Wireless Charging

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Wireless Charging

Postby expresso » 06 Oct 2019, 18:18

I have a friend who is in vegas for work - wheelchair stuff etc, - this is what was shown - whats your take on this ?

charges lithium also - how i dont know - 80% charge in 30 mins - all sounds great - but will it work and when
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Re: Wireless Charging

Postby expresso » 06 Oct 2019, 18:19

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Re: Wireless Charging

Postby Burgerman » 06 Oct 2019, 18:35

It is 250 watts maximum, and 80% efficient.

So in half an hour would give you 80% or its 250W div by 2 since its only 250 watts for half an hour. It can return at best 125 watt hours in 30 mins...

Thats about the same as a stock 8A wheelchair charger power level, less 20% waste. 12 hours to charge a 100Ah pack. 24 hours to charge a 200Ah one.

So basically you need 4 or 5 of them.
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Re: Wireless Charging

Postby expresso » 06 Oct 2019, 18:48

theres no info. on the site and no talk about lithium on the site - how would that even work - balance etc,
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Re: Wireless Charging

Postby rickystyx » 06 Oct 2019, 18:59

It looks like it is just a basic electrical transformer with one coil mounted on the chair and the other half on the stand - Transformers are very efficient so nothing really clever in it and you would have to ensure it lined up carefully or lose all of that efficiency - not that much better than connecting a plug really
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Re: Wireless Charging

Postby Burgerman » 06 Oct 2019, 19:07

heres no info. on the site and no talk about lithium on the site - how would that even work - balance etc,


Because 'everyone' knows that all lithium batteries MUST have a BMS...

Will it work? Yes slowly and wastes 10 percent of the electricity. At least.
Will it charge a battery in 30 mins to 80% ? Yes if thats a Lithium Ion 4Ah pack. (not 40.) So it could charge my tiny quadcopter LiPo at around 7A and thats 80% in 45 mins.
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Re: Wireless Charging

Postby Gnomatic » 06 Oct 2019, 19:27

That doesn't seem well thought out. I mean the charger itself is huge compared to a regular mobility charger. I understand its wireless, but that benefit seems small compared to having a big clunky post thats not very mobile and eats a lot of floor space.
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Re: Wireless Charging

Postby Burgerman » 06 Oct 2019, 19:32

You could invent a small plug in connector on a tiny wire, and save a lot of space. It could use an XLR connector as they are easy to plug in. Err. wait...

Another case of some bunch of EDU establisment students forcing some technolgy into a stupid place. No doubt a fortune spend n research and development grants etc already based on highly dubious claims.
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Re: Wireless Charging

Postby foghornleghorn » 06 Oct 2019, 20:08

Does it stand itself up again like a Weeble when you knock it over?
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Re: Wireless Charging

Postby c500user » 07 Oct 2019, 11:25

rickystyx wrote:It looks like it is just a basic electrical transformer with one coil mounted on the chair and the other half on the stand - Transformers are very efficient so nothing really clever in it and you would have to ensure it lined up carefully or lose all of that efficiency - not that much better than connecting a plug really


It is not quite as simple as you suggest. If you were to connect one coil of a transformer to your charger and the other to your chair make sure you move away very quickly. Be prepared for sparks and possibly fire because you would fry the transformer!
Transformers are AC only. They cannot be used for DC.
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Re: Wireless Charging

Postby Irving » 07 Oct 2019, 11:46

c500user wrote:
rickystyx wrote:It looks like it is just a basic electrical transformer with one coil mounted on the chair and the other half on the stand - Transformers are very efficient so nothing really clever in it and you would have to ensure it lined up carefully or lose all of that efficiency - not that much better than connecting a plug really


It is not quite as simple as you suggest. If you were to connect one coil of a transformer to your charger and the other to your chair make sure you move away very quickly. Be prepared for sparks and possibly fire because you would fry the transformer!
Transformers are AC only. They cannot be used for DC.

I don't think Ricky was advocating connecting DC to a transformer. He is indeed correct about the efficiency of transformers and that wireless charging is effectively a transformer. However, wireless charging uses much higher frequencies than a conventional mains transformer, which is a magnetic device, and is more akin to radio transmission and as such is a very lossy process. I've recently been working on remotely charging/powering medical implants from outside the body using wireless techniques and even at those short distances & low powers losses can be 30% or more!
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Re: Wireless Charging

Postby Burgerman » 07 Oct 2019, 12:04

Part of the issue is that a transformer gets its efficiency from its laminated iron core. And with wireless charging there is no continuous iron core. So high frequences are used to get it to transfer its power more efficiently. But it needs a lot of area, and the closer the better.

