How add 110 v indicator light to relay side of fan circuit

Thread Starter

lpowers

Joined Oct 20, 2017
8
Hi,

I have a basic understanding of electrical/electronics (please be gentle). This question is more electrical than electronics, but I hope it's close enough that it qualifies.

I have a friend that has a metal building with an exhaust fan near the ceiling. In the winter when it's cold outside and warm inside, condensation accumulates on the ceiling. The exhaust fan helps remove condensation, but it's currently on a light switch and he doesn't want to manually turn it on and off throughout the day. I offered to add a Raspberry Pi and solid state relay and program it to turn on the fan every hour for 15 mins.

The existing switch box has a 20 amp light switch connected to a red and blue wire (no neutral) so I'm guessing the light switch simply switches one side of the circuit. I should be able to swap in the Raspberry Pi and an SSR (3v - 32 v DC input, 24 v - 380 v AC output - 40A).

I have two questions:

1) I want him to be able to look at the switch box and know if the fan is on or not so I ordered an indicator light (LED but runs on 110 v). My initial thought was to just place this inline between one side of the SSR output and the wire going to the exhaust fan. After thinking about it, I believe this would send the entire circuit/motor amperage through the indicator light and blow it out. What is the easiest (fewest components) way to make this work?

I could add an LED to the Raspberry Pi side of it and that would tell me when the RPi was turning on the SSR, but I really would rather have the indicator show if the fan motor circuit is energized.

2) It would be nice to have a manual override switch in case the RPi/SSR stops working or if he just wants the fan on for an extended period of time. Can I safely wire the existing light switch in parallel with the outputs on the SSR so that either the RPi or the light switch can power the circuit? Will turning on the light switch cause any kind of damage on the SSR?

Thanks much,

Lance
 

GopherT

Joined Nov 23, 2012
8,009
Hi,

I have a basic understanding of electrical/electronics (please be gentle). This question is more electrical than electronics, but I hope it's close enough that it qualifies.

I have a friend that has a metal building with an exhaust fan near the ceiling. In the winter when it's cold outside and warm inside, condensation accumulates on the ceiling. The exhaust fan helps remove condensation, but it's currently on a light switch and he doesn't want to manually turn it on and off throughout the day. I offered to add a Raspberry Pi and solid state relay and program it to turn on the fan every hour for 15 mins.

The existing switch box has a 20 amp light switch connected to a red and blue wire (no neutral) so I'm guessing the light switch simply switches one side of the circuit. I should be able to swap in the Raspberry Pi and an SSR (3v - 32 v DC input, 24 v - 380 v AC output - 40A).

I have two questions:

1) I want him to be able to look at the switch box and know if the fan is on or not so I ordered an indicator light (LED but runs on 110 v). My initial thought was to just place this inline between one side of the SSR output and the wire going to the exhaust fan. After thinking about it, I believe this would send the entire circuit/motor amperage through the indicator light and blow it out. What is the easiest (fewest components) way to make this work?

I could add an LED to the Raspberry Pi side of it and that would tell me when the RPi was turning on the SSR, but I really would rather have the indicator show if the fan motor circuit is energized.

2) It would be nice to have a manual override switch in case the RPi/SSR stops working or if he just wants the fan on for an extended period of time. Can I safely wire the existing light switch in parallel with the outputs on the SSR so that either the RPi or the light switch can power the circuit? Will turning on the light switch cause any kind of damage on the SSR?

Thanks much,

Lance
Put the lamp in parallel with the fan motor (get a 220V bulb if the fan is 220v).
 

Reloadron

Joined Jan 15, 2015
7,546
I would measure exactly what is being switched. The reasoning is here in the US if the fan is a 240 volt AC fan the switch may be a Double Pole Single Throw switch. So if you have 240 VAC split phase when the motor is Off you don't have a hot line not switched Off in the motor. The colors Red and Blue are commonly used in schemes like this. I would start by seeing exactly what you have and how it is switched. Any pilot lamp or indicator lamp can go in parallel with the load as Gopher mentioned.

