electric wheelchair battery questions

[ken barrett]

im desperately trying to find lifepo4 batteries for my wheelchair. it calls for 2 agm 12v 55ah. all im finding is 50ah and 20ah lifepo4's. my question is can i link a 50ah and a 20 ah battery in parallel for a total of 75ah at 12v to my chairs controller. So total batteries to be used is 2 50ah and 2 20ah. this upgrade sounds feasible to me. Any ideas people? Size restriction is a problem otherwise id go with bigger batts. i have 2 12v 55ah agm right now and they suck. lifepo4 is the only way to go in my mind. so do i get a couple 50ah and 20ah or do i build my own batteries from scratch. I have room to add the extra 20ah batts. ill have to custom mount the 20ah batts. someware on my chair but its doable. Ideas? Links? Thanks beforehand for your comments.

 

[DIYrich]

aH refers to how much total power it stores. AGM discharge 30% (regular) to 50% (deep discharge) of their rated capacity. So the usable power of a 55ah AGM is 17-27 ah.

A 50ah LiFePO4 can discharge 70-80% of its capacity (stay within 10-80% or 10-90%), or 35-40aH, well above the 55ah AGM.

No need to link 2 batteries for the same power delivery as the AGM. If you want more run-time on a single charge, then linking will help.

If you want to link, the 50aH is the first connection from the wheelchair (existing battery connection). Then use a wire to connect to the same terminal (Red + to Red +; Black - to Black -) on the 20aH. That will wire them in parallel.

 

[MisterSandals]

im desperately trying to find lifepo4 batteries for my wheelchair.

What wheelchair do you have?
I looked into this for my father and found that shopping by physical battery size was the first step. If you can find a single 24V battery (assuming your 12V batteries are connected in series) it is a lot easier.
But knowing the physical size of the battery compartment is a good first step.

 

[Supervstech]

What is the amp draw on the batteries now? LFP is usually limited to the amp hour draw, lead acid batteries are not. Make sure you factor in the ampdraw factor into your build.
Also, LFP with a BMS can leave you stranded if the cells are drained too far. Lead acid will keep going until dead… LFP will shut off totally when dropping below the parameters of the BMS.

 

[Supervstech]

Also, wheelchairs often are designed with balance around the weight of lead batteries, and switching to LFP can make some wheelchairs tip on grades that would not be an issue with lead…

 

[MisterSandals]

Once you upgrade to LiFePO4 battery(s) your existing battery charger will likely need to be upgraded to a charger that has a lithium or user defined charge profile.
I am a little fuzzy on the details (its been 2 years) of using a new charger but i realized i would need to bypass the wheelchair charging port and connect directly to the battery (or a make new charge port). There are smaller chargers than the 10" cube 24V charger that came with the Jazzy so it was very easy to keep it on the wheelchair.

The wiring harness of the Jazzy beast my dad bought (but did not need just yet and never used) was very complicated, largely undocumented and not easily tapped into.

I was considering this pricy NOCO because it also had a gauge that i was hoping would work when not plugged into a receptacle. The wheelchairs gauge would not be very accurate as it is designed for lead acid. Maybe useful after a learning period?

https://www.amazon.com/NOCO-GX2440-Ultrasafe-Industrial-Battery/dp/B01FRQQKBE

 

[meetyg]

When I did my dad's Lifepo4 swap for his mobility scooter, I used an AiLi shunt with display instead of the existing guage (which still works but is inaccurate).
For a charger, I used a WATE 24v Lifepo4 charger, and added an XLR port for it. I didn't want to rely on the existing chargers port and wiring, as it seemed to be a bit flimsy.

 

[ken barrett]

What wheelchair do you have?
I looked into this for my father and found that shopping by physical battery size was the first step. If you can find a single 24V battery (assuming your 12V batteries are connected in series) it is a lot easier.
But knowing the physical size of the battery compartment is a good first step.

Hello Sir. thanks for the help. I'm using a quantum q6 edge now but after measuring i still cant find the size batts. i need for it. i'm thinking i can possibly fit larger batts, in my jazzy select HD. It has 2 12v 55ah gels and I've seen a small form factor (mini) LiTime 12v 100ah. i'd need 2 of them. there a bit wide but they would fit the jazzy. this sounds ideal to me but finding reviews for said batteries is not going well. i just cant seem to find 55ah or 60ah lifepo4. i only find 50ah lifepo4 with weak bms. any ideas? Thanks for your time.

 

[ken barrett]

When I did my dad's Lifepo4 swap for his mobility scooter, I used an AiLi shunt with display instead of the existing guage (which still works but is inaccurate).
For a charger, I used a WATE 24v Lifepo4 charger, and added an XLR port for it. I didn't want to rely on the existing chargers port and wiring, as it seemed to be a bit flimsy.

Hello Sir. I'm wondering at what point, (according to the shunt) do his batteries voltage drop enough to stop the chair? and at what voltage should i start worrying about not making it home? Thanks for replying. there is alot of misleading info online. appreciate your time.

 

[SamDeleted]

Hello Sir. I'm wondering at what point, (according to the shunt) do his batteries voltage drop enough to stop the chair? and at what voltage should i start worrying about not making it home? Thanks for replying. there is alot of misleading info online. appreciate your time.

Unlike lead acid/AGM/gel ... It's very hard to tell a LiFePo4 battery's state of charge (soc%) from voltage

Battery could be at 70%soc or 30%soc and show almost exactly the same voltage


The only true way to tell is with a shunt that accurately measures amps in and amps out , and gives you a SOC reading


Victron smart shunt, bmv712 ect.

Also some cheaper models available like the AiLi battery monitor

https://www.amazon.co.uk/Voltmeter-Ammeter-Voltage-Current-Caravan/dp/B07CTKMLVD/ref=asc_df_B07CTKMLVD/?tag=googshopuk-21&linkCode=df0&hvadid=309857966843&hvpos=&hvnetw=g&hvrand=4659837625221613074&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9045262&hvtargid=pla-727538865484&psc=1

When wiring , you need to make sure all power in and out the battery goes through the shunt , any power that gets to or from the battery not through the shunt doesn't get read so you'll get an inaccurate SOC% reading.

Shunt goes on the neg side