Questions on PMA wind/micro-hydro turbine setups.

[matt1309]

Hi Folks,

I have a decent sized solar setup with DIY LiFePO4 and understand the basics however I'm struggling with a few concepts I've seen within the wind/micro hydro generation space and was hoping someone could clear up my understandings/confusion.


The installations I've seen online, tend to be exactly the same as solar, the only difference being the choice of charge controller often being Midnite. The specific part where my understanding of the logic breaks down is dump loads and the requirements for them over a few other options that I would've guessed if i hadnt researched a bit.


I understand dump loads are needed to prevent overcharging of batteries in the event there's excess power within the system.
However in solar when batteries hit absorption phase, charge controllers keep voltage static and amps will decrease over time, preventing overcharging of the batteries.

For hydro/wind I understand in absorption phase to prevent overcharging a dump loads is used and controlled via PWM controller to turn load on and off.
And this is needed because the MPPT keeping voltage static not reduce the amps in a turbine system like it does with PV as PV will not produce power unless there's load? Am I correct in my understanding so far?

If so my questions are why is dump load used over these options.

1. Instead of a dump loads you still use a PWM but rather than turning on/off a dump load repeatedly it instead shorts the 2 of the wires coming out of the PMA acting as a break for the turbine but only temporarily. The only reason I can see this being worse than a dump load is maybe the breaking is too aggressive when compared to just introducing load to the system ie the break slow it too much vs just adding a load via PWM? Or is there another reason why this isn't used?

2. (Hydro only) Use PWM to just disconnect battery or turbine from the system altogether, assuming turbine can safely free at max speed (given you know pipe size/max water through pipe you know max power, I understand with wind this isn't an option as free spin would not be safe).



I unfortunately dont have the money for land that is able to use micro-hydro or wind but maybe oneday but just like to wrap my head around the logic of it all.

 

[RCinFLA]

On PV, input power can be limited just by letting panel dissipate unused power. On hydro you can modulate or shut off water valve. On wind you have to control speed of blades which is tougher than other two.

For wind turbines you should always have at least two methods of braking to avoid a catastrophic condition of over spinning turbine due to strong winds.

Many of the cheap Chinese wind turbines only use electrical load dump to control turbine speed. Load dump resistors or rectifiers often burn out leaving turbine speed to its fate.

Turning turbine away from wind flow or mechanical breaking is backup to load dump. Rotating blade pitch, used on large commercial turbines, is more complex.

 

[Whats_per_question]

Hi Folks,

I have a decent sized solar setup with DIY LiFePO4 and understand the basics however I'm struggling with a few concepts I've seen within the wind/micro hydro generation space and was hoping someone could clear up my understandings/confusion.


The installations I've seen online, tend to be exactly the same as solar, the only difference being the choice of charge controller often being Midnite. The specific part where my understanding of the logic breaks down is dump loads and the requirements for them over a few other options that I would've guessed if i hadnt researched a bit.


I understand dump loads are needed to prevent overcharging of batteries in the event there's excess power within the system.
However in solar when batteries hit absorption phase, charge controllers keep voltage static and amps will decrease over time, preventing overcharging of the batteries.

For hydro/wind I understand in absorption phase to prevent overcharging a dump loads is used and controlled via PWM controller to turn load on and off.
And this is needed because the MPPT keeping voltage static not reduce the amps in a turbine system like it does with PV as PV will not produce power unless there's load? Am I correct in my understanding so far?

If so my questions are why is dump load used over these options.

1. Instead of a dump loads you still use a PWM but rather than turning on/off a dump load repeatedly it instead shorts the 2 of the wires coming out of the PMA acting as a break for the turbine but only temporarily. The only reason I can see this being worse than a dump load is maybe the breaking is too aggressive when compared to just introducing load to the system ie the break slow it too much vs just adding a load via PWM? Or is there another reason why this isn't used?

2. (Hydro only) Use PWM to just disconnect battery or turbine from the system altogether, assuming turbine can safely free at max speed (given you know pipe size/max water through pipe you know max power, I understand with wind this isn't an option as free spin would not be safe).



I unfortunately dont have the money for land that is able to use micro-hydro or wind but maybe oneday but just like to wrap my head around the logic of it all.

Think of solar panels as being like a capacitor that is magically recharged by the sun. If you were to charge a capacitor (for example touch the capacitor legs on a battery's terminals), that capacitor can sit there for a long time with no problem. If you wanted to do work, you connect the legs to something and bleed off the energy (voltage) and do work in the process.
If you recharge the capacitor and leave it on the battery for a long time, nothing happens - once the capacitor has reached the same voltage as the battery, current stops flowing.
With a turbine, you can also leave the terminals disconnected, but now there is nothing to stop the turbine running to its maximum speed. For an overshot or undershot wheel, this is no problem - the max freerunning rpm is only a small percentage over the maximum power rpm (this is one of the biggest factors that limits the productivity of wheels) . In both wheel type cases bearing wear is low because rpm is (relatively) low, and a well made wheel will never fly apart.
For a Pelton wheel, you would be in the danger zone if the turbine is well designed, high performance, and you let it freerun. You could throw cups off, or go through a bearing in a matter of days.
Note that dump loads are not the only way to manage rpm. Some designs throttle the incoming flow - this is useful for situations where the water supply should be preserved, such as a national grid turbine, where you would turn down the water flow to preserve lake levels as demand decreased rather than dump power.
Some designs use both : dump loads as level 1 rpm management, and water diversion or throttle as level 2 rpm management.