New Wheelchair Batteries

[jbaker2290]

My son has a Permobile Koala Wheelchair it has two of the following battery inside

MK Battery 12v 40 AH Deep Cycle Sealed Gel Cell Battery

Batteries ship from various warehouses and usually arrive within 5 to 7 business days.

www.batterystuff.com

The dimensions of each battery is (LxWxH): 7.76 x 6.62 x 6.88 in
So total space is 7.76 x 13.24 x 6.88in.
I believe they are 12v, but wired in series for 24v system.
The current charger plugs into the joystick which I believe electrifies the 24v buss for the system to charge the batteries.
There is no other room then the space the batteries take up since it a smaller pediatric wheelchair.
We are going to be taking longer trips where he may be cruising around for 12-16 hour days. Im hoping to find a battery or build a battery (with guidance) that could give him longer days in the chair and make our trips easier.
Any advice, or ideas?

 

[John Frum]

Maybe this can be made to fit

50 Ah 24V LiFePO4 Deep Cycle Battery

The 50Ah 24V LiFePO4 Deep Cycle battery weighs a fraction of lead acid, is backed by a ten year warranty, and designed and assembled in the USA!

battlebornbatteries.com

That is 50ah@24 volts nominal
The benefit is you can use nearly 100% of it.
With the deep cycle lead acid you can only use 50%

What are the details of the charge profile?

Lifepo4 is not really a drop in lead acid replacement despite of what you might have heard.

 

[Sillyputty]

These might be a possibility - the 12V, 20AH batteries are 100% usable amp hours compared to the lead acid you've been using so they should give you at least as much range as you have now. The 12V, 40AH batteries are expensive, but should give you twice the range.

 

[curiouscarbon]

hello and welcome to the forum,

awesome idea!

i think it should be possible to figure out a lithium replacement battery that could charge properly from the existing charger, but more information is needed.

any info or photos of the chair? that might make it easier to look up into about the charger it has onboard.

looking forward to seeing where this goes

 

[Supervstech]

My son has a Permobile Koala Wheelchair it has two of the following battery inside

MK Battery 12v 40 AH Deep Cycle Sealed Gel Cell Battery

Batteries ship from various warehouses and usually arrive within 5 to 7 business days.

www.batterystuff.com

The dimensions of each battery is (LxWxH): 7.76 x 6.62 x 6.88 in
So total space is 7.76 x 13.24 x 6.88in.
I believe they are 12v, but wired in series for 24v system.
The current charger plugs into the joystick which I believe electrifies the 24v buss for the system to charge the batteries.
There is no other room then the space the batteries take up since it a smaller pediatric wheelchair.
We are going to be taking longer trips where he may be cruising around for 12-16 hour days. Im hoping to find a battery or build a battery (with guidance) that could give him longer days in the chair and make our trips easier.
Any advice, or ideas?

Two of these should drop right in,
Keep in mind they shut off if over 90C, or under 5C temps.

https://www.amazon.com/Phosphate-2500-7000-Lifetime-Applications-Iron-V/dp/B08P3YS9SD/ref=sr_1_34

 

[Substrate]

You may also want to visit the wheelchairdriver.com site and it's own forum.

Burgerman, a paraplegic engineer runs it. No Sales, so not commercial. Good forum too with a lot of information about lead-acid and LiFeP04 conversions, motors, welding etc etc. Their application (motive power) is different from here where we are mostly concerned with storage, so some design ideals are different and use different materials on purpose.

Those guys live on what they engineer, so a good resource for those in wheelchairs.

 

[Substrate]

The big thing that gets emphasized there in regards to GEL, which those MK's are is VERY strict control over your CV voltage, which in 12v terms would be no more than 14.1v, preferably temperature-compensated with a sensor. NOT 14.4v agm-type cv voltages.

(Of course double what I said here for a 24-volt system, ie no more than 28.2v for gel)

Decades back I went through the whole gel-vs-agm charging procedures and witnessed how industry and marketing tended to just tell users to use "sealed" cv voltages because the consumer couldn't understand the difference between sealed-gel and sealed-agm's!

Thus the tendency to say that it is "OK" for gel's to be charged to 14.4 like an agm. Wrong. That way the consumer doesn't have to have a specialized charger for each. So what if they damage the gel with 14.4? They just come back to buy new gel's sooner than later! Which by then had typically ballooned out and distorted.

When I came across Burgerman at wheelchairdriver say the same thing decades later, I freaked out. Thought I was the only one.

I've even seen gels have this wrong CV voltage printed on the case and spec-sheets! Marketing had taken it's hold over a few decades.

So please, no more than 14.1v CV - ever - on a gel even if the specs say so. Marketing relic from the old days if any higher voltages are spec'ed. Sells more gel's.

