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

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

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.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.



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