Author Topic: New Power Curve (Read 4143 times)

kitestrings · « **on:** December 28, 2018, 04:07:42 PM »

I've been experimenting for quite a while with the power curve settings for our turbine. We're running two Midnite Classic 250's. Each controller has a 16-step user-adjustable power curve. Below is the latest power curve (MEM7) that we've been running.

Generally I've been loading the turbine heavier, earlier (at a lower rpm). We're harvesting more power and that's good - we logged 11 kWh on 12/27 - but the primary benefit is that it keeps the thing at a lower overall rpm bandwidth from cut-in to full-furl. It used to be that we would regularly see peaks of about ~125-130 volts into the controllers. In the chart below I don't think we've logged over 115 VAC.

John Bouchard · « **Reply #1 on:** December 28, 2018, 04:25:48 PM »

Kitestrings. About how much more harvested wind power can one expect for battery charging using the midnight mppt controller vr. a simple dump without mppt? Sorry I find myself still in a huge learning curve.

kitestrings · « **Reply #2 on:** December 28, 2018, 05:28:52 PM »

Hi J. I'm not sure that I can definitively answer that, but anecdotally you get a lot more power over a wider range of windspeeds.

For a small turbine the expense of a MPPT controller may not be justified, but on anything 10' or 12' dia. or more, I would consider it. I probably should clarify what you mean when you say a "dump". There are charge controllers that are intended to load a small turbine effectively all of the time by diverting more load to a dump load as the batteries reach full charge and/or load on the bank is reduced, and this is a means of regulating the charge rate. I think this is what you mean.

Other times the charge regulation is separate, but a dump load is used as a means of diversion usually to a useful, but non-critical resistive load, such as water pre-heating, space heating or possibly refrigeration (with some ingenuity). A dump load can also be introduced to slow the turbine, for protection, when it becomes unloaded.

Setting aside the dump load for the moment. The goal in a good design is to get a good match between the power at the rotor and the alternator. The way the Classic does this is by allowing the characteristics of the alternator to be programmed into it. The voltage is allowed to fluctuate and the controller attempts to follow the programmed power curve as best it can based on the available wind.

With a direct-tie to a battery bank, you are forced to pick pretty much a straight line power curve, starting point, and and slope (which can only be affected by changing the resistance). It is much more challenging to hit a compromise that works in all situations.

~ks

John Bouchard · « **Reply #3 on:** December 28, 2018, 06:02:46 PM »

Yes its a TriStar 60 set as a diversion to a resistance load, heater. My goal at this point once I start flying my 13' is keeping batteries top off and less petrol generator usage in winter low solar. I've been doing some limited reading on Hugh Piggott blog using relays for diverting extra power at which some point I plan to do. In the mean time I'm taking baby steps cause I don't want to burn my house down! At some point I may also introduce a mppt controller for a better consistent power curves, makes great sense and thank you for posting/ responding!

John

SparWeb · « **Reply #4 on:** December 31, 2018, 12:52:18 PM »

That's an interesting gap between 105V and 115V on your second graph, red line.
Am I correct guessing that it's a furling lag that allows the power to spike a little before the tail completely activates?
For a 17' turbine, 4.5kW isn't excessive is it?

I gotta get me one of these Outbacks.

kitestrings · « **Reply #5 on:** January 01, 2019, 09:32:47 PM »

Hi Spar, Happy New Year.

Yes, I think that mostly right. In part I just haven't collected enough data on MEM7; in part it just doesn't spend much time there. It's already mostly furled above I dunno 90-95 volts - DC volts in to the Classics - or so I'd guess. The highs (>105) are usually when it has spun up pretty good, the tail is on a downward motion when it gets hit with the next surge/gust of wind, or there just hellishly high.

At 95V typically we're running 2-2.5 kW, with 1,800 watts on A; 200-300 watts on B. At 105V we're doing almost 3 kW, but the split is 2,400 watts on A (this one is set to current limit at 40A); 700 watts on B.

This is a 15' diameter. Peaks of 4.5 kW are pretty common, but short lived. Ideally I'd like to keep the load under about 2.5 kW on each controller. In practice the first one does most of the heavy lifting. I now have the second controller waking at 82V, and by 105V its potentially contributing 10-12 amps.

