If it is running at half the speed, then doesn't it produce half the voltage at half the frequency? So the current in a 120V coil would be the same in both cases, because the impedance is dominated by its inductance.

I would expect it to produce full voltage at half frequency via the Automatic Voltage Regulator, if it produces any voltage at all. But I would not expect it to produce any voltage at all, until the engine reaches proper RPM. If this "test" only goes up to half RPM then I would expect it is not possible to determine running status by measuring the generator output, as there won't be any.

I did think, however, that running a generator at half speed (750-800 rpm) would allow it to charge its starting battery, and wondered if that was the purpose.

That is my guess as well. Charge the battery, flush old fuel out of the system, re-coat the internals of the engine with oil to prevent rusting from condensation, knock dust off the commutator (if equipped), etc. It keeps being referred to as a "test" so imaginations are filling in gaps about what is being tested, and drawing all kinds of conclusions based on those assumptions. This does not sound to me like a "test" and there is no pass/fail; I think it is just automated routine maintenance. The same thing you do when you have a spare car that doesn't get ran often; you need to start it up every few weeks and let it get up to operating temp for a while; if you just leave it sitting there idle for months or years on end, it won't want to run when you need it to (especially if carbureted).

 

I would expect it to produce full voltage at half frequency via the Automatic Voltage Regulator, if it produces any voltage at all. But I would not expect it to produce any voltage at all, until the engine reaches proper RPM. If this "test" only goes up to half RPM then I would expect it is not possible to determine running status by measuring the generator output, as there won't be any.

Agreed. If it has an AVR, I wouldn't expect it to output anything unless it could output at somewhere near the correct frequency.

 

Just gen running and not sensing voltage or amps?

Forget connecting to voltage, just use a non-contact electric field sensor connected to your other "equipment".

 

Just put a microphone in the room with the generator.
I've never come across a quiet generator.

 

Just put a microphone in the room with the generator.
I've never come across a quiet generator.

Yep. No contact is the best way.
https://www.amazon.com/dp/B09652TJW5/

Just convert output to DC and clamp it with a zener to drive an opto, fet, or some other digi level input, etc.

The concern there is spurious noise, like a pinecone falls and hits gen, makes a noise, and opto get's triggered.
One way to get around spurious noises is to use a charging cap, make a resistive divider with cap in middle, with continous noise the cap charges and you trigger on a threshold, and when the gen noise stops the cap drains down to ground, etc.

 

Assuming that the generator isn't in the habit of starting when it shouldn't, then average the signal from the microphone over a minute and gate it with the output from the timer. Put the mic inside the generator canopy, so that the sound-deadening that keeps the room quiet(er) also keeps out external noise from the microphone.
For a 4-cylinder engine there should be a peak at twice the output frequency, which you could look for.

 

A 5 W resistor, a 1N4004, and just about any optocoupler will handle the entire voltage and frequency range, and give you a pulsed output that is galvanically isolated so you can connect it to just about anything.

To reduce power dissipation in the resistor by 50%, put the diode in series with the opto input LED, and add a 10 K resistor or another diode in parallel with the opto input LED. This will reduce the output pulse rate to 15 Hz, but I don't see that as a problem if this is driving something with enough brains to generate email.

ak

 

The generator's engine will have a magnet on the rotor. A hall sensor could detect that in ways that pinecones can't spoof.

 

The generator's engine will have a magnet on the rotor. A hall sensor could detect that in ways that pinecones can't spoof.

any idea how much magnatisum one can detect, externaly, Im wondering if ll that iron n the gen might compilcate things more than a virbratio detector with a time constant on it,

 

When was the last we heard from the OP, sorry if recently, phone signal not great here, so not easy to scroll lots.

 

My third suggestion - and this is how it is done on the generators I use - use the oil-pressure sensor switch.
You don't get oil pressure if the engine isn't running!

 

Acoustics tell you about the engine, but not about the generator. The generator is at heart a single-phase device. If you don't want a circuit that is wired directly to its output, a spool of hookup wire dangling somewhere near it should be enough of an air-core transformer to turn on a MOSFET.

ak

 

Out of interest
If gen is connected to mains, how are we checking the gen output is not just the main ?
Do we need to check the voltage or just that the gen is running ?

Given that in a half power check the generator set does not connect to replace the mains, an individual would be able to connect to a point before the transfer contacts. These units are out of warranty and so the TS can freely connect to the correct points inside the box.

 

My third suggestion - and this is how it is done on the generators I use - use the oil-pressure sensor switch.
You don't get oil pressure if the engine isn't running!

What is the "this" that you refer to on your generators? Do they have a monitoring circuit that utilizes the oil pressure switch to send a notification?

I ask because I don't know much about consumer generators and while I agree that oil pressure would be an excellent indicator of engine running, on the engines in this size range that I have experience with, there is no good way to interface with the oil pressure switch. It is a "kill switch" with a single set of contacts that short the magnetos to the block so that the spark plugs can't fire. You can't read a 12V signal off it or anything.

 

any idea how much magnatisum one can detect, externaly, Im wondering if ll that iron n the gen might compilcate things more than a virbratio detector with a time constant on it,

On all the small engines in my recent memory, it would not have been a problem to drill a hole in the fan shroud and pop a cylindrical hall sensor in to read the magnets on the flywheel.

I suggested the hall sensor because it would be fairly simple, no need to build a circuit around it or do any programming. But since the destination of the project dictates some sort of "smart" device to send emails anyway, that probably shouldn't be a priority. So vibration or hall sensor should probably be about equally viable options.

 

What is the "this" that you refer to on your generators? Do they have a monitoring circuit that utilizes the oil pressure switch to send a notification?

I ask because I don't know much about consumer generators and while I agree that oil pressure would be an excellent indicator of engine running, on the engines in this size range that I have experience with, there is no good way to interface with the oil pressure switch. It is a "kill switch" with a single set of contacts that short the magnetos to the block so that the spark plugs can't fire. You can't read a 12V signal off it or anything.

It's joined into the control electronics. Diesel, so no spark plugs.
I think Perkins supplies the engine with an oil-pressure switch, then the generator manufacturer adds a analogue sensor and a T-branch so that both sensors can join into the threaded port in the block. The analogue sensor is used to detect whether to shut down due to low oil pressure, and the switch gives the "engine running" signal.

 

It is a "kill switch" with a single set of contacts that short the magnetos to the block so that the spark plugs can't fire. You can't read a 12V signal off it or anything.

How do you get it started?

 

Unfortunately, the situation can exist in which the engine is running and the generator is spining and no power is being delivered to the intended load.So even the most basic test should verify that power is at least getting up to the transfer switch. It would be a simple matter to "TEE IN" a second pressure switch, but that is not an adequate way to verify being able to deliver power.

 

How do you get it started?

Turn the key.

Starter spins the engine which turns the pump which builds pressure which allows it to start.

If it's a pull-start and it starts on the first pull, it probably doesn't have an oil pressure switch.

 

If the gen has a cooling fan when engine runs (which I think they do), you can use a 99cent micro switch with a small flat paddle on it's arm to detect when that fan is blowing air.

Yeah, it's mechanical subject to dirt and stuff, but for 99 cents I think it can do the job. Heck, you can parallel two of them, makes an HA pair of switches.