Author Topic: Charging and Using Lithium Ion 18650 Batteries  (Read 7360 times)

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Offline solarnewbee

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #15 on: January 20, 2019, 10:47:25 am »
Thanks LH for the info, puts me at ease. The bms sensors are powered at each battery and then plugged into a bus that runs to a control module. The control module is powered by a 24v din rail ps. Still waiting on the English software so I’m depending on the CM screen data. There isn’t any balancing done as far as I know but communication with the Chinese company is sporadic.  I do get cell volts impedance and temperature. Current sensor on each bank show charge and discharge which seems useful. I have ordered 16 more cell sensors today to cover the other cells so I will have that covered before I head back to the states.

Can you explain what bottom balance means? I read somewhere that I should have bolted all of them together in parallel negatives to negatives positives to positives for a few hours and that would equalize them, any truth to that?  I put a meter to them when I got em and they all fairly close.



Thanks
SN

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Offline lighthunter

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #16 on: January 20, 2019, 06:03:41 pm »
Once you get the other cell monitors in place, this info becomes lots less important.
The discharge curve of an LFP cell has a pretty steep voltage drop around 2.8v indicating an empty cell. (dont change your 3v minimum bms setting unless all cells are monitored).

Bottom balancing refers to equalizing all cells to reach this (empty drop off ) at the same time.
Your cells are new and likely to have very similar capacities, therefore the upper voltage knee for full charge will occur at the same time for each cell as well as the lower knee will happen at the same time for all cells when they are balanced.  But lets assume they are getting along in years and capacities vary by 5-10AH. This would mean you could align the discharge knees of all cells to reach empty at the same time and when you charged them one with lower capacitiy would reach full and climb past 4.0v while the others are still reading high 3.3s. If you want an LFP to last avoid going below 3.0v or above 3.5v theres really not much capacity to gain on either end. Ross likely can improve on these numbers.

The bottom balancing trick comes from the EV guys who became frustrated with the poor reliability of the early BMS systems and in some cases decided they were better off without. (kind of like an oil pressure guage that leaks and causes your engine to run out of oil). If you get rid of the BMS the best way to protect your LFP cells is to meticulously align every cell at the lower knee on discharge and monitor the pack voltage for your fuel guage. EV fellas are trying to get the best range possible sometimes at the expense of the cell. Your application can be more conservative with the min and max points and treat the cell better.

Regarding bolting the cells together, Nope, i would not do for balancing. The current exchange without resistance could be damaging. If you want a simple way to balance manually then choose a low voltage 6v halogen lamp of 100w or whatever is handy. Then you can connect neg to neg and positives together through the lamp. Use something available and cheap, any low resistance filament or resistor will do.  Once two cells have equalized with low resistance then you can bolt together if building a pack etc.

Those prismatic cells though expensive are the closest thing ive ever seen to an ideal (textbook) battery. For all practical purposes of realistic calculations you can even skip the symbolic internal resistance. Do try to cover/insulate those terminals and fuse where strings join. Lead acids can source huge current but LFP  can produce current beyond anything you can imagine. Unless there is protection there may not be a tomorrow. Cant say ive seen one shorted but ive seen 4kw from a pack the size of 2 car batteries without much v sag.
Unless external equipment unbalances your cells, they dont need much balancing but monitoring is a necessity.

Good to see the progress, i feel your pain with the variable unexpected loads throughout day and night  :) imagine trying to manage the Grid. :(
Health Warning: May contain traces of nut!
LH

Offline rossw

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #17 on: January 20, 2019, 06:58:28 pm »
Ross likely can improve on these numbers.

I have my generator set to autostart if a cell gets to 3.125V (at light load) or 3.0V (at full load).
Overvoltage alarm (which has only gone off a couple of times, due to freakish high wind when batteries were already full, or due to a setting error on one of my low current chargers) - at 3.50V/cell.

Quote
Your application can be more conservative with the min and max points and treat the cell better.

Agreed.

Quote
Those prismatic cells though expensive are the closest thing ive ever seen to an ideal (textbook) battery. For all practical purposes of realistic calculations you can even skip the symbolic internal resistance.

I love 'em :)

Quote
Lead acids can source huge current but LFP  can produce current beyond anything you can imagine. Unless there is protection there may not be a tomorrow.

