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PostPosted: 30 Apr 2019, 17:56
by peatop
Im interested in comments on people who have made or even thinking or have thought about making li-ion/li-po batteries, as you may know i have gone to a 7" screen on my sounder this raised an issue with battery storage, so I've opted for an FPV 17.5 li-ion battery.

I have been investigating making my own battery using 18650 li-ion cells after several vids and forums later i decided on purchasing the FPV one, the reason for this was not because i wasn't confident to make it, it was because of sourcing genuine parts and testing equipment.

Sourcing the batteries was the easiest part, when making a battery bank you really need a BMS (battery management system) this regulates the input and output voltages to protect the battery from over/under charge/use it also balances the battery charge state, these can be defective so need testing and some circuit parts relaced, the cells (each 18650) could/should be tested to determine it's capacity and arranged in a specific order to get the best longivity out of the battery, then there is the charger, this is suitable to charging li-ion/li-pol batteries.

My issue is of a result of watching perhaps too many vids, ok if you find a reputable store (online or not) that you can buy everything needed then alls good but is it? You can buy cells (18650s or others) they are 3.6v nominal and upto 3.6ah this is there rating not what they are, as stated they should be tested to find where they are placed in your battery bank, for example to get 12v at 17ah i need to have a 3s5p bank of 3.5ah 18650 cells, 3s = 3 18650s in series 3 x 3.6v =10.8v nominal 12.6v charged, 5p = 4 18650s in parallel 5 x 3.5ah =17.5ah, now for proper and safe charging/discharging you need a 3s BMS the rated amps needed is determined by 1. That rated for the cells 2. What your intended usage will be so for a kayak battery i would be looking at 10amps rated output so the PMS would be 3s 10amp.

Ok to summarize so far your 18650s, need testing, this can be done using an of the shelf 2, 4 or 6 battery compartment li-ion/li-po charger/tester, your battery bank 3s 5p needs a BMS and a charger, all of these items, 18650s, cell tester, BMS, and charger need to be purchased from a reputable dealer? But have they been tested before they get to you? How accurate are they in their intended function?

After watching many videos on YouTube of people making battery banks of many shapes and sizes, anyone can do it! But can anyone do it properly? The item being made is only as good as the person making it. Does the person know what they are doing? The person in the vid is my teacher! How good is my teacher? Ok so i watched many vids of guys building these battery banks, then testing these banks only to the put a BMS rated to the job on the correctly built bank then test the input and output voltage to make sure it was within specifications. All looked good! However i then watch another guy build a similar bank, but! He tested the BMS and found it to be faulty.

Let me explain a bit about 18650s. They have a nominal voltage of 3.6v and a rating of a certain amperage, you can drain a 18650 pretty much to zero amps however the voltage should go now lower than 3v, and when charging they should not charge higher than 4.2v, also they they have an input/output rating in amps if you exceed any of these parameters then you reduce the life of the battery.

Now back to testing the BMS if when testing your built battery bank you find one channel or more on the BMS or battery bank (depending on your test location) charge over 4.2 (if this is the stated max for the cells) and or deplete lower than 3v (if this is the stated min) then the faulty charge or discharge ic's need to be replaced and retested.

When building a new battery bank you should test each cell to find it's capacity, so you can arrange the cells evenly in the bank, this protects the cells and bank for premature failure.

Chargers: in some situations banks dont have an internal BMS so the charger is required to have one, most of the better battery chargers for charging li-ion/ li-pol battery banks are made to charge remote control toys?..... but dont have built in BMS so the chargers do, as these are the better chargers suited to charging li-ion / li-pol battery banks then it's these that would be the best to use to get the best out of your battery bank :up:

My conundrum, am i garrenteed that if i buy/build my batter bank,tester, charger and BMS that they will be as stated? Even if all part are purchased from a reputable dealer? I dont think so! So without going to extremes, i need the tester, batteries, charger and BMS, the tester tels me the batteries are good or not, also where in my bank they shouod be placed for besr performance and if they are as rated (if not they are returned), the BMS this you have 2 choices build your own or buy but it MUST be tested in use, if not your bank will not last as it should, at worst it will explode, or catch on fire.