Ron
 

philba

Joined Aug 17, 2017
959
RaspPi is massive overkill though a PI zero would be relatively cost effective. Where is the PI located? I'd just put an indicator LED on that. Have your timer program toggle the LED, too.

For your override switch, just bridge it across the relay and you will be good.

And for what it's worth, you can buy timer modules that will do it all. There are even ones at your local hardware store.
 

Thread Starter

lpowers

Joined Oct 20, 2017
8
A little follow-up information:

I believe the light switch being used is a 20 amp switch. It's a normal looking Leviton light switch except it has a plastic red body. It has the ground screw on one side and two terminal screws on the other. There are three wires coming into the switch box (ground and a red and a blue wire). I think I measured across the terminals and got 120 v, but I need to go back and verify (I don't know if this guarantees that the fan motor is 120 v or if there is still the possibility that it might be 240 v).

This is in a large industrial building and the ceiling is too high for me to access the fan (I'm not even sure where it's located - I'm just starting to help him with this problem). Because of the condensation that accumulates on the ceiling, it's causing the paint to peel off. He wants a solution right away before it gets cold outside and causes more damage.

He has a commercial business in this building. We looked at all of the commercial timer switches (that would certainly be an easier solution). The problem is that we couldn't find a timer switch that will handle 20 Amps, not need a neutral and have enough programming functionality to turn on for 15 minutes every hour (which is the schedule he wants). Of the timer switches I could find, most would only do 3-4 on/offs a day - 20 or so settings per week. Although the RPi is overkill, it seemed like the easiest way to give him a fan turn on every 15 mins and also allow me to program it to not turn on during hours they are closed.

If anybody knows of a commercial timer switch that will fit the bill, I'd much rather go that route.

Otherwise, any testing advice to help me identify 120v vs 240v and ideas on how to hook up the indicator light would be much appreciated.

Thanks again,

Lance
 

GopherT

Joined Nov 23, 2012
8,009
A little follow-up information:

I believe the light switch being used is a 20 amp switch. It's a normal looking Leviton light switch except it has a plastic red body. It has the ground screw on one side and two terminal screws on the other. There are three wires coming into the switch box (ground and a red and a blue wire). I think I measured across the terminals and got 120 v, but I need to go back and verify (I don't know if this guarantees that the fan motor is 120 v or if there is still the possibility that it might be 240 v).

This is in a large industrial building and the ceiling is too high for me to access the fan (I'm not even sure where it's located - I'm just starting to help him with this problem). Because of the condensation that accumulates on the ceiling, it's causing the paint to peel off. He wants a solution right away before it gets cold outside and causes more damage.

He has a commercial business in this building. We looked at all of the commercial timer switches (that would certainly be an easier solution). The problem is that we couldn't find a timer switch that will handle 20 Amps, not need a neutral and have enough programming functionality to turn on for 15 minutes every hour (which is the schedule he wants). Of the timer switches I could find, most would only do 3-4 on/offs a day - 20 or so settings per week. Although the RPi is overkill, it seemed like the easiest way to give him a fan turn on every 15 mins and also allow me to program it to not turn on during hours they are closed.

If anybody knows of a commercial timer switch that will fit the bill, I'd much rather go that route.

Otherwise, any testing advice to help me identify 120v vs 240v and ideas on how to hook up the indicator light would be much appreciated.

Thanks again,

Lance

Measure the voltage from red to blue when the fan is off. It will likely be 220v. You have a 220V system (2 hot and a copper ground).

When you measure, make sure the fan is off and the meter is set to Volts AC.
 

philba

Joined Aug 17, 2017
959
Do you have any information on the fan unit? It might not pull 20 amps. With a clamp meter you could get a pretty good idea of what it does but I'd feel better knowing the actual spec.
 

Thread Starter

lpowers

Joined Oct 20, 2017
8
Hey guys,

Thanks so much for all of your helpful suggestions. I'll go to his place tomorrow morning and measure across the switch terminals and report back on the voltage. I'll try to find out more about the fan motor, but I don't think I'll be able to get that info (the building is owned by someone else and it's hard to get information).

