>500wh power bank that can power a pico psu

[Somerandomtechyboi]

 

someones selling a buncha these used lithium ion samsung batteries for cheap, dimensions = 7.33cm x 6.25cm x 0.6cm (L x W x H)

 

 

Theres also used lifepo4 battery thats literally the size of an atx mobo, 30cm x 19cm x 1cm

 

Just need a powerbank that can power a 300w pico psu and 2 24" lcds salvaged off tvs (will convert to run off dc) cause im interested in making an abomination of a 24x24" "laptop" with desktop parts that can be moved around cause i really dont like to be stuck in 1 area of the house

 

Money wont be much of an issue since income is mostly disposable, after june 6 though cause gotta build a somewhat fancy car to troll my highschool prom =p

 

Capacity wise im looking for >600wh which is ridicolous ik but pc components gonna consume lots of power at full tilt even with undervolt (dont think ill be bringing this on a plane), weight isnt gonna be too much of an issue, gotta get bigger arms anyways

 

 

max charge volt for lithium ion is 4.2v with discharge at 3v and max charge for lifepo4 is 3.65v w discharge at 2.5v atleast thats what ive found on the internet so based on that ill need to connect 4 lithium ion or 5 lifepo4 in series for the desired volt cause i dont think pico psu will take 10v input too well

 

I am absolutely confused with how the hell you go about measuring wh (like which volt do you use the discharge or charge volt?) So ill just take the numbers printed on the battery or on the desc of the batteries. For lifepo2 ill need 5 in series so 16x50 = 800wh, for the li-ion batteries need 4 in series and the wh is already on the battery so 77.2wh, to get close to 800wh on the lithium ions gonna need 10 banks of 4 batteries in series for 772wh. Price wise thatd be 63$ (lifepo4) vs 24$ (li-ion)

 

 

Now for the pros and cons for both

 

Lithium ion is alot more compact and cheaper but im pretty sure wiring the thing up and circuitry is going to be a nightmare which wil problably not be compact, also alot less resistant to abuse compared to lifepo4

 

Lifepo4 is more expensive and quite literally the size of an atx mobo but alot more abuse resistant, and since theres only 5 of em the circuitry should be alot simpler

 

 

As for questions

 

What kinda bms and how many would i need for both the lithium ion and lifepo4 batteries in their respective configs (4 series 10 banks, and 5 series)?

 

Howd i go about charging the batteries?

Id prefer it if i can charge quickly (<10 hours) even though itll be plugged in most of the time

 

Speaking of which, when plugged in how do i power the pico psu + monitor directly from the wall?

 

when the batteries discharge/charge and go over/under 12v, how do i ensure that the pico psu is getting 12v? Or is it not neccesary to be pegged at 12v and some variance is fine and the psu will deal with it on its own?

[Eigenvektor]

19 minutes ago, Somerandomtechyboi said:

I am absolutely confused with how the hell you go about measuring wh (like which volt do you use the discharge or charge volt?)

Wh simply tells you how long the battery should be able to sustain output (discharge) at a given wattage. Time = Wh / output W

 

If it has 600 Wh, then theoretically it should be able to provide 1W for 600 hours, 2W for 300 hours, 3W for 200h and so on. That does not mean the battery is able to provide any arbitrary wattage without bursting into flames. There is a limit how much current the battery can provide before it gets too hot and you risk thermal runaway.

 

So you measure it by putting a well known load onto the battery, then measure how long it is able to sustain that. So if you put a load of 1W on it, and it is able to power that for 600h you know it has 1W x 600h = 600 Wh.

[OhYou_]

I can speak for a lot of this

 

first and foremost, please look at a discharge rate chart for both lithium ion and LiFePo4
you should not charge lifepo4 to 3.65 because it is wasteful. they will be more happy in a range of about 3.38-3.0

 

wh is measured at nominal voltage and maximum capacity. this is different from expected capacity. four 50ah lifepo4 cells will provide you 640W max but probably closer to 500 realistically, potentially less depending on how used they are.

the phone batteries. well you need about 40 of them, I can not recommend this as a solution.

