5, 2022:
"Using four red 80x30mm die springs in a compression box, likely another case of being overly conservative.
Here's a good source: https://www.amazon.com/gp/product/B07GSNCYNK
The cells want 300kgf, so 75kg per spring, spring constant is 7.03kg/mm, so spring deflection is 75/7.03=10.67mm
Put roofing felt (tarpaper) between cells to make certain the metal cases didn't short through the thin plastic covers.
Rods are rebar with 1/2" bolts welded to one end (what I had on hand), a hole drilled in the other for
a washer and a nail. 3/4" plywood endplates, but still needs channel iron braces (drilled for the rods)
to keep it from bending. I'm building double wide, planning to eventually go 2P16S. For a single row of cells,
could get by with the yellow 80x30mm die springs at 1.8kg/mm."
 
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For what it's worth, post #808 from a couple months ago has a description of how I used four red die springs from Amazon for a 1P16S compression box. I have since moved to a 2P16S configuration using two red die springs down the middle at 150kgf per spring, the four outside rods use yellow die springs at 75kgf per spring.

From post #808 in this thread of July 5, 2022:
"Using four red 80x30mm die springs in a compression box, likely another case of being overly conservative.
Here's a good source: https://www.amazon.com/gp/product/B07GSNCYNK
The cells want 300kgf, so 75kg per spring, spring constant is 7.03kg/mm, so spring deflection is 75/7.03=10.67mm
Put roofing felt (tarpaper) between cells to make certain the metal cases didn't short through the thin plastic covers.
Rods are rebar with 1/2" bolts welded to one end (what I had on hand), a hole drilled in the other for
a washer and a nail. 3/4" plywood endplates, but still needs channel iron braces (drilled for the rods)
to keep it from bending. I'm building double wide, planning to eventually go 2P16S. For a single row of cells,
could get by with the yellow 80x30mm die springs at 1.8kg/mm."
Thank you very much for your description!

I don't know much about pressure, pressure distribution among several pressure sources (double the number of springs means half the pressure each spring needs to produce for a constant pressure, or is it non linear?), pressure change along spring compression, etc.

My setup is about to be 8S for a typical 24v with 280Ah Eve cells.
I also though about spreading into 4+4 in order to fine tune pressure distribution, but maybe it's nonsense...

Again, thanks for chiming in!
 
Thank you very much for your description!

I don't know much about pressure, pressure distribution among several pressure sources (double the number of springs means half the pressure each spring needs to produce for a constant pressure, or is it non linear?), pressure change along spring compression, etc.

My setup is about to be 8S for a typical 24v with 280Ah Eve cells.
I also though about spreading into 4+4 in order to fine tune pressure distribution, but maybe it's nonsense...

Again, thanks for chiming in!
First off, I'd recommend using the red 80x30mm die springs from Amazon, not the yellow ones which would slightly exceed their max load when used at 75 kgf per spring.

Most people in the forum don't really worry about compression boxes, or they do them wrong. Doesn't really matter that much. The Eve 280K datasheet states that we can get 6000 full charge/discharge cycles on these cells if they are kept in a "300kgf clamp". This means we press in on the broad side of the cells with a force of 300 kilograms (about 660 lbs). They no longer spec how many charge/discharge cycles to expect without a clamp, but I believe that is around 4000 or 5000 cycles. It would take most of us 20 years to get that much use out of these cells, by which point they will likely be dead of old age. But some of us are looking for interesting hobbies, and building a compression box is cheaper than a Ferrari. If you do build a compression box, know that the 300kgf figure is not terribly critical, most people use these cells at 0kgf, and up to 500kgf would probably not do any damage.

Springs are linear. They follow Hook's law, so the force exerted is proportional to how much they are compressed. Die springs follow the JIS spec: https://www.electronicfasteners.com/wp-content/uploads/2014/09/ASRaymond_JIS_Catalog.pdf The bottom of page 14 (pdf page 16) shows that a red 80x30mm spring deflects at a rate of 7.03 kgf/mm (kilograms force per millimeter), and has a maximum recommended deflection of 25.6mm beyond which the spring may be permanently deformed. Also check out the table on page 3 (pdf page 5).

