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Author Topic: Building a filter choke  (Read 4393 times)
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stevef
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« on: July 22, 2010, 07:58:50 AM »

I have a power transformer from a GPT-750 that I would like to build an amp power supply with.  Been looking for a 10H 750 mA filter choke with no luck, so am now considering building my own choke.

In The Radio Handbook, 13th ed, 1951, p. 578 in "Construction of Filter chokes", it suggests the following for a 750 mA choke;

3000 turns of No. 21 wire (6 lbs of wire) on a core 2.5" x 3" with 1/8" air gap, and core weight of 14 lbs.

First of all, this seems very small in comparison to a couple 400 - 500 mA chokes I have that are in the 30 - 40 lb range.

Secondly, what core dimension does the 2.5" x 3" refer to?  Is it the interior dimension of the winding space of the E/I laminations?  Or is it the dimension of the center leg of the E lamination only?

Third, what does "core weight" refer to?  The wire plus the E/I stack? or the E/I stack itself?




 
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Ed/KB1HYS
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« Reply #1 on: July 22, 2010, 08:42:08 AM »

I have a power transformer from a GPT-750 that I would like to build an amp power supply with.  Been looking for a 10H 750 mA filter choke with no luck, so am now considering building my own choke.

In The Radio Handbook, 13th ed, 1951, p. 578 in "Construction of Filter chokes", it suggests the following for a 750 mA choke;

3000 turns of No. 21 wire (6 lbs of wire) on a core 2.5" x 3" with 1/8" air gap, and core weight of 14 lbs.

First of all, this seems very small in comparison to a couple 400 - 500 mA chokes I have that are in the 30 - 40 lb range.

Secondly, what core dimension does the 2.5" x 3" refer to?  Is it the interior dimension of the winding space of the E/I laminations?  Or is it the dimension of the center leg of the E lamination only?

Third, what does "core weight" refer to?  The wire plus the E/I stack? or the E/I stack itself?

To try and answer your questions (I am no expert, but I've done some rewinding myself):

The design in the handbook is probably intended for intermittent (amatuer) service (see definitions of ICAS, ICCS), commercial products are often designed to be able to withstand the rated current constantly.  You will have to determine if the application is going to be pulling the full rated current the entire time, or if the Full rating will be a Peak event, with the average current throught the choke being much less than max design value.

The core dimensions refere to the size of the solid portion of the core that passes through the center of the coil (and all round). So in your example, one lamination would be 3 inches wide,with enough stacked up to add to 2.5 inches thick part. 

I have always interpreted core weight to mean the weight of the iron portion of the former alone.  I am not certain if that is correct.  I do know that one member of the board here rewinds transformers as a business, perhaps he can chime in.
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
John K5PRO
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« Reply #2 on: July 22, 2010, 03:05:15 PM »

I may have a big filter chokes from a Raytheon RA1000 that would fit the bill. Let me look tonight and let you know.
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John K5PRO
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« Reply #3 on: July 23, 2010, 12:55:06 AM »

i have a Raytheon U-11062. This is from the RF HV power supply, push-pull 833s. It is 12 Hy at 0.5 Amps DC. As it was made for AM broadcast carrier, it can do this all day and night, so for ICCS it would run more current, and the inductance might fall a little bit. Its very heavy duty, weighs 29 lbs., laminations are 5 x 7 inches, 2 inches thick. The overall dim are 8 tall (plus insulator bushings) x 7.25 long by 6 wide, plus feet. It is in a cast metal shell with some pitch potting in the bottom and top where the wires would be (photo); everything about the RA1000 was overdesigned. Contact me via PM if interested.


* P1050706.jpg (86.2 KB, 900x675 - viewed 662 times.)
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Gito
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« Reply #4 on: July 23, 2010, 01:42:24 AM »

Hi

there are two different Choke type.one with air gap,and with no air gap,
The purpose of air gap is to prevent core saturating ,if the current flow is high,
so it needs a smaller core type (lighter LBS}.

With a smaller air gap ,or no air gap ,to prevent from saturating it needs a bigger core.

in case 1 ,the  Henry is relative stable with an air gap,depending the width of the air gap.

in case 2 the inductance vary a lot depending on the current that flows trough it,sometime it's called swinging choke (if I'm not wrong).

The core 2.5 X 3 is like Ed wrote the iswidth  of the center leg of the E lamination X  the thickness  of the lamination stack together

Yes the wight is for Core only.

The more the wight the more power it can handle.

Gito.              



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WA1GFZ
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« Reply #5 on: July 23, 2010, 09:56:16 AM »

I think you can go with smaller wire for 750 ma. #23 should work. Larger wire will have less resistance at the expense of less turns and inductance. Heck a long time ago we did a choke and transformer in a mil rig with #26 that ran 500 ma.
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