View Full Version : How to control an AC motor with LOR hardware?

05-15-2013, 04:47 PM
I would like to be able to control some small AC motors and one garage door motor on some animated props. The small motors are taken from animated reindeers. Since those are small, low amp, 110 volt, could I plug those in directly to a LOR channel without risking damaging to the controller?

I think it was DanoNJ that a while back advised me that I should use a solid state coil relay between the motor and LOR controller. Is this the type of relay that I should get for the small motors; theyíre 110v, maybe drawing at most 2-3 amps (if that):

Ok, now for my really dumb questions, assuming this is the correct relay to use. What is the correct way to wire this relay? Is the output side towards the motor and input side from the electrical power source?

The garage door motor is a Ĺ hp motor, 120v. The Craftsman technical service rep said it draws 5 or 6 amps. I donít think that is correct. But if that is correct, I have a problem since the max amount of amps per channel of a CTB16 is 4 amps. My calculation is as follows:
1/2hp x 746 watts (per 1 hp)/120v = 3.1 amps
Now if my calculation is correct, Iím within the allow load the LOR controller can handle. Yea!
Since the above relay is rated at 10 amps, seems to me I should be able to use it as well; except one problem. The garage door opener has a 3-prong plug, where and how would I connect third wire, the ground? I remember my Dad used to cut the "d*mn" things off. I donít think I want to do that.

Thanks for your help!!

05-15-2013, 05:13 PM
The small motors would probably be fine run directly from the LOR controller. You will just be able to turn them on and off, not control the speed, so you want to either turn those channels full on or full off.

The GDO motor is probably too large of a load to drive from the LOR controller directly. AC Motor amperage is a tricky subject. It depends on the load on the motor among other things, and can often be considerably higher than expected. Because the motor is an inductive load, ohms law doesn't work here, and the 5-6 amp figure sounds about right.

You will need a relay. The relay just acts as a switch. You want a relay with a 120VAC coil. The relay coil connects to the output of the LOR controller. The relay acts like a switch, when you apply voltage to the coil it closes a set of switch contacts. You then wire those contacts in series with the 'hot' (black) wire of the motor's power cord. So the motor will stil have a plug and will need to be plugged into a source of 120VAC, but the relay will act as the switch that allows LOR to turn the motor on and off.

Either a solid state or mechanical relay would probably work fine, just find one with a 120VAC coil. There isn't an "in" and "out" to a relay, there's a coil and contacts. Think of a relay as an on/off switch that you control by applying a voltage to the coil. The LOR output will cause the relays contacts to close, and those contacts, when wired inline with the power lead to the motor, will apply the 120VAC to the motor.

05-15-2013, 06:57 PM
In addition to what Jim said you might need a little bigger load to get the LOR controller to see the coil. I've used several relay's and have had about 50/50 success in powering the coil by itself.
A simple fix is wire a C7/C9 in the same circuit with the coil so the LOR controller sees the load from the bulb. Which isn't a bad idea because you will have a "On" light when the relay is engaged.

05-16-2013, 09:11 AM
Thanks jstjohnz & Shubb for pointing me in the right direction.

Sometimes I think there should be a forum category for "dumb questions"; make it easy to find my posts :lol: Oh well, here are some more:

Is this a better choice of relay: http://www.mouser.com/ProductDetail/Omron-Industrial/G2R-2-S-AC120S/?qs=sGAEpiMZZMs8I5ltipPMAEFXB803aBvC
This relay is described as a "plug-in" relay. What does it plug into? An electrical receptacle?

Jim, you said the relay "connects to the output of the LOR Controller". Does this relay simply plug into the female plug on LOR controller channel? And then the power supply for the motor connects (somehow) to the relay?

Thanks again!

05-16-2013, 11:08 AM
It plugs into a socket that has the connection screws. You can just berely see the prongs on the bottom of the relay.
They have 1 piece relays that have the screw connections built in that may be a little cheaper.

For the project you are talking about doing you won't find components that just "plug in". You are going to have to do some wiring.

05-16-2013, 02:06 PM
The small motors would probably be fine run directly from the LOR controller. You will just be able to turn them on and off, not control the speed, so you want to either turn those channels full on or full off.Just for the recordÖ. You wonít have any problems connecting animated reindeer motors to a controller; Iíve been running mine for the last 6 years. Dimming them wonít hurt anything either. The motors are synchronous so they run the same speed other than stalling out when the current gets too low to overcome the friction.

Connecting a coil to a TRIAC isnít the same as a transistor. The controller turns on a TRIAC but the TRIAC turns itself off when the voltage and current are low. There is not a kickback voltage like there is with a transistor and DC.

There is a phase shift of current with respect to voltage. This messes with the TRIACís ability to turn off at the correct time. If you were to measure the voltage when the TRIAC is full on, youíll find that the voltage is somewhat less than it should be. It wonít hurt anything; it just wonít be what you expect. You can counteract this affect by adding a resistive load, i.e. a C7 bulb.

Using a larger motor wonít hurt anything either as long as the inrush is less than what the TRIAC can handle. Youíll still need to add a parallel resistance to counteract the inductance so the current doesnít shift. This may possibly require more load than the TRIAC can handle though.