A POWERCHAIR IS DESIGNED AROUND ITS BATTERIES, SINCE THEY ARE ITS WEAKEST LINK
A POWER Wheelchairs maximum speed, its level of torque and control, its range, and its physical external dimensions and its weight are all limited to, and totally determined by its batteries. They are the weakest link in ALL powerchairs & electric vehicles. Its all a balance here. More of one means less of another. Lead batteries as used by almost every powerchair manufacturer today are frankly hopeless!
As of 2011, I am now only building Lithium battery powered wheelchairs for my own personal use. Non of the real manufacturers do this yet, because they plainly do not "get it". Lead is DEAD, They should move on!
This image here is of my Headway Lithium Ion Phosphate,
completely safe, 78 cell battery pack. I am using
That's around THREE TIMES more stored power at the 1 hour
rate, (1 hour rate because we use powerchairs in bursts
Lithium battery power is available, usable and safe today in 2011. It already has been used in cars, models, hobby stuff, bikes, non mobility scooters etc for years now. They are used in everything from kids toys, to full sized electric cars and even aircraft. And laptops and phones, as well as hobby equipment like model aircraft and helicopters such as mine HERE!
Although more expensive to initially purchase, it is actually massively cheaper over the long term as well as MUCH better performing! Even without its huge range, speed, reliability and fast charge benefits. Contrary to many "experts opinions" its already as cheap, Ah for Ah today compared to "good" lead (GEL) based batteries.
Of all the different battery types available today, the old "Lead" or "Gel" battery is about the worst possible solution in a power wheelchair or any electric vehicle! Its as heavy as hell, slow charging, doesn't like big currents, suffers from the Peukert effect, and has a short service life.And it cant store much power size for size. It deteriorates fast and dies if not stored on a maintenance charger at the correct voltage. But its "easy" and cheap and readily available. Powerchair manufacturers are simply too damned lazy/slow to move on. They get their money far too easily. So 99 PERCENT of the power wheelchairs on the market are LEAD powered... And 100 PERCENT of Hi End powerchairs are LEAD powered! Which sucks big time.
SAFE LiFePO4 LITHIUM BATTERIES ARE READILY AVAILABLE TODAY IN 2011
But its not a simple "swap". So the manufacturers continue to use the old known quantity (but useless!) - Gel/lead batteries. Because developing easy plug and play chargers, or better control systems that take advantage and work with lithium's CORRECTLY takes them effort, time, and money.
Higher speed is possible too at least if used with the correct matched controllers/motors taking advantage of the added power and low resistance.
Safe. These are not the same as Lithium Ion batteries in your laptop or the LiPo (Lithium Polymer) batteries used in my helicopter and are fire, and damage "safe" in that they will not burn or explode if misused, overcharged, shorted out, or physically damaged.
It allows the weight of the powerchairs battery to be halved, (with more than double the energy stored) which in itself increases both range and ramp climbing capabilities and improves soft ground operation. And its kinder to carpets, floors, vehicles, and tyres too.
3000 watt hours of stored energy fits in the same space as 2, normal "Group 24" wheelchair batteries! That's around THREE TIMES as much usable power, (at the 1 hour rate) as a pair of "Group 24" lead (AGM / Gel) batteries. At around HALF THE WEIGHT! Or if you prefer, equal usable power, to SIX normal large gel batteries with the weight on just one! Think about this a bit...
That means 15 MPH and 45 Miles+ range. (Actually its a true 60 Miles if you were to use the manufacturers UNREALISTIC tennis court test! (ISO standard test) as they do...
While costing more initially they last around 2000 cycles compared to 500 maximum at 80 percent DOD compared to the BEST quality Gel battery available. And when you consider that Ah for Ah they are not *that* much more expensive (if at all from some sources). And each Ah takes you about 30 to 50 percent further than a Lead based battery equivalent Ah. Due to the Peukert value. And battery internal resistance.
HERE IS AN IMPORTANT OFTEN OVER LOOKED FACT... We know LiFePO4 batteries can do easily the quoted 2000 80% deep cycles. Many have been tested. This means 4 times the battery life of QUALITY gel batteries if charged daily.
