Questions about Li-Po & Safety

[Satoshi Deguchi]

Hello!

I am looking to research Li-Po and how to make hobby grade batteries safe to use for my application. I don't have very much knowledge in regards to electronics but would like to learn whatever I can.

It is my understanding that Li-Po batteries carry the same risks of any Li-Ion battery, but most Li-Po batteries do not have a protective circuit/PCB that is found in mobile devices such as phones and tablets.

How can I make a protective circuit (or buy a PCB) that has overcharge/overdischarge protection? I want to be able to utilize the power of Li-Po batteries for my hobby, Nerf blaster modding.

 

[Tony Stewart]

learn about battery characteristics on this site first https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

 

[rjenkinsgb]

How can I make a protective circuit (or buy a PCB) that has overcharge/overdischarge protection?

Suitable battery protection modules are readily available on ebay, amazon & aliexpress etc.

They are often labelled as "BMS" boards, battery management system - which is rather inaccurate, they are definitely not a complete management system!


For a single cell voltage, either one cell or two or more parallel so still the same voltage, you need under / over voltage protection and short circuit protection.

For two or more cells in series, it must also include cell balance, to avoid the cell voltages becoming uneven, as that is one of the common causes of battery failure or fire; if any one cell has a higher charge than the others, that can overcharge and fail before the overall battery voltage reaches the charge cut-off point.

Search eg. ebay for Lithium BMS and you will find a vast selection; a couple of example listings:

Lithium Battery BMS 18650 Charger Protection PCB 1S 2S 3S 4S 5S 6S Li-ion Li-Po | eBay

It also features over current and short circuit protection. Model 3S 12.6v 20A lithium battery protection plate (with Recovery function -AUTO Recovery). Module:1S Li-ion Lithium Battery Protection Board.

www.ebay.co.uk

8S/7S/6S/5S/4S/3S BMS PCB Protection Board For 18650 Li-ion Lithium Battery Cell | eBay

Note:The balancing board must need BMS to use together,and the BMS is without balancing function.

www.ebay.co.uk

1S/2S/ 3S/4S/ 5S/6S/ 7S/10S/13S 18650 Lithium Battery Protection Board Bms | eBay

1S / 2S / 3S / 4S / 5S / 6S / 7S / 10S / 13S 18650 Lithium Battery Protection Board BMS PCB Specifications: Fine workmanship and durable. For the rechargeable (generally refers to the lithium battery) from the protection of the integrated circuit board. Lithium battery (rechargeable type) so...

www.ebay.co.uk

To find ones for a specific number of series cells, add eg. 1S, 2S, 4S or whatever the cell count is, to the search.

Make sure the module is rated at far higher current than the motor rating you will be using (presumably for a flywheel gun?)
Dc motors take many times the rated current when starting or if loaded so the speed drops down a lot.

And, be sure the cells are rated for an even higher discharge current! Too high current can overheat the cells and cause failure.


As well as the battery protection, you still need a proper lithium cell or battery charger. The voltage regulation is critical, and it must have a current limit within the cell charge current ratings.

An alternative approach for multi-cell batteries, as used with such as radio controlled flight systems, is have the balance part in the charger rather than the battery.

In addition to the main power connections, wires are brought out from the pack end and each cell to cell junction, with the charger having both power and multi-way connectors to suit.

Chargers for this system are generally fully programmable for cell type, count and charging current.

Example:

Turnigy Accucell 6 50w 6A Balance Charger 1-6S LiPo LiHv LiFe NiMh NiCd PB+LEAD | eBay

Find many great new & used options and get the best deals for Turnigy Accucell 6 50w 6A Balance Charger 1-6S LiPo LiHv LiFe NiMh NiCd PB+LEAD at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Another advantage with those is that they can often operate either from such as a laptop power brick, or 12V from a vehicle.

(Or use standard size cells such as 18650 type, in holders, & remove / exchange them for charging).

 

[Satoshi Deguchi]

Suitable battery protection modules are readily available on ebay, amazon & aliexpress etc.

They are often labelled as "BMS" boards, battery management system - which is rather inaccurate, they are definitely not a complete management system!


For a single cell voltage, either one cell or two or more parallel so still the same voltage, you need under / over voltage protection and short circuit protection.

For two or more cells in series, it must also include cell balance, to avoid the cell voltages becoming uneven, as that is one of the common causes of battery failure or fire; if any one cell has a higher charge than the others, that can overcharge and fail before the overall battery voltage reaches the charge cut-off point.

