Easiest/most affordable way to make or get a LiFePo4 pack?

ambientvoid

10 mW
Joined
May 15, 2015
Messages
23
I have been recommended to purchase LiFePo4 cells and build a pack to power a small speaker project. I'm a complete noob at doing anything with batteries that isn't plug and play and I'm not comfortable with the idea of soldering batteries so if there's a sort of modular snap-together/screw-together option then please do point me in the direction of that. I have no idea what cells would be most suitable, what other stuff I'll need or how to put it all together safely. I'm UK based so I'm looking for trusted companies that ship to or are based in or near the UK, and that are hopefully fairly inexpensive as I'm on a pretty limited budget.

The resulting pack needs to be a maximum of 1' (30cm) long, 6.3" (16cm) wide and 5.5" (14cm) tall to fit in the battery compartment. The amplifiers I'm powering are 48v but I have a 500w boost converter that will boost a 12v to 27v input up to 48v. I would prefer an overall capacity of 20ah to 30ah.

Any help would be much appreciated.
 
There are screw together kits, like:
https://vruzend.com/product-category/battery-kits/

I think even with those the final discharge cable is soldered on to one of the screw on tabs, though. So I wouldn't try it if I wasn't comfortable soldering.

Crossing out making a pack, the next cheapest option is using a reclaimed pack that is already 48V from a place like:
https://www.batteryclearinghouse.com/

But even then you often need to do some soldering to put a different connector on. You can buy pre-soldered XT60 connector and cable pairs, but you are still stuck with soldering the other end of the cable even then...

Think that leaves you with buy new pack, buy used pack, or trade with a friend into making batteries. Needing custom requirements isn't a big deal, I buy from AliExpress all the time and specify this like only Samsung cells, Dean discharge connector, etc., etc . Anything from China takes a month to arrive, though.
 
In most cases there are crimpable connectors available for things so you don't need to solder (and used correctly they'll make a better lower resistance connection than soldering). But you would need to buy the correct crimper for the contacts you want to use. I would recommend a ratcheting crimper at minimum, so that it creates the correct amount of crimping force automatically. At a guess, a good-enough crimper will be in the $40+ range.

There are also ring terminals you can crimp onto cabling to use with bolt-together cell systems; depending on the terminal type and the connectors used above, you might be able to use the same crimper for the purpose.


With LiFePO4 you can buy screw-terminal Headway cells (IIRC Batteryhookup has used ones available, and new ones are available from various sources) and make your own copper interconnect plates, or buy them from various places, for however many series and parallel connections are required to make the voltage and capacity you're after. There are several kinds of Headway cells, some with higher current delivery (C-rate, A) and some with higher capacity (Ah), depending on what you need.


BTW, if you can build the pack to the right voltage range to run your amps directly, you're going to have significantly better efficiency and less potential for problems, than using a converter between pack and amp.
 
ambientvoid said:
The resulting pack needs to be a maximum of 1' (30cm) long, 6.3" (16cm) wide and 5.5" (14cm) tall to fit in the battery compartment. The amplifiers I'm powering are 48v but I have a 500w boost converter that will boost a 12v to 27v input up to 48v. I would prefer an overall capacity of 20ah to 30ah.
Does the compartment also have to house the boost converter and it's heatsink and fan and airflow space? If so, not using one will increase the pack size you can use.

How much current does the pack have to provide to the amp?

How long does the pack have to last at that current?

Alternately how many watt-hours do you need the pack to provide in total? Watts is volts x amps so this will be about the same number (not counting losses in the converter) whether you build the pack at lower voltage to supply higher current to the converter to make a higher voltage and lower current, or whether you build the pack at higher voltage to supply a lower current directly to the amp.

Example: If your 20Ah to 30Ah capacity is at 12v, then that's about 240 to 360Wh. So a pack at 48v would only have to provide about 7.5Ah to give you the 360Wh number.


Using say, headway cells like these:
https://batteryhookup.com/collections/headway-hookup/products/8-new-headway-3-2v-17ah-40152s-10c?variant=39501748240546
that claim 17Ah (at 8.5A drain rate) and 17A continuous output (with 170A 3-second-pulse output) at 3.2v nominal, it would take 15 of them in series to make actual-48v nominal (16s is normally used in ebike/scooter packs for 51.2v nominal, called 48v).

Each is 40mm wide by 152mm long, so a rectangular block of 15 in 3 rows of 5 could be about 40x3 x 40x5 = 120mm x 200mm and 152mm thick. I don't know if that 152mm includes the bolts on the ends or not. You can configure the block of cells any way you like to fit in the space available; you'll have to determine if this is possible.

