Urgent!!! Need Help on on an e-bike conversion to LiFePO4...

Thread Starter

dyckie

Joined Apr 26, 2023
5
Okay, so I'm having hip replacement in a few months and bought a mobility scooter from an estate sale recently and the old lead acid batteries are kaputt... specs are 5 x 12v, 500W motor:

https://ebikepros.com/e-bikes/mobil...ooter-scooter-for-disabled-comfort-black.html

Very similar model to the Daymak Roadstar and several Emmo models, you see them every day here in Southern Ontario...

But when you look at replacing the batteries, it's hard to get a straight answer. I went to two reputable e-bike shops here and they were oddly mum, trying to sell crappy lead acid replacements at 5 x $90...

Looking at five of these bad boys in series, which would cost around $900:
https://www.amazon.ca/gp/product/B08VD88Q9K/

I know that charging could be a hassle (periodic "rebalancing", etc.), along with a new charger, but this is the best way to go, right?
 

MrChips

Joined Oct 2, 2009
31,083
Welcome to AAC!
I would go to Sayal and buy replacement lead acid batteries.
Learn how to take care of the batteries and you should get 3-5 years life out of them.
 

Thread Starter

dyckie

Joined Apr 26, 2023
5
Welcome to AAC!
I would go to Sayal and buy replacement lead acid batteries.
Learn how to take care of the batteries and you should get 3-5 years life out of them.
Really, really wanna go lithium if I can keep the cost around $1000...
 

MrChips

Joined Oct 2, 2009
31,083
The three middle batteries were overcharged. They got hot and the cases got deformed under the internal high pressure.
 

Thread Starter

dyckie

Joined Apr 26, 2023
5
Okay thanks, but you're kinda proving my point here... why on God's green earth would anyone wanna go back to lead acid with long charge times, finnicky charging, cold temperature concerns and about three times the weight?!?!? There are thousands of these types of scooters on the road and virtually no one offering a viable 60V LiFePO4 battery swap/solution!!!
 

Sensacell

Joined Jun 19, 2012
3,501
Not that simple.
You basically need to re-engineer the charging system to suit the new battery chemistry.
That's why nobody wants to touch this- a liability nightmare.
 

Thread Starter

dyckie

Joined Apr 26, 2023
5
Not that simple.
You basically need to re-engineer the charging system to suit the new battery chemistry.
That's why nobody wants to touch this- a liability nightmare.
DING DING DING! The bike shops/sellers/mechanics don't want to touch it, yet the LiFePo battery guys are like "go nuts, buy my batteries, they will work waaaaay better!!!"

Does anyone have some tips on how to do this safely and properly?
 

MrChips

Joined Oct 2, 2009
31,083
Sealed lead acid battery (SLAB) is proven technology with a solid track record. They are very robust and can take a lot of abuse.
I use them on my ebike, lawn mover, UPS, emergency lighting, back up power, etc.
 
Lead acid batteries will tolerate overcharging due to imbalance to a certain point. In series configuration this is common practice after balancing electrolyte gravity and is known as an "equalization charge".

Lithium cells will absolutely NOT tolerate overcharging. Hence you will need to add a battery management system to keep all of the batteries balanced so none of them will overcharge. Failing that, you'll kill the cells as shown above.

You will also get less performance compared to lead acid. Lead-acid cells are nominally 2V, with 6 cells in series for 12V. Lithium cells are nominally 3.7V, with 3 cells in series for an average voltage of 11.1V. Lithium cells also have a wider operating voltage range, meaning they will drop well below that nominal value as they approach full discharge (3-3.5V/cell) and well above it at full charge (4.1-4.2V).

---

Biggest things that kill lead-acid batteries:
- Discharging them beyond 50% DOD
- Modern battery chargers with excessively high voltage settings repeatedly/continuously boiling off the electrolyte.

If you want to make lead-acid last, get deep-cycle wet cells that you can service. Maintain the electrolyte levels and keep the electrolyte gravities balanced, charge them at a gentle voltage and do not discharge them beyond 50%. Desulfate and equalize once in a while.
 
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