I need someone to design a circuit for me. It is a speed control for a 25hp steam engine. I already have safety features built into the mechanical design. This speed control will operate a 4 amp 12 volt linear actuator which will operate the steam valve adjusting steam volume into the cylinder. The circuit needs to be 12 volt. I need an RPM controlling rheostat and a rheostat also for a sensitivity/delay control so the actuator isn't moving too much for every little change. RPM of the engine will be around 150 (+ or - 10% is good). A magnet can be placed on the flywheel and a magnetic pickup sensor can be used unless you have a better way.

 

Quick question- does linear actuator have position information- slide pot or code strip??

 

Is this practical? There will be a certain amount of lag in an electrical system of governing. This is why even modern steam engines still use a 'fly-ball governor'.

 

You have a feedback control loop which will require PID or Fuzzy Logic compensation for the system to be stable and avoid "hunting". This is most readily performed with a microprocessor.

 

Is this practical? There will be a certain amount of lag in an electrical system of governing. This is why even modern steam engines still use a 'fly-ball governor'.

It's actually the lack of lag in the controller that tends to cause instability in a closed loop system with inertia. A fly-ball governor has a certain amount of built-in lag due to it's own inertia which helps the stability of the speed control.

But the only modern steam engines in significant use that I'm aware of are electrical steam turbines and I doubt they use fly-ball governors.

 

A 25hp steam angine is massive and will have a massive flywheel, and be very stable by speed control terms.

It's probably going to be fairly trivial to keeps its speed regulated with electronics.

How many power pulses does it have per revolution? Photos?

 

Here is the problem. I am using wood and the btu's will not be as consistent as say coal or fuel oil. The actuator will also control dampener and 12v fan to stoke or choke the fire assisting with btu regulation in the boiler. The pulses can be as many as needed. The flywheel in 48" and they can be placed anywhere. The engine is in design stage. Many of the parts have been acquired already. I need to have the circuit and actuators in the design before beginning.

 

Here's an idea: http://www.redlion.net/Products/Groups/PanelMounted/P48/Docs/05015.pdf

a general purpose PID controller. it doesn't accept pulse input, but it does accept analog voltage & current. you could put an analog tachogenerator on the flywheel or you could use a signal conditioner to turn pulses into analog voltage. Feed the analog speed signal to the PID controller. The controller has analog outputs which could be used (probably need a driver) to position your actuator, and relay alarm outputs which could switch your fan. see the diagram on page 5. It's basically exactly what you want to do.
replace the flow sensor with analog tach signal
replace the control valve with your actuator
replace the horn with your fan.
there you go
(but don't forget a driver for your actuator)