 

you may use 4 or 5 lifepo4 in series, with 5 being more costly for the BMS probably. 
the pico psu can accept 4 or 5 in series.  iirc its voltage range is like 10-18v
you can supply either type c pd or a 12v rail by buying a converter that is rated for at least 18v input max.

the charger can actually just be a CVCC, you can have this inboard or external, the only real thing to note is to set your charge voltage and current to something reasonable. 

 

bit of safety:

You want to ensure that your maximum charge ratings for the BMS and the cells will be significantly higher than your absolute maximum load. This is so that you can use a large enough charger that it will be able to both run the system and have currentl left over to charge the batteries, but also not go over current if the machine is pulling zero amps and all of it is dumping into the batteries.
You should use a bms which has cell temperature monitoring for charging. 
you should ideally have a low voltage shutoff.
 

[Somerandomtechyboi]

4 minutes ago, Eigenvektor said:

There is a limit how much current the battery can provide before it gets too hot and you risk thermal runaway.

Iirc lifepo4 doesnt suffer from thermal runaway and burst info flames like lithium ion but obviously it still has a max safe temp

 

Obviously the cheap way of getting around this is just pointing a fan at the batteries but is there a way to reduce the load on the batteries?

[Eigenvektor]

1 minute ago, Somerandomtechyboi said:

Obviously the cheap way of getting around this is just pointing a fan at the batteries but is there a way to reduce the load on the batteries?

Use multiple batteries in parallel to distribute the load, I suppose. Which you'd likely need to do anyway if you want to reach ~300W of output. You'll likely need additional circuitry to ensure they're running at the same voltage etc. so you don't get any current flowing between the batteries themselves. For that much wattage, you're probably better of with something off the shelf.

[manikyath]

if they're used, assume the capacity remaining is "not as advertised" at best, and "near failure" at worst.

 

past that.. i'd suggest you instead buy some 24 or 36 volt E-bike batteries or at least the BMS and suitable charger. they apparently can be had fairly cheap, and provide a pretty reliable platform that'll do >300 watts sustained load without breaking a sweat. past that there's DC-DC converters built essentially exactly for this purpose (or if you get a 24V BMS, some picoPSU's go up to 32 volts on the input side.)

 

on the note of how Wh is calculated: that's actually part of where the "nominal voltage" of the battery comes into play. past some nuances of exact (dis)charge cycle and cutoff voltage, and some rounding error, you essentially do nominal voltage times Ah rating.

[mariushm]

Don't waste your money on a 300w pico psu , and don't waste your money on those batteries.

 

Those picoPSUs don't regulate the 12v, they just pass it through. They're basically 2-3 dc-dc converters that take 12v and produce 3.3v , 5v , 5vSB and maybe -12v.

 

For monitors ... it depends if it's CCFL backlight or LED backlight.   The processor board with the video inputs and controller typically needs 5v or 3.3v , sometimes there's a 12v or 24v for optional headphones amplifier / speaker but board would run without that voltage.

The backlight , if it's CCFL based (old fluorescent tube style), you can get universal inverters that will run with minimum 10v but could go up to maybe 20v. 

For LED backlights, typically there's a bunch of leds in series, so it could be 30-80v required for the backlight. There's a led driver that boosts 12v..20v to that voltage the leds needs and pwm or limit current to get a specific brightness.

You can also get universal led drivers that should take 12v (and probably less) as input.

The display board shouldn't consume more than a few watts, 2-5 watts, probably less. The actual panel will consume maybe 1-2 watts, the backlight consumes the most , 10w+

 

There's a difference between LifePo4 and LithiumIon batteries ... LifePo4 shouldn't be charged with more than 4.1v while lithium-ion need 4.2v to charge.  That's the smallest thing.

They also have different discharge and charge currents ... for example here's a datasheet for a 26650 LifePo4 3.2v 2.3A  : https://docs.rs-online.com/4ad1/0900766b812fdd10.pdf

 

You can see it says max charge voltage 3.65v, nominal 3.2v, cutoff voltage 2.0v  and you can see the voltage as it discharges at various current loads :

1C =  a 1 Ah battery will provide 1A of current for 1 hour ... so for this battery it's  2.3A for one hour, and 0.5C means 1.15A discharge for one hour. So anyway, you can see that voltage will quickly drop to around 3.3v and for around half the battery capacity it will stay there, if the current draw is low. For high current draws, voltage quickly goes down to 3v.

