I'm trying to figure out the best way to power my amplifier using either a battery OR a 230V power supply.

The amplifier has a wide input range that'll happily take the ~12V from the battery or the 24V from the power supply, but i'm not really sure about the best way to handle all of it.

What i want is for the power supply to take priority whenever it has power, so that the battery is only used when there's no mains power. Additionally i also have a battery charger that i want to keep the battery topped up when the amp is running on mains power and battery isn't used.

How do i isolate and switch everything properly? Obviously i would like to waste as little power on the whole isolation/switching as possible to save battery power.

Do i just litter the circuit with relays to switch everything?

My devices is the following: J1: 230VAC input jack PS1: 230VAC to 24VDC power supply for the amp PS2: Battery charger for the battery

enter image description here

  • \$\begingroup\$ Diode from battery and diode from supply to load. Highest voltage wins. \$\endgroup\$
    – Russell McMahon
    Jun 6, 2021 at 11:49

1 Answer 1



simulate this circuit – Schematic created using CircuitLab

Figure 1. A 230 V AC relay detects presence of mains power and switches amplifier supply from battery to mains PSU.

The relay does not load the battery circuit at all.

  • \$\begingroup\$ Just to be sure: the reason you have RLY1 twice is just for simplicity in terms of the schematic, right? \$\endgroup\$
    – Jacob K
    Jun 5, 2021 at 13:16
  • \$\begingroup\$ No, it's for clarity rather than use the relay symbol and a rat's nest of wiring. It's the same device. The coil is on the left. The contact operated by the coil is on the right. \$\endgroup\$
    – Transistor
    Jun 5, 2021 at 13:20
  • \$\begingroup\$ Yeah. That's the question i was trying to purvey. But we got there :) \$\endgroup\$
    – Jacob K
    Jun 5, 2021 at 13:23
  • \$\begingroup\$ Good. Wait a while to encourage other useful answers and then accept the best one to indicate that your question is answered. \$\endgroup\$
    – Transistor
    Jun 5, 2021 at 13:24
  • \$\begingroup\$ The amp should be off when turning on AC to avoid contact wear from additional surge current on contact unless rated for this. Ic= CdV/dt or \$\Delta V/ESR\$ also a DPST may be better to isolate CM SMPS charger noise on the common Bat- \$\endgroup\$ Jun 5, 2021 at 13:31

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