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Electronic Devices, High In Rush Current, Surges

Posted by bltglt (My Page) on
Fri, Aug 20, 10 at 17:41

I've often heard that it is a bad idea to have a computer and an air conditioner, vacuum cleaner, microwave, refrigerator, etc... on the same circuit. I really do not understand why it is a bad idea to have both devices on the same circuit. I understand the importance of a surge protector for a computer to help divert excessive voltage resulting from a failing transformer on the pole or lightning. In that instance, you are dealing with excess voltage. However, I don't understand how a device that pulls 50A or more in-rush current could hurt a computer. If my understanding is correct, the air cond. would pull maybe 50A to start up the compressor and then quickly fall back to approx. 5A. All of that current is going straight to the air conditioner. How could that possibly damage a computer if the computer is not pulling that much power? With in rush current, the voltage remains constant but the amount of current is simply high for a brief moment, correct? How could an Air Cond. possibly pull more voltage than what the transformer on the pole will allow? If anything, I would think that the air cond. pulling a massive amount of power would temporarily create a lot of resistance on the wire that would slow down the current flowing to the computer on the same circuit, creating a sort of short brown out. Could someone please answer these questions?


Follow-Up Postings:

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RE: Electronic Devices, High In Rush Current, Surges

Fast and large changes in current create sags in voltage as the current increases, and then increases in voltage as the current falls back to the normal value.

Any changes in the magnetic field around a conductor is going to result in changes in the voltage on the conductor.

This is the principle of 'magnetic induction' that allows electric motors and transfomres to operate.

A changing magnetic field induces a voltage, just as a changing voltage induces a magnetic field.


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RE: Electronic Devices, High In Rush Current, Surges

Thank you, you answered my question. So it sort of has something to do with resistance in the wire then? Sags would be resistance, correct? So, would you have the same problem if you had a breaker box and a 5 foot wire run to a powerful motor from one breaker on leg A and a 5 foot wire run to a computer from another breaker on leg A? Would the "magnetic induction" have an effect on the computer circuit through the bus bar or is it considered large enough to avoid this problem? What about harmonics? Could they potentially travel back through the bus bar on a very short circuit to effect other circuits? ---- The reason I'm concerned is because we don't have central air in our house. We use window air conditioners but are planning on having central air installed next year. Most importantly, I have a computer that was plugged into a power strip on the same outlet as the window air conditioner in my bedroom. Recently, that computer has started acting very strange and has developed problems of starting up. I'm concerned because I have another computer on that circuit that is not on the same outlet. I also have a laser printer on that circuit. I've heard that they can create surges.


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RE: Electronic Devices, High In Rush Current, Surges

It is both a resistance problem (voltage drop in the wires) and a source impedance problem for starting high current loads.

The POCO does not have a zero source impedance in the pole transformers.
A large load sags the output voltage on the pole until enough current flows in the primary side.
This is the main cause of lights quickly dimming when a largbe load comes on (especially a 240 V load).

Whwn the large load is switched off the magnetic field around th ewires collapses, and this creaes a voltage surge in the wire.

Keeping electronics aay from large inductive loads is generally a good idea, along with usng a surge strip to pluyg the electronics into the wall.


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RE: Electronic Devices, High In Rush Current, Surges

O.k., thanks.


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