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@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@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@contesting.com [mailto:amps-bounces@contesting.com]
>On
>> Behalf Of Dan Hearn
>> Sent: Monday, May 08, 2006 2:53 PM
>> To: garyschafer@comcast.net; amps@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@contesting.com [mailto:amps-bounces@contesting.com]On
>> Behalf Of Gary Schafer
>> Sent: Sunday, May 07, 2006 7:59 PM
>> To: amps@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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