Load resistor for PVI 4000

[Paul Camilli]

Hi Chaps,

recently replaced my SMA WB6000 and 'Windy Boy Protection box' WBPB 500 with a 3.6kW Aurora and PVI4000 'Wind Interface'. The turbine supplying the power is an old 2.5kW Proven fitted with the latest carbon fiber blades and easily produces 3.2kW now. My question is, can I safely use the 42Ohm, 6kW, 600V with this combination? I hope so, because I have been doing so.

I do have the load resistors that came with the the inverter and interface but they were somehow wired to come on sequentially with a PLC, have different values and I've no idea of their power rating or voltage.

Cheers, Paul

[Rob Beckers]

Paul, there are a number of issues with the PVI Wind Interface box, which unfortunately are at the design level, making them hard to correct:

The Wind Interface doesn't switch on the dump load until it reaches 520 Volt DC. That is scary-close to the 600V limit where both wind box and inverter let out the magic smoke. Many wind turbines are meant to run at much lower Voltages (RPMs) and once they reach a Voltage that high they are hard to slow down, dumpload or not. So there's the risk of runaway.

The Wind Interface switches the dump load on in parallel with the inverter. The inverter is not switched off. That may be a good thing from the perspective of putting enough load on to slow the turbine down, but it's bad because it does not protect the inverter from over-Voltage. Again, go over 600V DC and it goes poof!

Because of the previous point, it's hard to size a dump load: The inverter may be on, or if there's a power failure the inverter may be off, and that could make the dump load alone insufficient to keep control. Worse, the bridge rectifier used in the wind box is grossly under-rated and under-cooled for the job, making them fail pretty easily. With a dump load it has to handle both the inverter and current into the dump load.

It is a really bad design unfortunately, and most people use it as just a glorified rectifier. The dump load function is too poorly implemented to make it of much use IMO.

-RoB-

[Paul Camilli]

Hi Rob,

thanks for that, I seem to recall hearing as much on the Internet, perhaps it was your good self that said so. Was there word of a circuit you'd designed to clamp the voltage or did I dream that? I wonder if that's what the PLC was for and the different sized resistors that came with mine.

I got my Aurora off eBlag a few months ago, it came in a lovely enclosure about the size of a regular European fridge. Inside was the inverter, interface, resistors a PLC, a 'frequency drive' type inverter and lots of other stuff. Sadly it was all 'bankrupt stock' from a turbine company that had folded (the guy I got mine from had a container load) so came with no info.

Any thoughts about using the SMA Windy Boy Protection Box 500 instead of the Aurora interface Rob. Seem to think that that starts to 'dump' around 480V.

Gotta say, I really do like the Aurora, streets ahead of the SMA as regards 'tweaking' the settings. Gonna fool around with my 'air gap' next week and see if I can squeeze a few more Watts out of it all.

Cheers, Paul

[Rob Beckers]

Paul, no experience on my side at all with the SMA Protection Box, so I can't help you with that one.

The Aurora wind inverter works very well, and I like the way the MPPT table is put in or changed. Unfortunately they didn't put the same amount of effort in the Wind Interface Box.

I did indeed publish an over-Voltage protection design that uses a Voltage sensing relay. You can find it at http://www.solacity.com/power-one-abb-aurora-solar-wind-inverters/ (scroll down to the bottom).

-RoB-

[Paul Camilli]

Exactly what I need Rob, thanks, just have to get the 230V version of the relay in circuit 1. The Proven/Kingspan turbines run quite happily unloaded, even in storms so no need for extra resistors. Just found some relays on eBlag for £46 which seems about half the UK price.

Cheers, Paul

[Andy Rhody]

Paul Said:

Was there word of a circuit you'd designed to clamp the voltage or did I dream that?

Not a Dream Paul. I had someone build Rob's Controller for me. It's industrial quality and can be adjusted to dump anywhere you need.

My turbine is down, my 3 Kw Power One inverter blew out, and Robs controller is the only thing that still works.

Here it is:

http://i41.photobucket.com/albums/e295/andy47bottles/Science/SANY1575_zps10aa4aca.jpg (http://s41.photobucket.com/user/andy47bottles/media/Science/SANY1575_zps10aa4aca.jpg.html)

[Paul Camilli]

Many thanks for posting that Andy, always better to see one 'in the flesh' so to speak. I'm guessing those two small resistors are on the output to stop that wee glitch mentioned on Rob's site.

There is one more little thing concerning Power-One Aurora wind inverters you should be aware of: Without a source the DC input ‘floats’ at about 55 – 60 Volt, and if the inverter is set to switch on at that low a Voltage it will never switch off. The stray Voltage will keep it “on”, wasting energy (the inverter consumes about 40 Watt when idle). There are two ways to resolve this: A 100 kOhm/5W resistor between DC positive and negative on the inverter input will lower this stray Voltage so the inverter will switch off even when the starting Voltage is set to 50 Volt. The other alternative is to raise the inverter startup Voltage and first point on your MPPT table to 70 Volt or higher.

Cheers, Paul

[Andy Rhody]

You nailed it Paul. You're pretty observant.