[GreenKeys] TTY-Connect 160V vs 80V

[Bob Camp]

Hi

One less than perfect solution is to use a small computer fan to blow  
some air over the heat sinks. It's amazing how much a little air motion  
can can cool off a heat sink.

Depending on what is attached to the heat sink the problem may be more  
or less of an issue. A pass transistor may have trouble at 240F. A  
normal ceramic power resistor can be very happy above 500 F. Either one  
will give a nasty burn if you bump into it. Either one will turn you  
nice green FR-4 board an ugly brown crispy color if you run it long  
enough.

Sounds like a good reason to use a 12 volt -> 160 volt adaptive  
switcher for the loop supply. Sixty ma max. at twelve volts and  
virtually no distortion at all.

	Take Care!

		Bob Camp
		KB8TQ



On Jul 1, 2004, at 12:06 PM, gil smith wrote:

> Hi Tim:
>
> It is not the transformers that run hot, it is the  
> power-resistor/heatsink that gets toasty.  The xfrms are oversized at  
> 43VA, but a smaller xfrm is about the same price, and I like to be  
> conservative, especially on a power design.  Which is why I don't like  
> a heatsink running at 175 F (160V loop).  With an 80V loop, the  
> heatsink is only 125 F, and the lower voltage is safer as well.
>
> No, I am not a ham.  Well, maybe after a few beers.  I did pick up an  
> HF transceiver, so I can start listening for HoffNet and other rtty  
> stuff.  I need to find a 12V supply for it so I can free up the lab  
> supply I have been using.  Maybe one day I'll get motivated and get a  
> license so I can transmit as well.
>
> thanks,
>
> gil
>
>
> At 08:00 AM 7/1/2004, you wrote:
>> The project is really looking good! I, too, wanted to thank you for  
>> all
>> your effort on this project!
>>
>> I don't know how much I will implement - probably at least one HV  
>> supply
>> and the computer section. I have a Heathkit HD-3030 (actually a  
>> Flesher 470
>> in disguise!) and it really is meant to be interfaced using RS-232.
>>
>> I am curious as to why the transformers run so hot especially in the  
>> 160
>> volt mode? You show the transformers to be 43 VA and I calculate that  
>> the
>> current at 115 volts should be 370 ma. Only drawing 60 ma should mean  
>> that
>> the transformer is loafing!!
>>
>> Tim Swarthout, WA5QEG
>>
>> P.S. I was wondering - do you have a ham license?
>
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