# How to use center tapped transformer's one connection?

Im trying to build a Battery charge controller described on this link http://www.circuitsgallery.com/2014/01/battery-charge-controller-circuit.html

in the circuit they used a 0-15V/2A Transformer with bridge rectifier, i couldn't find anywhere 0-15V/2A transformer, but i found a center tapped 2*15V / 2A transformer.

so my question is, will i be able to use center tapped transformer's middle wire and one of two wires of output as AC input for above circuit without changing the original circuit?

i meant will this work if i connect like below diagram?

• Yes. the second one is isolated (not connected). Sep 23 '15 at 15:44

You can use a 15-0-15 secondary like this: -

It works slightly better than a non-centre-tapped 15v secondary at producing the correct voltage. A single 15 volt secondary will produce 21.21 volts minus two forward diode drops = ~19.8 volts whereas the split secondary will produce 21.21 volts minus one diode drop = ~20.5 volts.

The other problem you may have relates to load current - the VA rating of the split secondary needs to be twice as much because each half of the winding is only supplying half wave rectified current.

Looking at the circuit you linked, I can't see where the battery-to-be-charged is meant to be connected so I'm guessing (possibly incorrectly) that the so-called "charge controller circuit" is just a control circuit to activate a remote battery charger? If that is true then the transformer VA rating will be fine but please do check.

• Hi, Thanks for the reply. To connect battery author commented on comment section that it needs to connect to 1 & 2 points of potentiometer. Sep 23 '15 at 18:57
• what will happen if i connect like this diagram i.imgur.com/6DJZj3U.png Sep 23 '15 at 19:05
• You are only using one half of the secondary winding so the VA of the transformer is halved however, if the split transformer has twice the VA rating of the unsplit transformer then you'll be fine. Given the current output is the same I suspect it will be OK. Sep 23 '15 at 20:05
• Thank you very much. on the transformer it showing 230V 2A 15Vx2. if i use one half of the secondary winding, this kind of transformer provides 2A current or do i have to use both 15V to get 2A current? Sep 23 '15 at 20:23
• @lasita the power on both sides must be equal. Since P=IV then 230x2=15xI. But this is the theoretical maximum. your secondary transformer windings may not be rated that high. In your case if the battery circuit draws 2A at 15V thats 30 watts. 30÷230 will give you the amps req on the primary side.
– BenG
Sep 23 '15 at 21:02