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

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

On Wednesday 20 May 2009, DJ Delorie wrote:
>> Then put a time delay to off of at least 3 to 5 minutes into the
>> condensor fan circuit only,
>
>I don't have that kind of control over it.  I have one low-voltage
>control loop to tell it on/off, and that's it.

It is _your_ AC, right?  You have every right to re-engineer the controls that 
were probably speced by some bean counter who wouldn't know what the high side 
pressure meant if his life depended on it.  I am not the least bit allergic to 
fixing what is plainly poorly engineered because they perceive that the extra 
50 bucks it would take to do it right costs them their competitive edge.

Scroooem, that what we do, the _real_ engineering, or we wouldn't be on this 
list.  It may take a while to decipher the drawing inside the outdoor unit to 
figure out where to add what, but it can be done.

>> By the same token, if the evaporator fan in the furnace is being
>> stopped at the same time as the compressor,
>
>It's not, it stays on for a while after that, until the air it's
>moving warms up.

That at least is correct.

>> On a long run cycle, long enough to reach steady state conditions,
>> gas charge can be somewhat judged by inspecting the big line where
>> it comes back out of the furnace.
>
>I have a thermocouple in the plenum right after the A/C exchanger, the
>air in there is nearly freezing.  It reads 41F but I think the
>software is bottoming out because it drops fast and just flat-lines at
>41F (that thermocouple system is designed for the woodstove - 0C to
>1023C).  I'm pretty sure it's OK.

I'd want to dbl check with a decent thermometer.  Even a $20 dial type for 
photo darkroom use may be more accurate than the thermocouple in those ranges.
But the outlet pipes condition is the better clue IMO.

>It did have a leak at one point,
>and we had an A/C specialist come and redo the joints and recharge it,
>it hasn't degraded since then.

Then the after run on the condenser fan should really make a diff.  The 
biggest concern for TD relays, when they are air bleed & bellows designs, is 
that being outside, they don't function well for long term use as they will 
corrode.  There is an electronic TD relay, with a knob on top of the case to 
adjust the delay, that I have used as replacements for the mercury based TD 
relays in older Harris transmitters that would appear capable of doing the 
job, but I don't have the catalog handy as its 1000 miles away in Upstate MI 
from me.  I actually got 3 of them from a local heating/ac place in Iron 
Mountain MI, IIRC I paid around $50 a copy.  Keep those dry and they should 
work for quite a while.

>> 25kVA, still small.  How many houses are they running from it?
>
>Just mine :-)
>
>I have 7200 VAC coming up the driveway (it's 0.3 miles to the road).

Ahh.  That explains a lot.  I _think_ its 14.4kv on the street here, but don't 
quote me in court. :)

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
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