Tiny House – 12V Only

Tiny House – 12V only

Very small setup for someone who just uses 12V equipment and no fancy AC-inverters.

In a tiny house or camper for example everything could be on 12V, lighting is easy with halogen or LED bulbs, but also a Radio, TV and most things that work from regular car-adapters like notebooks, cell phones or tablets is available.

To get 12V it’s enough to just use one 12V battery or a bank out of more than one. However if a bit more power is required, it’s always good to have a higher voltage. We learned from Ohm’s law that Power = Voltage x Current, so how higher we get the voltage the lower the current is going to be while the power remains the same.

For this setup four 6V/180Ah golf cart batteries are used, so we handle a total of 24V. To get the required 12V, DC-DC converters are used. Three different “Groups” of 12V/20A are made, so all together 720W continues power is possible, more than enough to handle everything.

DC-DC 24-12V 20A
DC-DC converter 24 to 12V / 20A

The DC-DC converters have an efficiency of over 90% and generate very little heat. On full output power of 240W they use approx.  11.2 Amps on the 24V input. A charge controller of 30-35 Amps is sufficient.


The Control Unit:

The Unit is build in a small metal cabinet of 12″ x 12″ x 8″, more than sufficient to house every thing, the charge controller, the circuit breakers, some fuses, the panel measuring meters and the DC-DC converters:

Control unit with charge controller, fuses and DC-DC converters on top
Control unit with charge controller, fuses and DC-DC converters on top

On the picture, taken on a cloudy day we spot that everything is ok, the green light is on, so we have power. The panelmeter in the middle shows the battery capacity and voltage (24.4V). The panelmeter on the left shows the output of the solar panels, they only give 24.6 Volts and charge 2.9 Amps.

After a while the second picture is taken:

The battery guage show all the LED’s in the bar and the voltage went up to 27 Volts, this about the floating charge voltage. The PV panels nog output 29.4 Volts but hardly charge anymore (0.2A) since the batteries are full.

Specs:

This setup contains:

    • 4x 150Wp solar panels
    • 4x 6Volt/180Ah golf cart batteries
    • 1x Charge controller 24V/40A
    • 3 DC circuit breakers
    • 3 DC-DC converters 24V-12V/20A

Some math:

Storage: 24V / 180Ah = 4320Wh, usable 20% (Our reason) a day = 864Wh

Battery charge: approx. 1/12 to 1/8 of the batteries Ah is 15A to 22.5 Amps (on average)

Solar panels output: 4x 150Wp (18.9V/7.9A) = 600Wp (2 parallel series 37.8V / 15.8A)

With a the regular controller approx. 350 to 400 Watts is charged, so it takes about 3 hours of daily sun to have the batteries fully charged again if the 864 Watts is used. A more expensive MPPT controller could charge approx. 540 Watts.


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