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Vertical0017
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Joined: 01/09/2010
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Posted: 10:45pm 31 Aug 2010

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Greetings, Is there a standard test setup for testing a PMA? Looking for standard test load. I was reading that most wind turbines in the USA use about 28 miles per hour wind speed for their power rating, but at what load? Thanks in advance for any help received.

VK4AYQ
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Joined: 02/12/2009
Location: Australia
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Posted: 09:43am 01 Sep 2010

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Hi Vertical

Looking at a few I see no real standard as such but the settings are at the wind speed as stated, with the PMA connected to a battery bank in low charge state at the rated voltage delivering the amount of amps X charge voltage to give the rated watts.

eg. 24 volt nominal system. charge volts 28 X 12 amps = 336 watts at the rated wind speed.

Clear as mud I spose.

All the best

Bob

Foolin Around

Vertical0017
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Posted: 01:41pm 01 Sep 2010

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Greetings, yes clear as mud. Especially when you consider that the PMA output voltage is clamped to the discharged battery voltage during charging. So for a 12 volt system you are saying the power rating is the current being crated at 28 MPH wind speed times 12.7 volts even if the PMA voltage output is clamped at the discharged voltage of the battery?

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 02:43pm 01 Sep 2010

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Hi Vertical

The output voltage will be a bit higher than the discharged battery voltage typically 13.8 to 14.2 if it still uses the internal regulator, if there isnt an internal regulator it can go higher depending on the ability of the battery to absorb the power produced.
Assuming you have a PMA rated at 60 amps output and a charge voltage of 14 volts.

14 X 60 = 840 watts

The power you will get from the alternator will vary of course with wind speed and turbine efficiency, the ability to harness the wind energy, so this is the crucial factor, the wind speed may be there, but the blade must be able to turn the wind energy into torque to turn the PMA at a rpm rate that can deliver the power to the battery.

Most car alternator type PMS's need to turn at a faster rpm to give rated power, this will be in the performance chart of the maker /modifier.

One that I have to hand states a rpm of 1500 to deliver 800 watts at 24 volts nominal which in reality is closer to 30 volts about 26 amps.

This demonstrates the higher efficiency of higher voltage as the amps are lower for the given energy transfer, and that gives less loss in the wiring given the same size conductor in both cases.

These auto conversion PMA's must use a high speed turbine to do any good at all, I have tried many blades of 72 inch diameter with 3 to 10 blades, and unless wind speed goes over 10 ms they are poor energy converters, suitable for 150 - 300 watt machines. once they get 15 ms wind they come into their own. I have had them doing over 2 KW on 15 ms gusts 34 mph that is in real measurements. 1200 rpm

Unless you live in a wind tunnel a more likely speed is 5 ms and on the high speed blades that is only 40 watts or so.

More mud.

All the best

Bob

Foolin Around

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