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Choke current

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Disabled Account
Joined 2004
Hi,

I did order the wrong choke. It is a Hammond max current 100 mA DC.
The amp i am building (pp6v6 stereo) needs 140mA DC. I am going to try it anyway...see if am lucky.But i would like to know what happens when the choke saturates, what kind of problems should i expect?

Thanks
 
According to standard textbook approach, you don't normally design a choke for saturation mode....
But there are cases in aerospace, due to size restriction that I have operated a choke in sat mode.... you get a bit more heat and losses but sometimes it don't mean much...
For example: if you examine the L vs I curve .....your L will creep up when applying increasing DC current..then hit a peak at sat point then the L will start to come down quickly....
If your minimum required L is say 7H , and your peak L is 10H ...the you will see the 7H twice....once on the way up to sat. and once on the way back down after your in sat. but this time with more DC current.... You will make for more current harmonics, but not to worry since these are higher order intervals and will average out in the filtering .... Will work in power supply..But not a good idea in RF filter circuits ...
You would need to first plot your L vs I curve and then see what you have will fit....
Depending on the value of this choke....you can re-gap it to handle a bit more DC current at the expense of lossing a few Henries....But you still might end up with enough Henries to get the job done..

Chris
 
Disabled Account
Joined 2004
Your heating in the choke will approximately double because of I squared. Your ripple at the output will increase; as the inductor saturates, the inductance value decreases.

Uff, doesn't sound good.

Will work in power supply

This sounds better:) .

Ok i get the picture it can be done but better not doing it. I'll order another and keep this for future projects. Another week of delay. This amp is taking forever!!!

Thanks for the replies, been a help.
 
Disabled Account
Joined 2004
Modify the power supply and use one choke per channel?

That, unfortunately, is not an option. I need a choke input filter to bring the voltage down.
Anyway when i said i may be lucky i was thinking that the core may not saturate. If the specs say 100mA it can possibly take more, maybe 140mA?:)
I have read Hammond are pretty conservative with their numbers.
 
Which stands to reason, it would take a series parallel array of 4 100ma chokes to make a 200ma choke of the same inductance.

Using 2 100ma chokes separating the channels seems a very good answer to your dilemma. Something like this:

______ L-C-Plate channel 1
Rect-C<
______ L-C-Plate channel 2

Edit, saw you need to bring the voltage down.

This solution is still tenable, it would just look like this:

____ L-C-Plate
Rect<
____ L-C-Plate
 
Good one tweeker...

The size of the core for the inductor, like heat diisipation, is determine by current squared... so twice the current... 4 times the core. And it will be 60% larger all around... cube root of 4.

So actually you're getting a better deal...

Now if you split the current in two paths you would want to double the inductance in each path to achieve equivalent filtering... 4 inductors again...
 
Anatech's suggestion, however, my post was worth (1,000/12=83.33) over 83 times his as it had a picture.

Yes, were still storing the same energy, to get the same filtration as the big choke we'd need more.

However, if the existing chokes are well over the critical value already, I think were ok, and the channel separation has its advantages. From what I understand, it would be better to add another LC section than go beyond 2x the critical value.
 
Disabled Account
Joined 2004
Anatech's suggestion, however, my post was worth (1,000/12=83.33) over 83 times his as it had a picture.
True:D I didn't quite get anatech suggestion but i did get your idea really fast thanks to the COOL pic.

Poobah i don't get it but you have explained well...i don't get it because i did study philosophy not electronics...i'm here just because of music...so
But i know if i split the channels the choke will see half the current right?
So it will not saturate. Choke is 10 H.
4 chokes is a no-no.
 
Stalker,

You will get half the current and the inductors will not operate in saturation... so that is good. But, to maintain the same performance you would want to double the inductance value and halve the capacitor values.

Now, if your inductor was spec'd as say 3H and you bought a 5H cuz' that's all they had, well you could get away with this. and if that is the case... do it... split the paths.

From a philosophical point of view: "Ya don't get something for nothing". So in that sense, were it possible to save on iron by splitting the paths... it would have happened looooooooong ago.

The inductor you need costing 3 times as much is actually 4 times the material. You looking at spending 50% more to get the right inductor as opposed to buying another like the one you have (this assumes they will refund the one you have).

Seriously though, what value was spec'd, and what value did you purchase? I ask because you could "fudge" this maybe. Let's look at the numbers. Can you post a schem or partial?

:D
 
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