ATS for Generator

hi, I made this schematic for an automatic transfer switch. The logic behind it is to automatically transfer power sources in case of a outage from normal power to generator power via contactor. Is my schematic ideal for this application? Please let me know if i should make any changes.

Don't they make double-pole contactors? Seems silly to put two in parallel if you can have a single device switch both sides.

Looks like it is designed to power the Emergency board from the generator whenever the generator is running, even if line power is available.

Why does CH2 allow the Arduino to select the 9V AC adapter for power?

Are the relay coils connected to the Arduino all rated 5V and less than 30 mA? If not you need switching transistors and resistors.

You need protection diodes across the relay coils driven by Arduino pins.

johnwasser: Don't they make double-pole contactors? Seems silly to put two in parallel if you can have a single device switch both sides.

2 pole contactors have been taken into consideration. i was half way done with the schematic before the 2 pole contacts came into consideration. so i just left it that way on the schematic.

johnwasser: Looks like it is designed to power the Emergency board from the generator whenever the generator is running, even if line power is available.

what do you mean? The emergency board is connected to the normal board. So it will be energized with or without the generator being on.

johnwasser: Why does CH2 allow the Arduino to select the 9V AC adapter for power?

Are the relay coils connected to the Arduino all rated 5V and less than 30 mA? If not you need switching transistors and resistors.

You need protection diodes across the relay coils driven by Arduino pins.

when relay 2 shuts off after a power outage, it will turn to the N.C. position which will turn to the 9v battery. After 20 seconds, CH2 will turn relay 3 on and transfer back to the 9v power adapter. The 9v battery is only used for a few seconds to keep the arduino from shutting off. I set this at 20 seconds because the generator will turn on 10 sec. after the outage.

as for the relays, I will be getting the relay boards that come with the diodes and transistors. :D

relay's 1 and 2 will remain energized during normal conditions, holding the N.O. leads. Will this put too much stress on the mechanical/electrical parts within these relays?

I would use 2 diodes at the battery / wallpack and use software sensors (resistor dividers) for the arduino to tell where the power is coming from. You could even use 2 wall transformers and 3 diodes and forget about the relays. A battery sensor could also tell you if the battery needs replacing. I am not sure what the 100 ohms resistor’s purpose is. Also, what happens when the power comes back? Does it go into the generator? I am probably missing something.

RobV15, my initial thought was, well, I couldn't understand your diagram at all.

Maybe for your description you could write a clear point form of what exactly you are wanting this transfer contraption to do. For example, what power level are you talking about, a power board on a cord or the main house panel, are you talking tens of Watts or tens of Kilo Watts?

I would suggest you look at using a two stage control from Arduino digital output to first small relay to control the main AC contactor. I don't see that you can get a mechanical relay that can be controlled from a small control signal such as from an Arduino and have it pulling in a large contactor.

Have you looked at using SSR, Solid State Relays, they are easy to use and can be driven directly from a logic output such as from your Arduino. As mentioned, if you use mechanical relays, use flyback diodes across the coil of any DC relay and for any AC contactor, use a snubber (RC) circuit.

RobV15 wrote: as for the relays, I will be getting the relay boards that come with the diodes and transistors

Which board is that, provide a link? And what ever board that is, is it designed and rated for use with your 120Vac mains supply system? You will provide the required barrier isolation between your Arduino and mains potential?

Instead of using a battery, look into 'supercaps', if you are only needing to keep the control circuit alive for tens of milliseconds.

Also, describe clearly how you want to process to happen, in terms of when mains power is lost to when mains power returns. I can only guess you are trying to emulate what a typical offline UPS does in the event of power loss?

Edit: RobV15, I just noticed another post by you in the 'Home Automation & Networked Objects' section, http://arduino.cc/forum/index.php/topic,147249.0.html

From the photo it seems you know about solide state relays (SSR) I mentioned above. The wiring looks to be neatly done in the enclosure, but I am concerned that it looks to be a metal box and just wondering if you have it earthed for safety?

Please tell me you understand the risks and have knowledge with working with mains power systems?

Also, is that the same type of relay board you are wanting to use in this project?

Paul