I'm volunteering at a place out in the country who are living off the grid. They already have a couple of windmills, which have been installed professionally. They are also working on a micro hydro system. This has been designed and partly built by a professional engineer during his spare time, but he has been unable to do any more work on it for some time (at least a year) due to other commitments. The turbine and alternator are finished, but none of the rest of the electrics, including the charge controller for the batteries (it's going to be a DC system with an inverter).
They have just got hold of a battery backup system of the kind which is used to supply emergency power to alarm systems, emergency lighting etc. (I think it used to run the emergency lighting for a nursing home). This is designed to charge some 12V batteries from the 240V mains, and there is also a separate inverter which supplies mains power from the batteries.
I was talking to one of the people there, and he was talking about using the battery backup system as a charge controller for the water turbine. I was advising him to be cautious, for the following reasons:
- you need to have some way of shunting power to a dump load when the batteries are fully charged and no current is being drawn, otherwise the alternator may burn out.
- The charger is as far as can tell (I may be wrong here though) a standard linear regulator, which I am not sure is suitable for this kind of application where the input voltage may be variable. I would have thought that a switch mode regulator would be more suitable, as these can deal with a wider range of input voltages. I think this is not so much an issue as with wind power, since the speed of the turbine and hence the output voltage is probably fairly constant, so should be tunable to whatever voltage is required.
Do either of these things matter as much as I thought, or am I being too cautious?
Any advice appreciated, particularly from anyone who has any practical experience with micro hydro or windpower electrics.