PV panel on wheelchair

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Posted by charles Lyle on September 27, 2009, 11:31:01 AM

I have a Hoveround wheelchair which is powered by 2 12V batteries. I have a 5 watt PV panel that I want to mount on the back of the chair. There is a junction box where the 2 batteries connect, Can I just connect my panels + wire to the + on the Jbox and the same for the - side?

Posted by Thomas Allen Schmidt on September 27, 2009, 01:42:37 PM

Re: PV panel on wheelchair (Reply #1)

Make sure the PV module is 12 volts nominal as well. Be sure you have an easy and convenient way to disconnect the PV module from the battery as well as a way to protect the wire from PV to battery and a way to see at a glance the battery state of charge.
The main concern here is your safety.
If for example the battery is already fully charged and you happen to roll out into full sunlight and stay for a considerable length of time there is the possibility the batteries might get over charged and explode. Not a pretty picture. This why you need a disconnect and a battery state of charge indicator. An automated high voltage set point disconnect would be highly advisable. What if you were not able to disconnect it manually, say, if you fell asleep under those condition stated above?
Remember that, the wire will not only be carring power from the PV to the battery but all of the power stored in the battery can be unleashed all at once if the wire falls prey to a dead short causing a fire. Not a pretty picture either.

Be sure voltages are compatible.
A means of manual disconnect as well as high voltage automatic disconnect.
The correct size wire well protected from physical damage and fused properly.
A means of knowing exactly what the battery state of charge is.
A one way diode of the correct size will help keep power from the battery escaping to the PV module during low or no light levels.
Be sure that all devices wired inline are rated for open circuit PV voltage.
A 5 watt PV module at 12 volts nominal might produce as much as .65 amps under the right conditions.
Also, get to know your chairs battery pack. The type it is, probably a sealed cell, what its amphour rating is, and most importantly its charging criteria, what is its maximum charging voltage and all. Here are few websites that might be interesting to you.
http://www.treehugger.com/files/2008/05/solar-powered-wheelchairs_.php
http://www.evparts.com/
http://www.kronosport.com/
Maybe a bit extreme but maybe interesting too and some cool weblinks as well.
http://www.speedace.info/index.htm
http://www.nedra.com/

Posted by Ken Hall on September 28, 2009, 12:53:43 PM

Re: PV panel on wheelchair (Reply #2)

What are you trying to achieve ?
What is the amp hour rating of your batteries ?

If your chair is using the 35AH batteries or larger, the 5 watt panel is not going to provide any significant contribution to range or length of use.

Is it worth the cost/trouble just for novelty value ?

Posted by Robert Dinion on October 02, 2009, 03:44:14 PM

Re: PV panel on wheelchair (Reply #3)

A 5 Watt panel is not going to overcharge two 12V deep cycle wheelchair batteries. That is more like a maintenance charger with no where near enough power to damage or make anything explode. I'd actually go for a high efficiency 80W 12V nominal panel. Mount it like a fold up table off the back and give you some meaningful extra power. And even then I would still hook it up directly unless you leave your chair sitting in the sun unused for more than a day.
My biggest question would be are the batteries wired in series or parrallel.

You want to make sure the battery current cannot flow into your wheelchair because of a short in the panel wires. That is the only real danger here. A 1 amp inline automotive fuse fuse in those cute rubber holders in the positive wire run as close to where it connects to the battery as possible will protect you from that.
Other than that for 5 watts directly to the battery is fine, pos to pos and neg to neg of ONE of the batteries. That will work even if they are wired in series.

Robert Dinion
http://www.energyallover.com

Posted by Thomas Allen Schmidt on October 23, 2009, 03:50:53 PM

Re: PV panel on wheelchair (Reply #4)

http://farm4.static.flickr.com/3424/3192435737_6d81f4bb88.jpg
I am just as die hard as the next guy, maybe more than most. One of the reasons I like to watch auto racing from time to time is to witness the crashes. Its not the reason but they will and do happen. Whats so fascinating about it isn't so much the crash but the fact that so many drivers are able to walk away from a crash that looks so lethal. Of course I am looking at it from the viewpoint of what that crash would be like in a civilian model vehicle not the viewpoint of a professional that designs race car safety features, who anticipates those type of crashes.
Its always been my understanding that anytime one modifies something for enhanced performance that safety is important. (This is where possibilities and probabilities come into play.) Take the picture above for example. I've done that whole down hill on a skateboard thing in my day. Nothing like what that boy is contemplating but I do know that all it takes is one little pebble the size of a pea and that skateboard stops on a dime but the rider doesn't! He keeps on going at 25+ miles per hour. It didn't take me long to get some protection. It was too exhilarating to just quit but there is no joy in road rash either.

Mr. Dinion, if I offended you, or you Mr. Lyle by taking Mr. Lyle's safety into consideration I humbly apologize. I would sincerely like to know how it all turns out for you though Mr. Lyle. Please, write back after a while and let us know? I am sure there are a lot of folks on a fixed budget that would love to be able to increase the range of there stock electric personal mobility vehicle with PV modules. It might even prove to be of benefit to you at energyallover Mr. Dinion.

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