But here's the bit most people miss. We probably only need to charge these every 3 to 4 days or so... Since they are 3x bigger electrically in use. So in real terms it means 2000 CYCLES x 3 days. Or a realistically 6,000 days before battery replacement. For a heavy daily user. 6000 days is around 16 years!!! And then they will be "down" to 80 percent capacity level. So STILL twice as good as a brand new set of gel/lead batteries are ANYWAY!!!
The days of Lead batteries are totally finished. This makes them MASSIVELY cheaper long term than lead based batteries are, as we will likely never need to replace them during a 10 year powerchair lifespan. Most serious powerchair users eat a set of gel or AGM lead deep cycle batteries every year to 18 months. I know I do.
But here's the real reason they are more expensive to BUY:
You can actually fit about 1.8x to 2x the AMOUNT of Amp Hours (GIVING around 3X
the RANGE) of battery into the same space your old lead ones came out! And
you SHOULD! This is where the advantage is! This means that you are actually
buying double or three times the battery. Like buying 4 or 6 Lead batteries.
This is what doubles or triples your range. And your cost, because:
THERE'S NO REAL POINT IN REPLACING 70AH OF LEAD BATTERIES WITH 70AH OF LITHIUM
IT WILL WORK. YOU WILL GAIN "SOME" RANGE, AND YOUR BATTERIES WILL BE MASSIVELY LIGHTER. AND YOUR BATTERY COMPARTMENT WILL BE JUST HALF FULL.
This is the sort of STUPID trick, that the manufacturers & marketing people will do, when they finally get around to using lithium batteries... They will "change" to Lithium for marketing purposes but there will be no huge range or performance gain since they will just swap one type of battery chemistry for the other. Ah for Ah and at 24v. As such the only range increases you will get will be simply due to the lower weight and some internal resistance and Peukert value improvements. Not the huge improvement that is actually POSSIBLE and desirable! And they will stay with 24v and the lower efficiency and speed that it allows. Because that's "easy"... I could have done that too. But that misses the point, and some of the advantages. Why do you suppose electric cars and bikes use much higher voltages? My HELICOPTER uses 24v, and its small. Some use 48 or more.
So ideally you need to FILL your battery compartment! As much battery Ah crammed in as humanly possible to increase the amount of Ah storage capacity that you have. But that costs real money!!! And do not do this! See MONOBLOC batteries here Again this is what the manufacturers will try to fit. Its "easy" and lazy.
With Lithium Ion batteries like LiFePO4 you do actually get about 1.4 to1.5 times the range from the lithium battery (per same Ah) that you get from Lead batteries due to fact that Lead batteries are rated at the ridiculously slow discharge 20 hour rate. At the 5 hour rate they are about 1/3rd less. That suits a five hour continuous roll in a straight line. But that's not what we do. Ramps, grass, steep hills, accelerating takes power at the 1 hour rate or much more in big short bursts. So your 70Ah lead batteries are really only going to give you half to two thirds of the rated capacity.
Lithium's are all rated at a much more realistic 1 hour rate. In fact it doesn't much matter how fast you take out or put back the power, capacity stays the same with high rate Lithium's like I am using. Whereas the actual capacity of a Lead (gel) battery is less than its "rated" value when the power is taken out faster than 20 hours. Lead batteries are useless when power is taken out really fast. Like in short powerful bursts, as we typically do in a powerchair. So a 70Ah lead battery is actually a much "smaller" battery in real terms (at about 38Ah) at a high rate than a 70Ah Lithium battery is. Which isn't obvious to most. You cannot just compare Ah to Ah...
There is less voltage drop under load with lithium too, so MORE of the available capacity can actually be used up at the end of the charge. So lithium's always give a range increase even with the same Ah capacity. So adding say an extra 50 to 60 percent in Ah capacity actually gives around double or three times the real world usable range.
So just replacing your 70 Ah Gel batteries with say 100 Ah of Lithium batteries (which will fit your battery box easily) will increase the range by around double in actual use. Or possibly a little more. Its hard to say without knowing the exact specs of the chair, the usage pattern, the old batteries exact specification etc.
But there are no guarantees your existing powerchair controller will not give "errors" if you tried this. With say 8x LiFePO4 cells to give a close approximation to two lead acids at 24v. But I doubt it will be a problem in most cases You would need to test. The battery "gauge" definitely wont read correctly though! Just ignore it!
