From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <1456380282.20170524154713@gmail.com> <5925A16B.7050100@posteo.de>
In-Reply-To: <5925A16B.7050100@posteo.de>
Date: Thu, 25 May 2017 12:35:52 +0200
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Subject: RE: LF: Iron dust toroids and heating
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Hi Stefan,

>115 uH appears to be very much for 137 kHz. Not sure what type 
>of filter you are using  

Chris has provided this link several times
http://www.w1vd.com/LPF.pdf

You can contemplate this filter as two 3-pole T-type low pass filters in series.
Then every element has 50 Ohm reactance,one half of the inner coil L2 belongs
to the first and one half belongs to the second part,hence +j100Ohm in sum.

73
Clemens
DL4RAJ 

>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org 
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
>Sent: Wednesday, May 24, 2017 5:06 PM
>To: rsgb_lf_group@blacksheep.org
>Subject: Re: LF: Iron dust toroids and heating
>
>Hi Chris,
>
>115 uH appears to be very much for 137 kHz. Not sure what type 
>of filter 
>you are using but the standard filters use j50 Ohm which is 59 
>turns on 
>a T200-2 if i remember correctly. I passed 1.5 kW through such type of 
>filters and the caroe became maybe just 60 C warm.
>So with a T225-2 you should have no problems at 2.5 kW :-)
>For an air coil you will need more wire and will have more 
>losses unless 
>you choose a big RF litz wire. But the size will be extreme and there 
>should be no lossy things in a radius of the length of the coil.
>I would build a LPF based on j50 Ohm coils and -j50 Ohm Cs (~ 22 nF at 
>LF) and use the T225-2 cores.
>
>73, Stefan
>
>Am 24.05.2017 16:47, schrieb Chris Wilson:
>> Hello LF'ers,
>>
>> 24 May 2017
>>
>>
>> If I run the combiner on my 2 amps the LPF centre toroid heats up. I
>> made a silly mistake with setting my U3S driver the other night and
>> instead of TX'ing every 30 minutes it went on an every two minute
>> rampage before it soon self halted. The centre toroid 
>winding has lost
>> most of its enamel coating and the Kaptan tape is crispy. It 
>no longer
>> functions as an LPF, and I suspect the T225A-2 toroid is compromised
>> in its crystalline structure, through the very high 
>temperatures, now.
>> 115uH seems to be the calculated figure, if not actually measured (73
>> turns 14 AWG enamelled wire) of the centre inductor. An air core coil
>> of similar inductance isn't THAT big, (at least not the size of a
>> "small car" as someone on a US forum estimated :)) Is an air 
>cored LPF
>> viable, or do i need to look at different core sizes or materials?
>> Thanks. LPF is at:
>>
>>
>> http://www.w1vd.com/LPF.html
>>
>> Thanks.
>>
>>
>>
>>    
>
>
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