It has been very windy thru much of December. Today we got .1 kWh from our PV and almost 7 kWh form the turbine (I started it this morning around 8 AM). There are plenty of days the reverse is true, and some where I don't even start it... but generally there not this time of the year. This is when the turbine earns its keep.

The tail actuator is working very well, and makes it easy to shut down when it is not needed, or the rough stuff hits - like last night actually.

kitestrings · « **Reply #6 on:** January 05, 2019, 07:39:07 PM »

Quote

I gotta get me one of these Outbacks.

Just to be clear Outback is not the manufacturer of the Classic charger controllers. It is Midnite Solar, though if I understand it right, at least some of the founding members of Midnite Solar where also involved in Outback, and before that Trace, and maybe even Heart (for anyone who remembers that far back).

ontfarmer · « **Reply #7 on:** January 06, 2019, 06:33:16 AM »

You get a lot of power from that turbine. Interested in what the wind speed would be, when this is happening?

kitestrings · « **Reply #8 on:** January 06, 2019, 03:39:10 PM »

Yes, I never have taken, or devoted, the time to putting up an anemometer. If I could plug the output easily into the same controller, it'd be much easier. I generally make decisions of when to run based on forecasted windspeeds. Some of the apps have gotten pretty good.

The tail of our turbine starts to leave the lower rest in pretty light winds overall - not more than 10-12 mph I'd guess. I do have instantaneous rpm readings on the rectifier box that I track, at least visually. I suspect it is pretty linear up to the point that it furls and dumps considerable output. The thing cuts-in at 92 rpm and about 59 V (this is maybe 7 mph); it is fully furled at roughly 150-160 rpm.

It's all interesting, but time-consuming. I'm more concerned overall with the ease that we can get 500-800 watts than anything that happens in the 2 kW range. The forecast winds today were genrally under 15 mph, with a few periods near 20 mph. I started the turbine this morning at 8:30. It's 3:30 PM now, we've logged 3.9 kWh and the batteries are at 51.5V - so if my math is right, that's about 557 Wh average. We did a bunch of laundry and vacuuming, I had a small amount of shop work earlier. I like the concept of a tangible transfer of energy from up there to say our washing machine, or my planer. One off-sets the other, hopefully a bit more on an average day. Conspicuous spending on sunny, windy days.

SparWeb · « **Reply #9 on:** January 07, 2019, 10:47:33 PM »

"conspicuous spending" Like turning ALL your lights on during a power outage...

Bruce S · « **Reply #10 on:** January 08, 2019, 08:32:52 AM »

Our making a pot of coffee when everyone else's power is out

DamonHD · « **Reply #11 on:** January 08, 2019, 12:45:55 PM »

Pure evil, Bruce. %-P

Surely the Geneva Conventions prevent such taunting during civil emergencies?

Rgds

Damon

Bruce S · « **Reply #12 on:** January 08, 2019, 03:01:52 PM »

BUT isn't it being civil when you offer your neighbor's coffee

.

clockmanFRA · « **Reply #13 on:** January 08, 2019, 03:57:34 PM »

We here in Normandy, France, keep a low profile when the main Grid is down, about 6 to 9 times a year, 12 hours to 5 minutes.

The lady over the road 400 meters away has enquired, 'that if she gets an extension lead, can she have some of our electricity'. !!!!

Bruce, the local French Fire Chief lady came to see me just before Christmas for there Christmas Box, she showed me her latest Uniform she was wearing. And she enjoyed my Christmas jumper with puddings on it that I was wearing.
I felt sorry for the new French young training lad that was with her, he looked scared to enter into the mad Englishman's house.

Bruce S · « **Reply #14 on:** January 08, 2019, 04:40:13 PM »

clockmanFRA
That look seems to be a "thing" for the recruits that have less than a year on.
They get around some of the BCs Battalion Chiefs and above and they get that deer in the headlights look about them.
They even call me "SIR".
Have they done their annual picture ? It would be interesting to see what reflective colour scheme they've gone to.

Here is St Louis, Missouri, USA; those of us who have power show up outside in droves.
It's kind of a right of passage for the Electric company

.

