Any risks of locating Cable Modem and router near A/C unit?

[mshan]

During warmer months, the ac cycles on and off frequently during the day.

Just wondering if there is any risk of long-term damage from say transmitted electromagnetic pulses of ac turning on and off to electronics located a couple feet away, but separated by house wall.

I have noticed spikes and surges on certain electrical outlets in home, and just wondering if the presumed electromagnetic pulses associated with off and on cycles could eventually lead to premature failure of electronics located close by?

Or are these pulses just too weak to be meaningful in anyway?

 

[DeathRayLoveMachine]

If your AC were generating large EMPs every time it turned on or off, the FCC* would be wanting a word with your AC's manufacturer. Just try to make sure the routers are on a different electrical circuit than the AC (as in, controlled by a different switch in your mains box) and maybe buy a surge suppressor.

(*I assume you're in the US.)

 

[Modelworks]

EMP not an issue. Dips and spikes in current very well could be. All depends on how the home is wired. In my apartment when the AC (central unit) switches on my ups always clicks over for about 3 seconds signifying that the power dipped below 118 volts, its trip point. Most things like a pc don't care, the PSU can ride out a short dip like that, other things can be more sensitive.

 

[mshan]

I put the modem and router on a small APC surge suppressor with some battery backup capabilities. Also put my iMac in second bedroom on same battery backup / surge suppresion.

My hi-fi rig is in another room that seems to get a temporary sag when ac kicks in in summer. No surge suppression here. DAC is always powered on, pre-amp in standby, and amps are only turned on when listening to system. Any risk of long-term damage here?

Based upon how my breaker box is labelled, I think AC is on it's own line separate from everything else.

 

[TastesLikeChicken]

Originally posted by: mshan
I put the modem and router on a small APC surge suppressor with some battery backup capabilities. Also put my iMac in second bedroom on same battery backup / surge suppresion.

My hi-fi rig is in another room that seems to get a temporary sag when ac kicks in in summer. No surge suppression here. DAC is always powered on, pre-amp in standby, and amps are only turned on when listening to system. Any risk of long-term damage here?

Based upon how my breaker box is labelled, I think AC is on it's own line separate from everything else.

Your A/C runs on its own 220V/240V circuit from the breaker box. It's code. All of the electricity in your house is provided from the same two lines coming in to the breaker box so when your A/C kicks on there is a current draw that can cause a momentary drop in your 120V circuits. Just about all electrical appliances and devices have power regulation circuitry built into them to compensate for those standard dips and spikes and in cases of your A/C cycling it really shouldn't be an issue. However, you should have surge suppression on those components in the case of a lightning strike; at least for the expensive components. No component's protection circuitry is going to guard against the surge created by lightning.

 

[mshan]

Can all of those spikes, surges, and dips transmitted through power lines lead to early, pre-mature failure of electronic components, if they are not protected by a surge suppressor?

Or is that really only an issue with lightning strike?

 

[DeathRayLoveMachine]

When I first read your post, I figured you had a window-mounted air conditioner unit running off 110VAC, but actually it sounds like you have professional-installed central air. In that case, everything should be wired up to code (unless your installer was an idiot).

Your UPS will protect your equipment from both over- and under-voltages, although that shouldn't really be an issue. Anything "UL-listed" shouldn't be bursting into flames just because of ordinary electrical problems.

TasteLikeChicken seems to know his stuff, but I wouldn't worry about lightning strikes. I've seen a house get struck by lightning: the damn roof caught fire, but because the wiring was up to code, the lights didn't even flicker.

 

[mshan]

Yes, it is a dedicated, professionally installed Carrier central air conditioning unit.

Just wondering because of what I observed on power lines in certain rooms.

I think it is mainly a transient current sag when ac turns on.

 

[TastesLikeChicken]

Originally posted by: DeathRayLoveMachine
TasteLikeChicken seems to know his stuff, but I wouldn't worry about lightning strikes. I've seen a house get struck by lightning: the damn roof caught fire, but because the wiring was up to code, the lights didn't even flicker.

Living in one of the areas in the US that receives an extraordinary amount of lightning strikes (Central Florida), I'm a bit paranoid. Not to mention that I've had a number of components taken out by surges from lightning, including a couple of motherboards and a DirecTV HD receiver that was ruined a couple of months ago during a nasty storm. All houses in this area have lightning rods that take strikes to ground but current can still run through your lines and unprotected components can be taken out.

 

[funkymatt]

install a large capacitor bank between your breaker and the AC, it will pull the initial jump from the cap and then get a constant feed.

 

[DeathRayLoveMachine]

Originally posted by: funkymatt
install a large capacitor bank between your breaker and the AC, it will pull the initial jump from the cap and then get a constant feed.

That's a good idea with direct current. That's a REALLY BAD idea with alternating current.

 

[bobsmith1492]

Originally posted by: DeathRayLoveMachine

Originally posted by: funkymatt
install a large capacitor bank between your breaker and the AC, it will pull the initial jump from the cap and then get a constant feed.