HOW I AM DOING IT:
The cells built in plastic blocks, are all linked with bus bars, and have cell balancing wires attached too!
LETS BE CLEAR. THERE IS NO GOOD PLUG AND PLAY LITHIUM BATTERY / POWERCHAIR SOLUTION. AND ITS UNLIKELY THAT THERE WILL BE.
Lithium's are not simple like the old lead batteries.
If you are looking for direct plug and play lithium's to SWAP your lead batteries for you will not find it. There is no lithium direct replacement battery you can just fit to your existing powerchair. Not yet, And its not likely for a number of reasons. Life's not that simple. Its a system. Not a battery. Once you understand how though, its actually surprisingly easy to change to lithium batteries.
Now when I designed the battery compartment of my new BM MK 3 powerchair I allowed for 6 different battery options. 2 different lead Odyssey and 4 Lithium. Its called flexibility! and with this controller that I am using ANY VOLTAGE up to 50v is great! The more the better. So any battery type is usable.
More voltage however, used with stock powerchair motors, means more speed without loss of torque or range, less amps on battery cables plus greater overall efficiency. It allows the controller to be effectively an efficient gearbox. So I gain speed "free" of charge so to speak.
I made / designed the chair so it was both Lead (Gel or AGM) friendly, for both 24v (2x Group 34/24 batteries) and 36v (3x Odyssey PC1200 batteries) as well as two different types of lithium ion cells in both 24 and 36 (or more) volt arrays. I will be using approximately 45v.
Lets never say I don't think ahead!!! All of these options will both fit and work properly in my newest powerchair.
THE 2011 BM3 POWERCHAIR WAS DESIGNED TO USE ALL OR ANY OF THE FOLLOWING BATTERY SOLUTIONS!
I now have my life and independence back. These things are not just a good idea they are essential! There are many new designs, and quality manufacturers in 2011/12 as I write this. Unlike the stagnated powerchair market wheelchair accessible cars and vans have become well developed, and there's lots of choice!
IN CASE YOU DIDN'T GRASP THE ABOVE FULLY HERE'S A VERY CONDENSED SUMMARY:
PLEASE READ THIS NEXT FEW LINES CAREFULLY
My new LITHIUM pack compared to a typical pair of HIGH QUALITY MK Group 24 Gel batteries:
Spec Sheet for MK As used in many hi end wheelchairs.
So at the 1 hour rate a pair of these Group 24 MK batteries gives just 1008 Watt Hours. Compared to 3098 Watt hours for the new lithium pack. That is 3x the capacity & half the weight!
That means MY HUGE Lithium battery is 3x (THREE TIMES!) better than a set of GOOD Gel batteries by size and usable capacity alone.
Or the Lithium Pack is as good as 6x group 24 MK batteries! At the same weight as just one! That means if your chair previously had A 20 mile range, now it has 60+ miles... And you saved 50lb in weight too.
PLEASE READ THIS PART AGAIN!!!
This is a summary, click the link for full details Charging my lithium battery -- full details
To charge any of the above lithium packs you will need a Lithium "balance" charger that can charge up to the number of cells you need. 8 cells for 24v, 12 cells for 36v, 13 cells in my case for 43v. Or a BMS system.
That needs a charger that can charge with a CC/CV of 3.600v per cell. Actually 3.600v is considered a better figure than the manufacturers 3.65v per cell if cell life is important to you.
And the charger needs to be able to balance all the cells during charge. I use the Hyperion advanced hobby charger for this. Its not ideal, but I already have several for charging my old LEAD batteries! And it does advanced graphing, PC control and logging, and works from 12v in my car too...
I use one of these Hyperion1420i chargers to both charge and balance the battery pack below. And to graph it on my PC screen at the same time. It can charge ANY battery type and balance it too.
THIS IS A PROTOTYPE/ONE OFF CUSTOM POWERCHAIR BUILT FOR ME, BY ME! SO TAKES MANY TYPES OF BATTERIES PROPERLY BY DESIGN...