Search eg. ebay for Lithium BMS and you will find a vast selection; a couple of example listings:

Lithium Battery BMS 18650 Charger Protection PCB 1S 2S 3S 4S 5S 6S Li-ion Li-Po | eBay

It also features over current and short circuit protection. Model 3S 12.6v 20A lithium battery protection plate (with Recovery function -AUTO Recovery). Module:1S Li-ion Lithium Battery Protection Board.

www.ebay.co.uk

8S/7S/6S/5S/4S/3S BMS PCB Protection Board For 18650 Li-ion Lithium Battery Cell | eBay

Note:The balancing board must need BMS to use together,and the BMS is without balancing function.

www.ebay.co.uk

1S/2S/ 3S/4S/ 5S/6S/ 7S/10S/13S 18650 Lithium Battery Protection Board Bms | eBay

1S / 2S / 3S / 4S / 5S / 6S / 7S / 10S / 13S 18650 Lithium Battery Protection Board BMS PCB Specifications: Fine workmanship and durable. For the rechargeable (generally refers to the lithium battery) from the protection of the integrated circuit board. Lithium battery (rechargeable type) so...

www.ebay.co.uk

To find ones for a specific number of series cells, add eg. 1S, 2S, 4S or whatever the cell count is, to the search.

Make sure the module is rated at far higher current than the motor rating you will be using (presumably for a flywheel gun?)
Dc motors take many times the rated current when starting or if loaded so the speed drops down a lot.

And, be sure the cells are rated for an even higher discharge current! Too high current can overheat the cells and cause failure.


As well as the battery protection, you still need a proper lithium cell or battery charger. The voltage regulation is critical, and it must have a current limit within the cell charge current ratings.

An alternative approach for multi-cell batteries, as used with such as radio controlled flight systems, is have the balance part in the charger rather than the battery.

In addition to the main power connections, wires are brought out from the pack end and each cell to cell junction, with the charger having both power and multi-way connectors to suit.

Chargers for this system are generally fully programmable for cell type, count and charging current.

Example:

Turnigy Accucell 6 50w 6A Balance Charger 1-6S LiPo LiHv LiFe NiMh NiCd PB+LEAD | eBay

Find many great new & used options and get the best deals for Turnigy Accucell 6 50w 6A Balance Charger 1-6S LiPo LiHv LiFe NiMh NiCd PB+LEAD at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Another advantage with those is that they can often operate either from such as a laptop power brick, or 12V from a vehicle.

(Or use standard size cells such as 18650 type, in holders, & remove / exchange them for charging).

Thank you for the very detailed response! I will come back to this in the morning with questions.

 

[audioguru]

My electric radio-controlled model airplanes use unprotected 2 cell LiPO batteries. The airplanes have over-current detection and shut off the motor if the current is too high. The airplanes also detect low battery voltage then shut off the motor when the battery needs re-charging.
The airplane manufacturer supplies a 2-cell charger that works perfectly.

My local hobby store sells high quality Li-PO batteries that are not the cheap junk sold online.
Look at this online fake battery:

 

[Satoshi Deguchi]

Suitable battery protection modules are readily available on ebay, amazon & aliexpress etc.

They are often labelled as "BMS" boards, battery management system - which is rather inaccurate, they are definitely not a complete management system!


For a single cell voltage, either one cell or two or more parallel so still the same voltage, you need under / over voltage protection and short circuit protection.

For two or more cells in series, it must also include cell balance, to avoid the cell voltages becoming uneven, as that is one of the common causes of battery failure or fire; if any one cell has a higher charge than the others, that can overcharge and fail before the overall battery voltage reaches the charge cut-off point.

Search eg. ebay for Lithium BMS and you will find a vast selection; a couple of example listings:

Lithium Battery BMS 18650 Charger Protection PCB 1S 2S 3S 4S 5S 6S Li-ion Li-Po | eBay

It also features over current and short circuit protection. Model 3S 12.6v 20A lithium battery protection plate (with Recovery function -AUTO Recovery). Module:1S Li-ion Lithium Battery Protection Board.

www.ebay.co.uk

8S/7S/6S/5S/4S/3S BMS PCB Protection Board For 18650 Li-ion Lithium Battery Cell | eBay

Note:The balancing board must need BMS to use together,and the BMS is without balancing function.

www.ebay.co.uk

1S/2S/ 3S/4S/ 5S/6S/ 7S/10S/13S 18650 Lithium Battery Protection Board Bms | eBay

1S / 2S / 3S / 4S / 5S / 6S / 7S / 10S / 13S 18650 Lithium Battery Protection Board BMS PCB Specifications: Fine workmanship and durable. For the rechargeable (generally refers to the lithium battery) from the protection of the integrated circuit board. Lithium battery (rechargeable type) so...

www.ebay.co.uk

To find ones for a specific number of series cells, add eg. 1S, 2S, 4S or whatever the cell count is, to the search.