One row of cells could be compressed with one spring on each of the four corners of one of the end plates, each spring exerting 300kgf/4 = 75 kgf.
Using red 80x30mm die springs, for 75 kgf we deflect it by 75/7.03=10.67mm.

If there's two separate rows of 280Ah Eve cells, we would have a total of 8 springs, each pressing in with 75 kilograms of force. Those 8 springs could be used on a single endplate, with four springs near the center. Or we could combine the four inside 75 kgf springs into two 150 kgf springs, leaving the corners at 75 kgf. Or we could have 4 springs at the corners each pressing in with 150 kgf, though the endplates had better be thick plate steel or they will bow out at the middle. For 150 kgf, deflect the 80x30mm red springs by 150/7.03 = 21.34mm, which is 26.7% of the total 80mm of length.

The internet pedants will now all gleefully chime in that a kilogram is a unit of mass, not force. The above is written on the assumption that most of us are living on the surface of the earth, where gravity exerts a force of roughly 9.8 Newtons per kilogram. Please correct any other errors I might have made.
 
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The internet pedants will now all gleefully chime in that a kilogram is a unit of mass, not force. The above is written on the assumption that most of us are living on the surface of the earth, where gravity exerts a force of roughly 9.8 Newtons per kilogram. Please correct any other errors I might have made.
Wow, you are a brave soul; asking for error correction immediately after referencing pedantry.
The result is replies full of information that is absolutely useless from people such as my self.

Gravity - not a force, but rather a warp in space-time caused by mass that results in a bend in the path of an object which would otherwise travel in a straight line. When the path of the object intersects with the mass causing the warp-age, it appears to be a force holding the objects together.

Newtons - when capitalized refers either to a person or a cookie made by Nabisco. Lower case it refers to the force required to accelerate a 1 kilogram mass at a rate of 1 meter per second squared. Since 150 times 9.8 Isaac Newton's seems like too much force on the batteries and 150 times 9.8 Fig Newtons seems like too little force, I assume you meant 'newtons'.

Hook's Law - thanks for mentioning this. It was something I was not familiar with. But in looking it up, I found that it is actually Hooke's Law, named after Robert Hooke who proposed the law in 1660. It seems this poor fellow is having his name misspelled all over the Internet, including on educational websites.

In all seriousness, thanks for the detailed evaluation of spring compression in your post. ...And I apologize for otherwise wasting everyone's time, but I had fun.:)
 
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...

The internet pedants will now all gleefully chime in that a kilogram is a unit of mass, not force. The above is written on the assumption that most of us are living on the surface of the earth, where gravity exerts a force of roughly 9.8 Newtons per kilogram. Please correct any other errors I might have made.
It is listed as kgf (kilogram force, ie standard reference weight in earths gravity) not kg (kilogram, ie measurement of mass).
 
It is listed as kgf (kilogram force, ie standard reference weight in earths gravity) not kg (kilogram, ie measurement of mass).
Ah, there's a couple of them already! :)
Anybody who's successfully messing with setting up a battery from scratch is going to be more than a little meticulous about things technical.
Like me.
And boring unlike minded people to tears.
Which is to say, we are pedants.

In my defense, I'm pretty sure that "Hooke" is the Olde spelling of "Hook".
They also used lots of f's where they should have used used s's: https://www.livescience.com/65560-long-s-old-texts.html

Thanks for the replies.
 
Wow, you are a brave soul; asking for error correction immediately after referencing pedantry.
The result is replies full of information that is absolutely useless from people such as my self.

Gravity - not a force, but rather a warp in space-time caused by mass that results in a bend in the path of an object which would otherwise travel in a straight line. When the path of the object intersects with the mass causing the warp-age, it appears to be a force holding the objects together.

Newtons - when capitalized refers either to a person or a cookie made by Nabisco. Lower case it refers to the force required to accelerate a 1 kilogram mass at a rate of 1 meter per second squared. Since 150 times 9.8 Isaac Newton's seems like too much force on the batteries and 150 times 9.8 Fig Newtons seems like too little force, I assume you meant 'newtons'.

