Varying Speed AC Generator to Steady DC 3

[Dawsonh4]

Hi all.

I have a 240 volt, 10 Amp AC generator being powered by excess compressed air that would otherwise be wasted. I want to use it to charge a bank of 12 V DC batteries wired to be 24 V. My issue is that the compressed air pressure varies slightly to the point that the generator run between 40 ad 59 Hz. The voltage varies along with the speed.

Is there off the shelf equipment that can take the varying AC voltage and turn it into something useful to charge the batteries?

I initially started with a PULS CPS20 Power supply, but found the lower end of the generator caused the power supply to trip when it gave the generator load. Under no load the generator is spinning around 63 Hz. When the power supply gave it load it would drop down to 40 Hz and the CPS20 would automatically shut it off.

Any help is much appreciated!

 

[BrianPetersen]

The 24 volts DC is the only hiccup that I see in the way of using any standard automotive alternator, but my understanding is that some transport-truck and off-road charging systems operate at 24 volts. A google search of "24v alternator" turns up quite a number of choices. Do that.

https://www.amazon.com/24-Volt-Alternator/s?k=24+Volt+Alternator

Cheap. Not worth doing anything else.

 

[waross]

With increasing specialization and miniturization of components it is becoming harder to hack circuits, but if you can access the voltage regulator input, a simple voltage divider will convert a 12 Volt alternator to a 24 Volt alternator.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

24 volt alternators are commercially available. There are differences in both the field windings and stator windings between 12 and 24 volt alternators of the same model. I don't know if that matters in this case. If you're charging the battery directly with the alternator you would typically need some method of limiting max power.

 

[Dawsonh4]

I don't think a car type alternator would be the best solution here. I am not looking to rewrite conversation of energy. I am trying to find the best possible solution. Although an alternator does solve the variable speed problem, it also requires much more torque. I digging into axial flux generators which might be a good solution.

This variable speed AC problem is solved currently in large scale wind turbines that see variable speed winds. Some of these large scale generator even convert from AC to DC then back to AC. There are benefits to using the AC generator, which is why they don't use a large version of a car alternator. This gets back to my initial post of trying to determine the best way to convert the power from variable AC to constant DC. Preferably with off the shelf equipment.

 

[3DDave]

Alternators are A/C - it is what is alternatoriing. They add a diode pack to convert the A/C into a DC output.

Torque = power/rate.

No power draw = no torque; real power generators aren't perfect, so torque is never zero, but will be there in all rotary machinery.

Any amount of power production from rotary motion requires torque.

Same power, same rate? Same torque, not much more.

 

[TugboatEng]

Can you please provide a datasheet for your turbine? That costs much more than an alternator. Let's figure out how to make the system work with your expensive turbine.

 

[BrianPetersen]

This variable speed AC problem is solved currently in large scale wind turbines that see variable speed winds. Some of these large scale generator even convert from AC to DC then back to AC. There are benefits to using the AC generator, which is why they don't use a large version of a car alternator. This gets back to my initial post of trying to determine the best way to convert the power from variable AC to constant DC. Preferably with off the shelf equipment.

Sure, but those wind turbines are on a megawatt scale (and operate in a very different range of speed, torque, and forces than what you are trying to do). Working with megawatts (and megadollars) makes stuff feasible that isn't feasible on your scale. Your "112 volts 4.1 amps" is about 460 watts. With an automotive-voltage 12 nominal (actual 14-ish) volts that's 33 amps. That's right in the size range of automotive alternators. Your RPM range of 60-ish Hz (assuming "Hz" = "revolution") is in the right range, too. OK, you need a 24-volt nominal alternator instead of a 12-volt one. Still in the same size range.

The "off the shelf equipment" that you are looking for ... with the information that you have provided to us ... sure sounds like a 24-volt off-road-equipment alternator.

 

[BrianPetersen]

Another choice would be the type of generator used in portable generators - for example, a Honda EU1000i (google that if you don't know what I'm referring to). Normally those are wound-rotor designs, which allow the output AC voltage from the stator to be controlled by varying the voltage supplied to the rotor. The inverter-type generators vary engine speed depending upon load demand, but voltage is held in a narrow range (by controlling the current supplied to the rotor) and they rectify that AC to DC before then using an electronic inverter to supply AC at a constant frequency independent of engine speed.

The complication there, is that those generators (actually alternators) are specifically designed to attach to the crankshaft of a small gasoline piston engine, and if you want to attach it to something else, that's on you.

 

[waross]

Respectfully, your last post indicates that you don't have enough basic knowledge to participate in your own conversation.

I am not looking to rewrite conversation of energy. I am trying to find the best possible solution

That is exactly what you are doing.
You have been presented with a solution in the form of a device that optimized to do what you want to do very efficiently.
But carry on.
By the time you get results from your present setup you will have constructed a poor and inefficient machine that poorly emulates an automotive alternator.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LittleInch]

" , it also requires much more torque."

Errr, this is the bit you need to explain as to most of us it didn't make sense. Same speed, same torque as your current set up will be the same power. Why do you think it will be any different?

This is a very small amount of power really so you will have some significant losses which will impact the efficiency.

Is it all worth it???

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.