I had a friend bring up his son to look at my system yesterday. He's an apprentice sparkie and interested in PV, batteries etc. Was fascinated by the "reality" rather than the BS he's being sprouted at work by knuckle-dragging know-nothings that may have all the book learning and papers but don't actually know how stuff really works.

Like he was surprised my battery packs were both "down-around-and back". They "always do them in one long run".
When I pointed out how short my cables were to the inverter it was like a light bulb came on.

He questioned my fuse at the MIDPOINT of my battery bank. (Ie, between cells 8 and 9, or at the 24V interconnect).
They only ever use a breaker on the +V connection. When I pointed out all the places along a battery bank (that went down and back) were you could conceivably have a short circuit and that with their arrangement NONE of them would have ANY protection - whereas with mine, virtually every likely scenario was covered.

Fusing with high rupture capacity fuses is a small expense compared to the safety they offer.

Quote
Unless external equipment unbalances your cells, they dont need much balancing but monitoring is a necessity.

I sleep well at night with the monitoring. Just KNOWING everything is as it should be has a value beyond money.

Offline solarnewbee

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #18 on: January 22, 2019, 08:28:49 am »
I have a plastic cover constructed that goes over the all the batteries  heat shrink tubing goes on this weekend and the daughter has come up with some laminated dielectric  rubber that will fit over the bolt heads. Each bank has 125a 10kva dc breakers. Since I only needed 8 for 24 and little space I had to run them in 1 line instead of down and back and then the next pack turned 180 to keep the positive short for all packs. Wondering if I should more breakers and where. I’ll post a drawing of what I have and I’ll certainly heed your advice on that subject. Cells are topping out all consistent at 3.33v at sun fade and 2.89v come morning.

I am installing a automatic starting 3000w dc inverter lp generator Friday. Just bought 10 meters of 30mm2 welding cable to connect it. This thing uses the batteries to start itself when the batteries voltage drops below 24v and shuts off when levels rise above 26v. At least that’s what the brochure claims ha! Next year we move and the windmill goes up, dual 3 phase 3000w  so that equates to an average of what, 800w? Except typhoon season of course.

As always thanks for the expert advice.
SN

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Offline WooferHound

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #19 on: February 20, 2019, 06:16:01 pm »
I've been educating myself on the difference between Lithium Ion and Lead Acid batteries.
The way I am understanding it is that you can replace Lead Acid batteries with Lithium Ion batteries in a 4:1 Ratio.
If you have 100 amphours of Lead Acid batteries, you will want to replace them with 25 amphours of Lithium Ion batteries.
This is because you get a 50% gain in charging efficiency, using less power in the charging and recovery of energy from the batteries.
Then you get another 50% because you can safely use 100% of the battery charge, where using Lead Acid batteries it is recommended to only discharge the batteries to 50% to increase their life.

I have been totally considering making a Lithium Ion Bank that is five 4.2v in series making a max charge of 21 volts. Then using a big Buck Converter to get back down to 12.6 volts for the loads.
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Offline rossw

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #20 on: February 20, 2019, 07:34:56 pm »
you can safely use 100% of the battery charge
.....
making a Lithium Ion Bank that is five 4.2v in series

This is FAR from "safe".
There WILL be differences between cells. In an unprotected, series pack like that, you WILL have one cell that gets to 0% charge before the others. Continuing to discharge the pack to what you think is 100% will LIKELY reverse bias that cell.
When then charging the pack, one cell WILL get to 100% capacity before the others.

Your best outcome is a destroyed cell. Your worst outcome is fire and/or explosion.

When playing with these cells, make sure you operate with a DECENT safety margin, and/or with suitable protection (electrical, thermal, physical containment or a combination thereof).

Offline WooferHound

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #21 on: February 21, 2019, 07:05:03 am »
Oh Yes
A battery management system was implied.
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Offline solarnewbee

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #22 on: March 17, 2019, 09:06:53 am »
Hey woof,

Are you building your own 4.2v lith ion batts from 18650’s? If so are you welding them together in parallel or in holders?  I saw a guy on YouTube that builds power walls with them and has boards with holders that have bms that plugs into board. Each cell is monitored constantly. No idea where he found that stuff but it intrigued me. Search jehugarcia and you might find something useful. I just went and watched and looks like the boards are a diy kit that he sells. The other video I saw he was using a digital bms instead of a hit or miss mosfet only based bms that fails short pass thru.

