Building a Simple Emergency Generator with 5.7hp Engine and 3kw DC Permanent Magnet Motor

Hi,

I am planning on putting together a simple emergency generator. I am planning on using a 5.7hp engine, and I understand that there are losses involved so I was thinking of running a DC Permanent Magnet Generator Motor... perhaps around 4hp / 3kw.

What I was hoping to do is run the output from that Motor straight into a cheap 3kw Inverter such as this one...
https://www.aliexpress.com/item/1005005069578...id=202402170041481338222772480000010299323_10

Now I see a lot of people who do generators use a battery... so my questions are will this work? and is there anything wrong with feeding straight into the inverter from the generator motor?

Thanks,
Matt.

If you want to build a simple emergency generator you will need the following materials.
5.7 horsepower Engine: Verify that it is in excellent operating order and has the power to run a generator.
3 kW DC Your generator will be a permanent magnet motor.
Frame Generator: Build or buy a frame to safely install the engine and motor.
The belt and pulley system is required to link the motor and engine shafts.
Switches, circuit breakers, and maybe a voltage regulator to regulate the output make up the control system.
Battery: Used to start the engine and, if needed, to store energy.
Connectors and wiring: To securely join everything together.
By following steps, you can build up a generator:
Ensuring that the engine and motor are correctly aligned for the belt and pulley system requires a secure mounting of the engine and motor on the frame.
System of Belt and Pulley: Fasten one pulley to the engine shaft and another to the motor shaft. Fasten a belt between them. Achieve the right amount of belt tension.
Wiring Connections: Use the proper switches and circuit breakers to connect the DC motor's output terminals to the load, such as batteries, appliances, etc.
To start the engine, connect the ignition system to a battery.
Safety Procedures: To regulate the flow of power, use switches and circuit breakers. Make sure that the generator frame is grounded correctly.
Testing: Turn on the engine and see the motor in action. It should be able to produce power. The output voltage may be measured with a multimeter. If needed, change the engine speed to get the required voltage.
Fine-tuning: To fit the power output to your demands, you may need to change the engine speed or the pulley diameters.
Enclosure: To shield the generator from the weather and cut down on noise, think about constructing an enclosure.
Maintenance: To guarantee optimum performance, inspect and maintain the engine and motor on a regular basis.
Always keep in mind that your primary concern while using generators and energy is safety. It is imperative that you adhere to all safety protocols and regional laws when constructing and managing your backup generator.

What voltage would this permanent magnet generator be? For 3KW, at least 24V would be needed.
I also assume you would use an alternator, instead of a generator (with suitable rectifiers?)

Wiring directly would be a very poor idea, even if it succeeded. This motor/generator will act partially as current source, and being an inductive device, any transients in power could generate voltage spikes well above the nominal output voltage. Also the output is pulsed DC (3 phase AC models with rectifier are better, but still some ripple) and permanent magnet devices don't have voltage regulation as the output will vary with speed (that's why car alternators use an electromagnet). Permanent magnet devices are not as easy to regulate as the ones with an electromagnet. Solutions based in SCR's instead of diodes exist, such as motorcycles, but never seen them above a few hundred watts.

Back when I was younger people did this with induction motors. Voltage regulation isn't the greatest and if you overload them they stop generating, but you could get off the shelf motors for that power and you would need no inverter, only a suitable induction motor and a bank of AC capacitors. Some examples I've found Link and Link

If you have access to a high voltage alternator you could also rectify the high voltage DC, add some capacitors and an output inverter such as this one Link. You can even use the induction motor generator for that with suitable rectifier. The inverter will take care of the regulation as long as you keep it's input it in the 300-400V range. You still need a capacitor bank for bulk storage and to absorb any voltage spikes, but that would also give you some buffer when starting a high power load, which the induction generator alone would not.