[SML] picky charger

[Jerry Durand]

The charger is two wire double insulated, but note it's a wireless one. 
It charges the device when it's just close to it.

The inverter output isn't floating, but I'm pretty sure the way it
generates a pure sine wave is the key.  In making a pure sine wave the
first thought that would come to mind is tying the neutral to ground in
the inverter and then just making a sine on the "hot", but that requires
it to have twice the internal DC voltage to go from positive peak to
negative peak.

So what this does is the "neutral" output is a pure square wave while
the "hot" output is two half sine waves.  When the "neutral" is at
ground, the "hot" makes a half wave from ground up to peak, then back to
ground.  When it gets back to ground, the "neutral" and "hot" are
switched together to peak voltage, then the "hot" makes an inverted wave
starting from the peak voltage, going down to ground at what would be
the - peak, then back up to peak voltage.  Both lines are then switched
together back to ground to start everything over again.

>From the point of view of any modern device (pretty much everything is
agnostic about which wire is "neutral" and which is "hot") this works great.

But, back to the wireless charger, this would be putting a mains
frequency (50/60Hz) bias into the air-coupled signal to the device to be
charged.  I suspect this either prevents the charger from detecting the
presence of a device to be charged or the device to be charged from
realizing it's within range of the charger.

Remember when battery chargers were a transformer, a full wave rectifier
if you were lucky, otherwise a single selenium rectifier, and that was
about it?

On 06/24/2018 04:47 AM, Dan Sheehan via Stagecraft wrote:
> 1) Is perhaps the charger miswired so it uses hot-to-ground instead of
> hot-to-neutral ?
>     You could check for this by making an adaptor with neutral opened.
>     If the charger works on this, it's wrong.
>
> 2) Inverter output is just floating ? 
>    That's perhaps a no-no, unless it's *specified* to be a ground
> isolator.
>    Should be OK, and desirable, to tie the inverter output  neutral to
> ground.
>
> 3) I've seen flourescent light fixtures (the 4-foot-long tube "shop
> light" kind)
>    not start if the metal case is not grounded, or in at least one case,
>   not start if the sheet metal cover is not present;  
>    touch the glass with your hand, and it lights up then runs find.
>   Apparently it requires capacitive coupling from the tube to ground
> to start.
>    
>
> On Sun, Jun 24, 2018 at 1:48 AM, Me via Stagecraft
> <stagecraft at theatrical.net <mailto:stagecraft at theatrical.net>> wrote:
>
>     I just had a wireless charger refuse to work on a pure sine wave
>     inverter.  I tried it on a wall outlet, works fine.  Tried again
>     on the inverter, no work.
>
>     I checked the inverter output with a 'scope in differential mode,
>     looked close to perfect.  So...???
>
>     Finally figured out the inverter isn't referenced to ground like
>     the mains are.  Nothing cares except this one charger.  Must be a
>     marginal design in the charger and the lack of a ground reference
>     kills the function.
>
>     Every day is a surprise!
>
>     -- 
>     Jerry Durand, Durand Interstellar, Inc.
>     www.DurandInterstellar.com <http://www.DurandInterstellar.com>
>     tel: +1 408 356-3886
>     @DurandInterstel
>
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>
>
> -- 
> ...Dan Sheehan
> Fixer of things that break
> TD Walpole (MA) Footlighters
>
>
>
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-- 
Jerry Durand, Durand Interstellar, Inc.
www.DurandInterstellar.com
tel: +1 408 356-3886
@DurandInterstel

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