Its OK to charge a proper powerchair with 70Ah batts with 8A as long as you have 8 or 10 hours or more.
Its not OK to charge a 200Ah lithium battery at 8A though because that would take a rather long time! Which is why the 40A PL8 charger is better. Even at 40A, you need 5 solid hours and a bit as CV declines.

So that gadget would need to be much, much bigger! And its already too big.
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Re: Wireless Charging

Postby Irving » 07 Oct 2019, 12:27

Burgerman wrote:Part of the issue is that a transformer gets its efficiency from its laminated iron core. And with wireless charging there is no continuous iron core. So high frequences are used to get it to transfer its power more efficiently. But it needs a lot of area, and the closer the better.

Its OK to charge a proper powerchair with 70Ah batts with 8A as long as you have 8 or 10 hours or more.
Its not OK to charge a 200Ah lithium battery at 8A though because that would take a rather long time! Which is why the 40A PL8 charger is better. Even at 40A, you need 5 solid hours and a bit as CV declines.

So that gadget would need to be much, much bigger! And its already too big.

Indeed! Wireless charging on the move, eg to charge a EV as it travels up the road at a low level might make sense in the future with massively efficient batteries, but for now its best-suited to low-power stuff, less mission-critical stuff, like charging a phone...
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Re: Wireless Charging

Postby ex-Gooserider » 08 Oct 2019, 02:12

I don't know if it works as claimed, (I'm not getting my hopes up....) but I could see it meeting a need for some users....

We have had plenty of discussions featuring users that did not have the ability to plug in even a low force plug like an XLR - and are therefore left at the mercy of clueless carers, etc... Even when plugging in isn't a problem, getting carers to work something as complex as a 'Shirley supply' let alone a PL8 is a challenge....

This device claims to have a robot arm carrying the transmitter that can automagically guide it into the chair mounted receiver unit, w/ little or no user / carer intervention needed - just get the chair in the right general area (they don't tell you how close to the ideal location you need to be) and the charger does the rest (might require a button push?)

Granted it wastes energy, and all the other issues mentioned, but the ease of use seems like it would be a big winner for some...

Even for one of us clueful types I can imagine (and have occasionally daydreamed about) the idea of driving into the bedroom, transferring to bed, then sending the chair back to the living room (either RC, or autonomously if dreaming big...) to charge... IMHO the biggest problem w/ doing something like this is plugging in to the charger, which this thing would solve....

I'm still not planning to buy one...

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Re: Wireless Charging

Postby Burgerman » 08 Oct 2019, 02:20

Since its large and complicated, and guides itself in, and positions itself correctly, wouldnt it just make more sense to have metal contacts... Like my auto mower, kettle base, etc.

They are just adding this wireless part for no sensible reason. Then it could charge faster. And with higher efficiency and 'save the planet'...
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Re: Wireless Charging

Postby Irving » 08 Oct 2019, 03:01

Quite! In the hospital they have a number of 'Harris' human-guided walk-along tractor units, used for towing refuse crates, beds, etc up the 6° slope in the main corridor. At each end of the slope and elsewhere there are charging bays which the tractor pretty much finds its own way into on a couple of guide rails to a set of contacts. About 10sec after it 'docks' the charging light goes on and it charges at 100A according to the label. The contacts are a sliding arrangement so the charge current is turned off before the tractor has moved about 50mm as it is pulled out if the bay and they disconnect. It's definitely not rocket science and, more importantly, hospital porter proof! Shouldn't be hard to come up with a similar arrangement on a wheelchair.
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Re: Wireless Charging

Postby Burgerman » 08 Oct 2019, 04:24

During the space race, the US developed a pen that worked in microgravity with a pump built in etc at some huge cost. The russians used a pencil.


