17' Grid Tied w/Power-one 6000

[Rob Littiken]

I am currently building a 17' Axial Flux turbine based on the Otherpower design, but will be grid-tied with no batteries. I currently have the stator wound to put out approximately the volts below:

RPM Coil Volts Total Volts Figured
80 10VAC 98VAC
135 17.2VAC 169VAC
200 28.3VAC 278VAC
325 42.9VAC 423VAC

I am thinking of using the Power-One PVI-6000-OUTD-US inverter and the PVI Wind Box Interface.

The Wind Box can turn on a resistive load when the voltage >530Vdc, that I will have dump to resistive load that I will build.

The turbine will be furling design and will have the ability to manually furl when needed too.

My question for Rob Beckers or anyone else that wants to chime in, is will this work? Is the voltage high enough or do I need to wind the coils to have a higher voltage that will run closer to the 530 Vdc dump?

Is their anything else that I'm not thinking of?

Thanks for any help you can provide.

Rob L

[Rob Beckers]

Hi Rob,

For 3-phase sine wave sources the ratio from AC to DC is 1.35. So, if rated power at around 12 m/s (just before you'd normally start furling) is around 423V AC then you're looking at 570V DC.

In other words, that's a bit much! I don't know if the voltage is loaded or unloaded (presumably unloaded since you don't have this put together just yet). You'll likely see at least a 10% drop for loaded voltage, bringing it down to the 520's V DC. If those assumptions are correct, you're doing OK with the coils as they are. Also, it's always possible to run the turbine at a higher or lower TSR than optimal for the top end, and get the 6kW out at a voltage that works.

Keep in mind though that you really, really have to keep that voltage under 600V DC!! It will blow if it hits 600V, with absolute certainty. There is not much 'room' between 530V and 600V to keep things under control. So, you really need to furl early and decisively, and get enough load on that turbine (even when the grid is down) to keep the voltage in check.

-RoB-

[Rob Littiken]

Thanks for the fast reply Rob B.

These test volts were unloaded from a single coil, then I did the math to come up with total Vac. The turbine was mounted in my milling machine and spun up to the various rpm's.
Here's the math I used (Coil Volts AC Measured X 4 (#coils in phase) X 1.73 / .7) - 1.4 = total volts

What kind of Diversion load have you or some of the other on this form used, and what size do you think I'll need to design it?

I am planning on purchasing the Wind Box rectifier. Will the crow bar overvoltage protection help protect the inverter if it was to hit over 600Vdc?

My last question is. I see you also sell the RS485-to-RS232 converter. Is this converter necessary for monitoring/programing or can that be done over the usb?

THANKS for your time.

Rob L

[Rob Beckers]

Thanks for the fast reply Rob B.

These test volts were unloaded from a single coil, then I did the math to come up with total Vac. The turbine was mounted in my milling machine and spun up to the various rpm's.
Here's the math I used (Coil Volts AC Measured X 4 (#coils in phase) X 1.73 / .7) - 1.4 = total volts

So it's a wye-connected alternator with 4 coils in series per phase? The phase-to-phase voltage would be:

Vtot = Vcoil * Ncoils * sqrt(3)

So, I'm not sure where the .7 is coming from. Or did you measure peak voltage and the .7 is meant as the sqrt(2) factor to get to RMS?


What kind of Diversion load have you or some of the other on this form used, and what size do you think I'll need to design it?

Actually, bolting a diversion load directly to the wind box seems to be an unpopular option. I don't know of anyone that uses it. Cor tried it with the Hummer turbines (see another thread) but found that while it worked as advertised, the voltage was too high for that wind turbine to keep things under control. By the time his turbine reached 530V there was no stopping it any more. Projects I've been involved in that used dump loads did so with an Omron measurement relay to switch the dump load on/off.

More in general, what people have been using for dump loads: Water heater elements, baseboard heaters, space heaters, light bulbs, and of course regular resistors meant for diversion loads. The value should be sufficient to keep the turbine under control even if there is no grid. How much this is depends on the turbine, when and how well it furls, what the alternator can handle etc.


