Bridge rectifier good enough?

giggleswicksam

Hi. I have 24 2v forklift cells, an ista breeze 2kw 3 phase AC turbine going through a bridge rectifier.

It is windy, say 30mph. If I switch off on the DC side of the turbine and on again I am seeing up to 1kw output, but this drops to a steady 80-100w in a few seconds.

My question is, if I bought the official ista breeze controller, would it keep the output higher by some witchcraft, like my mppt solar controller? Is my current large load acting as a brake? I'm sure that if I sat in the shed flicking the switch on and off, I could get much more out of it!

Sam

BB.

I assume this is a 48 volt battery bank? And the charge controller is not braking (slowing) the wind turbine because it thinks the 48 volt battery bank is full (what is the battery bank voltage when charging)?

The little I could find, the Ista charge controller does not appear to be an MPPT type charge controller. So--Yes, it is possible that a good quality MPPT type wind charge controller could get you more charging energy from your wind turbine (some early results I have read about from Midnite's MPPT testing showed that they could harvest 2-3 times as much energy from an otherwise properly designed and operating wind turbine).

MPPT is not magic--It is, for a good analogy, like an automatic transmission that lets the blades spin at optimum speed (for pulling the most power from blades+turbine) then down converting that higher voltage/lower current to the lower voltage and higher current needed to charge your battery bank.

Which then takes us to the next question--It does sound like your turbine is supplying too much torque to the blades and keeping them from spinning fast enough to efficiently harvest energy from the wind. If you are not harvesting 1,000 watts or more in 30 mph wind, then it would seem that your blade design (pitch, profile, diameter, etc.) does not match the torque/rpm curve of the alternator.

When you switch the load on and off to the turbine, you are simply letting the wind take the blades up to high rpm (no load), then dumping the load on is taking the rotational momentum and generating current+voltage at the capability of the alternator. However, the torque of the alternator is so high, it slows the rotation of the blades--probably enough to make them stall (not "fly efficiently") and stabilizes at a few hundred watts of output.

There is other possibility--Your turbine is not mounted on a high enough tower to get good/clean/non-turbulent airflow. Your tower should be (ideally) at least 20 meters/~66 feet above the ground, and at least 10 meters/33 feet above any nearby obstructions (trees, buildings, etc.). If the tower is less than 10 meters/33 feet tall (below tree/building line/etc.), it is not likely to be in undisturbed airflow.

If your turbine is flying in turbulent air--No change in blades or MPPT charge controller will help. Turbulent air just does not have much "useful" energy in it. The clean (laminar) airflow is converted into rolling/buffeting airflow which no turbine can harvest energy from.

An easy check to find where the non-turbulent air is--Go fly a kite (not too near the wind turbine) and see how high it must be before it flies straight and steady.

-Bill

giggleswicksam

Thanks. That's good advice. I did contact ista and it's definitely not mppt, so not worth wasting money on. The midnite unit looks great, but costs a fair bit. I know my tower is too small, I aim to get it higher next year, and make it a lowering tower so I don't have to climb my vertigo up it! Cheers Sam

giggleswicksam

Ps. There is no charge controller, and battery voltage is eg 50.8.