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

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

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.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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"Oh no, not again." 

- A bowl of petunias on it's way to certain death. 



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