This shows it in comparison for size with a pair of typical group 24 batteries as used in a HI END powerchair. The lithium battery is the exact same 520mm length. The same width of 171mm. 3x better range, half the weight! 3x the speed. Fast charging. 4x longer life (cycles)... That centre section is 2mm bigger in width than all of the battery options.
It is however 14mm taller than the terminals on the lead group 24 batteries. At least when using a 6 cell tall battery. Nothing stops you using a 5 cell tall one though. There is usually an extra 14mm to spare anyway, as it makes sure there in nothing touching the usual lead battery connection terminals.
I designed my powerchairs centre section/battery area to accept either 78 Lithium cells like these or less, or two group 24 old style Gel/AGM batteries, or 3 Odyssey PC1200 batteries for 36v.
My new BM3 (MK 3) chairs centre section, with a pair of group 24 batteries for comparison. Note terminal height and required clearance. And the very snug fit!
Same centre section, but with 3098 Watt hours of energy, and 52 lb lighter! Note battery is 14mm taller than the group 24 battery terminals. But no clearance required so not a problem.
Box of Cells. Have 78 of these 12Ah single cells. These are Headway cells. Available in 8, 10, 12, and 15Ah sizes. Mine came from http://eclipsebikes.com/lifepo4-battery-cells-accessories-c-77_69.html -- buy a lot? Rob will give you a good price, offers a fast service, and is very helpful... Or you can get them from China directly with fast delivery.
This is how it will be fitted to my new very modified powerchair! So it will look exactly like the photo of the older chair once its been powder coated and rebuilt! Just HUGELY faster, lighter, and with 3x the range. Remember its just 25.3 inches wide x 37 inches long. Great for indoors. And does 45 miles to a charge, and 15 miles per hour! And it works off road or on the beach too... One day the manufacturers will get some sort of a clue and do something similar, although I doubt it will be soon!
My LITHIUM battery (built from single Headway 12Ah cells as shown above) will have the following specification:
Cost just under Â£1200 UK pounds including all bus bars and cell building blocks. Considering it has almost 3x the usable Watt/hours capacity of a pair of the usual gel group 24 batteries, AND about 4 to 5 times the lifespan, and half the weight it is actually a bargain!!!
My lithium battery pack on test. Measuring capacity, balancing cells, measuring resistance, and graphing all the results automatically by using my Hyperion charger.
My laptops, model helicopters, RC transmitter, keyboard and mouse all use lithium's. As does my torch, many modern electric bikes and NON DISABLED scooters. And many full sized electric cars, trucks, submersibles, and all kinds of stuff. Many of these things like your phone have used them for 5 to 7 years.
1. They have another advantage too. They sit in the shelf in my torch/RC transmitter for a year with about 5 percent or less loss of power!
2. They do not sulphate and die if left unattended or discharged for a few weeks.
3. They are the SAME price Ah for Ah as premium deep cycle batteries TODAY.
4. And give MORE RANGE Ah per Ah due to no Peukert effect.
5. GOOD high C rate ones have much better high current capability meaning more torque, smaller lighter batteries.
6. They last 4 to 5 times as long in cycle life, and at least 3x longer in shelf life.
7. 2x the Ah can fit in the same space giving 3x the range... (Peukert!) So really 3x smaller...
8. They are 5x lighter Ah per Ah... That's not a typo.
9. They are SAFE as long as we are talking about LiFePO4 like I am using
10. And the real kicker! They are hugely cheaper right now than inferior lead as they will last the life of the chair at least if correctly sized and charged...
11. And because the high C ratings allow bigger currents from a smaller capacity battery it allows higher voltage packs to be used which means "free" extra speed through greater efficiency and using the controller as an efficient gearbox.
For those that don't believe that it has easy 45 mile range, (Actually 50) here is some calculations made using this -- details are shown below during a 2 degree climb... For full battery and for a 70 percent used battery @ 10 mph.
It also shows that the motors are well within their rated watts limit so will not overheat at a continuous 15 mph.
What's the purpose of the pages about the MK3 chair and the earlier MK1 and MK2 chairs since I don't sell them? To embarrass the manufacturers into getting with the show, and doing some real development work. And to show other wheelchair users especially Paraplegics like me, what is possible. As such there are others now doing the same or similar, many are members of myMessage board.
Anderson style connectors & why you need them
Battery planning How to organise yourself