Hook's Law - thanks for mentioning this. It was something I was not familiar with. But in looking it up, I found that it is actually Hooke's Law, named after Robert Hooke who proposed the law in 1660. It seems this poor fellow is having his name misspelled all over the Internet, including on educational websites.

In all seriousness, thanks for the detailed evaluation of spring compression in your post. ...And I apologize for otherwise wasting everyone's time, but I had fun.:)
Thanks for a proper good laugh!
 
kgf confused me at first.

300 kilograms on earth at sea level, whatever that force is, apply that amount.

how to do it varies, i like to think of it as like a horizontal 300kg weight on earth pressing the cells together for theory purpose
 
I bought a bunch of 304ah cells from Docan months ago. I've been methodically testing them, one per day since the middle of August. So far so good. I've built one 12 volt battery to use in testing the other cells. I have 14 more cells to go and then I'll post some about the results.

So there is some Docan talk. Now can we get this thread back off topic!
 
I bought a bunch of 304ah cells from Docan months ago. I've been methodically testing them, one per day since the middle of August. So far so good. I've built one 12 volt battery to use in testing the other cells. I have 14 more cells to go and then I'll post some about the results.

So there is some Docan talk. Now can we get this thread back off topic!
Good save! Looking forward to hearing what you find out.

For those not interested in building a compression box, there is one point from my recent posts that should be driven home. Be aware that on my Docan cells, top balancing at under 3.4v was removing charge from entirely different cells than top balancing at 3.5v. And since the cells generally spend far more time under 3.4v, the top balance can get badly messed up. Take care when setting the threshold voltage at which top balancing turns on. With that cleared up, my JBD BMS with its 200ma passive top balance seems to be working fine with my 2P16S pack of Eve 280K cells.
 
"top balancing at under 3.4v"?

Do you mean, after you top balanced once at 3.65V, you set your charge controller to charge to 3.4V (or 3.5V)?
I would think you might want to enable BMS to only balance above say 3.4V, charge to 3.5V for a period of time, then float at 3.45V or something like that. How long at 3.5V would depend on how much time rebalancing takes.

What you wouldn't want is for rebalancing to occur below the knee, where SoC can't be readily determined by voltage.

What various settings are you using for your SCC and BMS?
 
I would think you might want to enable BMS to only balance above say 3.4V, charge to 3.5V for a period of time, then float at 3.45V or something like that.
You have it about right.

But the JBD BMS from Docan has a factory default for enabling balance at 3.3v.
The only communication hardware they provided with my BMS was a bluetooth link.
The Android bluetooth app only allows you to monitor the BMS, not change parameters.
To change parameters you need to use a MSWindows PC program over a UART link.
Which is a PITA if you're like me and don't want anything to do with MSWindows.

As always, let me know if I have this wrong.
It's been awhile since I have looked into the various ways of communicating with a JBD BMS.
There are some projects to talk to the JBD BMS under other OS's,
but they would be a bit harder to get going.
 
The Android bluetooth app only allows you to monitor the BMS, not change parameters.
I'd be surprised if you can't use the more widely used Android App, which allows you to change parameters. I'm guessing the newer one (with no edits) is more stable than the one most of us use, but the old one - if you can get by the flakiness - is better for controlling the BMS.
 
I'd be surprised if you can't use the more widely used Android App, which allows you to change parameters. I'm guessing the newer one (with no edits) is more stable than the one most of us use, but the old one - if you can get by the flakiness - is better for controlling the BMS.
Can you point me to the older Android app?
 
To change parameters you need to use a MSWindows PC program over a UART link.
Which is a PITA if you're like me and don't want anything to do with MSWindows.

Is Windows XP supported?
That is a great, old, reliable OS. Look on eBay for a quality laptop having that loaded. I like Dell Precision workstation laptops.

A USB dongle to whatever UART may be the way to go. It is best for anything Ethernet that needs settings messed with (like IP address and firewall) because the settings can be associated with the RJ45 port on the dongle, leaving the built in RJ45 settings unaltered.

Does it need RS-232? RS-485?
 
I have had no problem changing my Docan JBD BMSs with the Android Bluetooth app. After you change the numbers on the setting page, touch the little check mark in the upper right to actually write them to the device.
 
You have it about right.

