4 switch conductors are required for running a reversing induction motor at
120VAC. There are drum type switches available as well as motor rated
3-position 3PDT toggle switches (9 terminals), or you can combine a
2-position DPDT toggle switch for reversing and a 2 position (I like
momentary) DPST toggle switch for engagement, all motor rated of course.
Drum switches are more reliable than toggle switches. With toggle switches
I like to use a local disconnect upstream in case the contacts arc and
stick. Regarding conductor length, there are standard wire gauge charts
available from a number of online sources based on motor HP. Be sure to
use the charts based on voltage drop because of distance.... Also be sure
to leave the local thermal overload in series with the line in at the motor
to protect your motor.
You can also wire most fractional motors for 240 VAC operation to reduce
current load, conductor size, and easier starting, but it typically requires
one additional switch wire to derive 120VAC from the center tap of the
series run winding to use for the start winding (do not use 240 VAC on the
start winding unless you want smoke...). You can alternatively derive 120
VAC from the source by using the available neutral and it only requires 4
switch conductors to the motor - however it's generally a good idea to be
sure you have your overload protection arranged to disengage both lines
simultaneously if you do this. Switch requirements are similar but wiring
is different.
Email me if you need a wiring diagram.
You may also want to consider using 24VAC coil contactors. I have built
some tower motor control boxes using Packard brand contactors and
transformers which are very economical and work fine. You can do some
pretty neat stuff with these using limit switches and ladder logic wiring -
or just to avoid having to run large line conductors back to a remote
switch.
Hope this info helps & good luck on your project.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Patrick Greenlee
Sent: Tuesday, January 01, 2019 8:40 PM
To: Richard (Rick) Karlquist <richard@karlquist.com>;
towertalk@contesting.com
Subject: Re: [TowerTalk] US Tower Up/Down Raising Fixture (MD-750) Motor
Switch
I should have not replied in haste to something of which I was not
properly informed. Fast on the trigger but slow on the draw. That's
no toes Pete.
If the length of the run and required wire gauge were within reasonable
limits, especially monetary limits and there were no strong contrary
electronic negatives I would certainly consider going without a relay.
I have been accused of being a belt and suspenders kind of guy.
Patrick
On 1/1/2019 5:28 PM, Richard (Rick) Karlquist wrote:
> As built, the switch on the control box energizes the coil of a relay
> that carries the motor current. That is the relay that can stick.
> Are you saying you are going to run the motor current (not just the
> relay coil current) through your remote switch and bypass the built in
> relay?
> Not following you...
>
> 73
> Rick N6RK
>
> On 1/1/2019 1:21 PM, Patrick Greenlee wrote:
>> I did not propose a relay. I was thinking of up-sizing the wire
>> sufficiently to obviate a relay. I concur with your low opinion of
>> the A/C contactors. I have replaced some of those too. Brute force
>> switching and HD wire run. Reliable and not prone to failure.
>>
>> Patrick NJ5G
>>
>> On 1/1/2019 1:03 PM, Richard (Rick) Karlquist wrote:
>>> On 1/1/2019 10:45 AM, Patrick Greenlee wrote:
>>>> As you mention, upsize the wire and operate in the dry. This
>>>> assumes that you aren't at the ragged edge of too much wire loss
>>>> now. Probably not but you could grab a meter and make sure.
>>>>
>>>> Patrick NJ5G
>>>>
>>>
>>> The trouble with what you describe is that if the relay sticks on,
>>> you are too far away from the tower to kill the power and stop the
>>> motor. The type of relay used is the same as is used in air
>>> conditioners, and AC relays are famous for sticking on. On my
>>> HDX-5106, the relay has stuck on twice.
>>>
>>> 73
>>> Rick N6RK
>>>
>>
>>
>
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