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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: Ferrite/plug test results posted by APM on June 19, 2000 at 03:29:35:
APM wrote:Let me get this straight with your last comment, you don't believe in shunting to earth? That is pretty common practice when designing a power conditioner. Not only do they use earth to handle the extra current they also use earth as a filter. Steve since I don't know your background: what type of EE are you?
Certainly nothing of your type.
And it has nothing to do with any beliefs with regard to shunting to earth.
Lets build a simple capacitor shunt filter shall we...
Let's.
Capacitor across hot to neutral.
Uh huh... Go on.
Capacitor across hot to earth.
Ok...
Capacitor across neutral to earth.
Groovy (though those last two wouldn't be allowed for use in medical equipment).
Only one problem. That doesn't quite describe vans Evers' description of the MOVs and fuses in his "enhancer." He says there are only two fuses (each in series with an MOV). One is tied across the line (hot to neutral) and the other is tied from neutral to ground. From his description, there apparently there is nothing between hot and ground.
But all that begs the question, what is he using the MOVs for? Is he using the MOVs as a substitute for capacitors in some sort of EMI/RFI filter arrangement or is he using them as MOVs for surge suppression as they're intended to be used? And what are the fuses being used for? Are they being used as fusible links for safety measures, or is he using the fuses as substitutes for resistors? Does vans Evers even know what he's doing? Or is he perhaps just as clueless as you seem to be?
My message addressed the situation assuming the MOVs and fuses were being used for surge suppression. And in that instance, tying an MOV between neutral and ground is pointless since neutral and ground are both tied toegether at the service panel and subsequently tied to earth at the grounding rod. So neutral, earth and ground are essentially one and the same so you're not going to have any significant voltage drop across them that would cause the MOV to trip in the first place. Further, placing fuses in series with the MOVs would defeat the whole purpose once the fuse blew.
Where have you been? With A/V equipment shunting either noise or a surge to earth is pretty common practice.
With regard to high voltage surges, those will only exist between hot and neutral, not neutral and ground since neutral and ground (and earth) are already tied together at the service panel. When an MOV trips, it goes to from a very high resistance to a very low resistance, effectively shorting across the two lines it is tied across. Tell me, Sparky, what is the benefit of shorting across two lines that are already tied together? Are you as clueless about basic house wiring as you are about most everything else you've been talking about here?
Perhaps this will help:
As you can see, neutral, ground and earth are all tied together at the bus bar in the service panel. So as far as high voltage surges go, you're not going to find them across the neutral and ground/earth so there's no point in placing an MOV across them if the purpose of the MOV is for surge protection.
But back to your filter description. Yes, that describes a fairly common filter topology used in line conditioning equipment (though again it doesn't describe the MOV/fuse arrangement as described by vans Evers over on AVS). But knowing that it is a commonly used topology is one thing. Knowing (and understanding) how it works and subsequently why it's used is quite another.
You seem to be saying that topology used in the vans Evers unit is the same topology that's commonly used in other line filters. But apparently the vans Evers unit stops short and only uses an MOV/fuse to earth from the neutral line, and not a matching MOV/fuse to earth from the hot line. So how can the circuit you described previously be used as an example?
Do you know why the topology you described has one capacitor across the hot and the neutral and then a pair of capacitors bridging between hot, neutral and ground? And if you don't understand this, how can you come to any meaningful conclusions about it other than "everyone else [except apparently vans Evers] does it"?
se
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Follow Ups
- Re: Ferrite/plug test results - Steve Eddy 11:33:10 06/19/00 (0)
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