Make sure the module is rated at far higher current than the motor rating you will be using (presumably for a flywheel gun?)
Dc motors take many times the rated current when starting or if loaded so the speed drops down a lot.

And, be sure the cells are rated for an even higher discharge current! Too high current can overheat the cells and cause failure.


As well as the battery protection, you still need a proper lithium cell or battery charger. The voltage regulation is critical, and it must have a current limit within the cell charge current ratings.

An alternative approach for multi-cell batteries, as used with such as radio controlled flight systems, is have the balance part in the charger rather than the battery.

In addition to the main power connections, wires are brought out from the pack end and each cell to cell junction, with the charger having both power and multi-way connectors to suit.

Chargers for this system are generally fully programmable for cell type, count and charging current.

Example:

Turnigy Accucell 6 50w 6A Balance Charger 1-6S LiPo LiHv LiFe NiMh NiCd PB+LEAD | eBay

Find many great new & used options and get the best deals for Turnigy Accucell 6 50w 6A Balance Charger 1-6S LiPo LiHv LiFe NiMh NiCd PB+LEAD at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Another advantage with those is that they can often operate either from such as a laptop power brick, or 12V from a vehicle.

(Or use standard size cells such as 18650 type, in holders, & remove / exchange them for charging).

For the 2s batteries I am looking at, I believe they are in series. I am using them for flywheel Nerf blasters.

If I buy a BMS board for a 2s battery, how would I install it? Do you know of any tutorials?
This is the style of battery I would be using:

Tattu 1050 mAh 95C 2s LiPo

PLEASE NOTE: LiPo batteries can only ship within the USA and have longer delivery times due to the way they are transported. Shipping options are UPS Ground or USPS Parcel Select Ground only. Please review our FAQ for up to date shipping estimates. *LiPo BATTERIES CAN BE DANGEROUS! OUT OF...

outofdarts.com

 

[audioguru]

Buy a BMS board that has a good translation of its foreign language into your language.
Many have only Chinese instructions.

 

[rjenkinsgb]

This is the style of battery I would be using:

That is a type intended for use with the separate balance charger; it has both the two main power connections, and a three pin balance connector.

As long as you get a suitable charger, the only protection needed in the gun is for undervoltage and short circuit protection.

This looks like it could be suitable, if you use the external balance charger; it does not appear to have components for balance, only protection:

2S 20A 3.7V BMS Balanced Charge LiPo Battery PCB Board 8.4V | eBay

Upper limit instantaneous current: 20A. Equalisers and Balance Boards. Short circuit protection. This module balances charging batteries, it does not balance discharging. If you want this as well, I have them here.

www.ebay.co.uk

Or this one if you want to keep everything fixed in the gun, and just use a two-pole charge connector, though it would do no harm with the removable battery:

2S 20A Balanced Charge & Discharge LiPo Battery BMS PCB Board 8.4V | eBay

Upper limit instantaneous current: 20A Storage condition: -40-- +80°C. Short circuit protection. Equalisers and Balance Boards. Internal resistance: less than 300mΩ. 4.2V : First cell Positive or where is first and second cell connection, middle connection.

www.ebay.co.uk

With either of those, the 0V, 4.2V and 8.4V connections are the battery (negative, cell to cell link & positive) and the gun circuit connects to the + and - pads.

Use an XT60 connector for the main battery connections, if you want to keep it as removable/swappable; the centre point tap only needs to be a smallish wire.

If you want to keep the balance connector on the battery, you will need a 3 pin JST pin header, with the middle pin connected to the BMS board 4.2V pad.

Or get a 2S balance extension & cut it down, eg.

JST-XH 2S Lipo Balance Extension Lead Cable 400mm | eBay

JST-XH 2S balance extension lead suitable for use with Lipo batteries, featuring 400mm length and PVC insulated cable.

www.ebay.co.uk

The outer pins on the balance plug are only needed with the separate balance charger.

If you want to put the balance board in the gun and use a simple charger, you will need a 8.4V lithium battery charger; they are commonly used for bike lights etc., and usually have a "Roca" style connector, 5.5 mm outer and either 2.1 or 2.5mm inner.

You would then use a socket like one of these on the gun:

DC Power Connector Socket Jack Female Panel Mount 1.3mm 2.1mm 2.5mm | eBay

Range of DC sockets available in the most popular sizes, suitable for a range of PCB, inline and panel mounting applications. 1.3mm x 3.5mm Panel Mount 1.3mm 3.5mm 8mm 0.5A 30VDC. 2.1mm x 5.5mm Chassis Mount 2.1mm 5.5mm NA 2A 16VDC.

www.ebay.co.uk

The charger wires would connect to the BMS + and -, the same as the gun power.