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:
>>>> 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 ;-)
> 
> Its no better on this side of the pond either, Joerg. ...


It think we are on the same side of the pond. Well, maybe the other pond 
(I am in California).


>                                               ... I stocked up on the 
> auto stuff 20 years ago when the handwriting was on the wall & I may have a 1 
> pound can in the basement yet that hasn't been tapped. ...


That can could be worth a whole lot of money these days.


>                                               ... My AC gages have R-134 
> scales on them, but the hoses can't take the R-134 pressures.  I'm not sure, 
> but I think my oldest vehicle (a 99 GMC 3 door, 4wd) now has R-134 in it, and 
> its working poorly, so I'll have to bite the bullet and get it serviced before 
> warm weather sets in for the summer.  Ditto for the wifes VW Jetta, a 2002, 
> but I have come to expect that, that Jetta was a lemon from the gitgo, costing 
> the dealer I bought it from almost $2500 in body electrics within the 90 day 
> warranty he gave me.  Both front door window motors failed ($400 ea) and the 
> motorized skylight ($1600) fell out!  And I still have a laundry list of 
> things that don't work right, like the passenger side seat heat, the radio, 
> and the inability to aim the OEM but aftermarket Helia headlights in it, they 
> are too low by about 5 degrees when cranked as high as I can get them.  The 
> OEM's were the usual sandblasted yellow sitting on the lot, and new ones, one 
> of which has already burned up its internal wiring & been replaced for gratis, 
> were part of the purchase deal.  And it still has only 20% of the lights my 
> GMC has, that thing can see through a 2 course brick wall with its 10 year 
> old, stock, original headlights yet!  Fresh lamps of course, but still, they 
> haven't yellowed a bit.  Whatever kind of plastic they are made of, its the 
> Right Stuff(TM).
> 
> Ya win some, and ya lose some. :)
> 

Ouch. Sad actually. I've had an Audi station wagon in Europe, same mfg 
family. But I always try to buy the vehicle with the least amount of 
electrics/electronics because automotive guys don't seem to master this 
field all that well. The Audi still runs just fine over there, 21 years 
old, no issues in all those years.

-- 
Regards, Joerg

http://www.analogconsultants.com/



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