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Warpspeed
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Posted: 22 August 2017 at 10:43pm | IP Logged Quote Warpspeed

Just realise that those 680uF capacitors have a maximum ripple current rating of 1.9 amps.

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DaveP68
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Posted: 23 August 2017 at 7:55am | IP Logged Quote DaveP68

You have picked up on a good point if it was required for continuous operation in a power supply providing filtering for DC.

The ripple current rating of 1.91 Amps is for 100 Hz. The F&P stators will output well above this frequency per phase exceeding 150 Hz at times as high as 240 Hz. That makes a big difference to the ripple current rating which is mostly calculated from the operating frequency for it's reactance value.

Under most conditions on a wind turbine's not going to be above that current of 1.91 Amps @ 100 Hz (more like 3 to 4 Amps at 150 to 200 Hz range) all the time. Yes it might go 2 or 3 times that 1.91 Amps at "peak operation" for short periods but the reactance value will be lower anyway. They can operate up to +105 deg C!

If the wind turbine is in an area where the wind is providing a more continuous high currant above 1.91 Amps @ 100 Hz per capacitor then use a different configuration.

Like I said haven't tested it so use at your own risk...

Edited by DaveP68 on 23 August 2017 at 8:51am
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DaveP68
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Posted: 23 August 2017 at 9:53pm | IP Logged Quote DaveP68

Another thing I noticed when looking at the wave forms on a scope of the current circulating in the capacitors is the number of 3rd, 4th, 5th etc order harmonics. These make the capacitors reactance drop even further thus increasing their ripple current carrying capacity.
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Warpspeed
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Posted: 23 August 2017 at 10:15pm | IP Logged Quote Warpspeed


Maximum rated ripple current is determined only from permissible temperature rise, which also strongly effects its expected life. Its the rms current through the internal resistance of a very long length of some extremely thin wound aluminium foil that creates the heating, not specifically the waveform or the frequency.

Electrolytics are basically designed to filter dc while having very small physical size for the large capacitance and energy storage. For very high ac current, solid film capacitors would be better. These are routinely used for power factor correction or for motor starting and running.

Low esr electrolytics would be much better than crappy standard aluminium electrolytics because the method of construction greatly reduces the internal resistance and raises the ripple current rating.

Electrolytics are fine for testing and experimentation, but if you want something that is going to be long term reliable (especially for a commercial product) thought probably needs to go into choosing a more suitable capacitor type.


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flc1
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Posted: 24 August 2017 at 12:49am | IP Logged Quote flc1

Most of what Dave is doing is testing ,its all about trail n error,I think he was only making a suggestion to Marcus as to what capacitor to use.
what capacitor type would you suggest Tony?

Edited by flc1 on 24 August 2017 at 12:49am
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Warpspeed
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Posted: 24 August 2017 at 2:09am | IP Logged Quote Warpspeed

Electrolytics are fine for testing.

For lower values up to about 50uF, those white power factor correction capacitors have suitable ratings. Something like these:
https://www.ebay.com.au/sch/i.html?_odkw=capacitor+i0uf&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR2.TRC0.A0.H0.X run+capacitor.TRS0&_nkw=run+capacitor&_sacat=0

For something slightly larger, motor start/run capacitors might be worth a look:
https://www.ebay.com.au/sch/i.html?_odkw=power+factor+correction+capacitor&_osacat=0&_from=R40&_trksid=p2045573.m570.l13 13.TR0.TRC0.H1.Xcapacitor+240v.TRS0&_nkw=capacitor+240v&_sacat=0

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flc1
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Posted: 24 August 2017 at 2:26am | IP Logged Quote flc1

cool, thanks Tony
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Warpspeed
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Posted: 24 August 2017 at 3:26am | IP Logged Quote Warpspeed

Probably most convenient to stick with the electrolytics you have for now.

But if you plan to build it up properly later on, in a metal box, then the larger and more expensive capacitors might be a good investment.

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Posted: 24 August 2017 at 7:02am | IP Logged Quote flc1

yep ,may do later,just a test setup at the moment.
the max current that will run in the system will be about 3 amps, so should be able to get away with what we are using now, for that system.
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Posted: 02 September 2017 at 9:20am | IP Logged Quote gpalterpower

Hi Tony,

Ive checked out both sorts of start/run caps on ebay as you have suggeseted above. So many to choose from there. I would like to try some and see if I can get a little more power out of the mill, but not sure of the value I need. Could you suggest a cap rating to try on my 24v dual system. They are easy to mount and I can easily find a spot to fit them. I'm assuming I will need 6 per stator if wired 2x6c.
Marcus



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Warpspeed
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Posted: 02 September 2017 at 9:32am | IP Logged Quote Warpspeed

I have no idea what value may be required.

Suggest you do some testing with whatever cheap electrolytic capacitors you have or can readily get.

Once it looks like the idea works, then you should have some idea of what values you need.

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DaveP68
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Posted: 03 September 2017 at 1:16am | IP Logged Quote DaveP68

Marcus

As already stated before, the main drive stator must wired 12x 1c Delta due to your 24 VDC system. Any deviation from this setup wont provide enough current.

Choose whatever capacitor type you like, which Tony has provided lots to choose from.

Also already suggested you can try a value of about 340 uF AC and do a test run to prove that value is the correct one to use. They do work over quite a wide RPM range when they kick in so that guess should be close to the mark.

All my testing has been above 50 VDC, so hope it works first time around.

David

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