 

[Somerandomtechyboi]

6 minutes ago, OhYou_ said:

first and foremost, please look at a discharge rate chart for both lithium ion and LiFePo4
you should not charge lifepo4 to 3.65 because it is wasteful. they will be more happy in a range of about 3.38-3.0

 

I have absolutely no idea how to read this chart if its even the correct one

 

7 minutes ago, OhYou_ said:

wh is measured at nominal voltage and maximum capacity. this is different from expected capacity. four 50ah lifepo4 cells will provide you 640W max but probably closer to 500 realistically, potentially less depending on how used they are.

Whats nominal volt

And maximum capacity as in maximum charge or something? Like testing the lifepo4 at 3.65v?

 

8 minutes ago, OhYou_ said:

you may use 4 or 5 lifepo4 in series, with 5 being more costly for the BMS probably. 
the pico psu can accept 4 or 5 in series.  iirc its voltage range is like 10-18v
you can supply either type c pd or a 12v rail by buying a converter that is rated for at least 18v input max.

the charger can actually just be a CVCC, you can have this inboard or external, the only real thing to note is to set your charge voltage and current to something reasonable. 

So i can just run 18v into the pico psu and itll deal with it?

 

I am abit worried about using a step down converter cause extra losses

 

And whats a cvcc? I intend on using a laptop power brick for charging, maybe find whatever used powerbrick that has shitloads of wattage capability, though i may need more than 1. Or maybe theres a higher wattage power brick that isnt a laptop or usbc power brick?

13 minutes ago, OhYou_ said:

You want to ensure that your maximum charge ratings for the BMS and the cells will be significantly higher than your absolute maximum load. This is so that you can use a large enough charger that it will be able to both run the system and have currentl left over to charge the batteries, but also not go over current if the machine is pulling zero amps and all of it is dumping into the batteries.
You should use a bms which has cell temperature monitoring for charging. 
you should ideally have a low voltage shutoff.

So basically a 500w bms for a 400w load?

And howd i go about implementing the extra safety if it isnt included in the bms?

[mariushm]

No, you can't give picopsu 18v unless it's a specially designed model that has wide range input - in that case it also has a input voltage -> 12v dc-dc converter on the board, but note such picoPSUs usually can only do a limited amount of current on 12v, like 6A-10A continuously.

Majority of picoPSUs that only work with 12v will just pass through 12v to the system.

 

cvcc  = constant voltage , constant current - go read about methods of charging batteries. Lithium batteries are charged in several stages. In one stage the voltage stays relatively fixed ( the 4.2v for lithium-ion or 4.1v (depends on formulations)  or 3.65v for lifepo4 or other voltages for other mixes) and the charging circuitry is supposed to monitor how much current the batteries "suck in", and once the current goes below some threshold the charging switches to a stage where it "tops" up the battery by giving some amount of current for some time. (the constant current stage)

 

If you connect multiple batteries in series, you need a power source that can supply the number of cells  x max charge voltage + maybe a couple volts. So for example if you want to make a 12v battery from lifepo4 , you'd want  at least 5 batteries/cells  because a single cell will still provide enough power even when voltage is close to 2.5v  ... and 5 x 2.5v = 12.5v

So to charge a battery with 5 such cells in series , you'd need a power supply that can give at least 5  x 3.65v + a couple volts , so you're looking at around 18.5v-20v

 

[Somerandomtechyboi]

10 minutes ago, Eigenvektor said:

Use multiple batteries in parallel to distribute the load, I suppose. Which you'd likely need to do anyway if you want to reach ~300W of output. You'll likely need additional circuitry to ensure they're running at the same voltage etc. so you don't get any current flowing between the batteries themselves. For that much wattage, you're probably better of with something off the shelf.

So i cant just have 5 batteries in series but another bank of 5 batteries to run in parallel for 100ah?

