How to keep costs down?

[not.py]

Complete newbie here,
Anyone got tips on keeping costs down on a battery build?

Currently looking at building a 52v 15-20ah ebike battery capable of around 40a constant.
Prebuilt ones retail around £250 for a 52v 15ah 40a.

Here is my cost estimation for if i were to build it myself:
Cells: £150 (Haven't decided on type yet, generally around 150 minimum)
Bms: £40
Materials: £50 (cell holders, tape, fish paper, nickel, ect)
Charger: £20
Total: £260

Am i missing something, or is it just better to buy pre built in this scenario?

 

[James340]

I have Chinese packs.They don't use cell holders.Cells are just bonded together.I did a capacity test for a cell from a UPP pack with "Tesla"21700 cell and it has 4430 mah from 4.2 volt to 2.8 volt.

 

[E-HP]

Complete newbie here,
Anyone got tips on keeping costs down on a battery build?

Currently looking at building a 52v 15-20ah ebike battery capable of around 40a constant.
Prebuilt ones retail around £250 for a 52v 15ah 40a.

Here is my cost estimation for if i were to build it myself:
Cells: £150 (Haven't decided on type yet, generally around 150 minimum)
Bms: £40
Materials: £50 (cell holders, tape, fish paper, nickel, ect)
Charger: £20
Total: £260

Am i missing something, or is it just better to buy pre built in this scenario?

You’re asking a good question. Math doesn’t lie. If you want a pack that can actually deliver 40A continuous, I doubt you can build it for 250, so that may tell you something about buying a prebuilt pack based on their claims. Do those prebuilt packs describe exactly what components they are prebuilt with?

 

[BlueSwordM]

Complete newbie here,
Anyone got tips on keeping costs down on a battery build?

Currently looking at building a 52v 15-20ah ebike battery capable of around 40a constant.
Prebuilt ones retail around £250 for a 52v 15ah 40a.

Here is my cost estimation for if i were to build it myself:
Cells: £150 (Haven't decided on type yet, generally around 150 minimum)
Bms: £40
Materials: £50 (cell holders, tape, fish paper, nickel, ect)
Charger: £20
Total: £260

Am i missing something, or is it just better to buy pre built in this scenario?

That cost seems around right for a 52V 20Ah pack if you use cells like this:

Tenpower INR21700-50ME 5000mAh - 15A

5000mAh - 15A Continuous Discharge Order by 3pm (Monday to Friday) for same day dispatch!Brand: TenpowerModel: 50MESize: 21700Chemistry: INRNominal Capacity: 5000mAhNominal Voltage: 3.6VDischarge: 15A Max ContinuousPositive: Flat TopProtected: NORechargeable: YesDimensions: 21mm x 70mmWeight...

www.cellsupply.co.uk

BTW, does the prebuilt battery even come with a charger?

 

[not.py]

BTW, does the prebuilt battery even come with a charger?

What you generally get ^

 

[not.py]

I have Chinese packs.They don't use cell holders.Cells are just bonded together.I did a capacity test for a cell from a UPP pack with "Tesla"21700 cell and it has 4430 mah from 4.2 volt to 2.8 volt.

Sure it highly depends upon manufacturer but all the e-bike battery's i've stripped have been to okay standards.
This is what's inside the generic e-bike "Hailong" cases:

(No clue what happened with the background)

 

[not.py]

Do those prebuilt packs describe exactly what components they are prebuilt with?

Most will give the cell models if they are proud of them, BMS's usually go unnamed though as they are generally random cheap chinese brands.

But that's usually all, I suppose technical specs could scare away the average consumer who wants to ride to work and back.

 

[docw009]

I think your cell budget is a little low at 150£, ($231USD),

I would suggest a 56 cell 4S-4P so that each cell is putting out 10A for your 40A constant, A Samsung 50S is 5AH 25A and a Molicell P45B is 4500mah 45A. I believe 10A continuous is fine for each, but my continuous is a few minutes. These cells are about $5 (on sale) in the USA. so you're spending $208£.

I am also a proponent of cell holders. Those are not expensive. Kapton tape and fish paper aren't that cheap, but figure that what you buy can be used on other projects. I prefer to put the battery in a stiff coroplastic box and shrink wrap. The coroplastic (election signs) is free, but shrinkwrap isn;t.

I am conservative on batteries, but they will last longer when you stay well under their maximum rating, Good to keep costs down, but you also should want to keep quality high.

 

[A-DamW]

Anyone got tips on keeping costs down on a battery build?

I think second hand pre-built automotive or telecom/datacenter modules are an option if you can find a form factor that fits.

Here in the US, I've bought a lot of batteries from BatteryHookup.com.

As an example, these 13s4p ~300wh modules go for $17, for me about $28 shipped to my door.
They have a bit older cells, Sanyo UR18650WX 1600mah cells manufactured by Panasonic which are 25a rated power cells.

The modules have worked great for a couple years now.

You may have some reclaim battery sellers in the UK.

 

[not.py]

batteries from BatteryHookup.com.

Thank you, these cells in particular look super good for this:

3.2v 15ah 48wh LiFePo4 Cylindrical Cells - Scratch/Dent

These cells have never been used, have good voltage, and the cells we tested were full capacity. Amazing deal at this price. Each cell has a slight scratch on the shrink wrap or a tiny dent. It's hard to notice unless you are looking at an angle. The tabs on both ends are copper which is nice...

batteryhookup.com

I've been tempted by lifepo4 but never seen the price right, is there any negatives to this?

Total cell cost would be £49 for 1p/£98 for 2p. (Accounting for a extra spare 6 cells incase)
Substantially cheaper than other cells i've found.

 

[A-DamW]

I've been tempted by lifepo4 but never seen the price right, is there any negatives to this?

The only major thing I can think of is lifepo4 is about 20-30% less energy dense than Liion.
So your battery will be a bit heavier and bigger for the same capacity.

Some upsides to lifepo4 are much longer cycle life and safer chemistry.

 

[docw009]

Estimates here. Run your own.
2.5"x13"x5.5" for a 16S Lipo, 48V15AH.
2.5"x11"x2.6" for 13S 21700. 48V15AH.

It's the extra width to fit on your bike. On a rear rack, you could do Lipo, but pay the extra $1 per cell and don't use dented cells.

They're not the 200A red Headway cells that BH used to sell for $9 used.