Battery Fires

[nigelbb]

Fire deaths over time in the UK. There has been a massive decline in deaths since 1985. A reduction of two thirds.

Fire-related fatalities in Britain 2023 | Statista

There were 321 fire-related fatalities in Great Britain in the 2022/23 reporting year, a decline on the previous reporting year when there were 335.

www.statista.com

There are many factors contributing to the fall in fire deaths. Non-flammable materials, materials that don't produce poisonous smoke etc & especially not forgetting oven chips (when did you last hear of a fire caused by a chip pan?).

 

[Woosh]

Just thinking off the top of my head, I wonder if the lower power density is more about the lower voltage of the LFP cells. Fully charged they are about 3.4v to 3.6v whereas the currently favoured cells are 4,2v. That difference is about 19% on its own and is obviously related to power output (P=IV).

here is a good LFP candidate for e-bike batteries: 32700-6AH LFP cells.
Typical specs: 32700-6.0Ah_Specification.pdf (shopify.com)
Each cell weighs 140g. 11S1P (1.5kgs) or 12S1P (1.7kgs) array is good enough for 16-20 miles.
You may need to add an energy meter to your pack because the discharge curve is different to what we are used to with NMC.

 

[Ghost1951]

There are many factors contributing to the fall in fire deaths. Non-flammable materials, materials that don't produce poisonous smoke etc & especially not forgetting oven chips (when did you last hear of a fire caused by a chip pan?).

Yeah - chip pans. I remember about forty years ago I was visiting my mum with my family and she made some chips to go with the meal and forgot to take the pan off the heat. We were just getting started on the meal and there was a sound of something falling over out in the kitchen. The dining room door was closed and Mum said, 'what was that'? and got up to look. When she opened the door, the smoke poured in and we quickly evacuated the kids and in the next twenty seconds Dad and I rushed to do something. The ceiling strip light and the nylon fan in the cooker hood were on fire and the pan had four or more foot flames pouring out of it. To be honest, the flames must have been higher at some point because the diffuser on the ceiling light was well ablaze. I switched off the mains (electric cooker) and rushed upstairs to get a towel to cover the pan (you couldn't really see much in the kitchen for black smoke, so I figured the bathroom towels would be easily got at) but when I got back down, I saw Dad had opened the back door and he made the mistake of taking the pan and throwing it outside. He burned his hair, face and hands and was bloody lucky not to have ended up a lot worse. The pan went off like a bomb outside when he chucked it.

The original warning sound was caused by a tile falling off the wall behind the cooker.

It cost a small fortune to repair all the smoke damage. The whole house was coated in sooty muck.

Not a great experience.

 

[StuartsProjects]

here is a good LFP candidate for e-bike batteries: 32700-6AH LFP cells.
Typical specs: 32700-6.0Ah_Specification.pdf (shopify.com)
Each cell weighs 140g. 11S1P (1.5kgs) or 12S1P (1.7kgs) array is good enough for 16-20 miles.
You may need to add an energy meter to your pack because the discharge curve is different to what we are used to with NMC.

So not withstanding that the battery monitor in a KT controller might be a tad confused by an LFP and not show the correct charge state, is there anyone building eBike batteries with these cells, even maybe custom ?

 

[Ghost1951]

here is a good LFP candidate for e-bike batteries: 32700-6AH LFP cells.
Typical specs: 32700-6.0Ah_Specification.pdf (shopify.com)
Each cell weighs 140g. 11S1P (1.5kgs) or 12S1P (1.7kgs) array is good enough for 16-20 miles.
You may need to add an energy meter to your pack because the discharge curve is different to what we are used to with NMC.

I wonder how the terminals are on that battery type. I did consider buying some LFE cells with screw terminals. Some have a stud at either end and others a threaded hole. That kind of format would suit amateur building since you could simply bolt the cells together on bus bars. No welding needed. I doubt I will do it, but I might do.

The specs and tips and warnings in that data sheet are pretty funny. 'Never knock, throw, or trample the battery.'

 

[saneagle]

You also have to think about how to mount the battery. You need a case of some sort and a way to fix it to the bike.

 

[Ghost1951]

You also have to think about how to mount the battery. You need a case of some sort and a way to fix it to the bike.

Yes - there is a fair bit to plan and do. Those triangle bags might help on that issue. On the other hand, you would need to protect the cells from damage if the bike was dropped or fell over while parked, a thing that happens more than i would like.

 

[Woosh]

So not withstanding that the battery monitor in a KT controller might be a tad confused by an LFP and not show the correct charge state, is there anyone building eBike batteries with these cells, even maybe custom ?

My regular supplier can build LFP-21700-3200mAH in 12S3P (36V9.6AH) into Hailong cases.
Who would be interested?
I am waiting for the new higher energy density generation of LFP cells.

 

[Ghost1951]

My regular supplier can build LFP-21700-3200mAH in 12S3P (36V9.6AH) into Hailong cases.
Who would be interested?
I am waiting for the new higher energy density generation of LFP cells.

I'd be interested in the future when my current mid drive bike battery needs replacing, but I would want about 13 Ahr really. I realise the difficulty of getting a lower output battery technology into a limited volume. I think we would need a different kind of case.

If I was making something, I might consider a kind of rack and pannier system with half of the battery on one side and the other half on the opposite side. That way, the weight could be kept low. My half baked idea is that we would have something around 20Ahr LFP cells with 6s on one side linked by suitable gauge wire to another 6s on the other side. How many in parallel would depend on the cells. One obvious problem might be to do with the length of the balance wires from the BMS. They would likely need to be extended. I am imagining the cells being sandwiched for protection in some sort of light plywood structure, so they could not easily be bashed if the bike fell over. Cables over the top of the pannier would be in trunking.

