diy solar

diy solar

scalability of LifePO4, an insane® battery pack.

wattmatters said:
Per se? No.

You could do it by applying a known resistance/load, measuring loaded and unloaded voltages and using Kirchhoff's and Ohm's law. You may not have equipment with sufficient precision as LiFePO4 has very low internal resistance.


3.29/3.30V is not fully charged, let alone over charged. All you know is the voltages are the same. You don't know their state of charge. The LiFePO4 voltage-SOC curve is very flat.
Click to expand...
great, thank you for the headsup.

So if I charge them all individually to 3.625V. Can I then consider the cells as fully charged individually and once configured in 16S top balanced?
 
currently looking for a charger that can deal with single 3.2v cells as I think that going for a BMS now does not make sense yet as I do not have a power source (wind turbine anyone? ;)) yet. Believe you me that will come!
https://diysolarforum.com/threads/building-the-sickest-®-vawt-ever-brilliant-minds-unite-please.31934

Can I also charge a single 3.2v cell with for example 12v or grater as long as the recommended charge amperage is not exceeded?

So e.g. 12v x 140a = 1680W, or 24v x 140a = 3360W.

Or should I never exceed charging with 3.2v x 140a = 448W?

Reason I ask is because for the life of me I do not find any 3.2v lifepo4 charger ;(
 
First, you charge with CC Constant Current to 90% and from there CConctant Voltage and Variable Current to finish to 100% full SOC.
Also 100% Full is NOT 3.560 That is 100% of Max Voltage Range allowable or the "Gross" range. Working Voltage Range is 3.000-3.400 and you can charge the cells to 3.650 and taking < 1 A and one hour after charge stops the cells WILL settle to around 3.500 +/- and within 2 hours they will be settle to their "resting" voltage.

Playing without a BMS is NOT Advisable, it is a sure fire way to loose control of the cells ad have them either over charge or drop too low IF there are runner cells which you will NOT know without active Cell Monitoring. Your excited Impatience could be causing damage... Do you only tighten 1 or 2 Lug Nuts when you change a wheel on your car ? No BMS no Lugnuts keeping you safe.

No typical DMM/DVOM will give you cell IR which is in MilliOhms ! You will require a device like a Yaorea YR1035+ also available on EBay & Amazon but NOTE "shipping from" locations. Yorea is the OEM but many sell them rebranded to their companies. NOTE Variations on the probes.

PLEASE download this resource, it WILL help you avoid some issues you are about to hit head first. Luyuan Tech Basic Lifepo4 Assembly Guide
 
Steve_S said:
First, you charge with CC Constant Current to 90% and from there CConctant Voltage and Variable Current to finish to 100% full SOC.
Also 100% Full is NOT 3.560 That is 100% of Max Voltage Range allowable or the "Gross" range. Working Voltage Range is 3.000-3.400 and you can charge the cells to 3.650 and taking < 1 A and one hour after charge stops the cells WILL settle to around 3.500 +/- and within 2 hours they will be settle to their "resting" voltage.

Playing without a BMS is NOT Advisable, it is a sure fire way to loose control of the cells ad have them either over charge or drop too low IF there are runner cells which you will NOT know without active Cell Monitoring. Your excited Impatience could be causing damage... Do you only tighten 1 or 2 Lug Nuts when you change a wheel on your car ? No BMS no Lugnuts keeping you safe.

No typical DMM/DVOM will give you cell IR which is in MilliOhms ! You will require a device like a Yaorea YR1035+ also available on EBay & Amazon but NOTE "shipping from" locations. Yorea is the OEM but many sell them rebranded to their companies. NOTE Variations on the probes.

PLEASE download this resource, it WILL help you avoid some issues you are about to hit head first. Luyuan Tech Basic Lifepo4 Assembly Guide
Click to expand...
Thank you Steve, I'll read that resource you referred to.
 
Steve_S said:
First, you charge with CC Constant Current to 90% and from there CConctant Voltage and Variable Current to finish to 100% full SOC.
Also 100% Full is NOT 3.560 That is 100% of Max Voltage Range allowable or the "Gross" range. Working Voltage Range is 3.000-3.400 and you can charge the cells to 3.650 and taking < 1 A and one hour after charge stops the cells WILL settle to around 3.500 +/- and within 2 hours they will be settle to their "resting" voltage.

