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< prev - next > Energy Wind power wind_turbine_pmg_manual (Printable PDF)
Using the PMG for hydro power
The PMG can also be used for charging batteries from small hydro turbines. It will
be ideal for low head, low power sites, because it is efficient even when producing
only a few watts. It can also be used for higher head higher power sites, because it
is capable of high power outputs at high rpm.
There is a danger of rust damage to the magnet rotors in a very humid or wet
environment such as in a hydro application. It is advisable to galvanise or plate the
steel components with zinc.
Low head sites
Here are some examples of conditions where the PMG could work without
modification (connected delta). It would need a simple 'impulse' runner mounted on
the front magnet rotor.
Head (metres)
10 10 5
Flow (litres/second)
1 55
Net Power(watts)
40 200 100
pcd runner (cm)
37 27 23
speed (rpm)
325 440 360
High head, high power
At higher rpm, higher power is available from the PMG. Doubling the speed can also
double the output voltage and the current, offering four times as much power with
the same efficiency as before. The PMG may overheat under these conditions, so it
may be better to keep the current the same, and have better efficiency. Much will
depend on whether the water is used for cooling.
In any case, increasing the speed improves the PMG's power handling abilities
considerably. It would be risky to run a wind turbine at high speeds, because of the
problem of gyroscopic forces on the rotors, but this problem does not arise with
hydro power, because the shaft axis is fixed.
If higher voltage is not required, then the stator winding can be changed to give 12
volts (as before) at the higher speed, but deliver higher current without overheating.
This is done by connecting the coils of each phase in parallel instead of in series. Or
the coils can be wound with fewer turns of thicker wire. This is better still,
because parallel and delta connections can suffer from parasitic internal currents.
Do not use the star/delta connection (diagram 49) for hydro power where the speed
is constant. There is no advantage.
PMG manual
page 51
June 2001