wheelchair overheating?

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wheelchair overheating?

Postby kendradog » 15 Aug 2019, 22:27

I drove about 4 miles over bumpy, hilly sidewalks and streets in 90 degree weather. At one point the wheelchair, an 8-year-old Permobil Street with high speed motors and fairly recent MK group 24 batteries, was unable to climb simple ramps. It would just not move. The joystick displayed a "joystick" icon. Sometimes it would not go up the ramp, sometimes it would not move at all.

I turned the wheelchair off and let it sit for a minute. Then it was fine.

Could this be due to overheating?

If so, is there some other warning or indication I can use before it just stops working? Or is it something more serious?
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Re: wheelchair overheating?

Postby Burgerman » 15 Aug 2019, 22:38

Its because the PM under the seat has overheated. To protect itself it automatically reduced maximum amps while it cools. Yes waiting a while is the only way. The thing can have a fan fitted if it becomes a problem, as in sport etc. No damage just frustrating. Its programmed to roll back power as it gets hot.
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Re: wheelchair overheating?

Postby Gnomatic » 17 Aug 2019, 23:04

I think the PM on my chair is worn out, possibly. The R-net PM90 on my V6. Evey summer I go to this particular park with miles of horse trails, with many steep long climbs and descents. Lots of change in elevation. The trails always give my chair a workout. If I take the trails as fast as possible, the chair would overheat pretty quick on the terrain. But typically on these trails, I'm going pretty slow, no faster than pedestrian walking/hiking speed. And as long as I'm not in a hurry, I've can pretty much stay on the trails all afternoon, as long as I want.(at least since I converted to lithium)

At least I was till this year's visit. This summer I've noticed the chair cutting power and overheating on less steep trails with certainly less lengthy ascents. So I figured I might have a problem on the horse trails of this park. But my chair performed much worse than I anticipated. It was overheating w/ in 10 minutes of my first ascent. It was done and I had to leave the park for flatter terrain. If I did a long decent, the chair would not have been able to climb out, and I would have been stuck. It was a real bummer because its one of my favorite hikes to do in the summer.

Not saying I haven't put on a pound or two over previous years, but if I did, its been nothing dramatic. So I suspect the PM might need replaced. But what about the motors, could they be worn out too? Maybe they are not efficient as they used to be and are drawing more amps??? The chair is a 4-5yr old V6, and in all previous years, it handled this challenging hike like a champ. But this year, it barely made it out of the starting blocks before it was kaput.
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Re: wheelchair overheating?

Postby Burgerman » 17 Aug 2019, 23:26

Motors lose efficiency over time and use. So take more Amps (more heat in the PM) all of the time. So that might be it. But I am not sure power modules wear out. They work or not. Unless you have a failing mosfet or something.

Also, user weight. Global warming :lol: , flatter tyres, mebe...
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Re: wheelchair overheating?

Postby Irving » 18 Aug 2019, 09:07

Could be dirty contacts on motor/battery cables into controller. Even a couple of extra mOhm will have a heating effect. Unlikely to be a MOSFET failing, but could be thermal paste has dried out so not good contact with heatsink, or heatsink fins clogged. Wouldn't hurt to get controller out and give it a once over & a clean. Also worn motor brushes could be detrimental. Any or all of these could tip it over the edge with those outside temperatures.
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Re: wheelchair overheating?

Postby ex-Gooserider » 20 Aug 2019, 02:08

I haven't opened up an R-net, but I know Pilot+ PM's use silicone rubber sheet rather than thermal paste so that is unlikely to be an issue (very few MFG's use thermal paste anymore, as sil-pad material is cheaper and easier, so lower labor costs - it is also claimed have greater thermal efficiency than the old thermal paste plus mica insulators...)

I agree that it is very unlikely to be any sort of 'wear' on the PM electronics - as a rule electronics don't wear, they either work or fail... However dirt on the module, connections, etc. can add heat and reduce cooling, ditto worn motors... However the most likely suspect (as usual) is batteries that aren't at their best....

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