Buying goods over the Internet as we all know can be risky, especially from overseas as overseas dealers arnt governed by our laws, this can be a major issue when spending lots of money on faulty items, the reason for buying items from overseas is usually the price, sometimes you just cant source what you need here or have trouble finding an Australian supplier, so in the case of li-ion/li-po and anything to do with safety, test, test, test.

Ok sorry for the long road to get here :geek: but now the questions, who has used 18650 or similar for use in kayaking, camping and any other activity? What are they used for? Where did you get them? Did you make your own bank? And if so did you use a BMS? What if any testing was done on it/them? And finally (for now) are you happy with them?

Ps, this is im hoping to open some discussion on the use of an alternative to using SLA batteries in mainly kayaking and associated camping and any other use you have for them.

Re: Batteries

PostPosted: 30 Apr 2019, 18:24
by vicyak
I've looked at doing stuff myself as well however the effort involved I should just go buy something decent. Most the 18650 batteries are El cheapos and good ones cost about $30 each. I have a few of these and they are 10x better than the El cheapos which quote more capacity.

I'm paranoid about Batteries catching fire. I do have cheap ones but I charge them away from the house. My good ones no problems. I personally wouldn't be making my own battery bank unless I was 100% confident in correct charging. I think the cost of building something quality will out weigh off the shelf options.

Re: Batteries

PostPosted: 30 Apr 2019, 20:29
by happyas
Maybe a look at some of the hobby r/c aircraft or car systems may help. Battery charging bags/boxes are fire safe containers that will contain your battery while on charge should something go amiss. The hobby industry also markets BMS/chargers and cell balancers to perfectly charge your battery bank. The better chargers are adjustable to battery type, capacity, voltage and discharge/charge rate.

Re: Batteries

PostPosted: 30 Apr 2019, 20:50
by shane
Perhaps do a search of the forum before embarking on such a long post Peter. :roll: There are plenty of posts on here about using 18650's including various DIY packs.

I've had a lot of experience with them. I started making 3S packs I could disassemble and charge cells individually. I bought a lot of ebay cells originally but they nearly all died. I changed to ordering quality Panasonic cells from Fastech but even these have had trouble with dieing prematurely. Postage can now be an issue with many suppliers. With some of my packs I went to balance charging circuits that would connect into my Li-ion digital charger to charge each cell. But even these proved unreliable. My best 18650 pack has been a self contained LED light with 3 cells taped into a triangle, soldered together and inserted into capped 50mm PVC. With this one I still have tags to charge each cel individually. I've found non-balance charging kills packs quickly but overall 18650's haven't proved very reliable. I keep using them for some uses as I can scavenge OK cells from old laptop batteries cheaply.

Currently for my main batteries I use 3S hobby pouch cell packs that have the balance circuits pre-wired. Something like these, although there are plenty out there: These have proved very resiliant when used with a proper balance charger. I have 2 in a waterproof case and use them in duty stand-by and have plenty of capacity. All my batteries go in a dry bag clipped to the yak near me. I don't believe in hard wiring Li-ion batteries into the hull and want them accessible at all times as I also don't use fuses.

I also have an FPV 17.5Ah battery that came with my newer AI. This is a good quality battery, not cheap but a solid solution. This capacity is overkill for my regular use. I mainly use this to run the live well pump, which can run my normal batteries flat but leaves plenty of capacity in the FPV. I can't vouch for its BMS but its still alive after several uses.

Re: Batteries

PostPosted: 30 Apr 2019, 23:22
by chrisw
[De-lurking after a long absence]

This is a subject I can be semi-authoritative in as I have designed and built an 18650-based 12v battery pack with in-built BMS for industrial use:

Early revision under test (hand-built)

First machine-assembled batch

These were designed as a replacement for an earlier one that didn't have a BMS and started to suffer premature failures of newer-generation cells (higher capacity and more sensitive; these were 100% genuine Panasonic cells sourced in large quantities from an official distributor).

