Strange electrical affect

Forums › Home Workshop DIY › Strange electrical affect

linw

2849 posts

Uber Geek

#279743 5-Nov-2020 07:15

Can't see how to google this one so will ask the experts here!

We have two recliner chairs with electric motors (29V Adaptor) to control them. On one of them I get an electrical "buzz" feeling if I touch the aluminium plate that holds the push buttons and USB socket. (I say buzz as I can't think of a word to describe the feel!).

And if I touch that plate with one hand, and touch my laptop keyboard surround (aluminium?) with the other hand, I get the "buzz" feel there, but only if the laptop has its charger connected.

Wondering what causes this and remembering it only happens on one of our chairs.

Not worried but definitely curious.

1 | 2

20575 posts

Uber Geek

Trusted

Lifetime subscriber

#2598027 5-Nov-2020 07:47

Sounds like what happened when I touched my metal dishwasher. Turned out to be a faulty mains circuit, which if left may have eventually electrocuted us. Try swapping the power supplies from the chairs to work out what's faulty, the chair or the PSU, then get whatever is faulty fixed.

gzt

17105 posts

Uber Geek

Lifetime subscriber

#2598031 5-Nov-2020 08:05

Super dangerous. Unplug that chair until you get it fixed. Have the other chair inspected for the same fault.

It's likely you are touching mains voltage and the only thing coincidentally saving you from death is an incomplete path to earth.

linw

2849 posts

Uber Geek

#2598041 5-Nov-2020 08:20

Swapped power supplies and the effect was felt only on the original chair so seems to rule out power supplies.

We have to remember that your dishwasher is a different beast being powered from the mains. These chairs are powered by 29V DC so not really concerned about electrocution. Just puzzled.

Technofreak

6530 posts

Uber Geek

Trusted

#2598059 5-Nov-2020 08:40

I had a similar issue with a power supply on my laptop. I had two, one I used for travel and another. It only happened with one of the power supplies. It never caused me any issues but I think it's worth getting it looked at.

Sony Xperia XA2 running Sailfish OS. https://sailfishos.org The true independent open source mobile OS
Samsung Galaxy Tab S6
Dell Inspiron 14z i5

mrdrifter

576 posts

Ultimate Geek

ID Verified

Trusted

#2598086 5-Nov-2020 08:51

Is this a similar sensation to that which many people report with electric blankets - a kind of 'buzz' feeling?

Technofreak

6530 posts

Uber Geek

Trusted

#2598100 5-Nov-2020 09:11

mrdrifter:

Is this a similar sensation to that which many people report with electric blankets - a kind of 'buzz' feeling?

I think so.

Sony Xperia XA2 running Sailfish OS. https://sailfishos.org The true independent open source mobile OS
Samsung Galaxy Tab S6
Dell Inspiron 14z i5

frankv

5680 posts

Uber Geek

Lifetime subscriber

#2598155 5-Nov-2020 10:22

linw:

These chairs are powered by 29V DC so not really concerned about electrocution.

You're sure that they are powered by DC? Some power supplies output AC.

Are they plugged into a circuit protected by an RCD, or just a fuse?

Equinox IT

Cloud spending continues to surge globally, but most organisations haven’t made the changes necessary to maximise the value and cost-efficiency benefits of their cloud investments. Download the whitepaper From Overspend to Advantage now.

Eva888

2428 posts

Uber Geek

Lifetime subscriber

#2598209 5-Nov-2020 11:27

Is there an electric blanket on the chair? Years ago on my side of the bed with the electric blanket on, if I touched the wooden wall behind me I would get that fuzzy buzz feeling in my hands. This would happen even if the blanket was off on my side. Eventually we figured out that unplugging the blanket stopped it. Needless to say, got a new blanket.

wellygary

8312 posts

Uber Geek

#2598243 5-Nov-2020 12:15

There is some current leaking...

-Changing the power supply wont fix it as its likely they wiring in the chair

-The most likely source is the 5V power feed to the USB socket - but it could be something else...

On the plus side its transformed voltage, but as I was told by my Electrician dad when I was a kid

"its the volt that jolts, and the mills (Mamps) that kills"

- Get it checked

DonH

230 posts

Master Geek

Lifetime subscriber

#2598267 5-Nov-2020 13:02

The fuzzy feeling is called by capacitive coupling between the live side of the mains and you or the surface that you touch. For example, laying on an electric blanket, the blanket is one "plate" of a capacitor and your body is the other. If you touch a grounded surface, you'll feel the fuzzy feeling. Alarming, but not dangerous in itself.

Are the power packs plugged in to a power strip, or 2 wall sockets? If wall sockets, swap them between sockets and see if the effect moves to the other chair. If they are electronic (SMPS) packs, they will have a small capacitor connected internally between the 29 volt DC side and (hopefully) the neutral mains pin. If one mains wall socket is miswired, the capacitor may be connected to the phase (live) pin.

Edit: If they have a 3 pin power cord, it's possible that the earth wire or the earth connection in the wall socket is faulty.

People hear what they see. - Doris Day

linw

2849 posts

Uber Geek

#2598284 5-Nov-2020 13:46

OK, no electric blanket.

Power pack definitely says DC.

Both packs are on the same power strip.

Two pin plugs.

This circuit will be RCD protected.

It has to be in the chair as there is no fuzz in the other chair with either pwr pack, I get the fuzz with both pwr packs in the problem chair, and each pwr pack is sourced from the same place.

hsvhel

1237 posts

Uber Geek

ID Verified

#2598288 5-Nov-2020 13:53

Can you isolate the power strip from the situation?

Referral Link Quic

Free Setup use R502152EQH6OK on check out

tripper1000

1617 posts

Uber Geek

#2598293 5-Nov-2020 14:07

Assuming you've confirmed that the power supply hasn't gotten wet or mechanically damaged, then this isn't uncommon with switch-mode-power supplies on metal items, that aren't referenced to earth. It's just a floating voltage on the DC side with respect to ground. The current is so microscopic it isn't dangerous. You will notice it more on sensitive skin (sides of fingers, inside of arm, lips, neck etc) but not usually through hands etc.

It happens on my car when using a supposedly double insulated smart charger. I've also noticed it on laptops and DVD's.

Here is the link on the Dell Website letting customers know that it's nothing to be alarmed about:

https://www.dell.com/community/Laptops-General-Read-Only/Two-prong-AC-adapters-tingling-sensation/td-p/3640871

DonH

230 posts

Master Geek

Lifetime subscriber

#2598322 5-Nov-2020 15:08

OK then, one chair may an electrical connection between the plate (or the chair's metal frame) and the DC supply and the other one doesn't. Easy to check with a multimeter.

From this distance there's no way to tell if the connection is intentional (both chairs should have it) or accidental (neither chair should have it).

Call an electrician.

People hear what they see. - Doris Day

gregmcc

2147 posts

Uber Geek

ID Verified

Trusted

Lifetime subscriber

#2598373 5-Nov-2020 17:09

wellygary:

There is some current leaking...

-Changing the power supply wont fix it as its likely they wiring in the chair

-The most likely source is the 5V power feed to the USB socket - but it could be something else...

On the plus side its transformed voltage, but as I was told by my Electrician dad when I was a kid

"its the volt that jolts, and the mills (Mamps) that kills"

- Get it checked

Most modern Power supplies are switchmode, while they have a transformer in the it is nowhere as big and heavy as the traditional old style power adapter. The older ones were fully isolated from the mains, the new one are not and a poorly designed PSU and a good earth return will let enough current flow to give you a tingle - That's a good sign that something is wrong. time to talk to the place you got it from as it may not be electrically safe.

1 | 2