Lithium Power Packs

[Carbon Brush]

There are a lot of threads on SGL where advice is being sought on buying lithium based power packs as an entire 'lump' or going down the DIY route.
There are a lot videos on news channels and social media showing big fires resulting from charging or using lithium powered devices.
Clearly lithium power is a big safety issue. How do we stay safe?

If (like 99.9% of the population) you have little knowledge of the safety aspects of using lithium power, you have to rely on the pack being built to a good standard.
Always stay with the known names. These people ensure you cannot charge or discharge the pack beyond a safe limit and they take other measures to prevent fires.
Buy a known name every time. I mean the likes of Tracer, though there are others.
Just because something is on the Long River site, it does not mean that it is safe. They are known to sell a lot of electrical junk with fake approvals markings.

In past few moths I have built up a few power packs (for an amateur radio club) using cells that have been removed from equipment, but are known to be good.
For the Battery Managment System (BMS) I used proprietary boards purchased from Long River.
This is a standard BMS assembly, used by the million world wide. Why re-invent the wheel?
1 out of an order for 5 units was dead on arrival.
A further unit is too enthusiastic. It shuts down the 10A pack if loaded to more than 0.5A for 10 minutes. At least it fails safe🤣.
The remaining uints are still in test.
So it looks like when you buy BMS assemblies for 3/4 cells (astro kit size) you need to test their performance on load resistors or lamps before putting them into service.
It may let you down part way through a sesion. It may not protect!
Do not believe that buying an assembled tested assembly from a retail seller gets you a working product.

Moving on now to an ebike (otherwise known as a domestic and commercial property destroyer) experience.
I was asked to look at one that would not charge. Normally I would say no. Reluctantly I agreed. It was for someone who was struggling otherwise I would have just said buy a new one.
After dismantling the battery pack (lots of acrylic sealant) I eastablished the cells were looking good. The BMS had failed.
Again, why re-invent the wheel? There are millions of ebikes worldwide using a 10S 5P configuration. I can just buy a suitable BMS for £20ish and not send a huge lithium stack to landfill.

The first BMS arrived from Long River. The PCB had pads that looked like thermistor connections. But the connection information did not mention a thermistor.
Web site pictures showed a thermistor on wires.

Why/what is this thermistor thingy? This is a temperature sensing device that is embedded somewhere in a battery pack.
Cells can only be charged or discharged in a limited temperature range. Work them outside the allowed range and best you damage them. At worst there is fire and explosion.
Knowing cell (not the room, or other parts of the equipment) temperature is therefore vital.

I queried the absence of a thermistor connection with the seller. He said that it did not need a thermistor and I should not attempt to fit one.
So should I fit the BMS without thermal protection because some nameless overseas seller claims it is not needed? Strangely lithium cell manufacturers think otherwise!
Do I risk my friends life and home if he does not diligently observe charging conditions for himself?
Fortunately Long River have easy returns.

A second BMS was ordered, again with a connected thermistor shown on the web page.
No prizes for guessing this did not have a thermistor, so it was was returned for refund. I did not engage with the seller this time.

A third BMS is on the way as I type. I shows a thermistor in the pictures - but also mentions thermal protection in the (broken English) product description.
Perhaps I will be 3rd time lucky? I await the delivery with interest!

Lithium power packs for astro kit are not any more dangerous than many of the other electrical power sources and flammable fuels that surround us daily.
The problems only start if they are not design and applied correctly.

Stick to the reputable manufacturers. They may be pricey.
But you won't cause you to have security camera footage showing your home in flames on the news web sites.

You may have successfully used a <insert brand> pack for a couple of years and not encountered a problem.
Have you asked the supplier for copies of the test certificates? He MUST be able to point you to them.
Have you tested that it switches off if too hot, or too cold?
What is the end of charge determination? Important if you walk away and leave it plugged in. Overcharge=fire.
If you leave it running into a load, at what point (voltage) does it switch off? Or does it just run until completely dead?

Bottom line. You have 3 options...
1.   Buy a known brand with traceable approvals certificates.
2.   Build for yourself and test every component.
3.   Do you feel lucky? Were you thinking of moving home anyway? Is you life insurance up to date?
 

[Elp]

The thing is, are you going to test absolutely every single battery that enters or is near your home (phones, tablets, laptops, smart devices, cars etc), what if guests come to your house and request to charge?

Some common sense needs to be placed with batteries like never leave them charging unattended, and place in clear spaces away from flammable materials.

One of the things that needs to be checked is battery bloat, I've had many older camera, phone and laptop batteries which have bloated over time certainly not safe for use and I'm sure not many people check for this, sometimes the change can be very minor. In the case of enclosed devices, well you can't really check for this at all unless something else goes pop (unresponsive screen or buttons for example, bloated chassis).

Edited July 2 by Elp

[Carbon Brush]

Battery bloat. Yes @Elp it is an issue. Thank you. Usually bloat means a battery has electrically degraded, prompting you to take a look inside the equipment.
I once had a really bloated cell in a dashcam. The bulging cover being the giveaway. Electrically it was dead. The electrolyte had been lost somehow.
It was something like the one shown below.

 

But of course 18650 and the larger 21700 cylindrical cells used for higher power have very robust cases.
If you detect bloat in these, it means there is very high internal pressure. Bang is imminent!

Certain batteries and equipment I will take on trust. For example a Samsung phone, a Canon camera.
These people will have chosen cells wisely, handled them correctly and sought approvals testing.
Certain others I will not trust. The <never heard of> powerbank for example just bought for a 'today deal' bargain price.
As for visitor equipment charging. The same rules apply.

The case shown can hold 16 cells, 18650 to make a power bank. You may buy known name cells that are safe.
But what is the charge regimen? What protection is in place?
The case does not have any safety approvals.
It is defintely on the 'not trusted' list!



If working with dodgy name products as @elp says, don't just leave the battery on unattended charge. In addition, ask yourself what happens if it goes bang?
An exploding battery will wreck your kitchen worktop and mean you have to redecorate - even if you are quick with a fire extinguisher.
If it pops on some paving outside, there may be a stubborn stain!

Going back to the ebike I mentioned earlier. All testing was done either outdoors, or in the garage sheltering from rain, with the door open.
The battery pack was left unattended outdoors between tests & BMS swapping - in a waterproof garden cable box, well away from the house and fencing.