I spent a long time learning about battery balance, BMS tuning and related topics when I designed and refined the controller, but I won't relate it all here (unless you are really interested in geek stuff). Put simply, LiIon and related chemistries require careful handling to get the maximum life out of them and to avoid losing cells prematurely, particularly when using any sort of series setup (and if you want to get extra good results, it helps if the BMS knows about the particular cells used).

If you really want to go full nerd :ugeek: you may like to read the Texas Instruments BQ78PL116 technical reference manual (this is the BMS chip I used) which goes into some detail about the sorts of things you need to consider programming into it (highly cell-specific). This device not only has factory setup files for dozens of well-known cells, but for proper performance in the field you need to 'train' it on the actual cells you buy built into the board you use, as it learns the specific behavior they take under those conditions.

Other files someone may want to look at if they're really interested is the BQ78PL116 chemistry selection guide and the BQ78PL116 evaluation board reference (I still have an eval board if someone who is technical enough to use one wants to have a play with it).

FWIW I found a good place for discussion of cells is the candlepower forums.

Anyhow ... having said all this, you can save yourself a lot of time and effort by just buying a pack with in-built BMS. Jaycar have an 18ah one. It's not cheap at $249 though.

Re: Batteries

PostPosted: 01 May 2019, 00:21
by chrisw
shane wrote:I've found non-balance charging kills packs quickly but overall 18650's haven't proved very reliable.

The latter is likely because of the seemingly not-well-known fact that unbalanced discharge can be as damaging as unbalanced charge. I’m a little rusty on the nitty-gritty as I last worked on these almost 5 years ago, but put simply, if a cell in a series arrangement gets too far out of sync with the other cells, the difference can kill it. The cause of this is usually mismatched cells: if a cell’s internal resistance is significantly different than that of the other ones, when current is being drawn it will have a different voltage drop across it. Additionally if it fades differently from the others (lower voltage earlier) this can result in the cell taking charge from the others when idle.

A multi-cell Li-Ion battery therefore needs to use matched cells if long life and reliability is needed. Once a cell starts behaving significantly differently from the others the end is near as this behaviour can lead to out-of-spec conditions under load which can further amplify the issue ... rinse, lather, repeat ... dead cell.

Re: Batteries

PostPosted: 01 May 2019, 10:33
by Galey
Wow! I legit get super proud of myself if I manage to get the three AAA batteries into my head torch in the right order.

Re: Batteries

PostPosted: 01 May 2019, 10:51
by Tim399
Galey wrote:Wow! I legit get super proud of myself if I manage to get the three AAA batteries into my head torch in the right order.

Sounds like me :lol:

Re: Batteries

PostPosted: 01 May 2019, 23:14
by peatop
Chris it sounds like ordering the FPV 17.5ah was the right choice, after reading some of your documentation about tuning each ic to match each cell, i only had a quick peruse over some of the information, which i would at a guess might be somewhat out of date? But none the less interesting to note that nowhere did this sort of information about cell care come up after numerous searches on both google or youtube, mind you this could be my fault as I've been out of touch with search peramitters for a long time. Given there is so much to read and then comprehend i don't think my current medication will allow me the opportunity to get this done in my vegetated state. Lol

I however would be interested in following this up on my days off the water, and medication permitting, if i can get to understand the basics this would allow easier understanding of the more technical parts giving me enough information to build my own battery banks, btw what exactly were you building these units for?

Re: Batteries

PostPosted: 03 May 2019, 19:35
by chrisw
peatop wrote:I only had a quick peruse over some of the information, which i would at a guess might be somewhat out of date?

Not really; the fundamentals of cell chemistry haven’t changed to any significant extent. While the BQ78PL116 is perhaps an extreme example (used when battery reliability is paramount and really intended for much larger packs) the concepts remain the same - some BMC’s allow tweaking all of these parameters, and some don’t. Those that don’t just default to some common value or don’t use the param at all.

btw what exactly were you building these units for?

The packs were used in hand-held industrial computers that had a bar-code scanner built in (more specifically, in cold stores to keep track of what inventory was in what location).

[And yeah the units were heated, LCD’s and batteries don’t like -40c :lol:]