I am sure this plan will be shot down in flames...

 

[Woosh]

I'd be interested in the future when my current mid drive bike battery needs replacing, but I would want about 13 Ahr really. I realise the difficulty of getting a lower output battery technology into a limited volume. I think we would need a different kind of case.

the output is 28A continuous OK for LFP-21700-3200mAH in 12S3P (36V9.6AH) batteries. Plenty of power. The problem is those cells are still not as energy dense as those going into current models from Chinese EVs like Geely or BYD.

 

[thelarkbox]

I'd be interested in the future when my current mid drive bike battery needs replacing, but I would want about 13 Ahr really. I realise the difficulty of getting a lower output battery technology into a limited volume. I think we would need a different kind of case.

If I was making something, I might consider a kind of rack and pannier system with half of the battery on one side and the other half on the opposite side. That way, the weight could be kept low. My half baked idea is that we would have something around 20Ahr LFP cells with 6s on one side linked by suitable gauge wire to another 6s on the other side. How many in parallel would depend on the cells. One obvious problem might be to do with the length of the balance wires from the BMS. They would likely need to be extended. I am imagining the cells being sandwiched for protection in some sort of light plywood structure, so they could not easily be bashed if the bike fell over. Cables over the top of the pannier would be in trunking.

I am sure this plan will be shot down in flames...

A one or 2 off passion project perhaps, as a viable product? You will need a suitable rack/container system to be provided at a reasonable cost, adding a £20 rack to the final price will be cheaper than ensuring a fit all racks solution, and then you may as well incorporate the rack base or its underside for the bms housing etc.

Its the sort of product that would grab my attention followed by a sharp intake of breath when the price is finally revealed. - but im so tight i squeak so..

keep mulling it over until inspiration hits

 

[Ghost1951]

the output is 28A continuous OK for LFP-21700-3200mAH in 12S3P (36V9.6AH) batteries. Plenty of power. The problem is those cells are still not as energy dense as those going into current models from Chinese EVs like Geely or BYD.

Do you think that the difference in energy density between LFP and our current cobalt/nickel/manganese chemistry might be about the lower voltage of the LFP cell, or is it something else? Just looking at it from an ignorant point of view, the voltage difference of the charged cells is 20% lower for the LFP ones. That will I think lower the energy you can get out of them. Of course for a 36v nominal battery you would for LFP go from 10s to 12 s to counteract that. Bigger and heavier of course by doing that.

 

[Ghost1951]

A one or 2 off passion project perhaps, as a viable product? You will need a suitable rack/container system to be provided at a reasonable cost, adding a £20 rack to the final price will be cheaper than ensuring a fit all racks solution, and then you may as well incorporate the rack base or its underside for the bms housing etc.

Its the sort of product that would grab my attention followed by a sharp intake of breath when the price is finally revealed. - but im so tight i squeak so..

keep mulling it over until inspiration hits

Yes - I keep reading that LFP cells are cheaper but when I look around for prices I don't see that. I am only thinking about this matter at all because of the safety issues of abused and defective manganese/cobalt/nickel chemistry.

I was not of course imagining a saleable product here. Just notions about how I could construct an LFP battery out of suitable cells for my own bike.

 

[Woosh]

Do you think that the difference in energy density between LFP and our current cobalt/nickel/manganese chemistry might be about the lower voltage of the LFP cell, or is it something else? Just looking at it from an ignorant point of view, the voltage difference of the charged cells is 20% lower for the LFP ones. That will I think lower the energy you can get out of them. Of course for a 36v nominal battery you would for LFP go from 10s to 12 s to counteract that. Bigger and heavier of course by doing that.

You can look at the lower gravimetric density from the voltage point of view. The issue remains that only a few companies and they are very large producers have the new technology to make denser cells. Until they make 21700 cells with their new technology, I am stuck with 5 year old technology.

 

[nigelbb]

Yeah - chip pans. I remember about forty years ago I was visiting my mum with my family and she made some chips to go with the meal and forgot to take the pan off the heat. We were just getting started on the meal and there was a sound of something falling over out in the kitchen. The dining room door was closed and Mum said, 'what was that'? and got up to look. When she opened the door, the smoke poured in and we quickly evacuated the kids and in the next twenty seconds Dad and I rushed to do something. The ceiling strip light and the nylon fan in the cooker hood were on fire and the pan had four or more foot flames pouring out of it. To be honest, the flames must have been higher at some point because the diffuser on the ceiling light was well ablaze. I switched off the mains (electric cooker) and rushed upstairs to get a towel to cover the pan (you couldn't really see much in the kitchen for black smoke, so I figured the bathroom towels would be easily got at) but when I got back down, I saw Dad had opened the back door and he made the mistake of taking the pan and throwing it outside. He burned his hair, face and hands and was bloody lucky not to have ended up a lot worse. The pan went off like a bomb outside when he chucked it.

The original warning sound was caused by a tile falling off the wall behind the cooker.

It cost a small fortune to repair all the smoke damage. The whole house was coated in sooty muck.

Not a great experience.

Does anyone remember those expanded polystyrene ceiling tiles that were all the fashion in the seventies that when ignited dropped gobs of napalm? It took quite a few years before those formulated without fire retardant were banned.

 

[lenny]

Delivery firm boss was unfairly sacked after warning his company's e-bike batteries could spontaneously burst into flames

Delivery boss unfairly sacked over e-bike warning

Sebastien Potts warned chief executive of Swedish delivery firm Urb-it that there was a high risk of fire in the hubs across London where the e-bikes were stored.

www.dailymail.co.uk