If you need more than 8.5A of current then they won't deliver 17Ah, so you may need three or four sets of (however many in series) in parallel to get the capacity you're after, if you're not using them at the higher voltage.

At the higher voltage they'd have about twice as much capacity than you need as long as the amp isn't drawing enough current to waste as much power in the cells as heat, reducing their deliverable capacity.

If those are too long or thick, you can use these
https://batteryhookup.com/collections/headway-hookup/products/8-new-headway-3-2v-10ah-38120-10c?variant=39501771669666
which are 38mm x 120mm. They aren't as high capacity (10Ah) and can't deliver as high a current (100A peak, 30A continuous),
 
Sorry for the late reply, I don't know why but I didn't get any email notification of replies.

Someone previously told me that the amplifiers should only be pulling about 10.4A peak power but that was worked out by dividing the wattage of the boost converter with voltage of the output, I don't know if that would still be the case with just a 48v battery instead. I saw a review video for one of the amplifiers that seems to indicate that at 45v I'd be looking at a continuous 5A for the wattage I need.

I'm a bit confused by the different voltage ratings and what they actually mean, if 48v is the nominal voltage does that mean that a fully charged battery pack would be putting out too much voltage for the amplifiers maximum which is 48v, would I be better off with a 1 or 2 cell smaller pack to avoid damaging the amplifiers at full charge?
 
Someone previously told me that the amplifiers should only be pulling about 10.4A peak power but that was worked out by dividing the wattage of the boost converter with voltage of the output, I don't know if that would still be the case with just a 48v battery instead. I saw a review video for one of the amplifiers that seems to indicate that at 45v I'd be looking at a continuous 5A for the wattage I need.
Depending on the amp design, it may draw more current at a lower voltage to give the same wattage, but some will draw less current at a lower voltage for less wattage, because of the resistance of the circuits, speakers, etc.

You can test this if you like, using a simple test signal pattern that you can use repeatedly to make the same test each time. Test at one voltage, then another, while monitoring both votlage and current into the amp.



I'm a bit confused by the different voltage ratings and what they actually mean, if 48v is the nominal voltage does that mean that a fully charged battery pack would be putting out too much voltage for the amplifiers maximum which is 48v, would I be better off with a 1 or 2 cell smaller pack to avoid damaging the amplifiers at full charge?

If the amps have a hard voltage limit of 48v, then to ensure you don't exceed that, then you can either not charge fully, or use less cells. Not charging fully won't lose you much capacity (a few percent or less), while using less cells loses you significant capacity.


An LFP cell is around 3-3.2v for most of it's discharge curve: Here's a randomly-found discharge curve of one version of a headway cell. Each colored curve is the voltage over time/capacity at a different current (1c is 10A, 2C is 20A, 3c is 30A, etc., for this 10Ah cell)
headway.png
It shows that at 1C (10A for a 10Ah cell) it would give you about 3.1-3.2v per cell for about half of it's capacity range (the first 5Ah or so). Then it starts to curve down in voltage more and more, staying above 3v for another quarter or so of it's capacity, then dropping faster and faster to empty around 2.5v (it's really empty at 2v, but there's not even a few hundred mAh between those points).

What that means is that for a 48v pack, if you assume 3.4v full charge (instead of 3.65) (it will sag down under load, probably to about 3.2v), then 48 / 3.4v = 14s, that gives 47.6v max. If you assume 2.5v empty, then 14 x 2.5v = 35v minimum. You'd probably get about 9Ah or more out of the 10Ah these specific cells could potentially give.

Different cell brands / models have different curves, so you can reference their spec sheets for this if you want to see what it is for any specific cell. But you can guesstimate that most LFP cells will give about 90%+ of their rated capacity if you use them within the 2.5-3.4v charge range.

If your amp would fail at 48.1v, you might want more margin than just half a volt of safety, though, and maybe go for 13s at 3.4v/cell max.


If you're not using a BMS on the pack, then you may want to periodically check them at either the empty or full state (not both) to see if they are all equal, and if not, either drain the high ones with a resistance or fill the low ones with a single-cell charger till they are.

