3S 18650 Battery Pack is not powering device - Page 1
Forum section: electronics / beginners

author: Joshs Name
author_rank: Newbie
timestamp: June 25, 2023, 09:48:35 am
content: I'm building a battery pack to power a Playstation 4.It's going to be 3s3p or 3s4p, but just for initial testing it's only 3s1p at the moment, which provides between 12.6V to about 9V. The PS4 also requires a 5V input, but i'm still using the ps4 psu for that at the moment, so ignore that.So, with my benchtop power supply, i've discovered the PS4 will still work between 9.75V and 12.6V. And will pull between 4A and 8A of current.My batteries are Efest IMR 18650 3500mAh 10A/20A Li-Ion. So the 4A-8A required by the PS4 is well covered by that.They are connected to a 3S 20A BMS, and i've also tried a different 25A BMS.Problem: The pack doesn't run the console, it will turn on but only last a couple of minutes. Record was 7mins.The Output voltage from the pack is still between 11-12V. The current draw from the battery pack is around 4A (same as my benchtop power supply) when the console is starting up, and sitting on home screen. I left it on the home screen and it lasted 7mins before turning off.I don't understand... The voltage is adequate, the battery rated discharge is more than adequate, the BMS output is adequate. The batteries aren't over heating. I've tried 2 different BMS boards. The batteries were bought from a reputable supplier (www.techaroundyou.com) and are brand new, charged with a Nightcore D4.My benchtop PSU powers the console no problems, even when i keep dropping the voltage. Is the BMS cutting off because the voltage is dropping too fast?Parts:- Efest IMR 18650 3500mAh 10A/20A Li-Ion -http://efestpower.com/index.php?ac=article&at=read&did=543- BMS 25A -https://www.aliexpress.com/item/1005001327267228.html- BMS 20A -https://www.aliexpress.com/item/1005001636556505.html

author: CountChocula
author_rank: Unknown
timestamp: June 25, 2023, 02:10:13 pm
content: My guess is that the voltage of the battery just tanks until it's no longer sufficient to run the PS4—regardless of the rating, if you're drawing over 4A you'll see an almost immediate drop in voltage, even if the batteries are stilltechnicallysupplying current. This is particularly going to be the case if the current draw from the console is “spiky” in nature, which means that even if your DMM is reading a good-enough voltage, it may not be fast enough to see short, sudden dips that are causing problems.Try measuring the voltage under load (ideally, you'd probably want to use an oscilloscope if you have one, or a DMM that can sample at very high rate and report on min/max values). I suspect you'll need more headroom in your battery bank capacity and a regulator to provide a stable voltage in order for things to run reliably.—CC

author: Rick Law
author_rank: Super Contributor
timestamp: June 26, 2023, 12:11:05 am
content: I also think likely it is likely your battery dying. It is a matter ofinterpretingthe specs.The battery is 3500mAH, and can discharge 20A, so far so good. It would seem to suggest that if you are drawing 4000mA, you have just under an hour run time (3500/4000 = 0.875 hours). But no, not that simple.Total capacity also depend on load. Typically, the larger the load (current drawn), the lower the total capacity.If you are only drawing 350mA which is 1/10 battery capacity, it likely will give you the 3500mAH total. But when you are drawing as much as 4000mA continuous... Not very likely you get anything close to 3500mAH.With some batteries, the specs will have a discharge graph showing capacity (mAH) for different current drawn. Lacking that, you may need to just test that yourself. You will need to load-test the batteries individually to see actually how many mAH can it give you when discharging at around 4A (4000mA).

author: Joshs Name
author_rank: Newbie
timestamp: June 26, 2023, 01:15:30 pm
content: Thanks so much for the reply! So I discovered that voltage drops under load! Lol, this is Beginners section right? hahaThis was the issue. I measured the voltage of the battery under load, and it was dropping down under 10V, until soon after booting it went under 9.7V and shut down.I wonder if I had 3 or 4 packs in parallel, would it be the same outcome? (So 3s3p or 3s4p). Battery voltage wouldn't be any higher, but would the voltage drop be less severe?Otherwise I'm going to have to get a voltage regulator or buck/boost converter I guess, even though it doesn't suit the build size restrictions.

