[Amps] Astron RS20A primary resistance

[Will Matney]

Right,

Where the current is 1/2 what it is on 120 Vac, they would use a smaller wire size and the resistance will be higher. If they used the same wire size, then you could multiply by 2, but they don't. The wire size is selected by the least size you can use for the duty cycle and current of the winding.

It sounds to me like Astron has figured a way to make more money. If you want to change line voltage, you either have to buy a new power supply or a new transformer! It's not hard, nor does it cost that much more to make a dual voltage transformer. All that is required is breaking the primary in half and bringing out the two wire ends for series/paralell connection.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 5/8/06 at 4:30 PM TexasRF at aol.com wrote:

>Since the primary current is half and the number of turns are two times, 
>the 
>resistance could be four times for 220v vs. 110vac.
> 
>Perhaps your original 6 ohm reading is right on the money.
> 
>73,
>Gerald K5GW
> 
> 
> 
>In a message dated 5/8/2006 3:26:07 P.M. Central Daylight Time,  
>garyschafer at comcast.net writes:
>
>Thanks  Dan,
>
>I have a VS35M also and it shows a resistance of around an ohm on  my Fluke
>77 meter so that sounds in the ball park. I wasn't sure if the  transformer
>in the 20 amp supply would be a lot higher than the 35 amp  supply or not
>but
>it sounds like it is about the same.
>
>Now if I can  find someone that has a 220 volt unit to make a comparison I
>will be all  set. It should be about twice that or around 2.2 ohms or so
>but
>I read  around 6 ohms on the one in question. 
>
>By the way Astron does not (at  least in the past) use dual primary
>transformers. It is either 120 or  220.
>
>Thanks
>Gary  K4FMX
>
>> -----Original  Message-----
>> From: amps-bounces at contesting.com  [mailto:amps-bounces at contesting.com]
>On
>> Behalf Of Dan Hearn
>>  Sent: Monday, May 08, 2006 2:53 PM
>> To: garyschafer at comcast.net;  amps at contesting.com
>> Subject: Re: [Amps] Astron RS20A primary  resistance
>> 
>> Gary, I have a VS20M Astron here which I suspect  has the same xfmr in
>it.
>> I
>> measure the primary R as 1 ohm with  my Tripplet 60NA. That seems awfully
>> low
>> so I measured it with  my Fluke 77 and get 1.1 ohms. I measured between
>the
>> blades on the  line cord with the power switch on. Still seems pretty low
>> but
>>  I believe my measurements. 73, Dan, N5AR
>> 
>> -----Original  Message-----
>> From: amps-bounces at contesting.com  [mailto:amps-bounces at contesting.com]On
>> Behalf Of Gary Schafer
>>  Sent: Sunday, May 07, 2006 7:59 PM
>> To: amps at contesting.com
>>  Subject: [Amps] Astron RS20A primary resistance
>> 
>> 
>> I  need to know what the primary resistance is of the Astron RS20A
>>  transformer. I would like to know the resistance of a 220 volt 
>transformer
>> and a 120 volt transformer.
>> 
>> Maybe someone  has a 220 volt RS20A that could measure the resistance
>> across
>>  the power plug, that will do it.
>> 
>> 
>> 
>> I have a  power supply here that is supposed to be a 120 volt unit but it
>> looks  like it has a 220 volt transformer as I only get around ½ the
>>  voltage
>> out on 120. This transformer measures around 6 ohms primary  resistance.
>> 
>> 
>> 
>> Thanks for any help.
>>  
>> 
>> 
>> 73
>> 
>> Gary  K4FMX
>>  
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