Weird Electric issue?

Scozzer · 12 May 2015 at 11:39

Hi Guys,

Not really sure of the best place for this but I'll start off here anyway.

First off I have an Electric Vehicle with a 7kw 32amp charger hooked up (This one) I got a new iMac yesterday and when (and only when) the vehicle is charging I get a high pitched whistle/hum from the computer. Its pretty much the same frequency as the hum that comes off the car. This happens when the computer is on power up or power down and will only stop if I unplug or cut the power at the socket (or the car stops charging). I also had another iMac before this one that did;t display this problem at all.

Knowing nothing about electrics I'd like some ideas if you guys have any? If you guys think it's the computer I can get it swapped out for a new one but maybe its some dodgy electrics or something?

TIA.

lord filbuster · 12 May 2015 at 12:43

Sounds like the charger is adding some harmonic distortion to your mains supply, and this is causing the hum from your Imacs power supply.

You could try switching it for a different Imac, but if they have the same model power supply it may well have issues anyway.

Scozzer · 12 May 2015 at 12:52

Thanks for the reply, much appreciated. That makes sense. Would there be any way to block harmonic distortion with a wall plug adapter or something?

lord filbuster · 12 May 2015 at 13:03

You'd probably have to get an uninterruptible power supply, but they are relatively large.

There are a few surge protector strips marketed as power conditioners, but that is a bit of a con, as I think they just protect against power surges, not remove distortion.

Have you tried speaking to the person who installed the charger?

Scozzer · 12 May 2015 at 13:18

Thanks for the info again, I didn't speak to them yet no as I wasn't sure where the issue actually lay. I guess that can be my next stop.

Another weird thing I just found out is that the volume is directly related to the brightness of the screen, the higher the brightness the lower the volume of the buzz.

This might sound like a stupid question but would it be damaging to the computer? I generally charge the car at night anyway so the actual impact of this would be minimal, although if it was fixable that would definitely be the route I'd take.

Hilly · 12 May 2015 at 13:28

It'll likely be the invertor within the lcd then; The more power you put through the screen (e.g. brightness), the higher the buzz.

Can't say for any certain whether or not it would affect the health of the system though I'm afraid!

Scozzer · 12 May 2015 at 14:03

hilly said:
It'll likely be the invertor within the lcd then; The more power you put through the screen (e.g. brightness), the higher the buzz.

Yeah its quite bizarre actually as this seems to be working in the opposite way to that, the lower the brightness (darker the screen) the louder the buzz. Frequency stays constant.

lord filbuster · 12 May 2015 at 15:22

It could probably damage very sensitive electronics, but I doubt it would cause any real issues for household stuff.

If anything it might be worth getting the charger checked, just to make sure it is all installed correctly.

bitslice · 12 May 2015 at 20:19

lord filbuster said:
Sounds like the charger is adding some harmonic distortion to your mains supply, and this is causing the hum from your Imacs power supply.

This,
and it's not going to damage anything.

It is fixable, ideally with an proper EMI line filter before the charger,
a "surge protector" is going to do squat.