GEL vs AGM for mobility scooter

[pollenface]

I'm just wondering if there's any specific reason that GEL might be better in powering a mobility scooter vs AGM. I recently picked up this speed demon for the kids to play with and it currently has a pair of 60ah GEL batteries. I might plan on replacing them with a pair of bigger AGMs unless I can be convinced otherwise....

 

[meetyg]

I actually did a 24v 40Ah Lifepo4 DIY swap for my dad's mobility scooter, instead of the AGMs he had.

I didn't have the time to take pictures of the installation, but I did take pictures of the build.

If your interested, I can elaborate more on the build and design.

My dad would replace the AGMs (2 x 12v 33Ah in series) about every two years (he uses the scooter daily, mainly around the house, about once a week outside of the house).

Now with the Lifepo4, it only goes down a few percent every week. Previously he needed to charge them every week.

I used a JBD BMS with Bluetooth, and installed a AiLi shunt with display.

 

[pollenface]

If your interested, I can elaborate more on the build and design.

yeah why not

 

[jberger]

Just remember that the scooter uses all that lead as ballast, so you can make it tippy if you lighten it up too much.

 

[meetyg]

I wanted to post a show and tell thread for a while... Maybe I will do that soon, and you will get all the info.
I'll keep you updated.

But for now:
The main reason for doing DIY and not just buying drop in Lifepo4 replacements for the AGMs, was size constraints.
I wasn't able to find a 24v Lifepo4 battery that would fit the battery compartment.
Maybe I could have gone with two 12v Lifepo4 in series, but I was worried about the batteries keeping balance during charging/discharging.

Also, I wanted to be able to monitor the battery closely. Relying on the battery meter he has on the scooter is not relevant for Lifepo4 batteries, because of their flat voltage curve. That's why I added a shunt with display, and installed it on the handle bars of the scooter.
The JBD BMS with the Bluetooth app is great, but takes a while to learn and tweak.

In short, if you plan to go DIY, you have to know what your doing.
This was my first DIY Lifepo4 build, but I did it after a few months of studying, reading, getting advice on this forum, and endless hours of YouTube videos.

I also was able to get the electrical schematics for the scooter and the manual for the motor controller, (Curtis 1210) which was very helpful in planning the build, installing and making sure everything is within spec and safe.

For now my dad is really happy with the Lifepo4 (installed it about two weeks ago). It made the scooter alot more peppy, and gives longer range: You can only discharge AGM/GEL/SLA batteries to 50% of their rated capacity, without damaging them. Even then, you only get a few hundred cycles (charge/discharge) out of them. With Lifepo4, you get a few thousand cycles with 80%-90% depth of discharge.
So if before my dad had around 16Ah net capacity (half of 33Ah), now he has 35Ah net capacity (out if 40Ah cells, which I limited to 35Ah using the BMS parameters and Lifepo4 charger voltage).

The scooter is a TGA Superlight SL3, with a 250w (nominal), 25A (max/peak) 24v motor (rear wheel drive).


It's fairly old (they don'tmake them anymore), but it's compact and my dad loves it.

 

[meetyg]

Just remember that the scooter uses all that lead as ballast, so you can make it tippy if you lighten it up too much.

Or do what I did: double the net capacity, and get twice as much range with around 50% of the weight.
My 24v 40Ah Lifepo4 battery weighs around 10-12kg, while each 12v AGM was around 10kg (20kg in total).
So still heavy, but less than before. I think the motor and transaxle weigh enough to keep these scooters fairly balanced.

 

[pollenface]

A bit of googling, I found this answer

Comparing the Two Battery Types​

Gel batteries tend to lose power faster than AGM batteries, especially at lower temperatures. This is because of the gelled Thixotropic composition of the battery. AGM batteries work in extreme weather, making them suitable for power-hungry winter utilities such as snow-mobiles.

When it comes to Depth of Discharge (DoD), Gel batteries make use of acid better than AGM batteries. Acid protects the Gel batteries’ plates, enhancing their deep discharge applications. However, a Gel battery must be recharged correctly, or else it will suffer premature failure. A scar inside its jelly material can create packets that will corrode the plates.

AGM batteries are comparably cheaper than Gel batteries, but they present a longer life span and offer bigger bursts of amps when needed. These batteries work best in high-power usage, such as sports vehicles.

Conclusion​

AGM Batteries outsell Gel types when it comes to durability, long life and charging. They are also less expensive and work in different weather conditions.

Gel batteries, due to their gelled composition, present less leaking percentage when compared to AGM batteries.

 

[Substrate]

To get the real scoop and avoid sales hype, read nearly 10 years of experience from those who actually live on these things - unlike marketing departments:

WheelchairDriver • View topic - PINNED - AGM & GEL battery info lead battery info

everything powerchair

www.wheelchairdriver.com

The gist is that in this application, low internal resistance and the largest capacity you can stuff in is the way to go. And if you go AGM, that usually means an expensive Odyssey pure-lead agm.

Unfortunately, most mobility chargers UNDER-charge batteries to death (hard sulfation walk down with inadequate time and the usual 8ah xlr connectors for charge). Charging the $$ Odysseys wth an external charger actually fit for the job is the way to go.

Tip: If replacing gel/agm for LFP, what you don't want to do is merely exchange like capacities for like - although that alone might give you a 30% boost in range, the better idea is to fit in as much LFP capacity as you can - which is many cases is achieved by NOT using prismatics, but constructing your own battery to take advantage of as much space as possible.

NO bms. Balance only during charge. High amperage inductive motors can easily exceed a bms' built-in protection shutdowns - like doing 180's on a carpet rug.

Highly recommend that site for this type of application, unlike here where sub-c general purpose power storage is the emphasis.

 

[pollenface]

Thanks for your answer, the one I'm working on has a 550w brushed motor.

 

[Substrate]

Glad to help. Search that site for brushless motor threads. You'll probably see what works best with other controllers like robotek and what have you...

Ultimately, wheelchair technology - apart from just batteries - is sadly so behind the times it isn't funny. Almost barely past turn-of-the-century heavy lead tank chairs etc..