Two contactors wired as changeover switch

[V_King]

Hello,

I'm a bit lost with contactors and their variety.

I have a small solar setup. The solar charger has a programmable load output of battery voltage, which I want to use as a power for a changeover switch. When the batteries are in good charge state, I want mains power to be powered from the batteries>inverter>AC. But when the batteries discharge would reach pre-set voltage level, the load output from solar charger goes off and I want a changeover switch to swap into mains power.

The batteries nominal is 24V, the mains is 240V / 16A  AC. Is there a simple way to wire two contactors as a changeover switch, with 24v dc control? When I google for contactor wirings, it leads me to industrial applications, with way too much details for my head.

Any advice much appreciated.

Thanks

[Ian.M]

While its theoretically possible to wire two contactors, interlocked via their auxiliary contacts, as a mains changeover switch, its doubtful that it would be possible to do so legally under the UK wiring regs.

If this is a fixed installation, you need a commercially availale automatic transfer switch and a licenced electrician to install it.

[sokoloff]

If this is a consumption device (given the low power, I assume it is), I see two approaches:
1. A simple DPDT relay with break-before-make guarantee by spec.
2. A mains to DC convertor to feed the DC stage before the inverter. At high solar output, you could turn this off, but that only gives you a modest reduction in losses.

1 is way more efficient, 2 is simpler to reason about enough to get to a conclusion of “yeah, that’s safe”. 2 is probably also more durable in terms of likely to keep working for a decade without screwing with it.

If this is a production device (in either sense, meaning not a lab project or intended to feed the mains distribution), I would not feel comfortable at all fiddling with it.

[V_King]

Thanks for the responses. Found the info elsewhere. The thread can be closed.