2- 1/2 value inductors on + and - sides

[DaveThreshold]

O.K. I need a 2.7 m.h. series inductor. It is the first part of a two component low pass xover going to the woofer. I was going to use an Erse Superq rated at 500 watts before saturation. If I use 2 - 1.35 m.h. inductors, one on the positive, and one on the negative, that would come out to 2.7 m.h. Would that part of the low pass take 1,000 watts before saturation? I think it would, but I'm not sure.

Better minds than me can answer this one.

[kevinkr]

In most cases the maximum power handling will still be that of one single inductor, if it is rated at 500W that is the total power that can be handled by that inductor, presumably due to resistive losses in the inductor resulting in excessive heat or? (Assuming air core, iron/steel core there is core saturation to contend with.)

The lossy component of your inductor, which in this case is resistance is what limits the overall power handling (again air core only, see above) - now if you were to put 2 x 5.4mH in parallel that would probably work, but would probably be a waste of money. There are foil inductors out there that will handle this kind of power from Solen, and others - they are unfortunately expensive.

In the case of a resistor that isn't true, obviously putting two identical value 250W resistors in series will result in a total rating of 500W.

Others will hopefully have a lot more to add to this. Note I haven't designed anything to operate anywhere close to these power levels so this is entirely conjectural on my part. YMMV..

[DaveThreshold]

Thanks a lot for answering Kevin. I'm not sure if I made it clear: Lets say we have one 2.7 mh iron core which will take 500 watts. (series of course) We put 500 watts over the circuit, and it's saturated. So then we take 2-1.35 mh and put one on the positive side, and the other on the negative side. I thought, not knowing ohms law that well, that at that point each inductor would be seeing/dissipating 250 watts each. I was then thinking that the circuit would then take 1,000 watts at the same saturation point.

It's hard to tell sometimes if I make a post like that, so that it makes sense.

[kevinkr]

Actually we need to correct a misapprehension here, actually perfect inductors dissipate no power at all, the power dissipated is due to the dcr in the wire used to make the inductor and core losses if present. (iron/steel/ferrite)

A better way to look at this would be to make a determination as to how much rms current will flow through that inductor at maximum output power which for 1kw will be approximately 11.2A into 8 ohms.. This is really what you need to know, and most 14ga foil inductors should handle this, although not with a lot of margin to spare, incidentally the voltage at this current will be about 89Vrms which is enough to be hazardous. For 4 ohms double the current and halve the voltage.

Something that might work in your favor is that most music is not going to run your power levels at anything close to this on a sustained basis, I would expect even on the most demanding music that the low frequency peak to average ratio would be at least 10dB, (10X) as long as you use air core inductors you might just get away with a 14 gauge inductor. If 12 gauge is available use that as it will result in significantly lower losses. Note that sustained operation at close to 1kw could have an inductor of say 0.25 ohms dcr dissipating about 30W which might be pushing it.

Here is a link to Goertz, they make 12ga foil inductors:
http://www.goertzaudio.com/foil.html
Their 2.7mH 12ga foil is about $45 - admittedly not so cheap.

You should ask the vendor what the dcr is, and what amount of power the inductor can safely dissipate.

[DaveThreshold]

Thanks again Kevin.

After I made this post I ordered two 14 GA. Goertz inductors from Madisound anyway. I thought I had a good idea though about dividing up the power among more than one inductor. The idea could be used in the future, or in a situation where one might not want to use an electronic crossover. Large subs with multi woofers for instance.

[infinia]

Power rating should be double for each, if using 2 inductors in series, ie saturation is determined by volts x time. In series for equal inductors each should now see 1/2 the Volts.

[DaveThreshold]

Thanks a lot infinia. That's what I thought. for the heck of it I just e-mailed goertz about the capacity of their 2.7 14 GA. In the ad it says, "no saturation distortion" so we'll see what they say.

Dave

[infinia]

Originally posted by DaveThreshold
"no saturation distortion" so we'll see what they say.

Probably any air coil could claim that.... ie no hysteresis.
Ask them about interwinding capacitance the effect of which is a parallel self resonance. The major draw back of this type of construction using foils. Probably not a problem for a LPF at AF.