WheelchairDriver

Substrate

Solar Enthusiast
Using a wheelchair and wanting to convert to LifeP04, or get the best out of your AGM/Gel?

Look into the site run by a paraplegic engineer, (Burgerman) who has a forum and done plenty of conversions. Please note that there are NO SALES on custom chairs, battery builds etc. Many of the users live the life in the chair, so not a lot of speculation.


and of course a forum that goes into detail about it all:


To save time: The users have a different application than us - theirs is motive power, not battery storage per-se. They do NOT use "drop-ins", but rely instead mostly on Revolectix PL8 chargers with custom firmware and balancers on custom batteries built from individual cells. They also do not use prismatics, as they are not totally suited for their motive-power needs.

They also don't use a BMS - the only balance occurs during charge, otherwise when out and about the battery is naked. The reason for this is that for the huge currents they pull, a typical BMS would shut down as they are trying to cross the street and get up a ramp.

Of course plenty of info on GEL and AGM. Back in the day the Optima and Odyssey AGM's were the thing to mod the chairs with. Still valid if you go this route.

Just wanted to point this valuable resource out even though their application is different than ours. Some threads are really long, so you may be tempted to read them backwards.

Anyway, if you live this life you may find the info there as well as here enlightening. Again - NO SALES as cool as his custom chairs are.
 

Diysolar123

Solar Addict
interesting topic...it certainly is a use-case where a coulomb counter would be absolutely mandatory for a lithium based solution so you know "exactly" how much capacity you have left so you do not get "stuck in the middle of the road".
 

GSXR1000

Solar Addict
first and most importantly use a BMS!!

you can wire the motors directly to the battery and everything else to the BMS so when it dies it stops the motors.. if safety issue... run 2 BMS set at 12v and 2nd one at 10v so you could have an emergency drive switch
 

Diysolar123

Solar Addict
first and most importantly use a BMS!!

you can wire the motors directly to the battery and everything else to the BMS so when it dies it stops the motors.. if safety issue... run 2 BMS set at 12v and 2nd one at 10v so you could have an emergency drive switch
If I had a wheelchair I would not put a BMS on it...
I certainly understand the critical design criteria.. the batteries are less important than the passenger; if they hit the go button, that had better go.
You would provide a state of charge indicator, but if the driver says use every bit of power you have to move me know, well, thats exactly what should happen.

This is why this topic is an interesting use-case..most of use are all worried about the health of our batteries, in this case there is a person who's health and safety are much more important.
 

GSXR1000

Solar Addict
If I had a wheelchair I would not put a BMS on it...
I certainly understand the critical design criteria.. the batteries are less important than the passenger; if they hit the go button, that had better go.
You would provide a state of charge indicator, but if the driver says use every bit of power you have to move me know, well, thats exactly what should happen.

This is why this topic is an interesting use-case..most of use are all worried about the health of our batteries, in this case there is a person who's health and safety are much more important.
no matter what if you run the chair below the "gauge" then it will stop working either way just one way it destroys the battery the other it doesn't...
if they watch the state of charge it won't die with or without a bms
I guess if you want it to keep going have it have a loud buzzer at 11.5v... still should have bms for charging

also that is why I stated an emergency run switch to get you back to safety
 

Substrate

Solar Enthusiast
Well, that's why they have a dedicated forum - things are different in that motive power world of LFP where one could be in the middle of the street.

Any balancing is done during charge, but no bms hardware exists when out and about discharging. They can't take the risk of a bms failure when crossing the street for example. And just as important they are drawing HUGE amounts of current for the motors which go beyond what any BMS we would use - which would see a wheelchair motor spike as over-current and shutdown.

And they use what would be called "High-C" rated LFP, (Ie 6 to 10C) rated cells, not just the low power types like 1 - 3C, which many prismatics are.

Sure you could also have an LVD or low-voltage disconnect if you wanted. They do modify and measure not just overall capacity, but do real-world "range testing" with their conversions. And yeah, metering recalibrated - stuff like that. At some point, you just test your range, being willing to call for a ride home if you blow it.

It's a different world where speculation vs real-world is truly apparent when you have to live on top of your creations.
 

Substrate

Solar Enthusiast
No, but what is happening is reducing a point-of-failure. Which in the middle of the street could be fatal.

And again, no BMS can handle the huge motor-spikes in current which is normal. They just see a wheelchair as an over-current situation and shut off the output.

The idea is that during discharge, there is no need for a BMS to be a total over-seer. The banks are properly engineered first with metering, range testing and so forth.

The best thing is that none of this is theoretical. It is born out of practice. But rather than debate it here, visit the site - here's the actual forum where most of the action takes place:


This single thread goes all the way back to 2012, so be sure to have a weekend handy to go through it. :)
 

Substrate

Solar Enthusiast
first and most importantly use a BMS!!

you can wire the motors directly to the battery and everything else to the BMS so when it dies it stops the motors.. if safety issue... run 2 BMS set at 12v and 2nd one at 10v so you could have an emergency drive switch
Sounds right, but the motors, especially if stalled put the hurt on BMS, which simply shut down.

Check out his builds. Not just battery but all the other custom chair stuff, which you'd probably dig. He's an actual engineer, who unfortunately got paraplegic while motorcycle racing. That didn't stop him from engineering the best chairs. Racing, off-road, general purpose etc. Many ask him to custom build or buy his frames, but NO. NO Sales or commercial interests.

It's a different take on using LFP for motive power, devoid of the usual marketing, and as such is an interesting sideline to our application of simple power storage.
 

GSXR1000

Solar Addict
I stated already that the motor load would not go thur the BMS just the control.

but yes I am not an expert wheel chairs.. I do stand by my ideal about 2 bms so you have a switch for reserve..
 
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