If you will use a BMS on them, then you'll need one that is programmable for HVC, LVC, and balancing points so it will work with the "nonstandard" max charge and min discharge points.

ambientvoid said:
Sorry for the late reply, I don't know why but I didn't get any email notification of replies.
Many providers autofilter out forum notifications because so many of them from the same domain pass thru their servers so it looks like spam. This is done before it gets to your inbox, so it doesn't even show up as spam in your email, they just never get sent anywhere. :( If you find them in your spam/junk folder you can setup a whitelist for them in your email options.
 
https://m.aliexpress.com/item/1005002306907257.html
I was recommended this BMS for use with the LiPo batteries but it appears to be more suitable for Lifepo4, according to the seller the parameters are fully adjustable but can you tell if it does have the full functionality that I'd need to intentionally and accurately undercharge the battery?

As well as the BMS what sort of charger would I need to charge a presumably 15s home made battery pack?
I have a Turnigy Reaktor LiPo charger but while it can be programmed for Lifepo4 batteries it's only designed to charge up to 6s packs.
 
That's a 3S LiIon / 4s LiFePO4 BMS. Meaning it only works with 3 or 4 cells in series, for a "12v" pack. If that's enough for you then it may work. Otherwise, if they sell a version that will do enough series cells for your pack, it might work, but you'd have to ask the seller. There are multiple versions there, some for LFP some for LI, so you order the one that matches the cells you're going to use.

They don't list the range of adjustability of values for the various parameters, so I can't tell you if it will adjust to the points you need them to.

The specs they list are these, which indicate you must also order a separate "module" from them (not linked anywhere on the page) to be able to talk to the BMS via your computer or the phone app or to program it and set it up.

Keep in mind that whatever app they use is just like any other app. It may work on your phone, or it may not. If it works now, then any future automatic update of anything on your phone may break it, and the app may even be made with a timeout function so it stops working after a certain date, forcing an update, which may or may not work with your phone.

I don't see a computer-based program listed, so if they don't have one and you want to use that function, you'd have to write one based on whatever communication protocol and dataset they provide (if they provide one).


1. Cell phone app monitors the battery charging and discharging status. Single battery overvoltage and undervoltage, battery pack overvoltage and undervoltage, balance voltage, high and low temperature, and release value can be adjusted.
2. The communication module is connected to computer to monitor the battery data, set parameters, read BMS communication protocol and communicate with the device.
3. Imported IC software and hardware dual protection. Software running real-time monitoring program plus secondary protection. Sleep and low standby power consumption, high-quality electronic components.
4. It calculates the remaining capacity and charge capacity of the battery based on the current versus time score.
5. Temperature control detection: BMS built-in balanced power temperature control to detect. Adjustable high and low temperature protection function, the temperature sensor is strong and not easy to break.
6. App display interface has speed measurement function. It can accurately detect the speed based on Hall pulse and calculate the remaining mileage.
7. Description of UART communication Port:
For example: LiFePO4 16S UART in the option means that BMS has UART communication port but does not include UART module. This port can be compatible with Bluetooth and UART module.
8. Function of UART communication port:
1) When the Bluetooth module is inserted into the UART port, it can only view the battery parameters in the Phone app.
2) When the UART module is inserted into the UART port, it can only view the parameters on the computer. They share the same port, so bluetooth and UART modules cannot be used at the same time.
9. Description of UART 485 communication port:
1 ) For example: LiFePO4 4S UART 485 in the option means that BMS has UART and 485 communication port, but does not include UART and 485 module. These two ports can be used for Bluetooth module and 485 module.
10. According to your needs:
1 ) If you want to view battery parameters on the cell phone and computer at the same time, you must purchase a 485 module and choose BMS with UART 485 port.
2 ) If you want to view battery parameters on your cell phone or use it on your computer, you can buy a UART module and choose BMS with UART port. You can switch between Bluetooth and UART module.
3) Just view parameters on the phone app you can choose BMS with UART port no need to order any module.
11. APP software reference interface display:
01) Percentage capacity
02) Temperature
03) Charge time
04) Total voltage
05) Remaining capacity
06) Power
07) Voltage range
08) Voltage diff
09) Charging turn on / off
10) Discharge turn on / off
11) Protection state
12) Cell balance
13) Each cell voltage
14) Nominal capacity
12. Warm tips:
1. Using app for the first time, please change nominal capacity to actual capacity, cycle capacity is actual capacity * 0.8
2. The order does not contain UART and 485 modules. If you need a module, please contact us to purchase.
 
For a charger, you need to use one that doesn't output more current than your pack is intended to charge at. Meaning that it's A rating is no higher than either the BMS charge port or the cells (as parallel groups) are designed to handle, preferably less (since it is less stressful to use things below their limits).

If the cells can handle 0.5A charge rate, for instance, and there are 6P in each group, then that's 6 x 0.5A = 3A max charge rate.

