Re: gEDA-user: [OFF] high current amplifier

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

Gene Heskett wrote:
> On Wednesday 20 May 2009, Joerg wrote:
>> Gene Heskett wrote:
>>> On Wednesday 20 May 2009, Joerg wrote:
>>>> DJ Delorie wrote:
>>>>> Levente Kovacs <leventelist@xxxxxxxxx> writes:
>>>>>> 230V times 100A is something I dont want to even calculate.
>>>>> It's 23000 :-)
>>>>>
>>>>> My air conditioner draws 123 amps at 240 volts for the first few
>>>>> seconds.  That's almost 30kW.
>>>> Seconds and not fractions or a second? Yikes! Unless it's a 10-15 ton
>>>> unit that doesn't sound normal. Did you find some of the power hogs with
>>>> your new board by now?
>>> Off topic reply, but could be germain too.
>>>
>>> Not even a 40 horse compressor in a 22 ton (rated, yeah sure) Lennox will
>>> draw that much for that long.  Its startup was a peak in the 250
>>> amps/phase area, and the reason I say area is that a std 400 amp scale on
>>> an amp-probe on any phase line swung up to 250 and back down to its
>>> running of about 39 amps/phase in a purely ballistic fashion as the
>>> startup surge was only 6 or 7 cycles of the 208/3 phase line.
>>>
>>> Now it really gets off-topic.
>>>
>>> That was one of those _must_ _work_ units else a tv station was off the
>>> air 10 (or less) minutes after it failed.  It was also probably
>>> responsible for some of the early ozone holes over the antarctic as it was
>>> severely under fanned on the condensor side, and I had to add 20 pounds of
>>> freon in the fall to keep it working right until it wasn't needed, and
>>> bleed that 20 pounds back off as spring turned into summer.  This went on
>>> for 8 years on my watch, back in the 70's, and long before they started
>>> regulating all that stuff.
>>>
>>> 2 ea. 1100rpm 1/2 horse motors turning 24" fans just didn't cut it.  I got
>>> tired of that one spring and fixed _some_ of it by taking a failed motor
>>> to town, having the brackets stretched to carry 2 horse 1800 rpm motors,
>>> replacing the motor with a 2 horse 1800 and repeating it the next week
>>> with the second one.  2 horse wasn't quite enough as they ran a couple of
>>> amps over nameplate when the condensor was relatively clean.  When those
>>> blades failed (fatigue cracks, caught before they made shrapnel), I
>>> replaced them with blades with an inch less pitch.  That allowed it to
>>> continue to work until the ambient went over 80 degrees without bleeding
>>> freon to keep the high side under 400 psi and the compressor currents
>>> under 43 amps/phase else the overcurrents in the compressor would trip. 
>>> Based on those results, I would have said that a single 20hp motor,
>>> running at full load pulling a quad torrington wheel with each half about
>>> 16" wide & 14" diameter, would have been about right.  That could have
>>> been throttled with a 4' square louver driven by a M-H proportional
>>> control Modutrol to regulate the high side pressures/temps and made it
>>> work all year.  Some of the crappy designs foisted off on the industry by
>>> supposedly reputable, old line makers are amazingly loaded with excrement.
>>>  I even called Lennox and they swore on a stack of bibles that those 2,
>>> 1/2 horse motors were enough.  I asked what was the expected operating
>>> temperature range and he said 75-90F outside.  I said "and what happens
>>> when you have enough heat load to need it, but the outside temp is 33F?" 
>>> "Its not designed to run at those temps."  Why did you sell it to the
>>> State of Nebraska then, you did have the specs, I've seen them?  Mumble.
>>>
>>> Obviously I wasn't talking to a real engineer so I asked him where he got
>>> his sheepskin.  More mumbling.
>>>
>>> Being a tv engineer for the state NETV commission, when the nearest help
>>> is 200 miles away in Star City, (Lincoln NE) means you truly are a Jack Of
>>> All Trades. :)  Those 8 years were _very_ educational, but I left because
>>> I was still not the lead dog, so the scenery never changed. :)
>> Thanks for sharing, that was a real story from the trenches.
>>
>> Not looking forward to the 105F days that are coming. I don't need A/C
>> even when it gets to 95F in the office but when visitors come I have to.
>> And then the compressor often goes into bypass mode making that awful
>> rarrrrr noise. Then it's waiting 5-10 mins, crossing fingers, make sure
>> no black cat crosses street from right to left, turn switch to the old
>> Lennox back on, hold breath.
> 
> Then it needs help like I've described.  That sort of a locked rotor shutdown 
> is pure hell on the compressors.  No other nice way to describe it unforch.
> 

But I can't really bleed off freon. Plus AFAIK they don't sell that 
stuff to ordinary folk anymore unless you have a contractor's license. I 
mean, I could get one, but that would go a bit far ;-)

-- 
Regards, Joerg

http://www.analogconsultants.com/



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