Playing without a BMS is NOT Advisable, it is a sure fire way to loose control of the cells ad have them either over charge or drop too low IF there are runner cells which you will NOT know without active Cell Monitoring. Your excited Impatience could be causing damage... Do you only tighten 1 or 2 Lug Nuts when you change a wheel on your car ? No BMS no Lugnuts keeping you safe.

No typical DMM/DVOM will give you cell IR which is in MilliOhms ! You will require a device like a Yaorea YR1035+ also available on EBay & Amazon but NOTE "shipping from" locations. Yorea is the OEM but many sell them rebranded to their companies. NOTE Variations on the probes.

PLEASE download this resource, it WILL help you avoid some issues you are about to hit head first. Luyuan Tech Basic Lifepo4 Assembly Guide
Click to expand...
pre balance method 1 states to charge each cell individually. That is exactly what I am trying to do but I am unsure on getting the correct charger.
 
regarding the BMS. I bought a daly smart bms 16s 48v 250a in the meantime. It will be here 27 dec.

I do hope I get the cells checked out before that time though so I am still looking for a suitable charger to get them charged one by one. Any suggestions are Welcome otherwise I will go with the CV/CC option but that will take a bit before it arrives
 
wow that is a slow process. I have gotten an 0-30V 0-10A CV/CC in the meantime and am charging a single cell at it's maximum setting.
so voltage all the way up and apms all the way up.

The values settle at 4.2V and 10.6 amps on the unit. And the Vdc is slowly creeping up on the lifepo4 cell. it's now at 3.33 almost an hour later.

is there nothing better to think of charging individual 3.2v cells with some more amps than 10? it will take weeks before I have gotten those 16 cells top balanced.
 
reason I am being all jumpy and nervous is because these cells are from our friends from the east so I have to check it now else risk missing some kind of arbitrary time window that is always in favor of the seller.
 
The thing with LFF and large cells like this, is that between 3.000-3.400 is tediously slow, once past 3.450 the charge goes faster.
I'm 24V in my system, I've charged 4-cells (280) with a tekPower TP1540E (0-15V/40A) bench charger and then the next 4 cells, once all done in parallel all 8 cells together for top balance. Doing a single 280AH from 3.29 to 3.65 <2A took 12 hours starting at 40A CC and auto switching to CV.
 
hahha this is ludicrous ;)

I have watched
and followed Will's advice.
So ive turned on the switching power source to 3.6V with the amps at max.
Then I hooked up the cell and now it is no longer charging. it is slowly discharging. Currently the charge is. 3.32V

Also in the description of his video i saw never to change the volts while charging. and of course I have done just that ;)

Anyway shall I configure the Cv/CC at 4.2V again and go with max amps? but then I do not dare to leave it unattended ;(

Any tips are welcome.

Also he is referring to a regular 12 volt charger in that video if one wants to charge quickly. That is exactly what I need but I can't find one.
Does someone have a link, any link will do ;)
 
brandnewb said:
Anyway shall I configure the Cv/CC at 4.2V again and go with max amps?
Click to expand...

Don't go higher than 3.65V, and set this when the power supply is not connected to the cells. You will damage them otherwise.
If you're not seeing the maximum current your supply can deliver with this setting, then you have to change your cables to proper gauge and put ring terminals on.
 
upnorthandpersonal said:
Don't go higher than 3.65V, and set this when the power supply is not connected to the cells. You will damage them otherwise.
If you're not seeing the maximum current your supply can deliver with this setting, then you have to change your cables to proper gauge and put ring terminals on.
Click to expand...
sweet, that hit the spot. finally I was able to get it to 3.6V (the SPS does not have a higher resolution) at 10.6 amps.

I'll turn it on tomorrow morning and monitor it while it is charging
 
wattmatters said:
Some DIY processes require patience. Top balancing your battery cells is one of those times.
Click to expand...
;) I am not known for my patience ;( So I found a 30V 30A SPS and a 120V 140A SPS. Whether I use the first or second I found as long as I set the V no higher than 3.65V and size the wires properly I will not blow out an Lifepo4 prismatic cell that has a continues charge rating of 0.5C (140A)
correct?
 
wattmatters said:
DIY batteries may not be for you then.
Click to expand...

hahah. not sure why it is not common knowledge by now how to quickly test possible shady cells ;) Aliexpress is very popular amongst us here

Anyway I found a 30V60A SPS in the meantime with which I will be going forward.
It will make a speed increase of 6 times.

140A will result in sleeping in the garage if my wife finds out.
 
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