Re: adding relay to AC fan circut
- From: "hr(bob) hofmann@xxxxxxx" <hrhofmann@xxxxxxx>
- Date: Thu, 5 Jun 2008 11:49:40 -0700 (PDT)
On Jun 5, 3:44 am, "Michael A. Terrell" <mike.terr...@xxxxxxxxxxxxx>
wrote:
philsvintageradios wrote:
I am trying to couple my air conditioner to a blower. I want the
blower to start when the fan in the AC does. It is a 3 speed motor ,
has 5 wires, neuteral and black ( across the AC supply with an
electrolytic cap between them) then yel,orange red , these three
wires go to solenoids on the PC board.
I bought a 110V relay, thinking I could connect it between neutral and
one of the three wires from the relay.
It does work, but it takes about 3 seconds before the relay clicks on.
I don't care about the 3 seconds but I am not really understanding how
these three wires affect the motor's speed.
Between the black and white, with the capacitor between I measure
about 170 Volts, I guessed that perhaps the cap is smoothing the sine
wave of the AC current , or somehow playing games with my digital
meter.
I get something close to 110 at all three wires from the solenoids
irreguardless of which fan speed is used. well that isn't exactly
true , I did notice the voltage very slowly dropping at some of these
points, but after 5 mins was still pretty close to 110. perhaps the
windings are not completely separated electrically and I am reading
voltage which is present because it is fed back through the windings
being interconnected?
I guess my main concern is that the windings of the relay aren't
connected in such a way that it is loading up the little PC board, and
I would like to understand better how the motor is being controlled by
these relays.
can anyone with a better understanding of motor control enlighten
me ? I have a scope I could connect to better understand ( by seeing
the waveform) if that would help, I assume the phase or lag of the
power is being changed by the circutry or something but I don't really
understand it.
Phil
Isn't there a schematic inside the unit? The AC for the fan motor
goes to the speed selector first, through the motor, then to neutral.
It sounds like you are trying to connect the relay to the compressor
motor, which is harder, since there are start and run capacitors
involved. You should just wire the relay so the booster fan runs
whenever the A/C is turned on.
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The OP did't say if the AC was 120 or 240V. Let's assume 120V AC
input. Depending on how many poles in the 3-speed motor, when there
is 120V across the active winding, there may be a higher voltage
measured across the unused windings that are not actually connected to
the power line. The OP need to connect his 120V-input relay to the
thermostat, before the three speed selection/switch gets involved.
.
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