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Diversion Loads & Aux Relays

If your battery is full or the grid is not available, there may not be sufficient load on your hydro turbine, and it will over-speed (run away).  This may cause excessive noise and wear, and it is a wasted opportunity to use the energy.  We offer diversion load heaters and solid state relays (SSRs) to utilise or remove this surplus energy.  Normally the SSR will be triggered by the "Auxiliary relay" or "Aux port" in your battery charge controller, which produces a 12V signal..

Overspeed will not be a problem on low head sites (PLT under 25m, TRG under 5m, LH under 2.4m) but you may still want to harvest your excess to heat water.
Occasional overspeed is acceptable at higher heads (PLT up to 60m, TRG to 12m, LH to 5m) but this should not be an everyday routine. At higher head sites you should never allow overspeed apart from voltage open circuit testing at no load for a brief duration, long running unloaded or partially loaded this will shorten bearing life.

There are 3 ways to divert surplus energy:

  • AC heating element via your inverter 
  • DC heating element at your battery voltage
  • DC heating element at your turbine generation voltage

If you do not have a hot water tank or do not need hot water then you can use an air diversion heater.  Bear in mind also that the water may overheat unless you make contingency plans.

Please note: We only offer equipment for DC power diversion (DC SSRs). For AC diversion the equipment required is widely available elsewhere.

For SSR applications above 100 VDC and for 120/240 VAC phase angle SSR applications Hugh Piggott (via a consultation) can assist/advise you.  

We recommend that you read our "PS MPPT Diversion Loads Guide".