Installation manual

USA NEC Requirements

To comply with NEC 690.72 (B), the following requirements will apply when

using a diversion charge controller on an unregulated charging source:

 Second Independent Means If the diversion load controller is the only means of

regulating the battery charging, then a second independent means to prevent

overcharging the battery must be added to the system. The second means can be

another diversion controller, or a different means of regulating the charging.

 150 Percent Rating The current rating of the diversion load must be at least 150% of

the source current rating (combined maximum hydro and PV input currents).

These requirements make sense for safety in the context of a hydro system, where the

diversion load is likely to work hard, and the consequences of failure will be certain damage

to the battery, and danger of explosion and fire. The backup need not be the same as your

primary controller. Often a simpler, relay-based solution can be found.

5.7. Maximum power point tracking (MPPT) controllers in detail

The "maximum power point tracking" controller is a device that sits between the solar array

and the battery, converting the voltage down (rather like a gearbox for voltage) so as to allow

the solar panel to deliver its maximum power.

The "MPPT controller" actually does two things:

 Its MPPT function is to step the voltage down from a high input level to battery

voltage whilst maximising the power, and

 Its charge control function which restricts the turbine current when the battery voltage

reaches its "set-point" for optimum charging. (This results in an even higher voltage

from the turbine which may cause damage if it has not been allowed for.)

5.7.1. Maximising power

This type of controller can also be used to optimise the speed of your PowerSpout turbine

automatically. It will work through a range of relatively high input voltages from the turbine

and choose the best operating voltage to give maximum power. This will coincide with the

voltage at which the turbine is running at its best speed for the water pressure at that time.

This is useful when commissioning the turbine as it avoids the need to dismantle and modify

the alternator. It can be a "life-saver" if the original head measurement was incorrect. It also

helps to maximise the output under changing conditions of battery voltage and water

pressure.

5.7.2. Higher cables voltages

The MPPT function has several advantages. Not only will the controller optimise the turbine

speed for us (as described above) but it will also allow us to use a higher voltage turbine.

This reduces the current in the long cable from the turbine to the battery. Charging a 12-volt

battery with a turbine at a distance is likely to incur a very high cable cost or a lot of energy

will be lost in heating up the cable. Even with a 48-volt battery the cable can be a significant

part of the installation budget. Using an MPPT device allows us to work at hundreds of volts,

and slashes the cost of the transmission cable.

5.7.3. Compatibility issues

Open circuit voltage (Voc) is relatively high in wind and hydro systems compared with PV, so

the controller often needs protection from over-voltage. This can be provided using a

"voltage clamp" but is not always needed, if you are careful in your selection. Different

PowerSpout turbines are available to match the maximum input voltages of common MPPT

devices and local wiring rules.