Request for a Improved guide for building DIY LifepO4 packs

[akumd]

Hi all, this is a kind request for a improved guide on building LifePo4 DIY battery packs.
Existing guide https://www.mobile-solarpower.com/design-your-own-12v-lifepo4-system.html does not mention details like below

- Compressing cells
- Direction to place cells
- Best cell arrangements (for 8s, 16s)
- Torque to be placed on Cell terminals
- Whether to keep a insulated material between cells
- Suitable enclosure type (Metal vs ABS material)
- Avoiding bus bars touching the battery case
- Avoiding battery casing touching the enclosure (if made from metal)
- Where to place the temperature sensors of BMS.
- What to do when the no of temperature sensors in BMS is less than cell count (which is usually the case)
- Ventilation requirements if any
- Placing more temperature sensors (in addition to ones from BMS)

 

[akumd]

pardon me if this information is already available in one or limited no of places in this forum.

 

[timselectric]

Compressing cells
- Direction to place cells
- Best cell arrangements (for 8s, 16s)

Personal preference

Torque to be placed on Cell terminals

According to cell manufacturers recommendations

Whether to keep a insulated material between cells

Recommended, if you choose to compress.

Suitable enclosure type (Metal vs ABS material)

Personal preference

Avoiding bus bars touching the battery case

Depends on what the case is made of.

Where to place the temperature sensors of BMS.
- What to do when the no of temperature sensors in BMS is less than cell count (which is usually the case)

Between cells, evenly spaced in the battery.

Ventilation requirements if any

Not required.

Placing more temperature sensors (in addition to ones from BMS)

For monitoring?
Also Personal preference.

 

[akumd]

@timselectric, thank you. few follow-up questions if you don't mind.

Compressing cells -> Personal preference.
If you don't compress wouldn't the (prismatic) cell gets bloated ? (I thought if you compress them any miniature gas build up gets released through the tiny hole which is close to the cap)


Where to place the temperature sensors of BMS -> Between cells, evenly spaced in the battery.
Could there be a case where the head of the temp sensor being metallic(thus conducting current between cell casings) ? If most prominent(e.g. JK BMS) has temp sensors with non-conductive heads then this will NOT be a problem.

Placing more temperature sensors -> For monitoring?
Yes, as a fail safe. In case BMS temp sensor fails to detect OR is not in contact with one or more cells.

 

[Brett V]

I’ve never compressed cells and have had no problems with bloating. I use filament tape to restrain the cells but that’s all. Simply attach the temperature sensors to the top of the pack with Kapton tape and forget about it.

 

[timselectric]

Compressing cells -> Personal preference.
If you don't compress wouldn't the (prismatic) cell gets bloated ? (I thought if you compress them any miniature gas build up gets released through the tiny hole which is close to the cap)

You would have to really push them hard to get any deformation.
Which will never happen in solar storage use. (Unless your battery is way undersized)

Where to place the temperature sensors of BMS -> Between cells, evenly spaced in the battery.
Could there be a case where the head of the temp sensor being metallic(thus conducting current between cell casings) ? If most prominent(e.g. JK BMS) has temp sensors with non-conductive heads then this will NOT be a problem.

I don't know of any that are metal. But that would require extra consideration.

Placing more temperature sensors -> For monitoring?
Yes, as a fail safe. In case BMS temp sensor fails to detect OR is not in contact with one or more cells.

I don't see the need. But if it makes you feel better, go for it.
My cells mostly remain at room temperature.

 

[akumd]

@timselectric, thanks.
Also Regarding NOT needing ventilation,
If we make it fully air tight, How can Cells dissipate heat in case of a temporary heat up ?

 

[timselectric]

@timselectric, thanks.
Also Regarding NOT needing ventilation,
If we make it fully air tight, How can Cells dissipate heat in case of a temporary heat up ?

I wouldn't go fully air tight, with pressure gasketing. (Although you could)
But , you don't have to add ventilation.
If your cells are heating up, you have a problem.