But the JBD BMS from Docan has a factory default for enabling balance at 3.3v.
The only communication hardware they provided with my BMS was a bluetooth link.
The Android bluetooth app only allows you to monitor the BMS, not change parameters.
To change parameters you need to use a MSWindows PC program over a UART link.
Which is a PITA if you're like me and don't want anything to do with MSWindows.

As always, let me know if I have this wrong.
It's been awhile since I have looked into the various ways of communicating with a JBD BMS.
There are some projects to talk to the JBD BMS under other OS's,
but they would be a bit harder to get going.
All of my JBD came set to only balance above 3.4v.
Side note, I found it hilarious when off grid garage used his JBD to top balance his cells, and then suddenly found that the balance capability of the BMS was more than adequate to keep them balanced. Always hard to tell what he is doing, but he is totally convinced you need an active balancer. No, you just need to top balance, leave the defaults set (in multiple videos he changes settings like 6 times in one charge cycle) and stop futzing with the settings.

Every version of the Android app I have used allows you to set the vast majority of the settings. Some calibration settings do require the PC software.

For IOS they have a pay version ($5 I think) that allows you to change settings, the free version does not.
 
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Same here for my Docan 200A “JBD” BMS, the overkill solar app allowed me to change every parameter I wanted. I was able to side load it on to multiple Amazon kindles.

That plus a couple free iOS apps on my phone and iPad that are read only it’s pretty handy to have multiple devices to check the BMS
 
I have had no problem changing my Docan JBD BMSs with the Android Bluetooth app. After you change the numbers on the setting page, touch the little check mark in the upper right to actually write them to the device.
Ah, that was the trick.
Need to hit that magical checkmark in the upper right.
Way better than messing with a borrowed 12yr old MSWin Netbook.

Have been using the xiaoxiang Android app, version 3.1.1026
And that is the most recent version that Overkill has on their website: https://overkillsolar.com/support-downloads/

I like what Overkill is doing, their documentation is the best I've seen for the JBD BMS's.
Would have bought from them if they offered the 200A 16S BMS.
Worth a few extra bucks to get good support on this stuff.

Thanks!
 
I like what Overkill is doing, their documentation is the best I've seen for the JBD BMS's.
Would have bought from them if they offered the 200A 16S BMS.
Worth a few extra bucks to get good support on this stuff.

I don't have any insight into what goes on a Overkill Solar, but my guess is that he's selling the most reliable BMS that JBD offers. Fewer hassles that way. He got swamped really bad a while back when Will recommended his website. When you have all the business you can handle, why add to your stress by expanding the product line with items that require more after-sales support?
 
Same here for my Docan 200A “JBD” BMS, the overkill solar app allowed me to change every parameter I wanted. I was able to side load it on to multiple Amazon kindles.

That plus a couple free iOS apps on my phone and iPad that are read only it’s pretty handy to have multiple devices to check the BMS
One more puzzle here.

Have a JBD 7S-20S-200A BMS with 32 Eve LF280K cells in a 2P16S configuration, so 2*280=560Ah.
Using the xiaoxiang Android app, version 3.1.1026.
The "nominal capacity" is set to 560 Ah

The settings for the "Charge Overcurrent" and "Discharge Overcurrent"
both went to 300A automatically when I set the nominal capacity to 560A Ah.

But down at the bottom of the settings under "Hardware Over Current and Short Params"
the "Hardware overcurrent protection" cannot be set any higher than 100A with a max delay of 1280ms
and the "Hardware short circuit protection" has a max of 200A with a max delay of 400uS.

My Magnum MS-PAE4448 4400W inverter spec says it can deliver a 5 sec surge at 8500W, or 8500W/48V=177A
The Magnum PT100 PV charger can give a max of 100A.


Still somewhat on subject, as the BMS was bought from Docan along with the LF280K's.
 
One more puzzle here.

Have a JBD 7S-20S-200A BMS with 32 Eve LF280K cells in a 2P16S configuration, so 2*280=560Ah.
Using the xiaoxiang Android app, version 3.1.1026.
The "nominal capacity" is set to 560 Ah

The settings for the "Charge Overcurrent" and "Discharge Overcurrent"
both went to 300A automatically when I set the nominal capacity to 560A Ah.