 

And what kind of off the shelf solution can do 300w+ and fit within 12cm of height? Cause i dont intend this thingy to be much taller than an expansion slot

 

9 minutes ago, manikyath said:

past that.. i'd suggest you instead buy some 24 or 36 volt E-bike batteries or at least the BMS and suitable charger. they apparently can be had fairly cheap, and provide a pretty reliable platform that'll do >300 watts sustained load without breaking a sweat. past that there's DC-DC converters built essentially exactly for this purpose (or if you get a 24V BMS, some picoPSU's go up to 32 volts on the input side.)

Spoiler

60$ but thats for a 12.8v 15ah battery

 

 

Spoiler

80$ for 36v 10ah

 

Though on a sidenote ebike chargers look to be very high wattage and theyre cheap

[manikyath]

9 minutes ago, Somerandomtechyboi said:

Whats nominal volt

to be brutally honest with you.. if you have to ask this question, designing a project around high power li-ion batteries might be a bit too far fetched for you. (read: you might set the house on fire.)

 

these batteries have A LOT of power. if you accidentially bridge them (or if the device on the receiving end shorts out) they'll melt the wiring in seconds.

[Somerandomtechyboi]

Just now, manikyath said:

to be brutally honest with you.. if you have to ask this question, designing a project around high power li-ion batteries might be a bit too far fetched for you. (read: you might set the house on fire.)

 

these batteries have A LOT of power. if you accidentially bridge them (or if the device on the receiving end shorts out) they'll melt the wiring in seconds.

I change my mind about the phone batteries think thatd be wayyy to much of a hassle to wire up compared to wiring 5 batteries in series, also just the abuse resistance of lifepo4

 

As for my safety ill just make sure to sit on something that isolates me and problably the batteries from ground, also wear stuff that insulates electricity so dw about that

[manikyath]

1 minute ago, Somerandomtechyboi said:

And what kind of off the shelf solution can do 300w+ and fit within 12cm of height?

probably these guys:

https://hdplex.com/hdplex-400w-hi-fi-dc-atx-power-supply-16v-24v-wide-range-voltage-input.html

 

but you'd still need a propper BMS to deal with high power li-ion batteries, returning back to the E-bike battery stuff here.

 

3 minutes ago, Somerandomtechyboi said:

60$ but thats for a 12.8v 15ah battery

3 minutes ago, Somerandomtechyboi said:

80$ for 36v 10ah

to stick within HDPLEX's input requirements, you'd need to find specificly 24V nominal voltage.

 

also - 24V 20Ah is probably around where you'd want to be for ~500Wh

but that's some killer battery power if you get stuff wrong.

[OhYou_]

19 minutes ago, Somerandomtechyboi said:

 

I have absolutely no idea how to read this chart if its even the correct one

 

Whats nominal volt

And maximum capacity as in maximum charge or something? Like testing the lifepo4 at 3.65v?

 

So i can just run 18v into the pico psu and itll deal with it?

 

I am abit worried about using a step down converter cause extra losses

 

And whats a cvcc? I intend on using a laptop power brick for charging, maybe find whatever used powerbrick that has shitloads of wattage capability, though i may need more than 1. Or maybe theres a higher wattage power brick that isnt a laptop or usbc power brick?

So basically a 500w bms for a 400w load?

And howd i go about implementing the extra safety if it isnt included in the bms?

nominal voltage is a set value, 3.2 for lifepo4, 3.7 for li-ion

on the larger picopsu, I looked it up, they offer an input range from 6v to like 25-30v. I guess its important to note the smaller ones only accept 12v in.
using a buck converter to step down the voltage has a very good efficiency, should be minimal losses if spec'd right.

cvcc, constant voltage, constant current. You literally dial in your charge voltage and charge current. it sounbds like you may want this internal to the machine so think of it lik the battery charger. it goes between the laptop power brick and your batteries to ensure they are charged to the proper voltage and current requirements.

I'd recommend a dell da220p, it is a 12v 220wh power brick.

simply buy a bms which has the safety features, or understand the risks of ignoring the safety features. they are not for your safety, they are for saving the batteries from getting ruined. 

