Any know a DIY Tunze safety switch?

csb123 · Jul 12, 2019

Hey folks,

Does anyone know a cheaper alternative for the Tunze safety switch? I’m setting up battery backups for Tunze stream pumps. I need 4 safety switches, but don’t want to shell out $200 for what appears to be a simple device.

Thanks for the input!

Big G · Jul 13, 2019

BornHandy · Jul 14, 2019

Are you talking about the float switch? If so, we use them in the HVAC industry every day.

csb123 · Jul 14, 2019

The safety switch is the device that switches from ac current to 12 v dc current (battery back up) when the power goes out.

George81 · Jul 14, 2019

Sounds like it’s just a relay

Michael Lane · Jul 14, 2019

It's a little more than just a relay. I think it typically involves a mosfet set up in an ideal diode configuration that may switch a relay if primary power is lost. I haven't studied these kinds of devices much, nor have I built them, so I'm just guessing as to how this switch is implemented.

@theatrus or @Roberto_b might have better guesses they could share.

BornHandy · Jul 15, 2019

Good call George 81.

I don't exactly know how the Tunze switch works, but I use relays fairly frequently, and it seems you could do it with a relay that's normally closed for the back-up side, and normally open on the main power side (all in one relay).

Main power closes the relay, and passes power to whatever you need, and when power is lost, the relay reverses position, and closes on the battery back-up side, passing power to wherever you need it. The're inexpensive, and might be worth a look.