[Amps] P/S upgrade

[Carl]

Ignoring the plate transformers efficiency, a variac having the same 
ratings as the primary should have the same I*R losses. The bigger the 
variac the less the losses and you can easily measure and calculate 
that.

For long runs its often easier to use stepup/stepdown transformers to 
reduce the drop. I have a 150' run to the garage that has a 5hp 
compressor, welders and some machine tools, and a 250' run to an 
equipment trailer at the base of the big tower that houses commercial 
radios. I come out of the mains box in the house at 240V and go into a 
5KVA 240/480 transformer (actually marked 220/440). Part way to the 
trailer a branch goes to the garage and both sites have an identical 
transformer. The runs are #8 and the voltage holds real steady. The 
transformers came from a company I used to work for that was upgrading 
and they were headed for the dumpster.

There are also 120 and 240 to 660V transformers available.

For the three AM KW amps the plate transformers are mostly old style 
110V primaries, even the 7500VCT @ 1A CCS one. I found a few more 
transformers a few years ago and for the 45-50' run I go 240/480 and 
480/120 using #12. The sag is minimal and a couple of variacs are used.

Carl
KM1H



----- Original Message ----- 
From: "Barrie Smith" <barrie at centric.net>
To: "Carl" <km1h at jeremy.mv.com>; "Mike Lucas" <w5chr at bellsouth.net>; 
<amps at contesting.com>
Sent: Monday, March 16, 2009 9:40 PM
Subject: Re: [Amps] P/S upgrade


>
> ----- Original Message ----- 
> From: "Carl" <km1h at jeremy.mv.com>
> To: "Mike Lucas" <w5chr at bellsouth.net>; <amps at contesting.com>
> Sent: Monday, March 16, 2009 7:20 PM
> Subject: Re: [Amps] P/S upgrade
>
>
>> Whats the value of the choke?? Old handbooks have all the info on 
>> thise
>> selections that you will ever need.
>>
>> Yes a variac is just an added stage of regulation to contend with 
>> unless
>> it is a monster.
>
> Carl:
>
> What qualifies as a monster?
>
> On my largest power supply here, which is an early, untapped, Peter 
> Dahl unit that runs 5000 volts at 2 amps, I use a 30 amp variac.
>
> Under a 1.5 amp load, with the output voltage set at 4200 volts, no 
> load, I see about 15% sag under key-down conditions.
>
> Part of that sag is very likely the variac, but when I had the shack 
> wired for 240 years ago I specified number 8 wire.  I got number 10. 
> It's over a hundred foot run, so I think I'm losing something there, 
> as well.
>
> 73, Barrie, W7ALW
>>
>> Carl
>> KM1H
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Mike Lucas" <w5chr at bellsouth.net>
>> To: <amps at contesting.com>
>> Sent: Monday, March 16, 2009 7:59 PM
>> Subject: [Amps] P/S upgrade
>>
>>
>>>I have an OLD homebrew supply for a single 4-1000,
>>> that needs some re-work before using it with an amp.Transformer 
>>> weighs
>>> 103lbs, with a 28 lb choke input in the neg lead. Rectifiers are 3 
>>> amp
>>> individual diodes in a bridge configuration.
>>> Questions are: is 16Mfd enough at 5 Kv and 540mils, if not, how 
>>> much?
>>> And
>>> why will a variac cause poor regulation?
>>>
>>> 73, Mike W5CHR
>>> Memphis
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>
>