Need to charge 20 lion cells in parallel.  - Page 1
Forum section: electronics / beginners

author: Lemonade1947
author_rank: Newbie
timestamp: August 15, 2016, 08:52:07 pm
content: I have 20 18650 lithium-ion cells, the kind you get from laptop batteries. I have them all wired in parallel, because I was hoping to build a custom power bank. I assumed they would be easy to charge, and I'd just have to put a current-limited supply of the correct voltage across them. However, after speaking with some friends about this, apparently it's not that simple.I have bought two boards, one of which bought for taking usb power -from- the cells, this has a usb input too, but as I said, from what I've been told it's not that simple.Thanks a lot.

author: Signal32
author_rank: Frequent Contributor
timestamp: August 15, 2016, 08:56:49 pm
content: Well initially you'll want to get them to the same voltage before hooking them up in parallel so they don't end up charging / discharging each other at ridiculous rates (and damaging themselves). But yes, a current - limited supply of the appropriate voltage would do the trick, why wouldn't it be that easy ?

author: Lemonade1947
author_rank: Newbie
timestamp: August 15, 2016, 08:59:32 pm
content: Quote from: Signal32 on August 15, 2016, 08:56:49 pmThe cells were given to me fully charged, they were going to be used in a different project that fell through, since they're all confirmed healthy, I'd assume they're all at the same voltage, yes.It may be this simple, yes, I thought so to, but then some people told me I was going to start a fire or kill myself and I got too nervous to put anything across them :/

author: tszaboo
author_rank: Super Contributor
timestamp: August 15, 2016, 09:02:09 pm
content: And when one of them fails to a short, all the others will dump all the energy into that one, causing a fire, and burning down your house. And the only person to blame will be you.I think I know of a dozen different failure mechanism for Li-ion. Most of them violent.

author: Signal32
author_rank: Frequent Contributor
timestamp: August 15, 2016, 09:06:07 pm
content: The only issue would be that putting them in parallel would most likely be more inefficient than series+parallel because of the very large current required to charge them.You'll need 20-40 amps to charge fast.The fail-to-short-circuit one might be somewhat legit though i'm assuming they have built-in protection + most laptop batteries have 2-3 cells in parallel and you don't hear about laptops spontaneously combusting every day ...

author: MosherIV
author_rank: Super Contributor
timestamp: August 15, 2016, 09:18:39 pm
content: QuoteAbsolutly NOT !Every data sheet I have ever seen about LiIon batteries say that there are 2/3 phases in charging.1st phase is constant current2nd phase is constant voltage3rd (optional phase) when battery reaches 90% (4V) capacity, pulse charge until 100% (4.2V)As signal32 says, you are going to have problems with the chargung current for that many cells in parallel.Personally, I would use a protection device per cell thereby protecting from the single cell short scenario and would allow charge balancing but that would be expensive.

author: Signal32
author_rank: Frequent Contributor
timestamp: August 15, 2016, 09:22:59 pm
content: Quote from: MosherIV on August 15, 2016, 09:18:39 pmThere is no contradiction here. Putting a 4.2V constant current supply across 20 cells will result in a constant current charge phase followed by a constant voltage charge phase ...Quote from: MosherIV on August 15, 2016, 09:18:39 pmThe cells probably have built-in protection.

author: tszaboo
author_rank: Super Contributor
timestamp: August 15, 2016, 09:26:06 pm
content: Quote from: Signal32 on August 15, 2016, 09:06:07 pm

author: Lemonade1947
author_rank: Newbie
timestamp: August 15, 2016, 11:32:12 pm
content: So what acctually are my options here?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 15, 2016, 11:37:40 pm
content: Quote from: Lemonade1947 on August 15, 2016, 11:32:12 pmhttp://www.ebay.ca/itm/iMAX-B6-LCD-Screen-Digital-RC-Lipo-NiMh-Battery-Balance-Charger-AC-Adapter-New-/361425168248?hash=item54269e6778:g:G-sAAOSwBLlVVhPT

author: amyk
author_rank: Super Contributor
timestamp: August 16, 2016, 01:57:12 am
content: https://www.eevblog.com/forum/projects/diagnosing-lithium-cells/Obligatory reading for anyone starting to experiment with lion cells.