The second take away is don't be stingy with charging, typically long float times of 12-16 hours. Most don't have that kind of time to waste in a chair, but do it at least once a week so you don't walk-down the capacity by not charging that last little 1%, which adds up over time with hard-sulfation.

 

[Ed Tech Sensei]

I have an out-of-production Quickie P100 Powerchair from Sunrise Medical. It has a 24V power system but came with two battery boxes with 12V Deka 8AU1 AGM 32ah batteries. Each box has ring connectors, a 30amp fuse, and SB175 connectors for plugging into the power control module. I replaced the AGM's with Ironworks 44.7ah, 573Wh LiFePO4 batteries. They are a little larger than the U-series batteries but fit in the battery boxes. I also purchased a LiFePO4 charger.

The LiFePO4 batteries are much lighter than the AGM's although I did not weigh them. My joystick controller has a tri-color 3-bar battery meter. Green, yellow, and red similar to the Koala. I try not to run the battery past the third green bar. It only takes about 75 to 90 minutes to charge from 1 green bar to full. I have a 10amp charger but it not programable and does not have a charging rate indicator. I don't use the electric wheelchair that often, but it seems to be working and charging well with the LiFePO4's. I don't use it for longer than 15-20 minutes at a time so I'm not sure what my maximum distance or run-time would be.

I looked at the Koala owner's manual. The battery tray looks large enough to accommodate a variety of batteries or DIY battery packs. It looks like it's set up to run two 12V batteries in series.

 

[Substrate]

Cool on the LFP upgrade.

My first thought might be to do a capacity test on the sytem, and then install a coulomb-counter to measure how many ah you take out during a trip. Range? A person going a mile up and down San Francisco hills vs a person going a mile in the Kansas flatland will have vastly different draw.

You can see why agm's get killed in chairs pretty quickly though. If you are stuck with sulfated old stock from a provider, well, not much you can do about that. Plus the built-in chargers typically suck. Some are set for lower gel cv's like 14.1, may drop to float too soon - pretty much ensuring that premature sulfation capacity walk-down from undercharge happens on a regular basis.

So the first mod is getting a decent agm-specific charger to apply externally.

And, even if you take a trip just down the hall and back - best to give an agm a charge and full float of at least 8-12 hours before the next day's outing! Even with only that small amount taken out.

BUT, you won't have to worry about that anymore! You'll dig the LFP I'm sure.

 

[Ed Tech Sensei]

Cool on the LFP upgrade.

My first thought might be to do a capacity test on the sytem, and then install a coulomb-counter to measure how many ah you take out during a trip. Range? A person going a mile up and down San Francisco hills vs a person going a mile in the Kansas flatland will have vastly different draw.

You can see why agm's get killed in chairs pretty quickly though. If you are stuck with sulfated old stock from a provider, well, not much you can do about that. Plus the built-in chargers typically suck. Some are set for lower gel cv's like 14.1, may drop to float too soon - pretty much ensuring that premature sulfation capacity walk-down from undercharge happens on a regular basis.

So the first mod is getting a decent agm-specific charger to apply externally.

And, even if you take a trip just down the hall and back - best to give an agm a charge and full float of at least 8-12 hours before the next day's outing! Even with only that small amount taken out.

BUT, you won't have to worry about that anymore! You'll dig the LFP I'm sure.

Yeah, the AGM's are dead. I was thinking about trying to bring them back just to have extra deep cycle batteries but I don't think it's worth the hassle. The Ironworks batteries are about 10 years-old so I don't expect much from them capacity-wise. I haven't capacity tested them. They were fairly inexpensive ($150 each shipped) for 573 x 2= 1.146 Kwh if I get that much.

The manual stated a range of 15 miles with the AGM's which is plenty for me. I work at a middle school and will see how many times I can make it around the track before the battery meter drops to the last green bar. I'll make sure there are some kids around if I need a push back to my room. Normally I just use my manual wheelchair and only transfer to the electric if I have to get someplace quickly at the other end of the school.

The school is mostly level ground. There are two wheel-chair ramps, but they are too steep for a kid in a manual wheel-chair. I think the ramps were designed for delivery people using hand-trucks, not people in wheel-chairs. If I didn't have wheelie-bars, I'd flip over backwards.

 

[Substrate]

Heh, the guys over at wheelchairdriver do have wheelie bars on some of their powder-coated custom-frame racing chairs!

Here's the thing - they've got the knowledge to let you know if maybe you *should* stick to lead-acid based upon the design parameters of your chair. What?

If your chair is designed around lead-acid and depends on Peukert for protection (voltage drops under high demand), putting LFP inside and going up a hill may smoke your oem motor since LFP doesn't suffer from Peukert. Or maybe your wiring infrastructure isn't up to snuff.

Similar to how guys DIY a huge LFP system for their yacht, and immediately smoke their alternators.

Not trying to scare you, I'm just saying that unlike our application, with motive power - even if small like in a wheelchair, has some additional things to think about at times...