Very cool and useful. It would be interesting to see if it was possible to modify the charge monitoring on the wheelchair main display. maybe some logic to convert from the LFP BMS charge monitor to a linear voltage output so the existing wc charge sensor could use it. It would be interesting to see some comparison of the battery types which you looked at in coming to your choice presented in more detail. thanks for the vid.
Cool project and really impressive to see a mobility device with not only that much range but also that gets used in suburban North America so regularly. I would recommend adding that balance circuit or more preferably a BMS with integrated balancing as right now the 100% SoC screenshot shows the BMS has disconnected the charge FETs due to a cell voltage high level 2 alarm (>3.65V), this will result in excessive wear on that individual cell and eventual premature failure (really common for batteries without balancing). Would've expected that BMS could do balancing though? Additionally what sort of circuit breaker did you use? AC breakers will not break DC reliably and many of the DC circuit breakers are designed for lead acid batteries which don't have high fault currents like found in lithium systems. Would recommend checking or replacing it with a proper HRC fuse rated to break the short circuit current of your batteries. The same advise applies to your home battery system you showed a picture of, I couldn't immediately see a fuse or disconnect device. Also the reason why the mobility device industry is stuck with older battery technologies is mostly to do with dangerous goods transport laws. Any company that built a wheelchair with a 2.1 kWh battery pack would have to put a big sticker on it saying "LITHIUM BATTERY - 2100 Wh - FORBIDDEN IN PASSENGER AIRCRAFT". The internationally set limit governed by IATA for lithium batteries on any aircraft is a "measly" 300 Wh (some local governments also have limits on trains and buses). However if you use an older technology that's not as energy dense and prone to energetic failures like lead acid or NiMH there is no energy limit, so the old 600 Wh lead acid is allowed. The laws are slowly changing but not without lots of effort as the laws affect everything from mobility devices to eBikes, camera batteries, drones, scientific equipment and anything carried as cargo.
Thank you for your comment! The regulations are a very believable and understandable hurdle that will need to be crossed. Hopefully we move toward that soon! Unfortunately, no balancing ability on this BMS (software has it, but hardware doesn't support). I might switch to a JK BMS with active balancing. Would feel better with it integrated. I guess an update video is coming sooner than I thought... I do have a DC rated circuit breaker that is certified for automotive applications (and voltages up to 50VDC). I don't see a specific fault current rating on it. I will add a 125A HRC fuse with a 2000A interrupt capacity to back it up for serious short circuit faults. I will also add one to my home battery backup. That system isn't completed yet. I have some upcoming modifications (including adding some solar to it), and will definitely factor that in. Really appreciate your input. Thanks!
Can I ask how many amps the controller for your daughters chair is? I have thought about doing as you have but have concerns about the BMS cutting out on my chair which has a controller that is rated for 120 amps.
I'm not sure what her controller is rated at, but her battery is protected by a 70 amp breaker. I also used a 70 amp breaker but ordered a 80 amp BMS just to be certain. Maybe check the fuse/breaker protecting your battery?
That is correct. When connecting in series, the voltages add up, but the Ah stay the same. The net result is a 24V 105Ah battery. The original design was two 12V 55 Ah AGM batters for a 24V 55Ah battery. Thanks for watching!
Sorry. I'm afraid there are too many liability issues to build one as a business. Hopefully you can find someone close to you who can? I would be happy to answer any questions they might have...
Great job Dave. So nice for Jessica
Thanks! It has been so rewarding to complete such a helpful project!
Wow! That really made a huge difference is how far it will go!
When I first did the calculations, I was sure I had made some sort of mistake! Was really glad when it worked out that way for real!
Very cool and useful. It would be interesting to see if it was possible to modify the charge monitoring on the wheelchair main display. maybe some logic to convert from the LFP BMS charge monitor to a linear voltage output so the existing wc charge sensor could use it.
It would be interesting to see some comparison of the battery types which you looked at in coming to your choice presented in more detail. thanks for the vid.
I could have made this a much longer video, but tried to keep it short and sweet. I might do a deeper dive later if there seems to be enough interest.
Cool project and really impressive to see a mobility device with not only that much range but also that gets used in suburban North America so regularly.
I would recommend adding that balance circuit or more preferably a BMS with integrated balancing as right now the 100% SoC screenshot shows the BMS has disconnected the charge FETs due to a cell voltage high level 2 alarm (>3.65V), this will result in excessive wear on that individual cell and eventual premature failure (really common for batteries without balancing). Would've expected that BMS could do balancing though?
Additionally what sort of circuit breaker did you use? AC breakers will not break DC reliably and many of the DC circuit breakers are designed for lead acid batteries which don't have high fault currents like found in lithium systems. Would recommend checking or replacing it with a proper HRC fuse rated to break the short circuit current of your batteries. The same advise applies to your home battery system you showed a picture of, I couldn't immediately see a fuse or disconnect device.
Also the reason why the mobility device industry is stuck with older battery technologies is mostly to do with dangerous goods transport laws. Any company that built a wheelchair with a 2.1 kWh battery pack would have to put a big sticker on it saying "LITHIUM BATTERY - 2100 Wh - FORBIDDEN IN PASSENGER AIRCRAFT". The internationally set limit governed by IATA for lithium batteries on any aircraft is a "measly" 300 Wh (some local governments also have limits on trains and buses). However if you use an older technology that's not as energy dense and prone to energetic failures like lead acid or NiMH there is no energy limit, so the old 600 Wh lead acid is allowed. The laws are slowly changing but not without lots of effort as the laws affect everything from mobility devices to eBikes, camera batteries, drones, scientific equipment and anything carried as cargo.
Thank you for your comment!
The regulations are a very believable and understandable hurdle that will need to be crossed. Hopefully we move toward that soon!
Unfortunately, no balancing ability on this BMS (software has it, but hardware doesn't support). I might switch to a JK BMS with active balancing. Would feel better with it integrated. I guess an update video is coming sooner than I thought...
I do have a DC rated circuit breaker that is certified for automotive applications (and voltages up to 50VDC). I don't see a specific fault current rating on it. I will add a 125A HRC fuse with a 2000A interrupt capacity to back it up for serious short circuit faults.
I will also add one to my home battery backup. That system isn't completed yet. I have some upcoming modifications (including adding some solar to it), and will definitely factor that in.
Really appreciate your input. Thanks!
Can I ask how many amps the controller for your daughters chair is? I have thought about doing as you have but have concerns about the BMS cutting out on my chair which has a controller that is rated for 120 amps.
I'm not sure what her controller is rated at, but her battery is protected by a 70 amp breaker. I also used a 70 amp breaker but ordered a 80 amp BMS just to be certain. Maybe check the fuse/breaker protecting your battery?
Since the battery was 24 v 105 ah?
I'm not sure what your question is?
@@AnotherNerdyCanuck I asked you about the amperage of the cells, are they 3.2v 105 ah cells? Since there are 8 cells, the battery is 24v 105 ah
That is correct. When connecting in series, the voltages add up, but the Ah stay the same. The net result is a 24V 105Ah battery. The original design was two 12V 55 Ah AGM batters for a 24V 55Ah battery. Thanks for watching!
Any chance you would build me one?
Sorry. I'm afraid there are too many liability issues to build one as a business. Hopefully you can find someone close to you who can? I would be happy to answer any questions they might have...