How do I calculate the Output current of a generator?

[RPS]

Hey Guys,

I got this axial flux generator form China for a small wind project. How should I calculate the output current (rated current) of this? I basically need this information for sizing the wire.

The output voltage ranges from 48-220VAC and the output power is 2kW. Is using the formula P=VI correct here? How should I go with it?

Thanks!

 

[LarryFine]

I could just tell you, but then I'd have to kill you, so: https://www.rapidtables.com/calc/electric/kW_to_Amp_Calculator.html

Come back and tell us your results, and we'll let you know whether you're right. Also tell us how far the wiring will be run.

 

[RPS]

I could just tell you, but then I'd have to kill you, so: https://www.rapidtables.com/calc/electric/kW_to_Amp_Calculator.html

Come back and tell us your results, and we'll let you know whether you're right. Also tell us how far the wiring will be run.

Haha! This is what I got:

https://imgur.com/a/viWvKRb

A=26.7A at 48V line to line (I am not sure about this, any help?) and pf=0.9
the run will be 100 feet

Thanks!

 

[LarryFine]

I did the calc using maximum voltage, not minimum. I took the voltages given to be a range that is dependent on rotation speed, mainly because 220 is not a multiple of 48.

You're correct to use minimum voltage if that involves rewiring the genny to put out max current at that voltage. So, before picking a wire size, let's be sure which voltage to use.

 

[RPS]

I did the calc using maximum voltage, not minimum. I took the voltages given to be a range that is dependent on rotation speed, mainly because 220 is not a multiple of 48.

You're correct to use minimum voltage if that involves rewiring the genny to put out max current at that voltage. So, before picking a wire size, let's be sure which voltage to use.

I am sorry, can you please elaborate on this: "I did the calc using maximum voltage, not minimum. I took the voltages given to be a range that is dependent on rotation speed, mainly because 220 is not a multiple of 48."? Thank you very much!

 

[LarryFine]

I'm saying that, like a multi-voltage motor, if a generator has multiple output windings, they can be wired in series for a higher voltage at a lesser current, or wired in parallel for a lesser voltage at a higher current. Picture using two batteries if it helps.

For example, a dual-winding generator could put out 200 volts at 5 amps, or 100 volts at 10 amps, both of which can deliver the same 1000 watts of power. How would you make a generator that can deliver full power at both 48 volts and at 220 volts?

 

[RPS]

I'm saying that, like a multi-voltage motor, if a generator has multiple output windings, they can be wired in series for a higher voltage at a lesser current, or wired in parallel for a lesser voltage at a higher current. Picture using two batteries if it helps.

For example, a dual-winding generator could put out 200 volts at 5 amps, or 100 volts at 10 amps, both of which can deliver the same 1000 watts of power. How would you make a generator that can deliver full power at both 48 volts and at 220 volts?

Got it thank you! so using 5A, and if I run it for 100', what are the derate factors should I consider?

 

[LarryFine]

Got it thank you! so using 5A, and if I run it for 100', what are the derate factors should I consider?

We're more concerned that you understand your question than with simply providing an answer. Most questions generate (no pun intended) more questions before an accurate answer can be given.

I would use #12 cu, which has a rating of well over 20 amps, and not worry about doing any more math. Presuming I'm right about the genny's output voltage, of course. Don't forget about grounding.

I looked again; the genny has a wye output, meaning there should be a neutral, which you should at least bond to ground, and probably extend to the equipment being supplied and bonded there.

Note: I don't mean to suggest that the neutral should be connected to a grounding conductor at both ends of the run, which would create a parallel pathway. Earth is not considered to be a parallel path.

 

[electrofelon]

We would really need to know what this is connected to. It is rather ambiguous that they give such a large voltage range. I am not sure if that is because it can be wired for different voltages, or they are giving unloaded voltage at various speeds. A machine like that will generate a certain number of volts per RPM unloaded, but under load it will not be a linear relationship so those unloaded figures are kinda meaningless. The machine is. or should be, designed to be connected to a certain voltage system. So what is this connected to?

 

[RPS]

We're more concerned that you understand your question than with simply providing an answer. Most questions generate (no pun intended) more questions before an accurate answer can be given.

I would use #12 cu, which has a rating of well over 20 amps, and not worry about doing any more math. Presuming I'm right about the genny's output voltage, of course. Don't forget about grounding.

I looked again; the genny has a wye output, meaning there should be a neutral, which you should at least bond to ground, and probably extend to the equipment being supplied and bonded there.

Note: I don't mean to suggest that the neutral should be connected to a grounding conductor at both ends of the run, which would create a parallel pathway. Earth is not considered to be a parallel path.

I understand, and my aim is also to learn and not to just get an answer, and I really appreciate your advice and helping me figure this out.
I just confirmed with the manufacturer that the generator at full load at 120 RPM will produce 48V, and I estimate the wire run to be 100 feet (subject to change).

 

[RPS]

We would really need to know what this is connected to. It is rather ambiguous that they give such a large voltage range. I am not sure if that is because it can be wired for different voltages, or they are giving unloaded voltage at various speeds. A machine like that will generate a certain number of volts per RPM unloaded, but under load it will not be a linear relationship so those unloaded figures are kinda meaningless. The machine is. or should be, designed to be connected to a certain voltage system. So what is this connected to?

The generator produces 48V at full load and 120 RPM. the plan is to connect it to a 48V charge controller/rectifier to charge a 48V battery

 

[electrofelon]

Is this connected to a batteey

The generator produces 48V at full load and 120 RPM. the plan is to connect it to a 48V charge controller/rectifier to charge a 48V battery

The generator produces 48V at full load and 120 RPM. the plan is to connect it to a 48V charge controller/rectifier to charge a 48V battery

Ok, then 48 volts is about what you can figure the three phase ac voltage will be. Your resultant DC after rectification will be 1.35 times the AC, but (assuming FLA) battery voltage will be around 60-65 so those two factors are about a wash. Does the charge control have built in diversion or resistors to keep the thing loaded? Diversion is nice because you can use that power for something like heating water.

 

[junkhound]

Lots of info missing for overall calculations if you are looking for overall system answers vs just wire size, As already said, 3 phase 12 AWG will be fine with no calculation needed.

What wind speed is needed for 48V, 2 kW for the prop you are contemplating? You will likely get that wind speed very few times.
IIRC, power is proportional to cube of wind speed.
Thus, to charge a 48 Vdc flooded lead acid battery to near full charge, you need over 53 volts. At 1/2 max wind speed you will only be getting 250 watts at 24 Vac. For any battery charging you need a boost power supply, preferably a peak power tracker.

Unless your wind turbine in near a mountain peak or on the seashore, don't count on much more that the 250 watts or even only 100 W typically.

 

[junkhound]

Somewhat surprised mods have not closed this as appears to be DIY wind greenie with no idea about how a generator works or what needs to drive a generator.
My apologies to OP if this is an incorrect guess. Would like to hear form OP if he/she is a wind turbine designer but with no electrical basics.

 

[electrofelon]

Lots of info missing for overall calculations if you are looking for overall system answers vs just wire size, As already said, 3 phase 12 AWG will be fine with no calculation needed.

What wind speed is needed for 48V, 2 kW for the prop you are contemplating? You will likely get that wind speed very few times.
IIRC, power is proportional to cube of wind speed.
Thus, to charge a 48 Vdc flooded lead acid battery to near full charge, you need over 53 volts. At 1/2 max wind speed you will only be getting 250 watts at 24 Vac. For any battery charging you need a boost power supply, preferably a peak power tracker.

Unless your wind turbine in near a mountain peak or on the seashore, don't count on much more that the 250 watts or even only 100 W typically.

He shouldn't need a boost converter. Unloaded voltage rises quickly until it is "clamped" to the battery voltage, so even in low wind he will get charging, just with less current. Even 100-200 wants is a god send when you are off grid. The peak power of these things is not really that relevant. With this thing being Chinese, you may be dealing with "Chinese watts" (it seems universally accepted that there is not a single screw pitch gauge in China, so not sure why they would have a wattmeter ) but still it's really going to come down to the available wind resource. Very few people have a good wind site and get their turbine up high enough.

An MPPT controller definitely helps, but as far as I know the only one is the midnite classic, and even then one has the issue of finding the power curve of the turbine.