Mary B · « **Reply #15 on:** January 08, 2019, 06:09:21 PM »

Quote from: DamonHD on January 08, 2019, 12:45:55 PM

Pure evil, Bruce. %-P

Surely the Geneva Conventions prevent such taunting during civil emergencies?

Rgds

Damon

Neighbor across the street calls me during the last power outage.

"Do you have power?"

No, mine is out too.

"How come your lights are on?"

Um, you know those solar panels I have? and a battery bank? Gives me electricity while you sit in the dark.

"Grumbles, some words I can't repeat..."

*click*

LOL

And I had told him what it takes to have a small backup system for lights and maybe the TV or a computer. A small simple system would not be that expensive.

Bruce S · « **Reply #16 on:** January 09, 2019, 08:54:21 AM »

Mary B;
Probably the same words I've hurdled at me a time or two...

clockmanFRA · « **Reply #17 on:** January 10, 2019, 04:48:52 AM »

Sorry 'Kitestrings' for this off topic pic.

'Bruce' likes to see this years French Fire fashions.

"This year its Black and White with white fluorescent, and a hint of yellow fluorescent."

Bruce S · « **Reply #18 on:** January 10, 2019, 08:29:34 AM »

kitestrings · « **Reply #19 on:** January 11, 2019, 09:12:56 AM »

Quote

We here in Normandy, France, keep a low profile when the main Grid is down

Here too. I work for a rural coop. I don't usually talk about the televised sporting event of the day when there are outages and we still have power....

I picture that when the Canadians invade in some future doomsday, zombie apocalypse - I know they're quietly posing as mild-mannered ham radio enthusiasts and forum moderators BTW - we'll be the first to be shot

Quote

"This year its Black and White with white fluorescent, and a hint of yellow fluorescent."

My boys are really into Lego's. Clockman's photo reminds me of their real-life action hero's.

SparWeb · « **Reply #20 on:** January 11, 2019, 08:42:37 PM »

Your overlords will demand payment in cake.
Or flapjacks - we hear you have lots of those too.

bigrockcandymountain · « **Reply #21 on:** January 14, 2019, 08:04:17 AM »

Does your homemade clipper end up doing anything with your current setup?

I am planning on using a classic with my turbine right away but have not set up a clipper. The furling should keep everything in check i think.

I am starting with a curve steeper than yours. I think to about 135v at the top. My generator makes less volts per rpm so hopefully it works somewhat decent. Your post here makes me think i am in the ballpark.

kitestrings · « **Reply #22 on:** January 14, 2019, 12:23:28 PM »

Quote

Does your homemade clipper end up doing anything with your current setup?

Yes. You can see an overview of our system here:
https://www.fieldlines.com/index.php/topic,149613.msg1045952.html#msg1045952

I've copied this explanation from an earlier discussion:

In normal operating mode, the charge controllers are attempting to first bulk, absorb and then float the batteries. Once they are fully charged, or whenever we bump against the the upper charge limits set, the voltage starts to climb if there is no place else for power to go. Initially the load diversion comes into play. Through the Aux 2 (PWM relay signal) the Classic diverts, or burns off, excess available power into the water heater.

When the batteries are full and the water heater is satisfied, the second Aux 2 (we have two Classic's) starts to engage our homemade 'clipper' or resistor dump via the 'dump relay' in the rectifier box. This one, unlike the diversion load, is on the 3-phase side of the rectifier. It's mission is just to keep the voltage input into the CC's below safe limits (overall 250VDC, 180VAC).

I've lowered the setting quite a bit from where we started, but it is around 115-120V IIRC, with a 5-volt spread (this is the voltage width or hysteresis from where it just starts to pulse to where it is fully on). I also use the load bank to shut the thing down manually. We actuate the motor operated the furling, then ~45 seconds later turn on Aux2. This keeps the rotor under 5 mph in most any wind we've encountered, and it is very gentle on things. Power furling is described here:
https://www.fieldlines.com/index.php/topic,149230.msg1041516.html#msg1041516

Lastly, we have a voltage sensing relay for a high-limit protection to the controllers. If it opens for any reason the load bank is also switched in.

Our load bank can be seen here:
https://www.fieldlines.com/index.php/topic,148411.msg1030333.html#msg1030333

bigrockcandymountain · « **Reply #23 on:** January 14, 2019, 09:13:47 PM »

Wow thanks. That was exactly what i was looking for.

