Re: adding relay to AC fan circut

On Jun 4, 6:07 pm, "hr(bob) hofm...@xxxxxxx" <hrhofm...@xxxxxxx>
wrote:
On Jun 4, 3:55 pm, philsvintageradios <philsvintagerad...@xxxxxxxx>
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

Your posting is confusing!   You don't say which motor you are talking
about when you give colors and voltages, youdon't say what the votlage
is on the AC motor, and are youtrying to connect it to the AC blower
motor in the furnace or to the AC compressor mnotor.  Try starting
over and maybe someone wioll eb able to understand you better.  Sorry,- Hide quoted text -

- Show quoted text -

sorry for the confusion.
I have a window type air conditioner , and I am trying to add a blower
to assist the fan in the AC unit because I am pushing the air through
some ducting.
The AC unit has a little control panel, circut board and three relays
to run it's internal 3 speed fan.

I am trying to wire it so when the AC unit turns it's fan on, the
added blower comes on at the same time. Since I didn't want to load
down the existing circutry in the AC unit I am trying to use a relay
to turn the extra blower on and off.

At first I thought it would be simple because I came to the
(incorrect ) conclusion that the 3 speed fan would use a neutral and 3
run windings that wouuld be turned on to give 3 different speeds. I
also assumed that at least one of these three wires would be hot all
the time, so I planned to use the 110 AC power to the fan to power the
coil in the relay. The contacts of the (added) relay would be used to
turn the fan on and off, and that is a separate circut not to be
concerned with.

When I went to install the relay , instead of one neutral and three
hot wires, I found there was one neutral, and a black wire and they
are also connected across an electrolytic cap. there are three
additional wires that run from the fan to the three relays on the
little circut board. ( so 5 wires to the 3 speed fan)

Correct me if I am wrong, I am trying to wrap my head around how the
circut works, but I assume the black and white wires are supplying
most of the current to the fan,and are used for start up, and the
three relays are turning on and off resistors which somehow affect
coils in the motor , perhaps switching in and out three different
loads to affect the induction and capacitance ratio, thus affecting
the speed of the fan. Take that with a pinch of salt as I am unsure
exactly how this circut works. ( and so I am asking)

when I measured 170 volts across the black and neutral and saw 170
volts I was afraid to use those wires to power the coil of the relay
as it is only rated for 120 or so. So instead I hooked the relay
between one of the three colored wires and the neutral.

To my surprise all three of these wires have something close to 110
and the relay works the way I wanted if it is hooked between neutral
and any of these three wires. There is a delay of about 3 seconds in
the relay being triggered. It appears to me that the fan is starting
by using only the black and white wires , then the electronics come
into play after this delay, and are switching on one of the 3 relays
(depending on which speed is set) on the circut board to affect the
speed of the fan.

I origionally thought the three wires from the relays were supplying
most of the current , but I think I am wrong about that.

So if my assumption is correct , then adding the coil into the circut
of any of these three wires probably affects one of the fan speeds
slightly because it does add in the resistance, inductance and power
draw of the holding coil of the relay to the circut run by the little
board.

I think having the relay connected here may be changing one of the
fan speeds slightly. I don't know if this is potentially damaging to
the fan in the AC unit or it's little circut board. I will probably
run the unit with it's fan on full speed most of the time that it is
being used.

someone I discussed this with said i could buy a "voltage sensing
relay" and that it could use only the neutral wire for it's trigger. I
asked at the electronics store where I bought the 110 V relay but they
hadn't heard of such a device.

So to sum up , my question is , is it ok hooked up like this ? is the
load of the coil in the relay enough to damage anything?

If that's not clear just ask me to rephrase anything, Again sorry if
my origional post wasn't well worded.

Phil

.

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