I like the prismatic lifepo4 3.2v myself but the initial cost can leave a burn. I got 800ah and I wonder as Oz once said that it sounds nice to have a large bank of ah but can you fill it. Batteries with fuel gages built in someday?

I was wondering about what you said about less ah with lithium but if your total kWh usage stays the same the battery bank will get a lower voltage level sooner and the inverter shut down? Well, whatever the results as long as your still having fun!

Adios Muchacho
SN

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Offline WooferHound

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What will Replace Lithium batteries
« Reply #23 on: March 20, 2019, 11:57:36 am »
What will make Lithium Batteries Obsolete ?

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Offline WooferHound

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #24 on: March 21, 2019, 07:25:53 am »
Hey woof,

Are you building your own 4.2v lith ion batts from 18650’s? If so are you welding them together in parallel or in holders?  I saw a guy on YouTube that builds power walls with them and has boards with holders that have bms that plugs into board. Each cell is monitored constantly.

I was wondering about what you said about less ah with lithium but if your total kWh usage stays the same the battery bank will get a lower voltage level sooner and the inverter shut down? Well, whatever the results as long as your still having fun!

Adios Muchacho

The 20ah lead acid battery on my small hobby 12v Solar Power has finally stopped being productive so a new project is materializing.

A friend of mine that lives down the street has moved to another city and left me a bunch of Old Laptops that I have recovered the batteries from them. Ended up with forty 18650 batteries. Charging and Testing them right now, and if they all work, I plan to make a 21v 20ah battery bank with them, easy expansion later. It will start out as 5s 8p. Eight batteries parallel, then Five groups in series.

I've seen many Battery Holder styles on YouTube and eBay and have decided to use sockets and not solder the batteries.
My solar panels are 23 volts (open) and I might not need a charge controller so much with this 21 volt bank.
Battery Bank voltage will be between 14v and 21 volts using the Battery management board I'm looking at.
A buck converter will be used to bring that voltage down to 12.6 for distribution and usage.

Here are the planned parts to be ordered soon, some of it from China . . .

Battery holders, groups of 4
https://www.ebay.com/itm/5Pcs-Li-ion-DIY-Battery-Plastic-Case-Holder-for-4x3-7V-18650-Battery-M6M1/252732634852

5s Charging Balancing board 20a
https://www.ebay.com/itm/5S-20A-w-Balance-Li-ion-Lithium-18650-Battery-Charger-BMS-Protection-PCB-Board/264077586312

Buck Converter 15a
https://www.ebay.com/itm/200W-15A-DC-DC-8-60V-TO-1-36V-Synchronous-Buck-Converter-Step-down-Module/112985055478

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Offline WooferHound

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #25 on: March 22, 2019, 09:19:32 am »
Ordered the parts this morning
all from China
Now to wait about a month for it all to get here
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Offline solarnewbee

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #26 on: March 22, 2019, 11:12:06 am »
Interesting, look forward to your progress. Minus the boom of course. Have fun with it!

😊
SN

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Offline WooferHound

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #27 on: April 19, 2019, 03:54:21 pm »
Today I made the standard DIY 18650 Lithium charger that you can find 100 times on YouTube.
It's four TP 4056 charger modules hooked up to 4 Battery Holders and powered with a 3 amp 5 volt wall-wart transformer.



This is just a prototype. The module on the right-hand side does not work. Ordered 15 more of these.
Was needing something that would reliably charge the cells to a known voltage for testing and assembly into some 5s 8p battery banks.
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Offline WooferHound

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Re: Charging and Using Lithium Ion 18650 Batteries
« Reply #28 on: May 12, 2019, 05:50:50 pm »
My first Lithium 18650 charger did 2 batteries and was just a 3 volt transformer rectified and going directly to the batteries. Max voltage on that would be just over 4.1



Yesterday I took the breadboard charger shown in the Last Post and mounted it permanently into that same box.



The charger modules were mounted behind holes drilled in the box so the indicator lights would show through.



Accidentally put a Cell in Reversed polarity and killed the module, replaced it this morning with the promise that I won't do that again.
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Offline WooferHound

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