Installation manual

Installers must put a large sign by the hot water tank that says “Do not drain

this tank without first turning off the hot water element in the power shed at the

location indicated”. In the power shed put a label that says “Before draining

the hot water system turn off this breaker”. If you have a PWM controller you

will also need a note to “turn off the hydro turbine before draining this tank”.

5.9.1. Common water elements 12/24/48V

A quick search of Ebay located the following elements all with 1” BSP/NPT threads:

 12V 200W

 12V 600W

 24V 400W

 24V 600W

 48V 1000W

5.9.2. Common water elements 120/240V

In some colder countries cars/trucks have block heaters to prevent the engine block from

freezing. These are normally in the 400-1000W range at 120 V and make excellent small

water heaters.

There are also 120V and 240V water elements made for motor home hot water tanks. These

are typically 1500W.

Then there are the larger 2000-4000W elements at 120 and 240V made for domestic

homes. These are rarely used as they are too large.

5.10. Diversion Load: Air-Resistive Coil

Where hot water is not required or if a secondary controller is fitted

as backup, air resistive elements should be used.

5.10.1. Common air elements 12/24/48 V

Air elements can be easily made from stainless steel wire, a baking

tray and a cooling rack as shown.

These can be made to suit your specific requirements.

Whatever diversion element you decide to use make sure it is robust, reliable and commonly

available.

Large wire wound resistors are also available from electronic

component suppliers. Such resistors (1kW 0.8 Ohm for example)

are well suited to 12/24/48 VDC applications when connected in

series or parallel.

Find the maximum voltage of the resistor as follows. Divide the

Watts by the Ohms, and take the square root of the answer.

1000W/0.8R = 1250 and the square root is 35VDC. These resistors

will work in parallel for diverting 12 or 24V systems but you need to

connect them in series for 48V batteries or they will be overloaded.

A 24V system will divert power at about 28VDC and the current in one resistor will be V/R =

28/.8 = 35A maximum (depending on the PWM duty cycle of the diversion load controller).