PowerSwitch

I've a new 450 watt 24V photovoltaic system on a separate controller from my existing 12v system. I'd like to be able to use the 24v system from time to time to time with 12v appliances rather than going through an inverter.

I've a 45amp box for stepping down 24v to 12v - is the maximum amperage calculated on the input only or will the 12v increased amperage mean that I can't use the unit ?

Is there a better, more reliable way of stepping down the 24v ?

What does your current convertor box do, if it's not an invertor?

I suspect a 24v to 12v invertor is going to be inefficient and expensive ....

I wonder if you can use 2 x 12-volt batteries in series to be charged at 24 volts ... but then use them to supply 12-volts when needed ...

It sounds as though you have a 24 volt to 12 volt converter, rated at 45 amps.
Such devices are generally rated by the out put current, so yours should be able to supply an output of 45 amps at 12 volts, or nearly 500 watts.

Two types of stepdown converter exist, some use power transistors and resistors to reduce the voltage, these are very inefficient since the input current is the same as the output current, with about half the input current being wasted.
Better units use a switched mode DC/DC converter, these units are much more efficient, and will have an inpout current appreciable less than the output current.

Remember that many types of stepdown converter are not rated for continual full current use.

Converting from one voltage to another should be avoided as far as possible since it entails losses.

Would it be possible to put the 24v from the cells into the inverter and charge the two 12v batteries from the output ?