Sensing supply presence when using a generator - ideas needed Featured

Does it really need to be contactless?

Wouldn't a relay, across the generator supply, switching a mains sounder, supplied from the mains input side of the changeover switch work?

The two supplies would be fully isolated from each other.

What do you mean by 'contactless'?

A bit of relay logic:

IF mains AND generator THEN ring_bell

A couple of DIN rail relays in a small CU-style box with a few minutes of wiring would do it.

Question is what sort of noise do you want, and can you find a thing to make it when mains is applied?

You could also put a DIN transfer switch in the same box. Also to note that transfer switches often have contacts which make when in one position or the other - that could be part of your 'if generator' logic: IF mains AND generator_contact_closed THEN ring_bell.

Or you could wire the transfer switch to change over automatically when mains is detected, since the transfer motor is just a mains input and it's the wiring that sets up the changeover logic.

Theo

A direct connection to the supply would need its own isolator and fuse.

Doing what I want with contactless sensing is easy enough (first thought is: a wire round the supply cable, connected via a resistor to the gate of a FET, which drives a relay, that switches a buzzer; needs a small PSU connected to the generator output) but I'd prefer to buy a gizzmo than make one.

Errr, without contact ;-)

There's no shortage of buzzers and sounders

I think it's simpler - see my earlier reply to SteveW

Auto-changeover isn't applicable because many of the RCDs and RCBOs need to be tripped to ensure the load stays within the gen's (modest) limits.>

BTSTGTTS, how about:

There is also a mod that would work for my specific setup since I notice that the electric meter has a LED that flashes under load. When power is restored to it, and there is no load, the LED stays lit.

Ah, by 'contactless' you mean 'inductive' and not something to do with contacts on your transfer switch, which is very not contactless?

Doesn't that depend on a sufficiently large current flowing, ie there being enough load to induce a voltage in your (homemade) current transformer?

Or are you planning on using capacitive sensing like in pipe and cable detectors?

For inductive a clamp multimeter that has some kind of threshold detection buzzer might work, but you'd need to arrange the multimeter is only powered if the mains is up.

ISTM using the outputs on the thing you're going to install will be more reliable than some analogue sensing device.

Theo

:-) That's a fun solution but my to-do list is already infinitely long so I'm looking for more of a KISS solution.

The meter LED is an interesting thought. I think mine is off when the supply is off (it's back on again now so I can't check) so a photo-sensor strapped to it would be an alternative to E-field sensing.

When the supply is off there will be no load (!) so sensing needs to be of the E-field.

I think there's a misunderstanding ...

Yes, I'm not seeing why you want a flaky capacitive sensor when the transfer switch will provide a dry contact with exactly the state you want...?

I mean the 'passive output' contacts on something like:

In the USA this is called a widow-maker, and that is generally for 110 volt.

Yes, I realise it's not a good idea. It's only accessible to me and attached to the generator ... and I, of course, never make mistakes ;-) ... but it needs to go.

That looks interesting, but I can't find any documentation for it. If the passive output contacts can be used to indicate the presence of supply then that's exactly what I need. However, it appears that the passive connections are just relays that need to be externally connected to the supply incomer - if that's the case this circuit is then only protected by the DNO 100A fuse and that would not be an acceptable situation.

Yup my genset change over procedure is:

(before that the UPSs hold up the important stuff)

The gen can do 3.2kW continuos and surge a bit more briefly. The house can run on that, but you just need to think a bit about not running too many "big" loads in parallel. e.g. toaster, microwave, kettle - pick any two!

There are lots of similar Chinese transfer switches. (of variable quality)

You can see there's a motored spindle which rotates from one position to the other - 'mains' to 'generator', or whatever you choose them to be. The rotation is what gives the break before make action.

For each position there's a microswitch with NO - COM - NC contacts, so when the spindle is in that position the microswitch closes and there's continuity between NO and COM, and in the other position continuity between NC and COM.

They are just switches and not circuit protection devices, so you would need external circuit protection. Also the microswitches are not sized to carry the full load current, they're intended to drive a lamp, relay, contactor or something else that only requires a few amps current.

Theo

Dave does a teardown on a couple of these here:

If the mains fails, the relay opens, but the switch will only move if power is present on the generator input. (since it needs power to activate the solenoid that moves the switches). In a manual start situation, it would "auto" switch when the genset input goes live. If the mains comes back then that will force a switch back to mains since that has priority.

You could rig a sounder powered from the generator side that is switched in circuit when the mains input is connected. That way it would only sound when you have the combination of mains and generator feeds present.

Slightly cheaper here:

It appears to be moved by two solenoids, rather than a motor

Yes, I understand that.

With the implementation shown in the product diagrams (I found a good one on Aliexpress) there is a serious safety concern. They need external wires to connect the supply to the control circuitry. These wires and the associated circuitry are only protected by the DNO fuse. This is a fire risk and I doubt would be approved. I certainly wouldn't install one, so it's back to a centre-off changeover switch and remote sensing.

That was what I was thinking of doing, the difficulty being the contactless sensing of mains presence.

Having looked at these auto-switches I'm surprised that anyone with any electrical nous would install them because of the fire risk.

It varies, some of them have a motor.

Like I said, you need external circuit protection. In this case for that extra input you might want a 6A MCB to protect your sounder and the control inputs.

If you're putting this in a DIN rail box then you can make space for extra MCBs. This is a component part not a turnkey solution - like any other component it's up to you to design the full installation.

I might not trust it with the full 100A supply (it could be rated in 'Chinese amps') but if it's just switching a low power circuit or two that might not matter. You could even just use this for the sounder functionality and ignore the main changeover current path.

You're right that I'd want to look carefully at safety certifications - I might feel a bit nervous about installing this in my primary mains feed, but less nervous if it's RCD protected and downstream of its own MCB so the worst it can do is trip that MCB (especially if your generator is not that powerful, it's not going to be running the house at 100A anyway).

Theo

Yes, the generator feed would have a 6A MCB, of course. All the implementation diagrams for these things just show wires from the supply inputs to what I now realise (thanks to you and John for the YouTube links) are the control circuit inputs, and they are therefore not protected - on reflection, a fuse or MCB in the feed to the control input for the main supply would solve the problem I've been concerned about.

But to perform the changeover function it *needs* to be installed in the main supply feed - that's the whole point.