I am planning on purchasing the Wind Box rectifier. Will the crow bar overvoltage protection help protect the inverter if it was to hit over 600Vdc?

I have a few wind boxes sitting next to me that were blown due to overvoltage, and they did protect the inverter in doing so. That is no guarantee though that the next time the voltage gets too high the wind box will protect it, it's somewhat of an unintended side effect. The crowbar circuit in the wind box was meant to blow the fuses, in practice it blows parts in the box, but not the fuses. So the wind box gets destroyed in the process. I suppose that's better than the inverter. Still, better not to rely on that.


My last question is. I see you also sell the RS485-to-RS232 converter. Is this converter necessary for monitoring/programing or can that be done over the usb?

THANKS for your time.

Rob L

USB works fine. The advantage of RS485 is that it lets you run very long lines (hundreds of feet if need be), while USB tops out at about 20 or 30 feet. If you need that line length it's far cheaper to get a USB-to-RS485 converter. Mel got one recently for under 20 bucks if I remember right.

-RoB-

[Dan Lenox]

Rob L,

I am intimately familiar with the OtherPower 17' design, as I built one 1-1/2 yrs ago (http:www.briery.com/wind_turbine/) and still playing with getting it to not become wind-seeking...

Are you using the 59 turns, two in hand #14 wire for your coils? And I assume 4 coils per phase for total of 16?

I would highly advise you to talk with Cor Van Houtum as he has been working successfully with interfacing large turbines with the Power One Aurora inverters.

Dan Lenox

[Rob Littiken]

I'm using 118 turns #14 wire 1 in hand to double the voltage. Does anyone know where I can get the Omron k8ab-vw3 relay in the U.S.?

Thanks,
Rob L

[Rob Beckers]

I'm using 118 turns #14 wire 1 in hand to double the voltage. Does anyone know where I can get the Omron k8ab-vw3 relay in the U.S.?

Thanks,
Rob L

Hi Rob,

Contact Redrive (http://www.redrive.net/), they don't list them on their site, but they do sell them. I've been using them for a while as well (and yes, the credit goes to Cor, he pointed these relays out to me); when stacking inverters (http://www.solacity.com/Docs/Dual-Inverter%20Wiring.pdf) they're used for undervoltage detection to switch off the inverters/transformers and avoid standby losses, and we installed one at Mel Tyree's place, so protect a dual-Aurora inverter setup that is being used with his Bergey Excel-S wind turbine (he actually has two Omrons installed now, one to protect against overvoltage, another to switch off the transformer on undervoltage).

-RoB-

[Rob Littiken]

Would you use the 110V or 220V version of the relay.

Thanks,
Rob

[Dan Lenox]

Rob L,

My last stator with 59 turns, #14, two in hand had about 54v generated at about 90rpm. Max realistic rpm's for this size wind turbine is about 300rpm.

With your stator you will be generating 2x the voltage, and assuming that it is linear, your turbine will be generating 250-300v max.

In a moderate 18-20mph winds your turbine will be turning about 180 rpm so I would easily expect to see 200+ volts from it in 'normal' operation.

Keeping your turbine output below 220v is at best going to be problematic.

Dan Lenox

[Rob Beckers]

Would you use the 110V or 220V version of the relay.

Thanks,
Rob

The 110V version. No reason to go to 220 (which is actually 240V).

-RoB-

[Rob Littiken]

Dan,
The 110 or 220 on the relay is just the power supply side of the relay. The swithching part of either relay can handle 600V. I just didn't know if one was better to wire up than the other.

I know that the voltage is going to be high. If you look at the third post in this thread you can see my computations. I'm planning on just having it grid tied, no batteries.

Thanks for the input.
Rob L.

[Rob Littiken]

The 110V version. No reason to go to 220 (which is actually 240V).

-RoB-

Thanks Rob Beckers

Rob L