author: CountChocula
author_rank: Unknown
timestamp: June 26, 2023, 01:35:53 pm
content: This is the part of the thread where we ask you for a bit more information about your use case. Without that, we don't know what to suggestIn the abstract, I think you should reevaluate your approach a bit; first of all, you will probably want to regulate the voltage going into the PS4 so that you can have a steady supply that doesn't droop like crazy under load. Among other things, this implies that you will needsomeheadroom in your voltage to account for regulation.If you want to stick with 18650s, you'll likely need quite the collection of batteries. It's doable, but before going that route, which involves quite a bit of complexity with balancing and recharging (and can be dangerous), you could look into LiFePO batteries instead, likethis random one from Amazon, which give you better discharge characteristics and are likely to be easier to recharge. I'm not super-familiar with them, but perhaps someone else on the forum can chime in. Or, you could switch to lead acid chemistry, for example.Another alternative would be to use an inverter: Get a beefy 12V battery, attach a power inverter to it, and then connect the PS4 to the power outlet like you would at home. You'll waste quite a bit of energy in the process, but it might well be the simplest approach (FWIW, I've used something similar while camping, and… it's good enough, with the added bonus that you can use it to power other things as well).—CC

author: Joshs Name
author_rank: Newbie
timestamp: June 26, 2023, 05:17:27 pm
content: Thanks for the info. That LiFePO battery is too big for my project unfortunately. That battery is the size of 40 x 18650 cells, but only 8Ah. My project has room for 9-12 x 18650 cells.My project is a portable "hand-held" PS4.I've chosen 18650 Li-ion batteries for their power to size ratio. Nothing else appears to be able to fit the task.Desired battery life from this "portable" is 1-2hrs.I have bought a MAX745 charging board to charge the batteries properly.https://a.aliexpress.com/_mtrwkPiThe PS4 has (or is having) the optical drive removed, the HDD swapped for a 2242 M.2 drive, a DualShock Controller integrated into it (0.1A draw), and a 7" LCD with speakers (0.4A).

author: BeBuLamar
author_rank: Super Contributor
timestamp: June 26, 2023, 05:44:58 pm
content: 3 lithium ion to operate a 12V device is a bit on the low side. The problem mainly you use a 3.5Ah battery for a device that draws 4A it's not a good thing.

author: Joshs Name
author_rank: Newbie
timestamp: July 02, 2023, 08:16:49 am
content: So I hooked up 9 x 3500mAh 18650 batteries, 3S3P. And it powered the PS4 for 40 minutes before shutting down at 9.65V (voltage under load)After it shut down the voltage of the battery pack was still 11.0VThat means I was only able to use about 50% of the battery's capacity.It appears I do need a boost voltage regulator to get the most out of the batteries capacity.40mins 40 secs of playtime was 6 minutes of Rocket League, and 34 min The Last of Us.

author: beanflying
author_rank: Super Contributor
timestamp: July 02, 2023, 09:27:12 am
content: Likely what is happening is your 18650's specs are rubbery (or one in the lot is trash). The basic spec on your link means the cells are 3C up to 6C (approximately) which is a little 'optimistic' if not a lie (certainly the 20A one is). Even name branded batteries are rated to about a maximum of 3C constant load current (so about 10A). Your 3S3P option will get around some of that issue but you are still about 1C so losing a few 100mV/cell is still 'reasonable' at this so this leads to the BMS triggering early or you getting to the PS shutdown 'early'.Random curve below but just to show an idea. Also note the basic idea that higher discharge will cost you some capacity as well.Several things where are you reading the voltage at the PS4 or at the pack? 8-10A draw is not insignificant for voltage drop over 1m. As an idea it might be a few hundred mV with wire near cheaper Test lead gauge but don't scrimp on the cable with your final solution and allow the PS to shutdown earlier than you want.Adding a Boost converter to this apart from the extra losses (likely 10-20% of your storage) will only work until the BMS kicks in with a chunk of the energy still available. I suspect this will be a zero sum gain to a net loss.While I get wanting to use gear via batteries as I have an R/C addiction issue why would you pick a more expensive and more complex option over a 12V AGM unless you are going hiking with your PS

author: Rick Law
author_rank: Super Contributor
timestamp: July 02, 2023, 06:26:01 pm
content: It is likely beneficial to test each individual cell to see how many mAH it can give at 1.33A (4A / 3 since you use 3P).An adjustable load would come in handy. Even as simple as fix resister(s) to discharge to obtain voltage vs time data, and do so for each cell. That should allow you to rank the weakest to strongest. Now you have the option to replace the weakest cell(s), or balance the pack by selectively mixing the strong and weak.