Inverter connection

[RA]

Hi all,

I am in last steps to get up my wind turbine. Just finished bench tests with 16 poles PMG and got reasonable numbers by current and voltage.

But my question is following. If anyone would share experience how connect 3 kW inverter correctly. Doubts arised after consideration of connection circuit suggested by Piggott in his book where inverter in parrallel to battery and turbine. But if output voltage of turbine will rise over rated number - lets say 15 volts instead normal 12 - inverter may be damage?  

Thank you.  

Moved to the proper section.

[DamonHD]

Hi,

I have no useful practical turbine experience, so regard everything I say as suspect...

The battery will act as a filter and voltage limiter: you just won't get a 12V lead-acid battery to go over about 14.75V unless it is totally full and you continue to pump in power so fast that you destroy the battery.

So you must have some way of limiting charge going into the system.  With a wind turbine that is usually a dump/diversion/shunt load that gets rid of the unwanted energy, often as heat.

(With other loads, such as solar PV, it may be safe to simply disconnect the power source when the battery gets full, but that is not safe with a powerful turbine as it will 'run away' (get too fast) and probably destroy itself at some physical danger to things around it.)

Rgds

Damon

[Flux]

Correct

Until the battery is well charged the battery will dictate the voltage not the mill.

As the battery approaches full charge the voltage will start to rise and you will need some form of charge controller to limit the voltage.

Inverters are normally designed to accept the fully charged voltage of a battery but most shut down if the voltage goes above about 14.4v. Sometimes it is a bit of a compromise to prevent the inverter shutting down on over voltage if the charge controller is set on the high side during an equalising charge.

Batteries should never exceed 15v and that should not damage an inverter but it may shut it down.

Flux

[Ungrounded Lightning Rod]

However there are a couple failure modes where the battery won't limit the voltage:

 1) If you don't do maintainence on the battery for several years (or several months if the dump load fails or is insufficient) the battery may boil dry.  This can escalate destruction of your battery bank into destruction of your inverter, too.

 2) If you unhook the battery, the wiring to it fails, or the fusable link blows.

You beat number 2) by making sure to not unhook your battery without first furling and shorting the mill, and by doing your cabling to minimize single points of failure.  For instance:  Separate input and output cables with separate fusable links, joining at the battery terminal, if you're using lug-under-screw connections.  Or paralleled strings with the cabling going from each string to a junction point, so you can unhook the batteries in some strings without unhooking them all.

Overvoltage protectors (varistors) are also a possibility for small mills.  But they're intended for short-term service and may fail after a bit if actually triggered.  So they're good for covering a momentary "oops" but shouldn't be counted on for long-term service (like swapping batteries with the mill live).

[RA]

Thanks to all for enlightenment. Looking for invertor with "pure" sine by optimal price :-).