If the BMS charge port can handle 5A, and the cells 3A, then the charger can output no more than 3A.

If the charger is programmable/adjustable, you just ensure it's set to output no more than that limit. If it's not programmable or adjustable then you have to buy one that has no more output than that.


The charger voltage needs to be whatever the max full charge voltage would be. If it's a 16s pack, for instance, and each cell is going to charge to a maximum of 3.4v, then that's 16 x 3.4 = 54.4v. If it's a 4s pack, at 3.4v / cell, that's 13.6v. Some are adjustable, most are not, so if you get a non-adjustable one you ave to get one with the right voltage already set.

LI and LFP chargers are "the same" in how they work, so either kind works for your purpose as long as it has the right max voltage and current limits. (LI chargers *should* shut off once current drops below some preset point, typically a few mA. Some LFP chargers may never turn off, depends on the specific design--I recommend one of whichever kind that turns itself off when "done").

If budget permits, the Cycle Satiator by Grin Tech is "fully programmable" with multiple presets, and is weatherproof and vibration resistant so you can even mount it on the bike/etc to keep it with you (typical chargers are neither of those so carrying them with you risks damage to them, if this is a feature you need).
 
I misread the voltage on one of the amplifiers and it tops out at 46v instead of 48v so I'm going to go for 45v as a shared voltage.

I had a look on the batteryhookup website and compared the cell and holder measurements to the battery space I have, depending on whether I go for the 8ah 38120 or the 15ah 40152 I should only be able to make a 12v (4s4p) or 24v (8s2p) pack respectively for roughly the same capacity if I also want to be able to fit a bms in there. So it looks like I'll have to use the boost converter for 45v after all, will using that have a noticeable impact on battery life vs just a roughly 45v pack?

Price aside I like the look of that Cycle Satiator charger so I'm leaning towards the 24v pack, the only problem I can think of currently is that batteryhookup doesn't seem to sell cell holders and busbars for the 40152 cells so I'm not sure where I'd get some from.

If I'm reading the specifications correctly then I think the 40152 cells are 165mm long with the screws in, it'll be tight but it should fit as I made a mistake in my measurements and the battery compartment should be 17cm wide.
 
ambientvoid said:
So it looks like I'll have to use the boost converter for 45v after all, will using that have a noticeable impact on battery life vs just a roughly 45v pack?
That depends on the converter efficiency. Some are pretty efficient in a wide range, some are terrible except at a specific part of their conversion range, some are terrible overall.

You can calculate efficiency by placing a constant load on the output, and using a wattmeter / coulometer on the converter input, then on the converter output. Divide the one by the other, such that the result is less than 1, and the number is the percent efficiency. The difference between the numbers includes the waste heat produced by the converter (which like the heat from the amp itself, must be able to be removed from the casing the converter is placed in, so if it goes in there with the battery, it doesn't heat the battery up--it only takes a few watts to make catastrophic heating in a confined insulated space).



Price aside I like the look of that Cycle Satiator charger so I'm leaning towards the 24v pack, the only problem I can think of currently is that batteryhookup doesn't seem to sell cell holders and busbars for the 40152 cells so I'm not sure where I'd get some from.
Holders you can 3D print (or have them printed); I'd just about guarantee that there are 3D models of cell holders for them, and if not, you could use models for the ohter size cells and rescale them appropriately for the larger cells. There's a "repository" thread here on ES for stuff like that, and a bunch of DIY battery threads, some of which have models in them.

Connecting hardware you can make yourself if necessary. A simple way would be to buy a copper sheet and cut it into the shapes you need for interconnects, based on the shapes used for the smaller cells. Copper could be scored deeply with a tool, then bent back and forth at the score until it snaps. Or cut with a hacksaw blade (with or without the hacksaw, depending on setup). Etc. File the edges if necessary. Then drill holes in the appropriate places to bolt to.

A google search on the phrase from your post
https://www.google.com/search?q=cell+holders+and+busbars+for+the+40152+cells
finds some pages that appear to have them for sale, too, though I didn't look to see if they're in stock or are a reasonable price.
 
I found another page showing the size of the 40152 cells mounted in the holders and they're just a bit too big to fit, I could tweak the battery compartment to fit by sacrificing driver space but I'd rather not do that so I had a look for alternative batteries and found Eve LFP batteries like these which seem to be a perfect fit at 12v https://batteryhookup.com/products/new-4-pack-eve-3-2v-75ah-240wh-lifepo4 and connect up in a similar way to the Headway cells at a much higher capacity, I would have to find an alternative charger but other than that would there be a downside I'm not seeing to using the Eve batteries?
 
