Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again

[Mike Stein]

Well, we indeed know the voltage (V or E) but not 
the current (I) used in your formula; since I is 
E/R then power is simply E^2/R, so 20 Ohms at 12V 
has to dissipate 144/20 = 7.2 W.

m

----- Original Message ----- 
From: "Ian Finder" <ian.finder at gmail.com>
To: "General Discussion: On-Topic and Off-Topic 
Posts" <cctalk at classiccmp.org>
Cc: <General at classiccmp.org>
Sent: Monday, October 26, 2015 2:32 PM
Subject: Re: Model 152 PSU dummy loads - Re: NeXT 
Cube - powers on briefly then off again


> Not sure how much of a noob you are, although 
> you repeatedly claim to be
> one so just on the safe side we'll cover some 
> Engineering for Poets (or
> Programmers) to reassure you ;) --
>
> V = I * R
> Power (watts) = I * V
>
> You know the voltage of the monitor. You know 
> the resistance of your
> resistor. So, you also know the maximum power 
> the resistor needs to be
> rated to dissipate.
>
> If the spec says the single air-cooled resistor 
> you're buying is good to
> dissipate X watts into ambient temperature Y, 
> I'd just go ahead and believe
> it.
>
> Make sure the numbers work out and you're fine, 
> no heavy duty HVAC needed.
> :-P
>
> Cheers,
>
> - Ian
>
> On Mon, Oct 26, 2015 at 10:52 AM, Toby Thain 
> <toby at telegraphics.com.au>
> wrote:
>
>> On 2015-10-26 1:23 PM, Ian Finder wrote:
>>
>>> This thread took a turn for the absurd. Oil? 
>>> Water? What a practical
>>> bunch of people. /s
>>>
>>> They make resistors with adequate cooling... 
>>> Almost as if they're
>>> rated for a certain number of watts of 
>>> dissipation and you can buy
>>> them based on that. They are resistors after 
>>> all.
>>>
>>> And if they overheat-- oh wait, they're heavy 
>>> duty resistors, not
>>> ICs. Get a couple, put them in a metal project 
>>> box, put it inline
>>> with the cable, and call it a day.
>>>
>>
>> Damn, I already ordered a pile of HVAC gear.
>>
>> j/k - yeah that was what I was basically 
>> planning, Ian ... just as a noob,
>> I'm not totally confident with what a single 
>> air cooled part can dissipate.
>>
>> (The thread was kind of interesting anyway!)
>>
>> --Toby
>>
>>
>> Sent from my iPhone
>>>
>>> On Oct 26, 2015, at 09:24, simon 
>>> <simski at dds.nl> wrote:
>>>>
>>>> please skip this ridicule and grab yourself a 
>>>> couple of headlights from
>>>> a car.
>>>>
>>>>
>>>>
>>>> On 26-10-15 17:16, Dale H. Cook wrote:
>>>>> My recommendation of oil is based upon my 
>>>>> decades of experience with
>>>>> broadband dummy loads from 60 watts to 2.5 
>>>>> kilowatts. The dummy loads that
>>>>> I have worked with for medium wave and below 
>>>>> and from 5 kilowatts down have
>>>>> all been convection air cooled. Broadband 
>>>>> dummy loads that I have used for
>>>>> higher powers (up to 25 kilowatts) have been 
>>>>> forced air cooled.
>>>>>
>>>>> I prefer to stick with what I have 
>>>>> experience with. As for water, YMMV.
>>>>>
>>>>> Dale H. Cook, Radio Contract Engineer, 
>>>>> Roanoke/Lynchburg, VA
>>>>> http://plymouthcolony.net/starcityeng/index.html
>>>>>
>>>>
>>>> --
>>>> Met vriendelijke Groet,
>>>>
>>>> Simon Claessen
>>>> drukknop.nl
>>>>
>>>
>>>
>>
>
>
> -- 
>   Ian Finder
>   (206) 395-MIPS
>   ian.finder at gmail.com