The United States is in the dog days of summer, with torturous temperatures in the 90s and triple
digits spanning from one coast to the other. Most recognize the effects of excessive heat on our pets,
cars, power grids, and certainly ourselves, where it's wise to reduce activities and maintain heat-related
awareness during sweltering summer temperatures. However, just like our pets, cars, power grids, and
ourselves, our powerchairs can also be affected by excessive heat, prone to thermal fold back, the condition
where power decreases due to excessive heat within the electronics.|
If you've ever noticed warmth
from an electrical appliance, you know that electrical current generates heat, and the greater the current,
the hotter a device can become. A powerchair, of course, is an electrical system, and as a result, generates
heat - specifically in the motors and controller. Now, motors certainly get hot - exceptionally hot
in some instances - and with enough heat, they will fail. But, in order to protect the motors and overall
powerchair system from overheating, the controller - a powerchair's central processor, you might say
- features thermal protection, where a thermometer tells the controller to reduce power at a certain
temperature to prevent additional generation of heat that could lead to component failure. Just as the
more energy you exert, the hotter you become, the same is true for a powerchair - but the powerchair's
thermal fold back knows at what point to reduce power, preventing damage to the electrical system. Thermal
fold back, then, is when a powerchair reduces its power during extreme heat and use, characterized by
noticeably less speed and power.
With thermal fold back relating to heat, hot air temperatures
make the condition far more likely to occur in the swelter of summer than during cooler times of year.
One may be able to drive his or her powerchair on grass or rough terrain for an extended period in 70-degree
weather without an issue; however, in 90-degree weather, the powerchair may go into thermal fold back
within minutes - hotter air temperatures simply create hotter controller temperatures from the start.
With all said, this doesn't mean that powerchairs don't function fine outdoors in extreme heat, as
they absolutely do - but under appropriate conditions. A powerchair is most efficient at a constant
speed on a smooth, hard, flat surface - such as cruising on a sidewalk - so most powerchairs have no
issues going to a store or bus stop in very hot weather. The thermal fold back issue comes into play
when demanding increased power from a powerchair - as with trying to tackle soft, grassy, hilly, or rough
terrain - in exceptional heat, where two or three times as much power is demanded over more hospitable
uses, drastically heating the system within minute. In this way, avoiding power-heavy outdoor conditions
in extreme heat is the surest way to avoid thermal fold back.
Just as thermal fold back is a factor
of temperature, its resolution is a factor of time - that is, letting a powerchair sit, turned off, allows
the system to cool, ultimately restoring full power. Allowing the system to cool can, however, take
a long time, and if the powerchair is driven before it's entirely cool, it may return to fold back very
rapidly. For this reason, if one finds his or her powerchair going into fold back, he or she should
get out of the terrain, to a safe spot, allowing the powerchair time to cool (typically 15- to 30 minutes,
but extreme temperatures can inhibit timely cooling). And, ideally, you should avoid such rough terrain
on extremely hot days, if possible.
In the end, play it safe: If it's too hot for you to safely
be outside, in the sun, for an extended period, it's likely too hot for your powerchair, as well. Understand
that thermal fold back can occur, and avoid those conditions. After all, take it from me, your powerchair
likes sitting in a nice air condition room, in front of the television on a scorching Sunday as much
as you do - or, at least that's what my powerchair tells me.
Published 8/06, Copyright 2006, WheelchairJunkie.com