Well, those cells are individually bigger and heavier than headway cells, but if they'll fit and do what you want, ahd the headway won't.... They'll certainly do the current you're after.

Each one is 4lbs, 5" wide, 1.5" deep, 8.5" tall. (I don't know if that includes the terminal posts--those might be another half inch or more to the 8.5" dimension).

Four of them for a 12v pack will be 16lbs, and if stacked the usual way will be 5" wide, 8.5" (or 9" with terminals?) tall, and 6" deep.

Buuuut: Every prismatic cell like these I've ever seen requires a containment scheme to keep the proper even pressure applied across at least the largest two surfaces to keep them from swelling up in use (which results in permanent cell damage). If these don't, that's great...but something you should check on from the manufacturer, since BH's page doesn't have this data.


Cylindrical cells don't because their casings already do this, being cylindrical. I don't know what the pressure spec is for this cell, hopefully that info is available from the manufacturer There is discussion on this around ES like this thread
https://endless-sphere.com/forums/viewtopic.php?f=14&t=97293
and others like the A123 thread referenced from there has info but not exact number from a member that worked at the A123 plant of a few PSI, all across the face of the cells.

Some DIY systems have used adjustable-tension strapping around the stack to hold thick inflexible end-plates across the cells to provide the compression.
 
metal shell cells also need non compressing insulating sheets between each one
 
amberwolf said:
Cylindrical cells don't because their casings already do this, being cylindrical.

I think I'll be sticking with cylindrical cells then. I have been messing around with cell orientation and if I reduce the battery count down from 4x12v packs to 3x12v packs and rearrange the cells so that they're rotated 90° I can fit them in without having to modify the enclosure. In order to best fit the cells in place it would be preferable to arrange the 12v packs in a 2 wide 2 inline cell configuration but is there a presumably threaded connector to connect the Headway cells inline?
YKyzZcw.jpg
 
ambientvoid said:
amberwolf said:
Cylindrical cells don't because their casings already do this, being cylindrical.

I think I'll be sticking with cylindrical cells then. I have been messing around with cell orientation and if I reduce the battery count down from 4x12v packs to 3x12v packs and rearrange the cells so that they're rotated 90° I can fit them in without having to modify the enclosure. In order to best fit the cells in place it would be preferable to arrange the 12v packs in a 2 wide 2 inline cell configuration but is there a presumably threaded connector to connect the Headway cells inline?
YKyzZcw.jpg

https://batteryhookup.com/products/headway-series-threaded-connector-rod

I'd bet you'd be able took something up from your local hardware store as well
 
harrisonpatm said:
https://batteryhookup.com/products/headway-series-threaded-connector-rod

I'd bet you'd be able took something up from your local hardware store as well

Oh I totally missed that, I was looking at a different website for connectors after not being able to see the plastic cell holders for the 40152s on Batteryhookup, thanks.

I wish I knew of a good local hardware store, I found one a few years ago that had been established for decades and then it closed for good 6 months later. :roll:
 
ambientvoid said:
I wish I knew of a good local hardware store, I found one a few years ago that had been established for decades and then it closed for good 6 months later.
ambientvoid,

Can't help you directly, but in the USA, if you go to the REAL Internet Yellow Pages (all of the others are wannabees) . . .
https://www.anywho.com
Go to the
Yellow Pages tab, and click on
FIND A BUSINESS. Enter the actual Yellow Pages heading that you want, in this case
NUTS AND BOLTS.
(It's a real, separate heading.) For the
LOCATION, enter a
ZIP Code, either yours or one near you. Click on
FIND. When you get the list, above the list of phone numbers, you will see "sort: DEFAULT." Click on the word
DEFAULT and you will get a menu of choices. Click on
DISTANCE. The list will then be sorted by DISTANCE from you, in miles. Click on the
MAP VIEW to see where the businesses really are located, near you.
ZOOM IN as needed. This list will show many local outlets for
NUTS AND BOLTS, not just the usual lame suspects.
Take your hardware samples in with you, and see what they can do for you.
You may choose to print out this message. HTH.
 
Well that was unfortunate, having left it until now to purchase the cells, it appears that Batteryhookup is out of (sufficient) stock of 40152s. Can anyone suggest anywhere else that stocks Headway 40152s cells and ships internationally for a reasonable price?

Thanks for the info Red, unfortunately I'm in the UK so I don't think that link will work for me but it never occurred to me that Yellow Pages might have a website so I'll have a look to see if there's a version for the UK. :)
 
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