On 10/24/2011 7:08 AM, N8N wrote:
On Oct 23, 6:13 pm, "Stormin Mormon"
wrote:
Ideally, HUM is powered when both heat and fan are
energized. In this case, might not make a lot of difference
if the hum runs a few more minutes, on warm up.

--
Christopher A. Young
Learn more about Jesus
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.

"Tony wrote in message

...

Hi,
No big deal as long as you remember humidifier comes on when
blower
runs and if humidistat calls for humidity.(so called AND
logic)
And is depending on what type of humidifier.

humidifier is old and I'm having a hard time finding info on it too
but it appears to have a 24V humidistat but runs off 120V. As another
data point I actually got the sail switch working again - just had too
much stuff built up on the sail, was staying locked "on" all the
time. Cleaned and now works. I was thinking rewiring properly but in
the same configuration as it was before, but ditching the 24V xformer
(actually more like 28V) and pulling the low voltage power for the
humidistat from the W/C terminals of the thermostat, that way low
voltage is not energized unless thermostat is calling for heat, 120V
is not energized unless air is flowing in return. If the sail switch
happens to fail while I am still there I could just get a current
sensing relay for the fan motor and switch the low voltage through
that as well. My only concern is the added load on the heat contact
in the thermostat. Not sure how much humidifier draws @ 24V in
operation, nor what the thermostat contacts are rated for (and I can't
take measurements until I get this operational again, still need to
find what the correct water panel is for this unit.)

nate

As you note the 24V water solenoid current may be an issue if you
connect the solenoid to W-C at the furnace. I think it is unlikely the
current is too high.

In the good old days the thermostat had a "heat anticipator" that caused
the stat to shut down heat a little early. The anticipator at the stat
was set to the gas valve current. The current would be higher if you add
the solenoid. This is probably not an issue with recent stats. The round
Honeywell T87s have an anticipator adjustment.

If the anticipator setting is a problem it is even more of a problem
when the water solenoid valve is switched on and off by the humidistat.
Connecting W-C to the coil of a control relay would eliminate that problem.

I used to replace the SPDT fan relay with a DPDT relay. There is a point
to connect a transformer for the humidifier where the humidifier is only
powered when the plenum gets hot and turns on the fan (like HUM in your
other post). (The circuit you posted has a SPDT fan relay.)

A sail switch control is OK. I would add a switch to shutdown the
humidifier in cooling season. I have a vague recollection that some
water solenoid valves were water cooled. You might check if the valve
gets a lot hotter if the water is turned off.

--
bud--