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Charging a Battery Powered Wheelchair
Fast!
I can charge my Power
Wheelchair quite safely in typically 1 hour after a whole
days use. At least I can charge it to 95 percent fully
charged in that time.
Warning... Don't do this
through the standard charging socket! Just got an email from
someone trying to find a suitable plug to do just that! You may fry the wiring! Connect directly to the batteries in the battery
box. Make a simple Anderson plug and socket
connection. If you don't understand what
you are doing and damage something then you are on your own!
I USED to
always be waiting for the chargers green light before I
could use my powerchair every morning... I actually use
my powerchair very heavily, and get through a set of motors
and a set of batteries roughly every 12 months.
I now use this 30 amp 24 volt
charger. Details are on my Disabled Vehicles
site
http://www.wheelchairdriver.com/inverters-chargers.htm
15 or 20 amp ones are also available - usually from leisure
/ caravan/ RV / camping type places for smaller wheelchairs
and scooters.
Apart
from rebuilding and modifying wheelchairs and
powerchairs I also happen to know a fair bit about
batteries!
And how to maintain them so that they last as
long as possible. I actually sell one of the best
batteries available here
www.optimabattery.co.uk or at least used to do so. I
stopped several years ago as the supply was a bit
intermittent and it became a pain in the bum. Anyway back to the story! They are
expensive as are all GOOD deep cycle batteries.
Many years ago
it was necessary to charge at very low rates because the
deep cycle batteries at the time that we used in our
wheelchairs (and golf carts, recreational vehicles, etc)
were a bit fragile! Too much charge rate damaged them
or shortened their lives. Actually it wasn't so much the
batteries but the TYPE of chargers people were using on them
then that was the issue.
Things changed over the years. But
the Wheelchair manufacturers still send out puny little
chargers that charge at the low level the older batteries/chargers
required. They haven't kept pace. (Or with anything else
much actually).
However
batteries have moved on and have a generally lower
internal resistance -- typical
wheelchair chargers are still only about 5 amps for a
smaller power chair to 8 amps for a bigger scooter or
powerchair. Smaller means 40ah. Bigger means say a pair of
55ah batteries up to say 100ah batteries.
But nowadays
with most recent modern Gel batteries or with almost all
AGM batteries you can safely charge at up to1/2C. (Or half
capacity rating). With some there is simply no current limit
at all. 100 amps from a cars alternator is fine. And not
considered punishing unless the temperature exceeds around
50 degrees centigrade.
Which means if the battery capacity is say 70 amp hour (ah)
you can charge at half of that so 35 amps then in this
example.
As long as maximum
voltage is controlled to 14.4v per battery (wet sealed and
GEL) or 14.7V (AGM type batteries).
The problem used to be one of heat. Runaway heat. Caused by
high internal resistance of deep cycle batteries. Which of
course heated them up! But then that heat caused even higher
resistance etc etc...
But modern AGM
batteries like the Optima, Hawker Odyssey and all the clones
can be used for starting duties in a car or truck as well!
Because they now have extremely low internal resistance.
It was this internal resistance that was the barrier to
higher charging currents in the past. The Optima's for e.g.
say that they can accept ANY inrush current. There is
absolutely NO limit on current at all. You can safely
connect them to a 500 amp charger if you wish and they say
that this is the PREFERRED method of charging in a cyclic
use. ... As long as
maximum battery voltage doesn't exceed 14.7v per battery.
(or 29.4 volts with the two optima's or hawker odyssey batteries in your wheelchair).
Most gels will happily accept a 1/2 c rate of charge. That's
typically 35 amps for a group 24 battery in a larger
powerchair.
Consequently they
are able to be charged quite safely by your 100 amp cars
alternator at fixed 14.4 volts. And many are quite obviously
every day!
When we use these in a powerchair we can actually charge at
any current we want to including 100 amps+... Because in a
few minutes the current will fall to about 30 amps anyway as
the battery voltage rises to match the 14.4 or 14.7 volts of
the charger.
Then as it becomes
charged up the current will fall further still. Once it stops
dropping verymuch and the charge rate falls to a couple of
amps naturally the charger will automatically revert to a
lower 13.2 or 13.4 volt controlled
"float" stage to keep the battery as healthy and ready for
use as possible forever.
There are other SERIOUS benefits apart from very fast
charging.
a) you can
give your chair a quick top up if you've been shopping for
example to almost fully charged in about half an hour
anytime in the day. So if you are going out later you know
you will have enough "juice" !!! Always feels better to
leave the house knowing you have a good charge/full tank!
b) topping
up regularly (say half way through every day) will vastly
lengthen the life of your batteries. I used to get just a
year by charging up every night. Because I USE my powerchair
very heavily. That means that I discharged my batteries
really deep (average of 80% discharged plus daily) -- But
because I now always recharge halfway through the day while
eating or sat at my computer the average discharge level is
now only 40 percent. You may read elsewhere that this
is a bad practice. Well its not! Although it does not mean
that you do not have to still do the overnight slow charge
as well every day that you use your chair. That slow multi
stage charger equalises the cells etc and completely tops up
your battery.
Now what difference does that make you may ask! Well
its like this...
You get many
thousands of discharge and recharge cycles if you don't
discharge your batteries much. Like a starter battery in a
car. That means they may last ten years if you are really
lucky! Keep your batteries topped up as much as possible it
pays dividends!
If you discharge
them at 50 percent you might get an estimated 600 or more
cycles. (Days?)
If you discharge
them 80 percent daily you will be lucky to get 300 cycles,
maybe less if you don't use really good batteries.
If you discharge
them to 90 percent you will get 100 cycles (days) if you are
lucky.
95 percent? Well
your chair will barely move, but count on 10 to 15 reliable
recharge cycles then throw them away. That's about 2 weeks
use.
Now do you see why
opportunity charging (say once a day for half an hour to 95
percent full) is such a good idea?
Things that murder Deep Cycle Batteries:
1. Being
discharged. Its true. Even deep cycle batteries are damaged
every time you use them. The deeper the discharge level the
more damage you do. The active plate material gets used up.
It gets used faster the deeper you cycle them. Think
about this. A single 100 percent discharge (flat battery)
may totally destroy your battery if its cheap. If its a
really good one you can do this between 3 and 7 times and
its fit only for the bin.
2. Being
left DISCHARGED. They sulphate internally. Fast. Discharged
means any state other than fully charged and preferably left
on a special Float or Maintenance charger. If you
don't have one then either buy one or use your powerchairs
charger once a week without fail overnight. If the batteries
are actually disconnected from the powerchair then top them
up once a month. The powerchair has a residual current drain
even when turned off! Some more than others. Even
disconnected the batteries have a natural self discharge,
meaning they go flat on their own! So keep them charged.
Things deep cycle
batteries like! (all lead based batteries in fact!):
1) Not being
discharged deeply.
2) Being kept as
close to fully charged as possible!
3) Being kept
cool. Don't store batteries anywhere warm. Outside or in a
garage is usually best. Batteries corrode and age
chemically as well as through discharge and sulphation - all
reactions happen slower in the cold!
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