Scooter Conversion

[aksel]

Thanks for the feedback, it gives me a starting point. My current batteries are a year old. Attach is a picture of the battery area. It seems that replacing the lead bricks is the simplest option space wise.

[expresso]

It may be the simplest solution for you - but also keep in mind - they wont last long either - in which case - this is another option - get new lead replacements and Also make a ADD ON - this way you will most likely double your range and keep the lead going much longer - its an idea -

the great thing about an ADD ON - is it can be removed and used on other chairs - scooters - etc, easily - its an idea you can consider - a 60ah ADD On

[flagman1776]

You need to invest the time figuring out how to get the most LiFePO4 amp hours into the space you have. Not only oriented as the existing bricks are but possibly crosswise or other configurations. Remember to insulate the center seat pedestal. You'll need to explore the different cell options to fit the space.
Last, you'll need to find a place for new charging plugs, under a rear hatch perhaps?

[ex-Gooserider]

There is a quite active thread on the many different sizes and shapes of cells that are becoming available - many 'unofficially' though our China connection Shirley... He lives in Hong Kong and can understand the Chinese websites and find the good stuff for us...

After you figure out just how much room you have, you can start playing with the sizes of the different cells and see what you can come up with that will let you build the largest pack you can stuff into the space... Biggest things to keep in mind is that all the cells have to be the same, and you need multiples of 8 cells to get 24V.

ex-Gooserider

[aksel]

Thank you.

The space of the two bricks will account for most of the space and I'll try to add a little more. Taking out the existing charger from the back deck will offer space but not much for the added wiring.

Are you referring to the conversion thread?

[aksel]

If I'm only replacing the bricks with 8 15ah cells each is it even worth it?

[pattherat]

Shirley has a really good point. Others have built LiFePO4 add on packs (look for the threads), usually suspended from the seat back, that connects to your existing batteries through a single plugin cable. You could greatly increase your range. Very quickly.
Just because its a scooter & not a wheelchair doesn't matter...

When you say existing batteries, do you mean lead acid or AGM? If so would you have to wait until your lead acid died, unplug them from the controller and then plug in the lithium pack. If you have both the lithium and AGM batteries connected to your controller wouldn't the lithiums keep the AGMs topped off until the lithiums died and then as you are draining the AGM you could be draining the lithium cells too low and damage them?

[aksel]

They are AGM, but I'm referring to if I got rid of them completely.

[pattherat]

I was referencing what Flagman1776 wrote. It seems like he is suggesting that you can run AGM and lithium in parallel. So I am trying to find out if that is correct or whether you have to isolate the two different battery chemistries from each other.

[Burgerman]

You can run LiFePO4 of a sensibe Ah (to reduce C rate on cells) with AGM or Gel. In parallel.

Ideally you need a large Diode on series with the lithium pack to make best use of both batteries. Since if you do not do this, the lithium gets used up by around 90% and the lead by around 1/3rd to half. You need a 100A capable low forward drop diode of the schottky type. So that you lose around .25V in use.

If you take a look, there are many here doing this now, starting with Shirley_hkg around a decade ago. Search ADDON. Also the first guy to test with the diode added that I suggested for him, so you can take a look at which one, was Expresso. He have been using various addons in new york, and getting a GPS 40 mile range on a regular basis. On an 8mph chair. Theres a few others too. He various sized packs, the biggest is 60Ah. Hangs on back of seat.

[pattherat]

I see, well that's good to know. For me it's actually easier to unplug the AGMs from the controller and plug in the add-on when I'm down to one blinking red light.

[Burgerman]

No thats the opposite to what you should do!

Because many reasons...

the range you get from the lead AGM depends on the RATE you discharge it. Do so slowly and get more miles from the lead. So running in parallel with lithium means it gets discharged slowly. And. Discharging it low is what reduces cycle life and means they dont last long. You will get twice as many cycles at 70% DOD as you do at 80%. And again you will only get very few if discharged almost fully.

And because lithium batteries hate high discharge rates. So having a relatively small addon pack, means that its helped by the lead. So you dont take big currents out of the addon pack alone. So both are happier, and you get better range than using seperately.

So you are best to connect together when both are fully charged. And charge both lead, and lithium as one battery. With carefully configured setting, and cell balancing and the PL8 charger we are mostly using.

[pattherat]

Okay then. I don't really worry about life cycles as I can change out the batteries once a year at an operating cost of about $10 a month. They're just 21ah but get me through most everyday on there own with quite a bit to spare. The add-on I use is a 24v18ah Li-ion bicycle battery with a smart charger that clips on the back of an armrest. It's too bulky to use everyday and only use it on rare occasion like going to a large car show or swap meet, amusement park etc. I can't be bothered with all the thought, work and maintenance you build your own lithium guys do. Balance wires, BMS's, hobby balance chargers, power supplies ugh. Maybe if I used my chair instead of a car and needed that kind of range but I don't. I live in L.A. and no one walks anywhere here. Not even us disabled.
But I do admire you guys for doing it. I just might try a smaller lithium add-on in the future though so I'll look for that schottky diode.

[Burgerman]

I wouldnt try it with your battery, as it will be 7S at 24v as lithium ion is a different voltage to LiFePO4. There will be smoke!

[aksel]

If I had 24 total cells, could I do 8s 16p ?

[snaker]

8s3p <- 8 x 3 = 24

[flagman1776]

One of us is confused.

If I had 24 total cells, could I do 8s 16p ?

8s 16p = 128 cells (16 parallel cells in each group, 8 series of groups)

What cell chemistry are we talking about?
We strongly prefer LiFePO4. LiFePO4 runs about 3.2V per cell (or parallel group of cells).
A series of 8 cells (or parallel groups of cells) is about 25.6v which is close enough for mobility controllers to run on as is. So on the operation side a conversion is relatively simple. You might use 8 cells, 16 cells, 24 cells, 32 cells...
A power supply, smart charger is required and a balance harness for charging.

If you had 24 total cells, you could do 8s, 3p. In fact I am running a 8s, 3p pack now... I have 6 years on it.