 

also this is the wrong chart, you should look at the other one posted, I thinl your load will lie between the 0.5C-5C line closer to the 5C. 

essentially, the big flat area is the only portion of the batteries you should use, once it starts going quickly down or up is waste. you can set your charger lower so it does not go up as high and then just the lower voltage is your soft stopping point where you should consider the battery depleted.  I'd have a hard shutoff of 2.5v though, 

[Somerandomtechyboi]

5 minutes ago, mariushm said:

No, you can't give picopsu 18v unless it's a specially designed model that has wide range input - in that case it also has a input voltage -> 12v dc-dc converter on the board, but note such picoPSUs usually can only do a limited amount of current on 12v, like 6A-10A continuously.

Majority of picoPSUs that only work with 12v will just pass through 12v to the system.

So theyre basically just glorified and compacted dc to dc converters? Makes sense why theyre so tiny and simple looking. So what psu should i buy or make for this thingy?

 

8 minutes ago, mariushm said:

cvcc  = constant voltage , constant current - go read about methods of charging batteries. Lithium batteries are charged in several stages. In one stage the voltage stays relatively fixed ( the 4.2v for lithium-ion or 4.1v (depends on formulations)  or 3.65v for lifepo4 or other voltages for other mixes) and the charging circuitry is supposed to monitor how much current the batteries "suck in", and once the current goes below some threshold the charging switches to a stage where it "tops" up the battery by giving some amount of current for some time. (the constant current stage)

 

If you connect multiple batteries in series, you need a power source that can supply the number of cells  x max charge voltage + maybe a couple volts. So for example if you want to make a 12v battery from lifepo4 , you'd want  at least 5 batteries/cells  because a single cell will still provide enough power even when voltage is close to 2.5v  ... and 5 x 2.5v = 12.5v

So to charge a battery with 5 such cells in series , you'd need a power supply that can give at least 5  x 3.65v + a couple volts , so you're looking at around 18.5v-20v

So basically gotta have a charging circuit that can deliver tons of amps but at a fixed volt?

 

How would i go about speeding the charging process up and implementing ocp + whatever other neccesary safety?

[manikyath]

9 minutes ago, Somerandomtechyboi said:

 

As for my safety ill just make sure to sit on something that isolates me and problably the batteries from ground, also wear stuff that insulates electricity so dw about that

the danger is not electrocution, the danger is these things cant wait to catch themselves or other things on fire.

 

you should never:

- short them out

- overcharge

- overdischarge

- pull too much current

- push too high charge current

- solder directly onto a battery (it might work, but it damages the cell's internal structure, leading to early failure / lost capacity)

- put them in series without a BMS

 

basicly, you have a power source that'll potentially deliver kilowatts of power, for as long as current is allowed to flow.

 

slight sidenote, i've had a bit of an incident at work today, where i accidentially poked some nickel tabs together.. it melted the nickel in the two seconds response time. literally "puddle of nickel on the desk" sort of melted.

 

EDIT: PS: i work as a battery repair technician.

 

4 minutes ago, Somerandomtechyboi said:

So basically gotta have a charging circuit that can deliver tons of amps but at a fixed volt?

basicly, either buy something off the shelf or dont at all. at this point i'm convinced you're gonna hurt yourself if you even attempt DIY'ing any of this.

[mariushm]

2 minutes ago, Somerandomtechyboi said:

So what psu should i buy or make for this thingy?

None. You don't have the technical knowledge and you don't even seem to be willing to learn the basics.

Spend on your money on a used laptop if you need something portable.

By the time you stack a bunch of those high Ah batteries and the charging circuitry and the components you're gonna have an matx case sized box that you won't carry around, so it's waste of time and money.

[Somerandomtechyboi]

8 minutes ago, mariushm said:

None. You don't have the technical knowledge and you don't even seem to be willing to learn the basics.

Spend on your money on a used laptop if you need something portable.

By the time you stack a bunch of those high Ah batteries and the charging circuitry and the components you're gonna have an matx case sized box that you won't carry around, so it's waste of time and money.

