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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