Hi guys
Im needing some help,

I'm running a hot water pump from a little 0-12v power transformer and 12v relay; the circuit looks like this:

As you can see the transformer is a single winding type (not centre-tapped)

What I want to do is, use this same transformer and in place of the relay (which has a finite life) use two transistors (2n3055) with resistors, but I dont know how to wire it up. If you can give any help, maybe a circuit diagram it'll be really appreciated. thanks. Paul.

 

You can not make a DC to AC Converter with a relay.

How many Amps does your 230-Volt Pump require ?

What are the specifications of your 12-Volt Battery ?

How many minutes must your Pump operate ?

With your current Electrical knowledge and experience,
You can not build a working DC to AC Converter,
and, even if You could,
it would be far less expensive to just purchase a commercial unit.
.
.
.

 

I agree with the above and additionally a Google of 2N3055 inverter circuits will yield a few dozen circuits including most using a center tapped transformer. You make no mention of your pump current which is important, very important. I read your other thread on the same subject. Next is most circuits you will see output a square wave output, will your pump run on a 50/60 Hz square wave verse a sine wave? Really with the pump current known it will be much easier and simpler to just buy a 12 VDC to 240 VAC inverter and if needed an inverter which outputs a MSW (Modified Sine Wave) or a TSW (True Sine Wave). Making sure the output power exceeds your pump locked rotor current draw by at least 20%.

Just My Take....
Ron