Thanks,

Lance
 

Thread Starter

lpowers

Joined Oct 20, 2017
8
Hi Guys,

I went to the building this morning and took photos and measured voltage. I have to apologize because I realize I stated the wire coloring wrong (which completely throws everybody off). The wires going to the switch are blue and black. I measured 120 VAC across the switch terminals. I also found that panel that I believe has the breaker for the exhaust fan. It appears to be a 120VAC 20 amp breaker.

As a refresher, I want to install a Raspberry Pi and a SSR in place of the switch so I can program it to turn on for 15 mins every hours (and not run when the business is closed). If possible, I'd like to keep the current switch and run it in parallel with the SSR so it could be used as a manual override in case the RPi/SSR fails or if he just wants to run the fan for an extended period of time.

My main question is how can I install a 120VAC (LED) indicator light on the SSR output side. I really want him to be able to glance at the switch box and visually see if the fan is running. I know I could put an LED on the RPi side of it, but I'm concerned that if the SSR blows out, the indicator light will continue to turn on and give the appearance that the fan is running when it really isn't.

I'm guessing with the current setup, the switch is inline on one side of the motor. If I add the indicator inline (in series) it means all the circuit amperage would go through the indicator and blow it. Can I add it in parallel to the switch/SSR Output? Do I need to add another component in order to power (but protect) the indicator light?

Thanks again for all the suggestions and help,

Lance
 

Attachments

GopherT

Joined Nov 23, 2012
8,009
Hi Guys,

I went to the building this morning and took photos and measured voltage. I have to apologize because I realize I stated the wire coloring wrong (which completely throws everybody off). The wires going to the switch are blue and black. I measured 120 VAC across the switch terminals. I also found that panel that I believe has the breaker for the exhaust fan. It appears to be a 120VAC 20 amp breaker.

As a refresher, I want to install a Raspberry Pi and a SSR in place of the switch so I can program it to turn on for 15 mins every hours (and not run when the business is closed). If possible, I'd like to keep the current switch and run it in parallel with the SSR so it could be used as a manual override in case the RPi/SSR fails or if he just wants to run the fan for an extended period of time.

My main question is how can I install a 120VAC (LED) indicator light on the SSR output side. I really want him to be able to glance at the switch box and visually see if the fan is running. I know I could put an LED on the RPi side of it, but I'm concerned that if the SSR blows out, the indicator light will continue to turn on and give the appearance that the fan is running when it really isn't.

I'm guessing with the current setup, the switch is inline on one side of the motor. If I add the indicator inline (in series) it means all the circuit amperage would go through the indicator and blow it. Can I add it in parallel to the switch/SSR Output? Do I need to add another component in order to power (but protect) the indicator light?

Thanks again for all the suggestions and help,

Lance

Again, put the bulb in parallel with the fan to make sure the bulb lights when the fan runs.
 

Reloadron

Joined Jan 15, 2015
7,546
Given your options your switch looks to be in a 4X4 box. I would just go to Lowe's, Home Depot or any home improvement store and buy a timer made for a single gang box and add a box beside the existing. Most of the timers will fit a single gang but are limited to 15 Amp so I would shove a 120 volt controlled SSR in the existing box and just put a cover on it. Your llight just goes on the output of the SSR. (across the load) . Your voltage measurement was across the switch and I am guessing with the switch off. I see the green ground but you will need to get a neutral from somewhere. Actually the 2011 NED code calls for a neutral to be run through the switch box. Anyway I would not use a micro controller, I would just get an inexpensive programmable timer with 120 VAC out and let that be the control voltage of the SSR. .

Ron
 

Thread Starter

lpowers

Joined Oct 20, 2017
8
I'd love to use an off-the-shelf timer but I haven't found any timers with this many potential on/offs. He wants it to run every hour for 15 minutes and most timers just don't have the option for that many on/offs. If anybody knows of one, I'd love to hear about it. For this reason, I figured the Raspberry Pi would be the best solution. It's overkill for sure, but it would allow me to program it for his 15 minute runs every hour and also allow me to have the fan not run when his business is closed.