That's a good idea with direct current. That's a REALLY BAD idea with alternating current.

It works for high frequency EMI suppression. In fact, with the right amount of capacitance, you could balance out the inductance of the AC motor and restore unity power factor. I'm not sure exactly how well it would help during the startup surge, though.

 

[DeathRayLoveMachine]

OK, you got me on the first part. A TINY capacitor in line with a resistor makes a low-pass filter. I don't think you'd want a capacitor BANK for this, though; you'd need a capacitor so small that it can charge/discharge in a lot less than 1/60th of a second (because line frequency is ~60Hz). If it takes longer than that to charge/discharge, it will start to filter lower and lower frequencies, eventually turning your 110VAC into 0VDC.

Also, this setup only protects for ultra-short duration surges or drops (less than a quarter of an AC cycle - 1/240th of a second), and only if the magnitude of the charge is smaller than what the capacitor can hold.

In fact, with the right amount of capacitance, you could balance out the inductance of the AC motor and restore unity power factor.

Yup. And all it takes is university-level math and physics, plus extensive knowledge of electrical safety. I don't think that's what mshan was looking for, though.

 

[bobsmith1492]

DeathRay: the impedance of a capacitor (Xc) is determined by:

Xc = 1/(2(pi)FC)

where F is the applied frequency and C is the capacitance in Farads. It's common practice to put a rather small (say 1uF) capacitor directly across 120VAC power lines coming into a power supply; your computer PSU probably has one. At 60Hz AC, the impedance is quite high (2.6Kohms). However, at high frequencies, the impedance is much lower. Let's say your computer PSU, which is a switching power supply, switches at 100KHz. The capacitor presents an impedance of 1.6ohms at that frequency. So, it will help to filter out the 100KHz switching noise but will not affect the 60Hz AC signal.

For power factor correction, all you need to know is the above formula for the reactance (imaginary component of impedance) of the capacitor and the power factor of your AC motor. If you AC motor is a 1000W motor with a power factor of 0.85, then (1-0.85)*1000 is the reactive component of the motor, 150W. Convert that to ohms using P^2 = V^2/R to get a reactance of 1.56ohms.

Most AC motors have an inductive-type reactance, which is the opposite of capacitive reactance. So, you can cancel it out by applying a capacitor with the same reactance as the AC motor - 1.56 ohms. In this case, by manipulating the formula for capacitive reactance, C = 1/(2(pi)FXc), where F is again 60Hz and Xc is 1.56 ohms. That gives you a capacitance of 1700uF. So, you can restore unity power factor by applying a 1700uF capacitor in parallel with your motor.

Anyway, DON'T TRY THIS AT HOME unless you know what you're doing. The capacitor must be rated for 120VAC or higher, for starters.

Another way to think of it is to remember that capacitors resist changes in voltage while inductors resist changes in current. As the voltage on your AC sine wave ramps up, a capacitor will draw current to charge to that voltage - it is resisting the increasing voltage. Then, as the voltage ramps down, the capacitor supplies extra current to discharge to the AC voltage. So, it will sit there and absorb current and push it back every cycle. An inductor does the opposite, pushing current to the line as the voltage increases and pulling current from the line as the voltage decreases.

So, the problem with low power factor in typical household motors is that there is all this extra current being pushed back and forth from the motor inductors without actually doing anything useful. It simply gets dissipated in the wiring resistance and lowers the amount of power the electrical grid can supply. By adding power factor correction capacitors, instead of all the current being pushed and pulled to and from the generating station, it is pushed into and pulled out of the capacitor instead, reducing the amount of current drawn through the power lines.

 

[DeathRayLoveMachine]

Yeargh, LC circuits. I've had enough of those for one lifetime, thank you.

Anyway, I wasn't reading funkymatt's post as being about power correction, although I guess it could have been.

 

[William Gaatjes]

Originally posted by: TastesLikeChicken

Originally posted by: DeathRayLoveMachine
TasteLikeChicken seems to know his stuff, but I wouldn't worry about lightning strikes. I've seen a house get struck by lightning: the damn roof caught fire, but because the wiring was up to code, the lights didn't even flicker.

Living in one of the areas in the US that receives an extraordinary amount of lightning strikes (Central Florida), I'm a bit paranoid. Not to mention that I've had a number of components taken out by surges from lightning, including a couple of motherboards and a DirecTV HD receiver that was ruined a couple of months ago during a nasty storm. All houses in this area have lightning rods that take strikes to ground but current can still run through your lines and unprotected components can be taken out.

True.
It is even theoretically possible :

The lighting strike hits the rod, travels down the rod and to the ground.
This very high (in shape spike like) electrical current through the ionised air and the rod causes a strong spike like magnetic field. This field can induce an electrical voltage difference in surrounding conductors ( placed in the same plane and not perpendicular)causing a current to flow. The level of this current depends on the voltage induced. High voltage is lot's of current, is possible burn out of sensitive circuits. A lightning strike can theoretically act as an EMP when all circumstances are right.




EDIT: typing errors.

(I dont read words , i see them and internal recognition and error correction does the rest)