Automatic generator start

It would seem that you need a battery or uninterruptible power supply to run the Raspberry Pi when the power fails.

A simpler method would be to have a relay that is powered by mains voltage. When the mains power fails the (normally open) relay switches on and triggers the generator start sequence.

Hi Andre,

I like dougw  suggestion and I would also look to include some sort of Hysteresis so that once the relay triggers the start of the generator and the switching of the power grid from external to internal this process continues for 10 minutes or more even if the external power grid comes back on. You will need a mechanized transfer switch so that your electrical service sees only the external grid or the generator and not both. This switch should also rule out the possibility of the generator being connected to the external grid. The coil of the relay Doug recommended will be connected to the external grid even if the system is on the generator. You will have to make sure there is isolation between the internal system and this relay coil so that you do not accidentally bridge the two grids. There may be some commercial products that do these procedures for you. If you make the modifications and design yourself you are signing up for some serious liability if things go wrong. Depending on where you live in the world this may be regulated or not. In any case do it safely. I remember the recommendation of a friend who was admittedly ignorant of electricity. He used to say that he only knew two things about electricity. #1 If you don't pay the bill they turn it off. #2 If you play with it, it will kill you.

John

Mr. Douglas your idea is very good and practical, but the generator can not be triggered immediately. I would also like to register some data by raspberry for reporting. I think the best alternative would be to monitor the electrical grid with sensors.

Is there any digital sensor that identifies phase failure?

Hi, Mr. John, I need to send more details of the operation that is done manually today.

I agree with your friend, electricity punishes the inattentive.

https://www.youtube.com/watch?v=jwBI-rd3-I4

Andre,

The simplist verson of monitoring mains voltage is a relay with a 380V coil, and a normally closed secondary. This would open on power failure, and the RPI can start the generator (assuming an electronic ignition).

Please remember to introduce a delay on start up and shut down - out of phase generator and mains electricity on grid restoration will blow everything up! This could be a 2 pole relay (phase and neutral) with a timed delay switching from mains to generator. This is where the UPS would come in.

In commercial installations, the critical load is driven by a UPS, with perhaps 20 minutes of autonomy. The UPS input would have 2 feeds, mains and a generator backup. In normal operation the mains charges the UPS and powers the Critical devices. When power fails, critical devices are supplied by the batteries, the supply changes over and the generator starts to charge the batteries. Some other supplies may be deemed necessary, which will be generator supplied, but 15 -20 seconds of generator start up is acceptable. On restoration of power the generator will shut down and mains power will switch over.

ATS (automatic transfer switches) are the commercial switching product, but a good quality relay / contactor with a delay would do.

Of course, if you are having brown outs, not just blackouts, that's a whole different thing. Then you are definitely into phase monitoring (I would reccomend a meter with Modbus, some have aux output contacts that can drive relays).

I hope that makes sense and helps!