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Choke coil quandary

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HexKrak

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First of all I'm pretty much a noob when it comes to electronics. I took one semester course back in high school, but that's been a while now. After doing some searching on the forums here I was still unable to determine the answer to my quandary.

I'm looking at building a "dimmer" circuit based on **broken link removed** for an oven. I've found all the other parts that will handle the 30 amps but it seems choke coils have very few options in that range. So could I just wire them in parallel, and if so do I just add the amperage or is there an equation similar to wiring resistors in parallel that I have to consider?
 
You can connect identical chokes in parallel and just add the amperage. But the inductance is reduced by the number in parallel, the same as for parallel resistors. Thus the inductance would be reduced to 1/2 for two in parallel, 1/3 for three in parallel, etc.
 
Thanks a ton for your reply.

To make sure I understand then...
If I wanted 100uH of inductance I would need 3 x 300uH 10 amp rated coils?
 
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To make sure I understand then...
If I wanted 100uH of inductance I would need 3 x 300uH 10 amp rated coils?
That is correct.
 
Ok so I understand that I need this part of the circuit to reduce EMI but I'm having a really hard time finding an applicable set of coils. They're either have far too low uH or Amps.

First, seeings as this is an oven and not lights (as the original circuit was designed for) is this still prone to cause a lot of EMI?

Second since I'm having a hard time finding a coil would it possibly be more effective to stick the whole circuitry in a Faraday shield, or something similar, or would the heating elements need to be covered too (sorry I'm not exactly sure where the emi would be radiating from)?

Any idea would be much appreciated! Thanks!
 
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The EMI is sent along the wires and they act as a radiator, just like the antenna of a transmitter. You cannot cover the circuitry and prevent this type of radiation.
That's why you need the inductor.
 
The sharp turn-on current transients generated by the the triacs causes EMI radiation from the power lines. This can be readily heard from an AM radio if you use typical light dimmers, which are not well EMI suppressed.

The purpose of the chokes is to slow the speed of the transients, reducing the high frequency content, and reducing the EMI. Putting the circuitry in a shield will have little effect on the EMI since it's mostly coming from the power lines.

As you noted, high current inductors in the 100µH range are not readily available.
Here are some choices:
1. Leave out the choke and live with the EMI.
2. Wind you own choke
3. Have a magnetic manufacturer make a custom one.
4. Try an EMI filter I've seen on Ebay such as **broken link removed**
 
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He's looking at 3kW at 110v or 6kW at 240v, so an auto transformer would be too expensive and too bulky.
 
Thanks again for all of the replies. And yeah I'm looking at about 4kW @240v. I'm looking into finding something like the linked ebay item now.
 
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