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 02:48:23 am
content: There are a lot of modules on ebay and aliexpress like thesehttp://www.ebay.ca/itm/5PCS-5V-Micro-USB-TP4056-1A-18650-Lithium-Battery-Charging-Board-Charger-Module-/142004893160?hash=item211026b5e8:g:S8MAAOSwMHdXRlsdModules that are designed to be used on one battery, so 20 modules. I wonder if these can be used in series.I think a battery from a laptop may not have protection. Probably the only way to find out is open one up (and thus destroy it). There might be a size difference so check this first.My guess is there is enough protection inside the battery pack not inside the battery.Curious what you can power with these in parallel? Something that is designed to be powered by one 18650? I cannot think of anything? I wonder if this would be used with a buck and be easier to rig up than a series-parallel configuration.this looks like it uses one cell so it can be donehttp://www.ebay.ca/itm/Backup-External-USB-Power-Bank-Battery-Charger-DIY-18650-Case-Box-for-Cell-Phone-/291793872612?var=&hash=item43f04526e4:m:mk1EL0UzkHcgno6C9V3cKsASo for the brainies: using 20 cells in parallel vs 10 parallel / 2 series for a USB charger - power usages ? There are so many things that can be powered by USB that I would like to make a USB power supply with my 18650s. So I wonder if it is better to go down in voltage (series - parallel) or up in voltage (parallel only). I may need to start a new topic on this.No matter which way you go there will be a hell of a lot of wires.

author: Audioguru
author_rank: Super Contributor
timestamp: August 16, 2016, 03:40:53 am
content: I have opened many laptop batteries and none have cells with built in protection, the battery has a pretty big protection circuit in it.A Lithium cell is about 70% fully charged when its voltage reaches 4.20V. Then phase three keeps it charging until the cell's current drops to a few percent of its mAh rating when it is fully charged and the charger MUST be disconnected.

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 03:55:38 am
content: Quote from: Audioguru on August 16, 2016, 03:40:53 amI would correct this to "the batterypackhas a pretty big protection circuit in it".thanks for confirming the batteries do not have built in protection, I did not think so

author: Lemonade1947
author_rank: Newbie
timestamp: August 16, 2016, 12:34:28 pm
content: Quote from: Alex Eisenhut on August 15, 2016, 11:37:40 pmPurchased. Thanks a lot.

author: Monkeh
author_rank: Super Contributor
timestamp: August 16, 2016, 12:41:50 pm
content: Quote from: ez24 on August 16, 2016, 03:55:38 amIt does not need correcting. It is a battery. It contains cells.

author: Brumby
author_rank: Unknown
timestamp: August 17, 2016, 05:32:43 am
content: If we want to get technical, then a battery is a collection of cells - but that is all it is. When you add a protection circuit, then it becomes something more. The term 'Battery pack' covers this quite nicely. (IMO)Also, it avoids the confusion that can arise from the incorrect usage of the term 'battery' for a single cell, which is so widespread these days that AAA, AA, C and D cells are advertised, discussed and discarded as 'Batteries'.

author: ez24
author_rank: Super Contributor
timestamp: August 17, 2016, 06:04:10 am
content: Quote from: Lemonade1947 on August 16, 2016, 12:34:28 pmI do not get it. You asked how to charge 20 cells in parallel and bought a 6 cell charger. Now I assume you just have 20 batteries you want to charge.

author: Srbel
author_rank: Frequent Contributor
timestamp: August 17, 2016, 06:54:41 am
content: He asked for help, and believed that Alex Eisenhut actually helped him.

author: KL27x
author_rank: Super Contributor
timestamp: August 17, 2016, 09:11:50 am
content: QuoteWell, sure, why not? It can do up to 6 cells in series. OP's "battery" is only 1S. It claims 6A charge current. That's a lot more than you'll get from your iPhone charger, anyway.

author: Kilrah
author_rank: Unknown
timestamp: August 17, 2016, 11:34:55 am
content: Yep, perfectly appropriate advice.One more thing though:Quote from: Lemonade1947 on August 15, 2016, 08:59:32 pmDon't assume, take your multimeter out and confirm.

author: Watth
author_rank: Frequent Contributor
timestamp: August 17, 2016, 01:04:58 pm
content: Quote from: Lemonade1947 on August 15, 2016, 08:52:07 pmLocking these noble felines in cages is inhuman, you heartless monster.

