WheelchairDriver

Substrate

Solar Addict
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 Addict
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.
 

GSXR1000

Solar Addict
so you are telling me that a lithium battery without a bms can't die in the middle of the street?
 

Substrate

Solar Addict
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 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
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..
 

Ed Tech Sensei

New Member
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.
Thanks for the links. I spend my day in a manual wheelchair but have an old electric. The AGM 8AU1 32 amp hour batteries for my chair finally died. I happened to have two Ironworks LiFePO4 12V 44.6 amp hour batteries in my garage. The Ironworks fit in the battery box so I hooked them up. I bought a LiFePO4 charger and everything seems fine.

I'll have to read the articles you linked and pinned. My batteries have a BMS. I need to figure out the pros and cons.
 

Substrate

Solar Addict
Well, I'll let them speak for themselves. Just know that some may be put off by the no BS matter-of-fact approach. It's simply the fastest way to cut down on armchair-engineering and bench racing specifications talk since they live on what they build.

Hands down the best advice there from the old days before LFP about premature walk-down problems of not having enough float which kills agms and even gels prematurely. No BS. Although not a wheelchair-user myself, I knew from my earlier EV days that this guy knew what he was doing since I was a pure-lead agm fan from way back for motive applications.

Enjoy your drop-ins. Don't be disheartened when they advise against it - the abruptness is not personal.

Keep that in mind, and don't take anything personally if some advice seems curt. You'll be good to go!
 

Ed Tech Sensei

New Member
Well, I'll let them speak for themselves. Just know that some may be put off by the no BS matter-of-fact approach. It's simply the fastest way to cut down on armchair-engineering and bench racing specifications talk since they live on what they build.

Hands down the best advice there from the old days before LFP about premature walk-down problems of not having enough float which kills agms and even gels prematurely. No BS. Although not a wheelchair-user myself, I knew from my earlier EV days that this guy knew what he was doing since I was a pure-lead agm fan from way back for motive applications.

Enjoy your drop-ins. Don't be disheartened when they advise against it - the abruptness is not personal.

Keep that in mind, and don't take anything personally if some advice seems curt. You'll be good to go!

I'm only using the LiFePO4's because I had them already and I wanted to see whether or not they would even work with my wheelchair. I don't use the chair much, and the original AGM's for the chair are rather small and inexpensive. I think I'll buy a pair of AGM's for the chair and figure out another use for the LiFePO4's. I have a few little solar off-grid/back-up power projects I'm working on.

I was thinking of building out my wheelchair into something off-road. Now my interest is piqued again.
 

Substrate

Solar Addict
Cool - and again these guys can help you best with common issues like this. To them, lead-is-dead and LFP rocks!

However, there are drop-in LFP sharks out there, that don't take into account ALL the motive-power variables, such as available space in the chair, and you could come out lacking in range due to early bms cutoff.

Stuff like that. Worth a visit no matter what you decide.
 

Ed Tech Sensei

New Member
Cool - and again these guys can help you best with common issues like this. To them, lead-is-dead and LFP rocks!

However, there are drop-in LFP sharks out there, that don't take into account ALL the motive-power variables, such as available space in the chair, and you could come out lacking in range due to early bms cutoff.

Stuff like that. Worth a visit no matter what you decide.

It is interesting but not surprising they advocate for no BMS. The Ironworks batteries have a BMS but so far haven't affected anything as far as I can tell. I do have four 50ah 3.7 LiFePO4 cells I bought a while ago to build a battery but I haven't gotten the cheap Ebay BMS to work. I would need another four cells to make another battery, but the price of locally sourced cells has gone way up since the purchase of the original cells. I'm going to wait for the price of locally sourced cells to drop. The ports are finally starting to unload all the ships that have been stuck off-shore.

This should give me some time to fully explore the wheelchair forum. As you said, there is a ton of material there.
 

Substrate

Solar Addict
Well the only reason they don't advocate a bms, is that apparently none can handle what they do. Not sure how far they've kept up with things though.

Like doing high-amperage zero-speed 360-degree turns on carpet.

Recently the question came up about if their beloved Revolectrix PL-8 (which the author woked with to rewrite some of their firmware) were to be unavailable, what BMS would they choose?

They are mostly familiar with dinky drop-in bms' that have 50ma bleeders, which are insufficient - that kind of thing amongst others.

Perhaps someone waaay more familiar with BMS than I am, could work with them to determine what their needs are in that application? That would be cool. Run it by Burgerman and see if anything is practical for them to use - I don't know.

Times have changed a little too - some are using prismatics - once frowned upon - only because of the wasted space that could better be used for more capacity. Some are pretty slim these days.

AND, recently some have built "Add-on" LFP packs to enhance either their existing lead-acid setup, or their bigger custom LFP packs. Like 30 - 40ah LFP. Small enough to hang on the back, and add range. It's pretty simple, without having to go to great lengths to get started. Of course these "add-ons" are going to take a hammering first, and be more or less sacrificial. :) But it's a way to get started if you dont / can't make a custom main LFP battery underneath.
 
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