Advice Needed for Elderly/Mobility Scooter upgrade
I'm TJWhiteStar and I'm looking into ways to help our local elderly/mobility scooter users to upgrade their scooters to Lithium Ion Battery Packs.
I have done some preliminary calculations and was wondering if you could confirm they are in the right ball park and then point me to the correct components for getting them here in the UK. Okay here goes.
Current setup is: 2 x 12v 12Ah Lead Acid Batteries use to give 24v 12Ah in total (I'm nearly positive this is right for the Ah but 24v is definitely right).
To get a Lithium Ion Pack of the same voltage and approximate capacity I came up with the below.
Based on the cells I initially looked at 2500 x 3.7v (nominal voltage) = 9.25Wh
12000mAh x 24v = 288Wh
288Wh / 9.25Wh = 31 cells (rounded down) for the approximately same capacity as the Lead Acid Battery Pack.
24v / 3.7v (nominal) = 6 cells (rounded down) in series for the 24v required.
6 x 4.2v (fully charged) = 25.2v when cells fully charged and the system is able to handle this easily.
31 (total cells needed) / 6 (cells per series string) = 5 Parallel Rows of 6 Cells in series (rounded down as need full series strings of 6 cells and can't have a string of 1 cell)
So as far as I can work out we'll need 30 cells to make a 24v 12Ah (ish) 6S5P Lithium Ion Battery Pack per elderly/mobility scooter.
Obviously space wise we could fit more but I'm looking at direct comparisons at the second to try get my calculations correct. Plus with the reduced weight the users would probably get better runtime out of the scooter purely through weight savings.
Sorry if this was a long post but I'm trying to get this right as I'm doing this as a volunteer to give back to my community. Yeah fund raising might be next but firstly I'll look to convert the 2 in my family (my mother's and my own, yes I'm disabled so this is why the project is close to my heart and dear to me as I know how much these vehicles are needed). I'll use ours as test subjects before opening up to others and trying to get funds to cover the costs for them as pensions don't go as far as they used to)
Thank you in advance for your help
Your math and the process you used looks correct to me.
One note: 24V systems with li-ion are usually 7s, not 6s. The problem with 6s is that when it gets near the fully discharged state, you'll be down to about 18V. You just have to make sure your 24V electrical system can handle this and doesn't have a fault or low voltage cut off. 7s would mean that you'd be closer to 21V when you're empty, but it'd charge up to 29.4V, so you have to make sure your system can handle it on the high end as well.
Ah right I understand thank you. I'm glad that my math and process somewhat worked out. But yes I remembered to check for voltage on upper limit for charging but missed the lower limit for when discharged.
The system can manage more on the upper than lower end. Just need to check motors but I think they have a wide voltage range so 7S should be okay.
What should I be looking at BMS wises as I see you only start at 10S for those? I need these to be as easy and as close to Plug and Play as possible because memory is not a commodity that is in abundance haha. Lots of forgetful folk I'm afraid.
Could I install the 10S unit but only connect up to +7 and then upgrade to 10S later if systems can handle it (I'll have to double check upper and lower limits)
I appreciate your reply and help as this will help our elderly and disabled communities immensely once I've got it working on the test scooters plus I'll also know what I will need to raise money wise for each user.
You'll definitely want to use a BMS. It will make charging easy. Basically, they'll charge it just like a cell phone, plug it in and forget about it.
We don't currently have a 7s BMS offered. You can find plenty on Aliexpress, but you'll have to wait a few weeks for shipping: https://www.aliexpress.com/store/product/7S-Li-ion-Lipo-Batteries-Protection-Board-BMS-System-24V-29-4V-15A-Continuous-Discharge-250W/313864_32336417500.html?spm=2114.12010612.0.0.TTDkPR
I wouldn't recommend installing a 10s BMS for a 7s battery. Most won't work as they'll be expecting more cells and it will appear like a fault to the BMS when 3 cells are 'missing'. Plus the low voltage cutoff won't work, as it will be programmed for a higher voltage.