Motor and DC-DC converter matching

[mukunthko]

I have is that i bought an off the shelf buck-boost converter. 20-56VDC  to 13.6 VDC. However on most commercially available dc motors including the axial flux ones, the voltage corresponding to the power on the curve is quite shallow. They need about 100-150 watts on an average to produce power at 20 volts, 400 rpm. My windmill would probably yield about 20 watts at 40 rpm.

So i've been thinking on building my own permanent magnet ac axial flux generator , use a transformer to step up the voltage and then rectify it. I'd have to build the transformr as well in this case. Alternatively, I could use a cycle dynamo and step up the voltage in a transformer as well. I need my cut in voltage to be higher than 20 volts to be able to use the buck-boost converter.

I am not sure how the frequency comes into play while designing generators and transformers as well. I am looking into it.

This dc-dc converter also needs an idling current of about 100mA, doesnt specify wat what voltage. i suppose it means 12 volts but not sure.

It also talks about a switching frequence, not sure what that is either.

The datasheet is here and the model number is 36-12-6 which they've stopped making now.

http://www.newmarpower.com/DC-DC_Converters_Standard_Isolated_Series/DC-DC_Converters_Standard_Isola



ted_Series.html

I was wondering if it is possible to connect the battery being charged back to the input of the dc-dc converter to be able to provide it with its idling current.

Do you think this is a possibility.

[veewee77]

My guess about putting the battery back into the input is a recipe for Magic Smoke. . .

JMHO - YMMV

Doug

[Nando]

First:

You do not have a buck-boost converter. You Have a BUCK converter.

Second:

Your communication is in rambles not well defined and not clearly stated.

Third:

A bad choice using transformers attached to wind mill, this indicates that your electrical and electronic experience is quite limited.

Fourth:

If you are going to build an Axial generator, build it producing the higher initial voltage necessary for proper operation and NO transformers.

Fifth:

In this case, do not use such Buck converter, get one with MPPT (Maximum Power Point Tracking) and the proper final high voltage of the generator plus a safety increment capability.

Sixth:

A well designed converter now a days does not require such a high idle current, the one You have chosen is geared for a more robust power systems.

Seventh:

Yes and Not. Connection to the battery to supply the idle current is possible but normally it is not advantageous to do, to avoid discharging the battery, it is best to draw the power from the wind.

Eighth:

Back to your Buck converter You said:

>They need about 100-150 watts on an average to produce power at 20 volts, 400 rpm. My windmill would probably yield about 20 watts at 40 rpm.

WRONG, this clearly indicates that you do not have the proper electronic principles

The converter needs, as you defined by the 100 ma, about, 11.5 volts per data sheet and around 1.2 watts to starting to work and just a bit higher input voltage than the battery voltage.

The wind mill, at 40 RPM, is producing 20 watts then the converter may be able to convert around 18 - 19 watts into the load if the generator voltage is about 2 - 3 volts higher than the battery voltage.

So produce the voltage, then the amps = convertible watts.

Nando

[Opera House]

I don't see a 36-12-6 so assume you meant to say 32.  What you need at a minimum is a shutdown terminal on this device in order to get it to work.  I think even I would have a problem getting this to work without major modification or adding enough extra parts that negate the value of using a commercial unit.  In this application you want to regulate the input voltage and not the output.  The other concern is to provide a dump on the input in the event of overspeed/voltage. Monitoring generator speed serves no purpose.

[mukunthko]

Thanks Nando

I agree with most of your points.

But when I said they need 100-150 watts to produce 20 volts, i meant the generators like the ametek 38VDC generator.

Since my windmill produces 20 watts at 40 rpm, do you think it is possible to build a generator that shall yield over 20 volts at the same power without having to step up the voltage?

Could you also suggest some literature or possibly an article on the board for the various parameters to be taken into account while designing a generator please. I havent had much luck finding anything.

[Nando]

Read this site experiments and ask questions regarding the Axial Generator build and how to produce the higher voltages.

Also, many sites, ask about them, that teach generator build etc.

A good Wind mill system requires a compromise of blades, generator power and voltage, wind mill controller ( Charger, power conversion, ballast load etc).

Using the Amtek motor as a generator is just one compromise of the many the builder has to decide in the path of producing Wind Power.

Some build Wind mills for heating, some for electrical power generation, some for both, and some for compressed air for different uses, and the power level is another consideration which may include the wind mill site limitations or capabilities.

Also. if for experimentation or urgent energy needs.

Do start slow and not with a high power, you need to learn the wind mill behavior and the power generation problems.

Nando