Shock from Dyson handheld battery vac...

[Deuce]

So, here is one to debate.

Wifey bought one of the cordless V8 dyson vacs, on the basis that all her friends have one. It's pretty handy.

But today I discovered an unusual feature. If it detects the motor is working too hard (in this case as the filter was blocked with dust), it will switch off until you release the trigger. However... As it cuts out it sends a hefty shock back out the charging port, sufficient to transfer into the palm of the user - in this case, me! After the first and second shock, I took it over to a radiator and held the charging port next to it, sure enough each time it cut out it would arc to the radiator. Each time I released the trigger before it cut out, no arc.

So, did Dyson protect against this problem, but only if the trigger is released, not if the vac cuts itself off - basically an oversight? Or is it perhaps some cruel way of forcing the user to clean the filter?

I did google, found this and others: https://forums.whirlpool.net.au/archive/2531043

Theories? I suspect the stupidly fast (100,000+ rpm) motor builds up quite some floating voltage which might be responsible for this 'feature'.

 

[Silly Sausage]

On the flip side, the motor does spin at over 100,000rpm - so when it does work, it's really very powerful at least.

Sounds like you want to be careful where you point that thing ...

 

[Deuce]

Sounds like you want to be careful where you point that thing ...

I'm a guy. The first thing I did to test the powerrrrrrr was obviously push it against my arm to see.

As I'm also a geek... The suction fan is 55mm diameter, so it has a circumference of 141.1mm. At 108,000 rpm. That means that each minute the outer tips of that fan are travelling a distance of 15.24km, or 567mph. So I guess they had to work quite hard to avoid the risk of a disintegrated motor/fan shooting through the housing

 

[static zap]

....... 15.24km, or 567mph. So I guess they had to work quite hard to avoid the risk of a disintegrated motor/fan shooting through the housing

Not quite breaking the sound barrier (depending on air conditions)
..I too remember similar calcs for a 4-1/2" 115mm angle grinder disk
doing near 600mph ... (why they are hard to break at speed)

 

[Deuce]

Not quite breaking the sound barrier (depending on air conditions)
..I too remember similar calcs for a 4-1/2" 115mm angle grinder disk
doing near 600mph ... (why they are hard to break at speed)

Another commonplace comparison - most modern turbo chargers in diesel cars spin at around 200,000 rpm under full duty. Apparently most turbo compressors are around 40mm dia so I guess the trailing edges are breaking the speed of sound. The aftershock effect of that would normally destroy a compressor but I guess they channel the air through in such a way as to avoid that effect.

 

[CACJL]

So, here is one to debate.

Wifey bought one of the cordless V8 dyson vacs, on the basis that all her friends have one. It's pretty handy.

But today I discovered an unusual feature. If it detects the motor is working too hard (in this case as the filter was blocked with dust), it will switch off until you release the trigger. However... As it cuts out it sends a hefty shock back out the charging port, sufficient to transfer into the palm of the user - in this case, me! After the first and second shock, I took it over to a radiator and held the charging port next to it, sure enough each time it cut out it would arc to the radiator. Each time I released the trigger before it cut out, no arc.

So, did Dyson protect against this problem, but only if the trigger is released, not if the vac cuts itself off - basically an oversight? Or is it perhaps some cruel way of forcing the user to clean the filter?

I did google, found this and others: https://forums.whirlpool.net.au/archive/2531043

Theories? I suspect the stupidly fast (100,000+ rpm) motor builds up quite some floating voltage which might be responsible for this 'feature'.

The motor is a high frequency squirrel cage induction type fed buy an inverter, so I suspect this static caused by friction with the carpet.

 

[stevels4]

“Are you sure it was just digestive biscuit crumbs you tried to suck up?”

 

[stevels4]

Got to be back EMF causing the spark I would think.

 

[static zap]

Higher frequencies , break the air down more easily ?
...and love leaking out of circuits capacitively...
(Still don't know exact protection - like a thermal disk/air pressure switch causing an O/C )
(Need BigClive to rip-one-apart!)

 

[static zap]

Higher frequencies , break the air down more easily ?
...and love leaking out of circuits capacitively...
(Still don't know exact protection - like a thermal disk/air pressure switch causing an O/C )
(Need BigClive to rip-one-apart!)

 

[Deuce]

The motor is a high frequency squirrel cage induction type fed buy an inverter, so I suspect this static caused by friction with the carpet.

It happens repeatedly even when holding it mid-air, and only when it cuts out itself, never when the trigger is released to turn it off.

I'm convinced they have snubbing for the flyback but for some reason the circuit doesn't work if the trigger is still held down when it cuts out.

I'd be interested to find out. It would make sense that when the trigger is released, the current is sent to a cap and held as a charge to kick start the motor when it's next turned on - such an arrangement could explain why de-energising the motor with the trigger held results in the current not having a path to the cap as intended.