author: ez24
author_rank: Super Contributor
timestamp: August 17, 2016, 10:14:56 pm
content: Quote from: Srbel on August 17, 2016, 06:54:41 amI wanted someone to come up with a 20 cell parallel charger and explain why such a device.I made the mistake of thinking this was going to be a 20 cell pack. Now I know it was just a way of charging 20 cells, big differenceDid not mean to offend anyone.

author: Monkeh
author_rank: Super Contributor
timestamp: August 17, 2016, 10:16:47 pm
content: Quote from: ez24 on August 17, 2016, 10:14:56 pmCharging 20 cells in parallel is the same as charging one cell 20 times the size.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 17, 2016, 10:44:21 pm
content: Well, even in the pro-hobby world you'd be hard-pressed to find a charger that handles more than 6S lithium. The big helicopters use ridiculous configurations like 12S2P and people simply charge the pack in two 6S chunks.I suppose 6S means about 26V across a pack, not a "high voltage". Imagine a 20S charger, that'll have about 85V across the pack, that gets a bit dangerous.Quote from: Lemonade1947 on August 16, 2016, 12:34:28 pmYou're welcome. Of course, never charge cells unattended, and please start with 1 cell and play with the charger, it's not hard to learn to use.

author: johansen
author_rank: Super Contributor
timestamp: August 18, 2016, 01:59:54 am
content: Quote from: Audioguru on August 16, 2016, 03:40:53 amcitation needed.did anyone else read this and ignore it for whatever reason?

author: KL27x
author_rank: Super Contributor
timestamp: August 18, 2016, 02:35:58 am
content: If it is discharged to begin with, AND if it is charged at a specific percentage of C rating... then yes, it CAN have 70% charge when the voltage at the cell reaches 4.2V WHILE current is being pumped into it at specified percentage of C to hold that voltage up. Remove it from the charger while at 70% charge, and the float voltage will go down to under 4V, tada.Keep it at 4.2V at that point with simple CV @4.2V, and it will be fully charged.And no, there is no practical reason to cut off the CV charge at a specified number of milliamps current, except that if kept there indefinitely (like a laptop that is left plugged in 24/7 for months) it may accelerate cell degradation, and in this specific case there is no practical reason to not simply set CV phase to 4.1V, or whatnot.As someone previously stated, OP's original plan of using a CC-CV setup was perfectly reasonable.The voodoo people attribute to Li ion charging....If you can understand the datasheet, you know exactly why it is described this way and what it means. It is not voodoo. CC-CV. Auto cutoff to prevent cell degradation if left plugged in. And to have a nice little cutoff point so an indicator light can go on. There is no voodoo. If you want voodoo, you have to play with NiMh.Phase 1: CC - Pump current limited to a reasonable percentage of C... Because simply doing CV limiting to 4.2V will allow a greater current draw than that.Phase 2: Once 4.2V is reached, duh, you don't want it to go higher. Switch to CV at 4.2V, and the current draw naturally decreases in a curve.Phase 3: Keeping the cell at 4.2V indefinitely MAY cause cumulative degradation of the cell over time. And c'mon, we need an LED to go off when the cell is done charging.... you gotta call it somewhere. Let's say call it like 20mA for a 1Ah cell.

author: Audioguru
author_rank: Super Contributor
timestamp: August 18, 2016, 03:07:02 am
content: Quote from: johansen on August 18, 2016, 01:59:54 amThe Battery university tells us all about it.

author: ez24
author_rank: Super Contributor
timestamp: August 18, 2016, 03:14:38 am
content: Quote from: Alex Eisenhut on August 17, 2016, 10:44:21 pmThis topic started with 4.2 volts max (I wanted to know what to do with 4.2 volts). A 20P charger.But good to know about the 12s2p packs. I do not think charging a cell 20 times qualifies as a 20P charger.

author: KL27x
author_rank: Super Contributor
timestamp: August 18, 2016, 04:20:15 am
content: QuoteMaybe you are not getting it? You can charge a 1S20P 18650 "battery" with any single cell charger, even a 500mA one, if you want to wait a few days. The current limited phase 1 will last a long, long time; the battery WILL be charged way higher than 70% by the time it hits the CV stage, hence phase 2 will be quite short (potentially non-existent); and the fully charged light will never go on (unless the cells are all pristine), because the current draw will never drop below cutoff. But provided the charger meets specifications, it will be completely safe.The charger that was linked was a good suggestion because it gives a pretty high amperage for the price, and it has the ability to balance charge up to 6S batteries, if the need should ever arise. The cutoff point (bing! done!-current) may even be adjustable. And you're going to be hard pressed to find a 1S-only charger that can do 6A, any cheaper.

