400Hz line frequency transformers on 50Hz?? - diyAudio
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Old 2nd January 2004, 11:11 AM   #1
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Default 400Hz line frequency transformers on 50Hz??

I have bought some very nice Military surplus transformers (steel potted, apparently very high quality) .
primary 115V/0.7A and sek. 6.3V/12A (and with shield)
I intended to connect two primary windings in series for 230V line voltage application.
So far so good.
But one thing I have overlooked - they`re rated for 400Hz line frequency (as most of the Military power stuff)

Is there any way to use them on 50Hz line frequency though?

I believe it should be possible but very likely don`t get the rated power out of them.


Do You think I can use them on 50Hz at all?

If yes, what do You think which amount of decrease in output power I have to expect - 20%- 30% - or even more?

Thank You for any kind of input!
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Old 2nd January 2004, 11:43 AM   #2
dhaen is offline dhaen  Europe
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Default No...

Not enough primary inductance

I think they'll just blow the fuse or seriously overheat.

Sorry,
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Old 2nd January 2004, 11:50 AM   #3
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Probably the core will go into saturation because of the increased number of volt-seconds, causing excessive currents and blown fuses or overheating.

At 50Hz, a transformer with one primary winding intended for 115V, 400Hz should be able to handle 115V*50Hz/400Hz=14.375V without saturation. With two windings in series, you can go up to 28.75V. Not very useful with 230V mains.
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Old 2nd January 2004, 12:09 PM   #4
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Quote:
Do You think I can use them on 50Hz at all?
Forget is completely!

Only if you lower your mains 8 times also

400Hz is/was common on aeroplanes to save weight and these trannies probably come from that area. But these are completely unsuitable for 50/60 Hz, period. Be careful with 50 Hz, they will for sure go into saturation and because these are hermetically canned, will for sure explode with a big bang when given sufficient time, and that can be lethal!

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Old 2nd January 2004, 01:28 PM   #5
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Unhappy it`s a pity

Quote:
Not enough primary inductance
I think they'll just blow the fuse or seriously overheat.

Sorry,
dhaen,

that`s what I thought too.
But it has still inductance also at a lower level.
So when I load them with a (much) lower current than rated I thought it should be possible.

Quote:
At 50Hz, a transformer with one primary winding intended for 115V, 400Hz should be able to handle 115V*50Hz/400Hz=14.375V without saturation. With two windings in series, you can go up to 28.75V. Not very useful with 230V mains.
MarcelvdG,

I wanted to hook up the two primaries in series not secondary windings - so with series connected primaries and 230V I should get about the same secondary voltage as rated for 115V (6,3VAC - for tube filaments).
Moreover saturation is current/power dependend and I don`t think voltage ratings alone tell anything about saturation.



Quote:
400Hz is/was common on aeroplanes to save weight and these trannies probably come from that area. But these are completely unsuitable for 50/60 Hz, period. Be careful with 50 Hz, they will for sure go into saturation and because these are hermetically canned, will for sure explode with a big bang when given sufficient time, and that can be lethal!
Pjotr,

after Your responds it seems to be clear that I can`t use them for what I have them intended but I would be satiesfied with a much lower secondary current rating in order I can use them at all for something else.

Do You think it`safe enough when I power one up very slowly with a variac and load it increasingly with an adjustable power resistor while monitoring the temperature of the transformer?
For additional safety precaution I could test them outside under some sort of enclosure.
Me thinks the temperature should be a good indicator if the transformer is overloaded - isn`t it?
If this would be reasonable, what do You think how far up I can go in temperature?


Anyway, many thanks for Your help !!!
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Old 2nd January 2004, 01:59 PM   #6
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Dear Cocolino,

I'm also talking about primary voltages. A transformer with two 115V, 400Hz primaries connected in series should be able to handle 28.75V of primary voltage at 50Hz (giving the same primary current as 230V, 400Hz). Of course the secondary voltage will then become about 6.3V*50Hz/400Hz=0.7875V.
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Old 2nd January 2004, 02:15 PM   #7
bocka is offline bocka  Germany
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cocolino,

unfortunately you cannot use the 400Hz transformers @50/60Hz without lowering the primary voltage, because the core saturates.

With Uind = -dPhi/dt = -L*dB/dt

you can see, when you increasing dt by 8 (one eigth of the frequency) you must decrease Uind (=primary voltage) by 8. Because of economical reasons the core is driven near by the saturation Bmax.
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Old 2nd January 2004, 02:38 PM   #8
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Well, it looks like that I can actually forget them completely.

Anyone needs some nice and cheap transformers?

Thanks to everybody for the lesson!!
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Old 2nd January 2004, 06:54 PM   #9
Magura is offline Magura  Denmark
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Sell them as copper scrap, and buy yourself a "sad experience diminsher" beer for the money.

Magura
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Old 2nd January 2004, 07:16 PM   #10
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Quote:
Originally posted by cocolino
Well, it looks like that I can actually forget them completely.

Anyone needs some nice and cheap transformers?

Thanks to everybody for the lesson!!
Those might be actually pretty good if used with AC power regeneration circuits, just like ML does. But the secondary is a bit low for any practical SS applications (maybe only in 5v digital circuits?).
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