ac voltage divder

Voltage? Frequency? Aren't they the same??

A 120 to 15 transformer?

As a 'stupid' graduate student I used a capacitor to limit the AC current going to the heater of a diffusion pump. It seemed to work just fine. Do you need me to calculate the value for you also?

George Herold

Variac?

Best regards, Spehro Pefhany

A number of ways:

Same as a transformer, but gives no isolaton.

At 400Hz a normal mains transformer is not a good idea.

Hardy

This is under the previous response for a reason. What kind of isolation would a 120:15 tranformer give in when properly connected in the application suggested by the OP?

Also, I might point out that most tranformers, and many autotransformers, don't have adjustment knobs to alter the turns ratio.

Note that these particular ones are rated for 400Hz operation, and are not unreasonably priced ($250 or so), but are a bit overrated for the application.

Best regards, Spehro Pefhany

On a sunny day (Wed, 29 Apr 2009 06:39:13 -0700 (PDT)) it happened jabriol wrote in :

Small transformer 120 V primary, 15 V secudary at 385 mA, secundary in series with input in opposite phase.

-------------------------------- | | )|| |

So a 6 VA transformer would do.

:On Apr 30, 1:39 am, jabriol wrote: :> All, :>

:> I need to design a voltage divider, that is going to drop 15vac. :> like 120 to 105 at .385 amps. voltage is running 400Hz :>

:> Any ideas? : :At 400Hz a normal mains transformer is not a good idea. : : :Hardy

The OP didn't say that the transformer was a "normal mains transformer". Perhaps it is rated for 400Hz operation?

:All, : :I need to design a voltage divider, that is going to drop 15vac. :like 120 to 105 at .385 amps. voltage is running 400Hz : :Any ideas?

I wouldn't muck around with fudging a voltage dropper as it will probably not be reliable or safe in the long run. Buy a specified 400 Hz step down transformer

:On a sunny day (Wed, 29 Apr 2009 06:39:13 -0700 (PDT)) it happened jabriol : wrote in :: : :>All, :>

:>I need to design a voltage divider, that is going to drop 15vac. :>like 120 to 105 at .385 amps. voltage is running 400Hz :>

:>Any ideas? : :Small transformer 120 V primary, 15 V secudary at 385 mA, secundary in series with input :in opposite phase. : : : : -------------------------------- : | | : )|| | :120 V 120 V )||( 15 V / 385 mA : )|| |_______________ : )|| 105 V : | : -------------------------------------------------- : :So a 6 VA transformer would do.

Good solution - provided the small transformer is also rated for 400Hz operation. It would probably be just as costly as a new 400Hz 115V : 100V @500mA transformer from Rayco. Also a more space consuming arrangement.

Nice-- what do those things cost, roughly? lead time?

I'm looking at some applications that have to run at "wild frequency", but it's centered around 400Hz.

@500mA

so it would also be smaller and cheaper (if done with comparable parts)

Sure - look up Ohm's law.

Good Luck! Rich

be

Come on, Spehro - you _must_ knowe how to operate Google!

In the USAF (and probably commercial aircraft and ships), everything was

Good Luck! Rich

be

Yeah, I know. This is going on an aircraft. I don't think Google is going to find any Rayco prices -- am I wrong?

My rule of thumb is that on price..

marine: at least 3:1 aircraft: at least 10:1 space or rad-hard: could be 100:1 and up

not be

transformer

Admittedly, reliability is a major consideration - it'd be a bitch to find oneself in the middle of the ocean, suddenly lacking some vital system or another. Also in the air, albeit if you're over land, it's possible to make an emergency landing. Witness the "miracle landing" on the Hudson recently. I don't remember the heroic pilot's name. )-; ) I saw one short clip from some security cam; the rooster tails were impressive!

Cheers! Rich