Installation manual

over-voltage protection built in) may be used with MPPT controllers but you must be careful

if you do this. This is because the risk of over-voltage and hence controller damage is greatly

increased.

The turbine operating voltage on load (known as maximum power point voltage MPPV)

needs to be above battery charging voltage. In fact even higher voltages are useful in

reducing the cost of the cable. But when the turbine runs without load it will overspeed and

produce a higher open circuit voltage (Voc) that is 2-3 times higher than MPPV, depending

on the turbine type.

In the case of 12 and 24 V batteries (using for example the PLT40 turbine) this will not

impact on your choice of controller, but to charge a 48 V battery you will need an operating

MPPV above 60 V. Losses in the cable may well push this figure higher still. The Voc may

be 3 times higher, reaching over 180 V and ruling out the 150 V range of controllers. If you

wish to use a 150V controller with a 48 V battery then you will need to choose the additional

crowbar option PLT/TRG100C. Or you can use a 250 V controller with the PLT/TRG 80 and

no crowbar.

If you intend to use a PowerSpout turbine directly connected to a MPPT

controller/inverter without crowbar protection, then you must do a runaway

voltage test prior to connection.

Very often during early trial runs of the turbine the pipe has air locks in it, it is worth repeating

this test the next day when the pipe has fully purged of air and the full head is available for

an accurate measurement.

5.7.6. Factoring in the cable voltage drop

PowerSpout turbine notation lists many voltage options. For PLT and TRG turbines the

number indicates the approximate voltage the turbine is designed to best run at. Voltage

drop in the cable has to be allowed for when working out the maximum possible battery

voltage.

For example a PLT/TRG80 turbine the cable calculations are done at 80 V DC to determine

cable size required (in the Advanced Calculator tool). Voltage drops of 5% (5% of your

power will be lost) are common, so the voltage at the MPPT controller would only be 76 V.

For example:

 A PLT40 turbine has been installed and when tested on site had a recorded runaway

(open circuit) voltage of 130 V DC. It is to be connected to an Outback FM60.

o PLT cable voltage = 130 * 0.33 = 43 V DC approx.

o Hence it can only be used to charge 12 or 24 V DC systems

o Cable loss calculations are done at 40 V DC in the calculation tool

 A PLT80 turbine has been installed and when tested on site had a recorded runaway

voltage of 230 V DC. It is to be connected to a Midnight Classic 250.

o PLT cable voltage = 230 / 3 = 76 V DC approx.

o Hence it can be used to charge 12, 24 or 48 V DC systems

o Cable loss calculations are done at 80 V DC in the calculation tool

It is important to remember that a PLT80 (for example) will nominally give maximum

power at 80 V but in practice could be in the range 70-90 MPPV. This range could

be even wider if the site data you supplied at time of order was not accurate.

It is therefore very important that the runaway Voc is measured on site prior to

connection to your MPP controller.