Clipper Resistor Modules

[Trevorsolar]

Hi Midnite
Thanks for the great work on the Clipper,
Can you put together a chart showing the resistor modules that suit the various wind turbine power and voltages ?
What are the correct resistor values for the various series , parallel configs etc ?
I see you have 3 resistors on your price list and 4 resistor wiring diagrams in the Clipper Manual (Rev A )
but no resistor modules on the price list or product list and no resistor values on the diagrams in the manual.
How do we know what module to order for which turbine ?

Cheers Trevor

[TomW]

Trevor;

Great question.

I am currently trying to sort out a proper loading for my rather unusual 24 volt nominal turbine for feeding a Classic through a Clipper.

So far I cannot sort out a proper combination to get enough load to control the thing when Murphy shows up and stay within the rating of the 100 amp SSR. Most are feeding much higher voltage in so do not need the low resistance a lower voltage turbine does. Ohms law at work.

So any discussion of the resistors interests me.

Tom

[RomoJack]

I'm guessing there has been little to no progress on this? I'm looking at getting the AC Clipper and would like to have some idea of how to choose the right resistor size.

[Halfcrazy]

I am trying to get answers out of the engineers. As of now I have done a trial and error list that works very well. It can be found here http://kb1uas.com/MidNite/PDF's/turbine%20matrix.pdf

This list needs a lot more work as I have a lot more info to add to it. I have also asked boB and a couple of the other Engineers to help me devise a formula for getting the correct resistance value.

Ryan

[RomoJack]

Thanks for the reply, what's great is that the windmax turbine I'm looking at is actually listed.

[boB]

It's not real easy to pick the proper resistor for a turbine.   One thing you have to make sure of is that the resistor value is not too high.  Better to make it too low of resistance than too high of value.  This is because the PWM attempts to make the installed resistors higher resistance.  It cannot make a resistor that is too high of value to slow the turbine down a lower value than it really is.

Also, you should not normally use a transformer to down-convert a 600 VAC turbine down to be a 150 or 250V DC turbine because the transformer will "reflect" a higher clipper resistance up to a value that is proportional to the square of the turns ratio of that transformer.
Sometimes a low ratio transformer might be OK, like maybe 2:1 ratio.  Even with a 2:1 ratio transformer, it will apply a resistance value that is 4 times the value that is on the Clipper itself.  A 4:1 ratio transformer will multiply that resistance by 16 times the original value.

The down conversion can also make it harder to brake the turbine with the Clippers' internal brake switch because the current goes up by the turns ratio.  If the wind is blowing hard, it can pop the breaker.

It's best to match the turbine windings closer in voltage to what the Classic is going to see on its input without the transformer if at all possible.

As far as picking the resistor values, knowing the resistance of the turbine windings is a good start but that does not tell if it is necessarily going to slow the turbine down enough.  Think of it this way, if the turbine is an axial flux type and there is a large gap between the magnets and the coils, the braking/slowing action may be too low in higher winds because the coupling is too low.
(Look up Lenz's Law for how it actually brakes)

Also, in general, radial flux turbines with lamination in the magnetic path will usually have a much higher inductance which offers more reactance in series with the Clipper resistors and can hinder the slowing and braking action.  Evidently the high inductance and sudden  loading (lower resistance) of the turbine in high winds can make it go up in speed up.  I know... It does sound sort of counter-intuitive, doesn't it ?  The Clipper does work with radial flux turbines though, like the Bergey XL.1 but you want to be careful not to load it down hard at high wind speeds if it doesn't want to slow down.  Shutting down the turbine in a storm may be the best option for any wind system just to be on the safe side.

So, we are trying to compile a list of known resistance values for certain known turbines.  If a new turbine is not on the list, you may want to try some resistance values to see what the highest value will slow it down enough in high winds and then drop that resistance by, say, 50% or maybe more to be on the safe side.

We would love to hear what you have found for certain turbines and what the maximum wind speeds were that it was exposed to.

It is possible to actually have the Clipper and/or Classic learn wheather the turbine is slowing down and either sound an alarm or let it fly open and protect the Classic and turbine windings so that it doesn't burn up when it just doesn't want to stop.  Another thing that can be done is to detect a storm and shut the turbine down while it still can.  Loading it down to a stall will usually keep it stalled as long as its gap isn't too large or inductance too high.

boB

[TomW]

Great info, boB!

I have a nominal 24 volt DC 12 footer and ended up with a very non standard load. If my feeble memory serves me well I have 3 of the lowest resistance resistors you had in parallel and a load of .266 ohms? Any higher resistance and I could not keep it under control. If I know a big blow is expected I sacrifice some power and flip the brake (shorting) switch just to be safe. Gotten too old to be futzing with repairs on that heavy beast or climbing.

This set up would probably exceed the power ratings in a big blow which is why I shut it off if I expect high winds. It does indeed keep the turbine under control up to 30 MPH where it is fully furled and lower on power easily but I see no reason to let the equipment get beat up.

Would have been  much easier dialing in a standard load with a higher voltage turbine.

I had thought of the step up transformer but did not want another device in the system and another possible point of failure. Maybe building a higher voltage stator would be wise but I doubt I will go that far. Wind is just not a big % of my power collection.

Kind of hard for you guys to predict every strange combination we users will come up with.

Tom

[kitestrings]

boB, Ryan,

I can't seem to get this link to work.  Is it possible something got moved?  Perhaps another way to get to it?  thanks, ~ks

[boB]

boB, Ryan,

I can't seem to get this link to work.  Is it possible something got moved?  Perhaps another way to get to it?  thanks, ~ks

It appears to be gone now.  Not sure what happened to the turbine matrix pdf

boB

[ChrisOlson]

Sometimes a low ratio transformer might be OK, like maybe 2:1 ratio.  Even with a 2:1 ratio transformer, it will apply a resistance value that is 4 times the value that is on the Clipper itself.  A 4:1 ratio transformer will multiply that resistance by 16 times the original value.

We have a 2.5:1 step-down transformer on our Excel-R.  Never clip on the secondary side of the transformer.  Always clip ahead of the transformer on the 300V side, otherwise it's virtually impossible to stop the turbine.
--
Chris