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No cushion, Click for larger view!BM3   BM3 Home


Charging a large Lithium ion Phosphate battery is easy right?

Everyone knows you just use a simple dumb charger and fit a universal BMS (Battery Management System) as sold to you by every lithium battery supplier. And it "fixes" everything for you and balances all the cells... Done!

Well you could do that and it may sort of work in a fashion (or intermittently) for a bit. Sooner or later you will have problems. Usually sooner.

Certainly you will never see the full service life of your battery pack even if it seems to work initially. The real purpose of a BMS equipped battery is to allow ignorant users to install a "lithium battery" into a device or situation that is not properly designed to look after it correctly.

Or where cell C rate capability is too low for the stall current. Or where a cheap dumb non balancing charger is being used. Or a non current limiting controller (ESC) is used or used incorrectly. It simply allows battery sellers to sell lithium batteries to frankly ignorant users to fit to devices where REAL battery management logic and planning hasn't been built into the system. This includes both driving and charging.  The BMS protects the battery or cells (in a sudden fashion) from serious abuse. And balances cells (badly) during a badly controlled charge.

BM3 version 2011 to 2015:      BM3 Home
       BM3 Lithium Battery
       BM3 15 MPH
       Charging Lithium
       Construction Detail  
       Roboteq Controller
       PDF Summary Printable
BM2 old version 2006:      BM2 Powerchair
BM1 very old version 1998:      BM1 Powerchair  



BMS are unreliable, cause endless problems with ruined cells for a bunch of different reasons, cause fires and worse. And finding one that allows a few hundred amps to drive a powerchair up a curb without it cutting out or failing at the worst possible moment is a nightmare too due to the way they work. For a number of quite technical reasons you really do not want a generic BMS! 

Fortunately if you know what you are doing you don't need one. They serve no purpose in a properly designed SYSTEM as the chairs controller and cell balancing charger take over all the jobs the BMS would have previously been doing.

But these do so properly in proportional controlled way and much more accurately. Nothing cutting in or out or repeatedly going over voltage as it charges for hours on end.

Lithium used CORRECTLY forms part of a thought out integrated propulsion system. Its not a battery you just buy and fit where some lead batteries came out!  



This is a cell balancing 550 Watt HOBBY charger. It charges this battery super accurately @ 3.600v per cell @ 20 Amps, 46.80 Volts.

It uses an Anderson 50A connector + a 15 pin OBD11 connector to balance all the cells accurately as it charges.

This charger works at home or from 12V to 24V so it can charge your chair from your car as you drive.

  lithium powerchair battery


Charging, also controllable via PC & Bluetooth connectivity if you wish. Logs data, shows cell balance, Ah in/out and battery state and much more as it charges. Data logged so you can see what is happening over time.

In addition this charger can charge ANY battery chemistry, any cell count up to 14 series cells (60V limit) as well as your chair!

It can also charge your lead powered chairs, in your vehicle at 12V or 24V.

Or your model planes, phone, or anything else you may have.

Here is the last part of a charge ZOOMED in so we can see how accurately it balances the cells. There are 13 separate curves on this graph.

All cells are within 0.002V of the 3.600v target.

End voltage is 46.815.  Just 0.015 of a volt over.


Charge connector, and balance connector are visible under seat above front caster.

BM3 chassis / wheels / battery / footplate

Battery fitted  BM3 Home


BM3 version 2011 to date::      BM3 Home
       BM3 Lithium battery
       BM3 15 MPH
       Charging Lithium
       Construction detail  
       Roboteq controller
       PDF Summary Printable
BM2 version 2006:      BM2 Powerchair
BM1 version 1998:      BM1 Powerchair  


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