But down at the bottom of the settings under "Hardware Over Current and Short Params"
the "Hardware overcurrent protection" cannot be set any higher than 100A with a max delay of 1280ms
and the "Hardware short circuit protection" has a max of 200A with a max delay of 400uS.

My Magnum MS-PAE4448 4400W inverter spec says it can deliver a 5 sec surge at 8500W, or 8500W/48V=177A
The Magnum PT100 PV charger can give a max of 100A.


Still somewhat on subject, as the BMS was bought from Docan along with the LF280K's.
Well, it is a 200A BMS, so asking it for much more could lead to trouble at some point. The BMS also comes with 4 gauge wire, which I don't think is really big enough. I'm changing mine to 2/0 instead. I prefer to keep cables cool under normal use.

Total current is the main reason that I bought two BMS units to run 16S2P. I have 4/0 cable to run from the battery combiner lugs to the inverter (also a PAE4448). A feature of two in parallel is that I can remove one battery for service if needed and still keep the power online.

Each battery has a 300A Class T fuse protecting it.
 
Well, it is a 200A BMS, so asking it for much more could lead to trouble at some point. The BMS also comes with 4 gauge wire, which I don't think is really big enough. I'm changing mine to 2/0 instead. I prefer to keep cables cool under normal use.

Total current is the main reason that I bought two BMS units to run 16S2P. I have 4/0 cable to run from the battery combiner lugs to the inverter (also a PAE4448). A feature of two in parallel is that I can remove one battery for service if needed and still keep the power online.

Each battery has a 300A Class T fuse protecting it.

The 580 Amp-Hours of capacity should be fine.
I'm not asking the BMS to charge or discharge at over 200 Amps.
Weird that the "Hardware overcurrent protection" cannot be set any higher than 100A
on a 200A BMS.

Multiple BMS's mean more stuff to keep track of, and many more
wire connections that could fail. Not an obvious win.
I have redundancy in the form of a separate 24v system using some old lead acid batteries
and a cheapo modified sine wave inverter to keep the refrigeration and lights going.
 
Is Docan still going to sell the LF280K?

They've been out of stock of the LF280K since the end of August.
I suspect they would sell them if they could obtain more.
Not currently listed on the Houston website: http://www.powerwholesale.net/Wholesale-Discount-battery-lifepo4-battery_c34.html
Note that only the first few items say "USA Stock", the rest are probably shipped from China.
The only US stock prisimatic cell is the 100AH Eve cell.

They do have CATL and Lishen at 280AH and 272AH for $110 listed toward the bottom,
plus shipping from China.

You could send an email to Jenny Wu: Jenny Wu <jennywu896@gmail.com>
or Amy Zheng <amy@docanpower.com> or any of the other Docan reps.
They can tell you if new stock is expected.
 
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Anyone know what the prices are currently?
It is a moving target and I have no current quotes, The ladies in some of the previous posts can give you a current quote. I have done business with several of them and freight and prices are a constantly changing and volume matters
Several years ago I purchased cells for less than$125/kWh DDR to my home. I got a quote six months ago for a small volume from US stock but deferred until that project was better defined.
 
It is a moving target and I have no current quotes, The ladies in some of the previous posts can give you a current quote. I have done business with several of them and freight and prices are a constantly changing and volume matters
Several years ago I purchased cells for less than$125/kWh DDR to my home. I got a quote six months ago for a small volume from US stock but deferred until that project was better defined.


Couple years ago I paid around 90 shipped from China for 280ah cells. Last ones I bought I think they were around 110 shipped.

Right now I have 96 in use and I need to double my battery bank eventually. Trying to power a house uses a lot more batteries than you think. Especially in winter and no sun for days
 
Heating loads?
If so, I'd think H2O, SiO2, or NaCl would be cheaper than Li.
(power density depends on high vs. low grade heat. And optional phase change.)
 
Heating loads?
Yes, I use a heat pump. It has to work harder for the few hours that the outside temperature is around 32 F. Most of the time it is pretty efficient, only using 15 kWhs per day. That is the reason I run a deficit in kWhs for the first few months of my relevant period. However my Spring and Summer generation erase that and I am hoping to net out to zero at next true up.
 
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