Its another student project. They are reinventing the wheel, and are after research, grant or other funding to 'develop' the device... And dumb investors will oblige because they are stupid. Thats why we now have those oddball stair climbing tracked powerchairs. And the whill powerchair... Those will vanish without trace in the end.
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Re: Wireless Charging

Postby ex-Gooserider » 15 Oct 2019, 05:45

In the US kettles seem to use wireless connections, ditto electric toothbrushes and lots of other small electronics (but our phones still have to plug in... ) czy :(

However they are using very close coupling in that you have a charger base that the device drops onto so basically just the two layers of plastic housing is all that separates the inductors...

This has the advantage of totally isolating the shocking bits from the user, and also means that there is no concern about water / dirt / corrosion, etc. on metal contacts... OTOH I could see the same sort of 'docking arm' arrangement being used w/ an XLR plug or other low-insertion force connector, assuming there was good enough guidance for the arm to find the right hole... As always, its a question of picking the trade-offs....

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Burgerman wrote:Since its large and complicated, and guides itself in, and positions itself correctly, wouldnt it just make more sense to have metal contacts... Like my auto mower, kettle base, etc.

They are just adding this wireless part for no sensible reason. Then it could charge faster. And with higher efficiency and 'save the planet'...
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Re: Wireless Charging

Postby Irving » 15 Oct 2019, 07:39

ex-Gooserider wrote:In the US kettles seem to use wireless connections, ditto electric toothbrushes and lots of other small electronics (but our phones still have to plug in... ) czy :(

However they are using very close coupling in that you have a charger base that the device drops onto so basically just the two layers of plastic housing is all that separates the inductors...

This has the advantage of totally isolating the shocking bits from the user, and also means that there is no concern about water / dirt / corrosion, etc. on metal contacts... OTOH I could see the same sort of 'docking arm' arrangement being used w/ an XLR plug or other low-insertion force connector, assuming there was good enough guidance for the arm to find the right hole... As always, its a question of picking the trade-offs....

ex-Gooserider

Burgerman wrote:Since its large and complicated, and guides itself in, and positions itself correctly, wouldnt it just make more sense to have metal contacts... Like my auto mower, kettle base, etc.

They are just adding this wireless part for no sensible reason. Then it could charge faster. And with higher efficiency and 'save the planet'...

No, they aren't technically wireless as the coupling is magnetic - it's a 50/60Hz transformer with a large air gap. Though for the kettle I'd be surprised if it wasn't a hidden contact. On my De'longhi there's a neat retracting cover over the contacts that slides away as the kettle is put on the base - the design makes it virtually impossible to slide it away by hand. For a 3kW kettle the 'wireless' loss of the air gap would be enormous and I doubt it would meet power factor or energy efficiency ratings.
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Re: Wireless Charging

Postby Burgerman » 15 Oct 2019, 10:34

Yes there is. That was my point. The mower too. And many things that transfer power.

Since its large and complicated, and guides itself in, and positions itself correctly, wouldnt it just make more sense to have metal contacts... Like my auto mower, kettle base, etc.
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Re: Wireless Charging

Postby rickystyx » 15 Oct 2019, 15:47

Irving wrote:
c500user wrote:
rickystyx wrote:It looks like it is just a basic electrical transformer with one coil mounted on the chair and the other half on the stand - Transformers are very efficient so nothing really clever in it and you would have to ensure it lined up carefully or lose all of that efficiency - not that much better than connecting a plug really


It is not quite as simple as you suggest. If you were to connect one coil of a transformer to your charger and the other to your chair make sure you move away very quickly. Be prepared for sparks and possibly fire because you would fry the transformer!
Transformers are AC only. They cannot be used for DC.

I don't think Ricky was advocating connecting DC to a transformer. He is indeed correct about the efficiency of transformers and that wireless charging is effectively a transformer. However, wireless charging uses much higher frequencies than a conventional mains transformer, which is a magnetic device, and is more akin to radio transmission and as such is a very lossy process. I've recently been working on remotely charging/powering medical implants from outside the body using wireless techniques and even at those short distances & low powers losses can be 30% or more!


I certainly wasn't suggesting such an idea. As an Electrical engineer who has worked on our transmission supply I have a very good knowledge of how transformers work and although this is an idea that "could work" its very design and practicability rules it out as anything other than a daft idea in my book. yes it could be done but then again you could have a two rail drive over system that would do a much better job and much easier with virtually no losses but it doesn't really make it much better than plugging something in - both would restrict the use of the chair during charging.
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