Laptops are just bad for compute, garbage throttling issues due to retarded arbitrary power limits or bad heatsink design, no upgradability, weak and untunable hardware, etc. ofc ill still keep one around for non compute heavy stuff

 

And i dont mind "wasting" money when its disposable cause im just a teenager with literally no responsibilities other than study, besides its interesting to learn and try out new things which is not a waste of money unlike spending hundreds of $ on aesthetics that you wont even look at most of the time

 

8 minutes ago, manikyath said:

the danger is not electrocution, the danger is these things cant wait to catch themselves or other things on fire.

 

you should never:

- short them out

- overcharge

- overdischarge

- pull too much current

- push too high charge current

- solder directly onto a battery (it might work, but it damages the cell's internal structure, leading to early failure / lost capacity)

- put them in series without a BMS

 

basicly, you have a power source that'll potentially deliver kilowatts of power, for as long as current is allowed to flow.

 

slight sidenote, i've had a bit of an incident at work today, where i accidentially poked some nickel tabs together.. it melted the nickel in the two seconds response time. literally "puddle of nickel on the desk" sort of melted.

 

EDIT: PS: i work as a battery repair technician.

 

basicly, either buy something off the shelf or dont at all. at this point i'm convinced you're gonna hurt yourself if you even attempt DIY'ing any of this.

Damn metal melting batteries

 

 

I appreciate your guys concern and honestly yea maybe i should start with a smaller project cause i am very much aware of my ignorance that causes me to literally become fearless

 

ight change of plans maybe ill make something abit more basic like a diy powerbank as a starter project

[OhYou_]

my honest opinion, in this use case, you should not build a battery yourself, instead get a ready made lifepo4 battery resigned as a drop in replacement pack for like a ups or solar install. 

Specifically one with a low voltage protection, and current protection and smart Bluetooth monitoring features. 
This will remove a lot of complexity from the build. 
with that you can focus more on building the rest of the system around set values of the battery you buy vs having to engineer it yourself.

[Somerandomtechyboi]

15 minutes ago, OhYou_ said:

my honest opinion, in this use case, you should not build a battery yourself, instead get a ready made lifepo4 battery resigned as a drop in replacement pack for like a ups or solar install. 

Specifically one with a low voltage protection, and current protection and smart Bluetooth monitoring features. 
This will remove a lot of complexity from the build. 
with that you can focus more on building the rest of the system around set values of the battery you buy vs having to engineer it yourself.

So im better off removing as much complexity as possible?

 

In that case

Spoiler

Looks like this will do

Just add a bms and a charging system and done

 

@mariushm @manikyath anything im missing here? And any way to dumb this down even further so its retard proof and i dont burn the batteries and my house down?

 

think ill be ok with a temporary solution thatll hold me over till i have some experience dealing with batteries and build a more capable battery pack down the line

 

Though i expect to build this problably quite abit after june, maybe late june early july after i recover from spending a crapton from dressing up and slapping a turbo on an 80s cressida so i may already have more experience by then

[manikyath]

5 minutes ago, Somerandomtechyboi said:

 

@mariushm @manikyath anything im missing here? And any way to dumb this down even further so its retard proof and i dont burn the batteries and my house down?

well.. i've no idea about if those packs have their own BMS, or if it's just lifepo4 in series.

 

past that.. you still need an appropriate charger, and an appropriate DC-DC converter, or specificly one of  the picoPSU's that does DC-DC conversion.

i assume the seller will have some directions for a suitable charger, if they dont... avoid like the plague?

[Somerandomtechyboi]

15 minutes ago, manikyath said:

well.. i've no idea about if those packs have their own BMS, or if it's just lifepo4 in series.

 

past that.. you still need an appropriate charger, and an appropriate DC-DC converter, or specificly one of  the picoPSU's that does DC-DC conversion.

i assume the seller will have some directions for a suitable charger, if they dont... avoid like the plague?

It is intended to be put inside a motorcycle thats what the desc says

 

Nominal volt is 12.8v and all the pico psus i can find are tiny and 20$ so ill problably have to get something to regulate volt to be at 12v constantly cause max volt is 14.4v