EMI and a hard drive

[jman1310]

i thinking of putting a ehiem 1250 about 3" from a hard drive
i believe the EMI won't be a problem (you need a massive amount of magnetic force to write to a HD and then it's nearly touching the platter) but if anyone has had a different experience...

i'm also wondering if it's mistake to use silver solder vs tin solder in a all copper loop
the res is made from 1.5" copper pipe

thanks

jman

[JamesAvery22]

Someone here did the calculations and found out it takes something like those huge junk yard crane magnets that pick up cars to damage the platter and even then the magnet has to be close to the HD.

Dunno about the redox potential of silver/copper though... All I know is silver and aluminum is very bad

[BGP Spook]

Under standard conditions of 1 atm, and 1 M worth of ions in solution.
Ag+ to Ag has a reduction potential of 0.799 volts.
Cu++ to Cu has a reduction potential of 0.337 volts.
Sn++ to Sn has a reduction potential of -0.14 volts.

If under standard conditions with Ag used, then 0.799 - 0.337 = 0.662 volts with the Ag as the cathod. Therefore, the Cu would dissolve and the Ag would plate if a reaction were to occur.

I think it is important to point out that you will almost certainly see little reaction unless you introduce a large amount of some electrolyte.

But maybe I am wrong.

[bobkoure]

I suspect the question had more to do with whether the EMI from a pump withing 3" could create enough flux to either change bits on the media or maybe to somehow impede action of the arm.
AFAIK there is no solution inside a hard drive, just atmosphere - or am I missing something here.

Oh - and I'm pretty sure that the pump should be no problem - the casing of a hard drive should be a pretty good Faraday cage...

[BGP Spook]

Originally Posted by jman1310

i'm also wondering if it's mistake to use silver solder vs tin solder in a all copper loop
the res is made from 1.5" copper pipe

Something perhaps....

[metarinka]

don't think silver solder should be a problem as it's specced for residential water pipes, and the amount of silver your talking about is soo small as on a properly sweated joint I would say only a few sq MM of solder are ever exposed to water.

as far as the pump, they have never disturbed Hdd's to my knowledge. I could only see it being a problem if you had a 12v pump, on the same rail, with a crappy psu, and the pump was putting a lot of interference in the rail. Also modern HDD's already have an extremely powerful rare earth magnet in them, and they still are cast steel cases so it would take a lot to mess em up

[Butcher]

Bear in mind also that the motor of a HDD is likely to put out more EMI than your pump at that distance...

As for what's in a HDD - it's just air at standard atmospheric pressure.

[Ice Czar]

HDDs are well shielded
the real issue would be the pump's EMF and any unshielded data cable
of course EMF obeys the inverse square law, and you can always shield the cable

[redleader]

The 1250 doesn't seem to put out much of a field. Put it on a TV and you get nothing, where as my doorknob causes the same TV to blur at 1/10 that distance. Should be ok.

At least mine has been fine since 2001 sitting in an HD bay