Convert Power Wheelchair to Lithium Ion Phosphate

If you are searching for "group 24" lithium monobloc batteries that look like your familiar lead acid batteries, (for e.g.) it is very unlikely you will find any of them suitable for a bunch of quite serious reasons discussed later. Even though they are available as shown in the image above.

There are actually quite a few manufacturers trying to provide a simple "swap" with standardised group 22, 24, 34, 27 batteries that is familiar to users of old style lead batteries. But these are (as of Nov 2011) not any real use in a hi end powerchair.

My OWN powerchairs for e.g. DO already use safe, Lithium Ion Nano Phosphate batteries (But NOT monobloc batteries.) with MASSIVE benefits. Not least of which is all day (or all week!) use, even with a real world 45 mile range between charges! And a 10 year expected service life.

So, why not use today's Monobloc "replacement" lithium group 24 or 22nf batteries?

This cannot be done today in 2011 with a pair of "replacement" 12v group 24 lithium monobloc batteries as seen in the image above at top of page. They either do not have enough Amp (C RATE capability) or they lack the capacity that your battery compartment COULD hold. In a car, this doesn't matter.

In a powerchair it seriously does! The battery area (volume) is limited by the chairs length/width/seat height.

The image shown here shows why 1/3rd of your battery compartment is filled with wasted space rather than cells. Above the cells, and on all sides.

Because although a battery is a group 24 "size" it now only has the same 70 Ah capacity of a cheap lead battery due to this wasted space. So no real gain. And some can do only a limited amount of amp draw, a maximum of 50 Amps discharge rate in some cases before its internal protection circuitry disconnects it! We need 5x that! Be careful what you buy!

Another Monobloc Lithium. There are lots. Non are really suited to getting the best range/performance from a powerchair, and are aimed at people that want to fit lithium's without understanding much about them.

a) they have much wasted space, packing in the cells, and the electronics, meaning reduced capacity compared to doing it this way: My OWN Lithium battery powerchair -- Remember the WHOLE POINT of lithium batteries is to fit more Ah (Amp Hour Capacity) into the same space!

b) Lithium cells (or batteries) cannot be used in "dumb" mode like lead, they have to be monitored during charge, and discharge, and the individual cells have to be monitored and protected and controlled to keep them "balanced". In a standard "Lithium group 24" battery solution, this is BUILT IN to the battery case. (In most aftermarket solutions). This costs space, and Ah capacity.

c) Lithium batteries come in many types and capabilities. A Hi end power wheelchair with say a 120 Amp control system can require 120 Amps PER MOTOR simultaneously, so an intermittent 240 Amp battery draw is a regular occurrence. Many MONOBLOC battery solutions are limited to 50 or maybe 100 Amps max! Its not enough for our needs.

d) Most monobloc batteries either need a dumb charger, or one that integrates with the electronics inside the battery. So the charging system becomes tied to whatever is inside the battery case.

The NON MONOBLOC batteries below, allows my new powerchair TO SIDESTEP all of these issues above. They are very high C rate cells, that are able to deliver some huge currents, around 5 times more than required at many hundreds of amps.

And because there is no built in electronics, or space wasted trying to fit them into familiar shaped battery cases to please the uninitiated. So more capacity can be fitted into the same battery Volume/space. So doing it this way allows about 30 percent extra battery capacity to be utilized.

72 such cells makes a PAIR of 12v batteries that are physically the same size or less than two conventional group 24 batteries. Although there are actually 78 cells in this one big pack.

This battery below gives you: