Hi,
I have a 6Kw wind turbine that has a generator output of 0 to 250Vdc depending on the windspeed. I am planning to put a 24Vdc battery in the wind turbine to power some electronics and motors that I am adding to it.

What I want to do is have a circuit that will take say 50 to 250Vdc as it's input and provide 26Vdc at it's output to keep the 24V battery charged. Max output current would need to be about 1 to 2A. The largest draw of current from the battery would be a motor requiring 4A for a max of about 1 minute.

I don't want to run a cable from the mains in the house as it's over 100m away, so I have to use the power from the wind turbine generator to keep the battery charged.

Please can you suggest ways to achieve the desired result. I have looked into buck and flyback converters but there are so many variations that I don't know where to focus my attention. Is there something off the shelf that I could purchase? Would it be possible to modify a laptop charger or computer power supply to do what I want? I'm sure I could buy something very expensive somewhere but I am looking for a reasonably priced solution if possible.

I done a search and found a similar topic but no real answers were given for a solution.

http://forum.allaboutcircuits.com/archive/index.php/t-68628.html

Thanks for any help or suggestions to possible solutions.

 

You say the generator produces DC, but do you know if it does that directly or by rectifying an AC output (one you could access)?

One way to think about this is to realize that you need control over the current going to the battery. The battery itself will hold the voltage where it needs to be, as long as current is in an acceptable range.

 

The generator is a 3phase AC which is then rectified outside the generator to DC which I have access to.

I was thinking that if I could get a voltage of 28V with the capacitity to supply 1 to 2A then I could connect a standard lead acid charging circuit using an LM317T.

I have the circuit working already using a mains transformer that goes from 230VAC to 28VDC after rectification, what I want to do now is change the transformer that takes a steady 230VAC for something that can take a range from 50 to 250V DC or AC and output a steady 28V or so. I can then attach the charging circuit to that.

I'm open to any other possible methods!

P.S. The wind turbine is a grid connected turbine that uses a grid connected inverter which accepts the 0 to 250VDC and inverts it to mains. So there is no battery bank to clamp the voltage. If the generator voltage was clamped to 24V then the grid inverter could not operate.

 

I'm confused. How can the grid converter work if it has no connection to the mains? You stated you were 100m from the mains in the house and didn't want to run a cable.

 

The inverter is in the house 100m away, there is a 2core cable running from the turbine to the inverter carrying the DC. The AC is rectified at the turbine.

So the mains doesn't leave the house. What I meant is that I don't want to run a second cable.

I used the transformer to help me develop the battery charging circuit in my workshop, but now that the circuit has to go out to the turbine I have to replace the transformer, which is what I am looking for help with, what do I replace it with?

 

I think you may have answered this but humor me; Do you have access to the AC from the generator, before rectification? Maybe at the rectifier itself?

Tapping existing AC would simplify this, IMHO. Otherwise you'll need to first convert DC to AC.

 

Using the AC output is possible but the difficulty is handling the wide range in voltage and AC frequency.

For reasonable efficiency you may have to consider a high voltage input DC-DC regulator. Those likely aren't cheap.

 

Yes, I have access to the AC at the rectifier. How can I use the AC to simplify this?

I have found this circuit that looks similar to what I need. It takes 100Vdc to 300Vdc and outputs 5V. I wonder how this circuit could be modified to output the higher voltage of 28V and maybe accept 50Vdc to 300Vdc???

http://cds.linear.com/docs/Design Note/dn260f.pdf

 

I don't know if this is always true, but at least some switching power supplies will run on a DC input even though they're generally used running off the AC line. For instance, there's this type that's pretty widely available:
http://www.meanwell.com/search/SP-75/SP-75-spec.pdf

The spec for input voltage says "85 ~ 264VAC 120 ~ 370VDC"
A 27 volt 2.8 amp unit would be $43 at Jameco.

That doesn't meet all your requirements as it needs at least a 120V input, but maybe it's a clue to what to look for.

 

That looks like it could do the trick but it's a bit bulky for the space I have to fit it in.

If I connected a standard 24V laptop charger would that do what I want? I see one on ebay with the following specs:

Input Voltage: 95-265V, 50-60Hz 1.5A MAX
Output Voltage: 12/15/16/18/19V 4.5A MAX
20/24V 5A MAX
Power: 96W
Model: GL S-96-A

I'm not familiar with how laptop chargers work so I could be wrong about this.

It costs €10. The turbine generator has a frequency of about 30Hz at 95V, would the low frequency have any other effect than lowering the efficiency? This could be the solution unless someone can point out why not please?

 

If you want to charge a 24V lead-acid battery you will need at least 28V, so the laptop charger wouldn't appear to work for that.