I don't have access to the exhaust fan or the wiring for it (this is a very large building with high ceilings) so I don't think I can "place" the indicator light in parallel to the motor. All I have access to is the switch box in the equipment room. From my very basic understanding of electrical, I'm guessing that this switch is inline with only one-side of the fan motor circuit. This is my main question. If I replace the switch with an SSR, can I place the indicator light across the outputs of the SSR? To me, this would put the indicator light in parallel with the SSR but it would also seem to put the indicator light in series with the fan motor. Won't that blow the indicator light out and won't it stay on all the time since it completes the motor circuit even if the SSR is "off"? I just don't know how to get the indicator light on the output side of the SSR but still isolate it from the motor amperage. I don't have access to a neutral wire (we're trying to keep this simple enough that he doesn't have to call in an electrician). Maybe I'm overlooking obvious electrical principles.

Thanks much,

Lance
 

GopherT

Joined Nov 23, 2012
8,009
I'd love to use an off-the-shelf timer but I haven't found any timers with this many potential on/offs. He wants it to run every hour for 15 minutes and most timers just don't have the option for that many on/offs. If anybody knows of one, I'd love to hear about it. For this reason, I figured the Raspberry Pi would be the best solution. It's overkill for sure, but it would allow me to program it for his 15 minute runs every hour and also allow me to have the fan not run when his business is closed.

I don't have access to the exhaust fan or the wiring for it (this is a very large building with high ceilings) so I don't think I can "place" the indicator light in parallel to the motor. All I have access to is the switch box in the equipment room. From my very basic understanding of electrical, I'm guessing that this switch is inline with only one-side of the fan motor circuit. This is my main question. If I replace the switch with an SSR, can I place the indicator light across the outputs of the SSR? To me, this would put the indicator light in parallel with the SSR but it would also seem to put the indicator light in series with the fan motor. Won't that blow the indicator light out and won't it stay on all the time since it completes the motor circuit even if the SSR is "off"? I just don't know how to get the indicator light on the output side of the SSR but still isolate it from the motor amperage. I don't have access to a neutral wire (we're trying to keep this simple enough that he doesn't have to call in an electrician). Maybe I'm overlooking obvious electrical principles.

Thanks much,

Lance

Ceiling fan controllers exist that have thermostats AND humidistats. They just run as appropriate to prevent condensation in attics.

https://www.walmart.com/reviews/product/409561567
 

MaxHeadRoom

Joined Jul 18, 2013
28,767
I'd love to use an off-the-shelf timer but I haven't found any timers with this many potential on/offs. He wants it to run every hour for 15 minutes and most timers just don't have the option for that many on/offs. If anybody knows of one, I'd love to hear about it.
Lance
You could look at lawn irrigation timers, they usually provide options for different times of day.
And have real time clock.
Max.
 

Alec_t

Joined Sep 17, 2013
14,377
How about a good old-fashioned timer like this? Each tab gives a 15 minute switch closure. If the contact rating is insufficient for the fan you could use an intervening relay/contactor.
 

Reloadron

Joined Jan 15, 2015
7,546
I don't have access to the exhaust fan or the wiring for it (this is a very large building with high ceilings) so I don't think I can "place" the indicator light in parallel to the motor.
You don't need to be at the motor to parallel a light with the motor. The Line Out to the motor from the switch box to a Neutral is in parallel with the motor. There is likely a conduit going up to the motor. That conduit should have a switched hot, a neutral and maybe a ground. You do not need to be physically at the motor to wire in parallel with the motor.

You may also want to look at lawn sprinkler controllers or irrigation controllers at any home improvement store like Lowe's or Home Depot. Also try a Google of "programmable relays' and "programmable relay timers" for some timing solutions. What you are looking to do is not hard to find. If you really want to program a PIC you can but there are simple off the shelf solutions.

I see as I typed Max mentioned irrigation sprinkler timers.

Ron
 

Thread Starter

lpowers

Joined Oct 20, 2017
8
All of the above are great suggestions. The thermostat/humidistat would work perfect for bypassing a timer. An irrigation timer might work as well.

Thanks again for all of your suggestions.

-Lance
 
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