Choosing battery chemistry for a light mobility scooter

[Valman]

I'm based in the UK.

Existing family member's mobility scooter has 2x 60w motors 12v 5.5A going through a

https://scooterland.net.au/wp-content/uploads/2017/04/DS60-70-Dynamic-Controller.pdf

24v motor controller connected to 2x 12v 7ah SLA batteries

The battery compartment is solid aluminium so I'm limited to its dimensions of 151mm wide X 235mm long - it would be nice if I could keep height below 90mm but I could go higher and modify the plastic cover if necessary.

I'm looking to convert the battery to something lithium-based. How can I choose between NMC and LiFePO4?

I cant find specs for those 2x motors, but I can't imagine they're pushing the limits of the controller where the specs say it limits current to 74a for 10 seconds

It seems like LiFePO4 has longevity with around 2000 cycles, NMC seems to be significantly less cycles, about 500-600, but with higher capacity. So far nmc seems to be much more expensive than LiFePO4, but I'm really lost among so many chemistries, cell formats and sizes pouches, 18650s, 21700s and just today I'm discovering that there are even more cylindrical cell sizes in lifepo4
http://www.headway-cn.com/en/products.php?pid=95

I'm trying to take some sort of logical approach here, and I'm thinking - decide chemistry first, then decide cells?

the objective is to maximise the scooter's range, (lighter is a bonus too as it's taken in/out of car regularly)

So.. any advice on choosing LiFePO4 vs NMC? I've read in a few places that everyone seems to be moving to NMC, but I'm not sure I fully understand why, or whether for my needs NMC would somehow be a better choice - any help appreciated!

 

[flippy]

I built several batteries for these exact scooters.

Grab/build a 7S lipo battery and ignore chemistries. Just dont bother with lifepo, its too expensive and cumbersome.
If you fill the entire battery bay you can increase the range by about 5 times compared to a normal lead acid.

 

[john61ct]

LFP will indeed last much longer, even a decade if cared for well.

It is also much safer, less likely to ignite, aka "thermal runaway".

But the range per charge, while 3-5x greater than the original setup, will it's true be lower than the higher density lower lifetime LI chemistries.

And it's more expensive.

 

[flippy]

if cared for you can get thousands of cycles out of regular lipo as well, so that's not an argument, same goes with fire. this load is so low that the cells would never see any stress.
the last battery i made for a mobility scooter like this i gave 10 years warranty because it simply wont wear out until the owner does something to total the scooter.

 

[Valman]

Thanks for the responses -

"Ignore chemistries"?

what's "Regular lipo"? thanks! LiFePO4 = LFP = Li-phosphate (short forms), right?

 

[john61ct]

LiPo is Lithium Polymer.

A physical packaging technique, not indicative in itself of the actual specific chemistry, used over time with many different ones.

compared to LFP, LiFe, LiFePO4, iron (ferrous) phosphate


All LiPo are

higher-energy density
higher-power density
higher thermal risk

under equivalent treatment, much shorter lasting, by a factor of at least 4-10x number of lifetime cycles

lots cheaper

These days most LiPo are lithium cobalt oxide (LiCoO2, a.k.a. LCO)

 

[dogman dan]

For the best safety,( no fires when charging) there is only one choice, lifepo4. Pingbattery is a vendor with a very long track record.


Lifepo4 is the one chemistry with a great deal of tolerance for an overcharge, others, bad things can happen if a bms fails to operate as normal during charging.


I run lots of lipo myself, but I don't allow it in my house. Maybe I'm biased, since an 18650 cell lithium manganese cobalt battery burned my house while I was sleeping. That was supposed to be the "safe enough" chemistry. Even before the fire, I did not treat lipo (lithium cobalt) casualy. Lots of lithium cobalt batteries have started fires.


FWIW, you will get a ton more range just switching to lifepo4. But yes, a more compact chemistry such as used in the 18650 round cells would pack more capacity in the same space. But since my fire, I keep those kind of batteries outside now, with my known to be hazardous lipos.

 

[flippy]

guy's please dial down the doomsday rethoric about lipo. its misplaced and you know it.

there are litteraly dozens of lipo's in EVERY house and room and even your pocket or your hands right now (if you read this on a phone) that dont explode.

 

[john61ct]

No, I do think that extreme caution is appropriate.

LI batteries are randomly exploding in people's pockets and starting house fires, cars, airplanes all the time.

They even give much safer LFP a bad name, which is completely unjustified.

I even feel OK charging LFP unattended under my bed in a small enclosed mobile living space with my kids.

I would never do anything like that with any other LI chemistry.

 

[john61ct]

In use close to humans, especially charging with automated gear not observing the voltage

I would not use anything other than LFP, except when the higher energy density is absolutely critical to the use case.

As for example with flying models.

 

[flippy]

Litteraly billions of people (INCLUDING YOU!) charge their phones, laptops, cars and tools without any issue every day. Please dont let singular events you see FW:FW:FW:FW on youtube and facebook as what they are: extremely rare events that are so rare it still makes the news if it happens.

 

[docware]

Flippy is absolutely right. We use bilions phones and laptops with Lipo every day. I also appreciate his ample experiences. But, there is one factor we have to consider - producer :

https://www.mpoweruk.com/china_batteries.pdf


So, if you choose Lipo, try to have one from reliable production.
By the way, LFP is probably not exluded from the risk if not sourced from reliable factory.

 

[Headrc]

This is a guy who knows batteries and explains why he chose the batteries he uses for his powerchairs ....it is at least worth a read.

http://www.wheelchairdriver.com/

Check out the forums also from his website ...he and the folks on his forum need to pick the right technology for their application ...their life and well being depend on it.

 

[999zip999]

Bye from a reliable vendor such as ping ,em3ev or ? No fleabay.