author: ez24
author_rank: Super Contributor
timestamp: August 18, 2016, 04:49:14 am
content: Quote from: KL27x on August 18, 2016, 04:20:15 amMy mistake. I thought "Need to charge 20 lion cells in parallel." meant "charge 20 lion cells in parallel"

author: Brumby
author_rank: Unknown
timestamp: August 18, 2016, 07:10:22 am
content: It seems to me the OP might have been asking about aNeed to charge 20 lion cellsat the same time.

author: ez24
author_rank: Super Contributor
timestamp: August 18, 2016, 07:15:03 am
content: Quote from: Brumby on August 18, 2016, 07:10:22 amProbably

author: Srbel
author_rank: Frequent Contributor
timestamp: August 18, 2016, 08:32:34 am
content: Quote from: Brumby on August 18, 2016, 07:10:22 amWell, what else???

author: Brumby
author_rank: Unknown
timestamp: August 18, 2016, 09:31:06 am
content: Quote from: Srbel on August 18, 2016, 08:32:34 amParallel connection of all cells. That is, having all 20 positive terminals joined together and all 20 negative terminals joined together.You know ... the first concept that comes to mind when you use the word 'parallel' in front of those familiar with electrical stuff.Parallelin timeis not a common usage.

author: Srbel
author_rank: Frequent Contributor
timestamp: August 18, 2016, 09:50:02 am
content: Quote from: Brumby on August 18, 2016, 09:31:06 amI thought you said at thesametime. -.- That is why I was confused by how can somebody interpret "Need to charge 20 lion cells in parallel" differently.

author: Brumby
author_rank: Unknown
timestamp: August 18, 2016, 10:12:26 am
content: The Op stated "in parallel".For those whose first language is English - especially EEs and hobbyists - the term parallel in this context means:Quote from: Brumby on August 18, 2016, 09:31:06 am... and initial replies were addressing this arrangement. Thisphysical setupis what we would think of using the word parallel. Nothing to do with time.

author: ez24
author_rank: Super Contributor
timestamp: August 18, 2016, 10:30:19 am
content: Quote from: Brumby on August 18, 2016, 10:12:26 amUnless you are watching the Twilight Zone

author: KL27x
author_rank: Super Contributor
timestamp: August 21, 2016, 10:32:07 pm
content: I am confused what charging 20 cells "in time" means, lol.I had to go back and read the OP.QuoteIs this "in time" or "out of time?"

author: tszaboo
author_rank: Super Contributor
timestamp: August 22, 2016, 10:43:24 am
content: Quote from: KL27x on August 21, 2016, 10:32:07 pmThat is OUTATIME.

author: Brumby
author_rank: Unknown
timestamp: August 22, 2016, 11:12:35 am
content: BTTF reference....?

author: Srbel
author_rank: Frequent Contributor
timestamp: August 22, 2016, 12:45:26 pm
content: Even in time domain, "parallel" means "at the same time". Where is the confusion???

author: Brumby
author_rank: Unknown
timestamp: August 22, 2016, 01:18:12 pm
content: General usage.Using parallel in the time domain is not particularly common usage.

author: grifftech
author_rank: Frequent Contributor
timestamp: August 22, 2016, 03:34:50 pm
content: use this image to help you

author: Srbel
author_rank: Frequent Contributor
timestamp: August 23, 2016, 06:21:24 am
content: To help whom? I am not the one that is confused.

author: KL27x
author_rank: Super Contributor
timestamp: August 23, 2016, 08:17:15 am
content: QuoteYou ever watch any of Dave's original videos?

author: Brumby
author_rank: Unknown
timestamp: August 23, 2016, 01:49:20 pm
content: I started in at around the 600 mark.Been picking up the odd earlier video as they come up in random searches.

author: grifftech
author_rank: Frequent Contributor
timestamp: August 23, 2016, 08:39:38 pm
content: Quote from: Srbel on August 23, 2016, 06:21:24 amthe OP