One question...how did you figure out size for the resistors on the ac side?
Could they be hooked up delta if they were say 120v rated so a little more power would flow. 120v water heater elements are very cheap and available. My dump load will likely live in the thermal storage tank. It is 250 gal and unpressurized so its almost unlimited in the amount of power that can be dumped in it.

kitestrings · « **Reply #24 on:** January 15, 2019, 12:34:21 PM »

Early on I started with something like this, just looking at the theoretical power available at the prop. The upper end of this chart corresponds to about a 27 mph wind speed, and the straight line â€œdump wattsâ€ are using our resistors, though we don't actually go near the upper limit because we furl long before these speeds.

By the time I actually built the thing we had the benefit of some output data. The goal is the same though, which is to simply match the power from the turbine, if otherwise unloaded, over the bandwidth where you might be dumping (and not burn anything up). If for example, if we want to dump about 3 kW at 141V (DC into the controller)â€¦ the math would be:

line volts = rms volts/ph x 1.732, and
DC volts = rms volts/ph x 1.732 x 1.4, therefore:

rms volts/ph = DC Volts / 1.73 / 1.4 =    RMS Volts / ph
141   1.732   1.414        57.56
            line volts
            99.70

We have pairs of 6.8 ohm, 700 watt resistors, so 58Vph/3.4 ohms = 17 amps, then 100Vline * 17A * 1.732 = 2,941 watts, 2.94 kW. And, each resistor should be carrying just under 500 watts. This is just one point, but you can chart a line from this method.

Notice that in delta the same resistors would dump 8.8 kW, not good here, but other combinations are certainly possible.

If you are working with water heater elements you would need to see if the resistance is workable for your needs. A 120V 2,000 watt would be 16.8A, so 7.2 ohms. In pairs you could double that (in series), or cut it in half (in parallel). If my math is right in delta at 7.2 ohms you'd dump 4.2 kW (120% over the element rating); in wye you dump 1.4 kW.

bigrockcandymountain · « **Reply #25 on:** January 15, 2019, 09:48:23 PM »

Ok that is a great template for plugging numbers in. I am not as good with ohms law as i thought.

When you say delta will be 4.2kw with the 2000w 120v elements that means each element will see 1400w. Is that correct? It seems about right if so.

1500w 120v elements comes out right around 3kw or 1000w per element.

Ok but for the next few days when i get the turbine running and have nothing set up. My second classic is programmed to remain in bulk and just mppt all day long. I have never seen this turbine make over 3000w. I set the furling for even less top end power. Hopefully under 2500w.

Am i going to wreck my charge controller? It should handle 3500w right. Classic 200 on 48v bank

The existing dump load had no problem keeping the batteries at correct voltage so i am not worried on that end.

Maybe i should just direct connect to the batteries again. I at least have manual furling now so i can shut it off.

JW · « **Reply #26 on:** January 15, 2019, 10:05:16 PM »

Notice that the use RMS-voltage is noted by kitestrings, this is where the discrepancy is occuring.

kitestrings · « **Reply #27 on:** January 16, 2019, 08:01:48 AM »

Quote

When you say delta will be 4.2kw with the 2000w 120v elements that means each element will see 1400w. Is that correct? It seems about right if so.

Yes, and I'm sorry the 120% is not right. This would be within the rating of the element. I may have calculated the DC voltage in error,as JW suggested.

I think you are on track. Your 120V, 1,500 watt elements should have a resistance of (1,500w/120V = 12.5A, 120V/12.5A) = 9.6 ohms. In delta at 100 volts they would draw 3,125 watts, 1,042 on each element. Running the thing in light - to moderate winds will give you a read on where the voltage will actually fall.

A Classic 200 should be able to operate to 200V and survive to 200V + nom. battery voltage, or about 250V, and your AC voltage from the turbine will be lower by the sqrt (2) factor, 1.414.

bigrockcandymountain · « **Reply #28 on:** January 16, 2019, 01:29:19 PM »

Ok thank you very much kitestrings.

I really like the way your system is set up. That is why all the questions.

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Author Topic: New Power Curve (Read 4143 times)