# Using two identical 115V input transformers on 230V mains

Discussion in 'The Projects Forum' started by Markus Juhani Leinonen, Mar 6, 2016.

1. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
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0
Hey, I found four ringcore transformers in trash bin. Theres 2 pairs of identical transformers with same specs. Only problem is that the primary voltage on them is marked at 115V and I happen to live in a country where the mains voltage is 230V, so my question is would two of these function as they should if their primary wires would be connected in series, since 230 / 2 = 115?

Apr 5, 2008
15,802
2,388
Hello,

It will ONLY work when the load on each transformer is exactly the same.
When the loads are not the same, the voltage balance will be wrong.

Bertus

3. ### crutschow Expert

Mar 14, 2008
13,501
3,374
Only if their identical outputs are also put in series or parallel so that each transformer provides the same output current into the transformer load.

4. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
0
Okay thanks, I must try this out, I assume the power handling versus using only one, will double or atleast increase abit aswell?

5. ### crutschow Expert

Mar 14, 2008
13,501
3,374
The maximum output power will be twice that of one transformer.
If you connect the outputs in series, then the current will be the same as one transformer with twice the voltage.
If you connect the outputs in parallel then the output current will be double but the voltage will be the same as one transformer.
Note that if you connect the outputs in parallel, be sure and observe proper polarity as connecting them with the incorrect polarity will short the outputs and burn out the transformers.
To check polarity if not labeled, connect one lead from each transformer together and measure the AC voltage between the other two leads.
If the polarity is correct, it should be a low voltage, much less than the voltage across one winding.

6. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
0

Okay, these transformers are pretty complicated, the total wattage is marked as 160W and they have two different output voltages, two of both but, with different wattage, marked like this: GREEN-VIOLET 10V 25W/BLUE-GREY 10V 45W, YELLOW-ORANGE 18V 25W/RED-WHITE 18V 70W... I assume the power must be AC though theres only two wires for each different output...

7. ### crutschow Expert

Mar 14, 2008
13,501
3,374
It is an AC output from the windings.
Each transformer output only has two wires. Why do you think there would be more?

8. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
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I have only seen ringcore transformers with only one voltage, which have four wires for it so far :FF

So If I want to test these tomorrow with two identical fans I I connect the 10V output wirings in parellal with them but what should I do with the other many wires? I quess I need to connect the current trough receiters also?

Last edited: Mar 6, 2016
9. ### crutschow Expert

Mar 14, 2008
13,501
3,374
No need to.
Just leave any unused windings unconnected, the same as you would with a single transformer.

10. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
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So no need for receiters? is this true since I will be using computer fans with 12V DC marked on em, or did you mean on the unused wiring?

11. ### hrs Member

Jun 13, 2014
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7
I've read somewhere that transformers for 50Hz mains can be used on 60Hz mains, but transformers for 60Hz mains cannot be used on 50Hz mains.

12. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
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There's marking: 1-phase 50 - 60 Hz on these.

Jul 18, 2013
10,851
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If Toroidal type there should be no problem.
Max.

14. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
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When I said receiters on the earlier posts, I meant rectifiers, sorry for the english

15. ### #12 Expert

Nov 30, 2010
16,702
7,336
Using rectifiers to make DC is a completely different subject. We started here with, "Two identical transformers, can they work together?"
Yes, if you do it right.
Next question: "Can I make DC out of this?"
Yes, if you do it right.
Most simple DC motors will work without rectifiers. If they are internally converted to a switched frequency drive like a computer fan, they need DC.
Know this: When you add rectifiers and a capacitor to make DC, the DC voltage will be 1.4 times the AC voltage.
If you want to arrive at 12 VDC, you need to start with 9.5 volts AC.

Last edited: Mar 6, 2016
16. ### Markus Juhani Leinonen Thread Starter New Member

Mar 6, 2016
15
0
According to my calculations 9.5 x 1.4 makes 13,3. 8.57 would be the right number to get 12 when multiplied with 1.4

17. ### crutschow Expert

Mar 14, 2008
13,501
3,374
You neglected the rectifier voltage drop in your calculations.
A normal bridge rectifier will subtract about 1.5V from the peak, so that would give a required AC voltage of (12+1.5) / 1.4 = 9.6Vac (or 9.5Vac as #12 noted).
The 10Vac output should work fine for powering the 12V fan from a bridge rectifier and filter.

#12 likes this.
18. ### crutschow Expert

Mar 14, 2008
13,501
3,374
I meant the unused outputs don't need any connections.

19. ### KeepItSimpleStupid Well-Known Member

Mar 4, 2014
1,276
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I'm having trouble, so the OP/TS has to be having trouble.

My take, anyway:

Multiple secondary phasing:

Connect 2 secondaries in series. Connect the primary. They will either add or subtract.

e.g.

1 S1 2 3 S2 4
So, say between 1 & 2 you have 6V and between 3 and 4 you have 6V. If connected in series, then you will either have ~0V or 12 VAC.
When it's 12 VAC, pins 1 and 3 you can call it the DOT side.

Now, since your transformers are identical, you can connect them in series. The wire colors would indicate polarity,

In any event, if the primaries are in series, then connect the secondary from one xformer + the secondary of the other.

Green(1) + VIOLET (1) *connect* GREEN(2) + VIOLET(2)

If you don't get 20 V between (Green(1) and VIOLET(2) then reverse one of the primaries. You should get 20 or nearly zero.

So, you can arbitrarily mark say green with a dot. Mark the primaries in the same way, except start at the known 0V side (Your neutral) as the first dot.

Now, you safely connect the secondaries in parallel. If your still unsure, temporarily fuse each secondary.

20. ### atferrari AAC Fanatic!

Jan 6, 2004
2,666
784
Sorry, can simple schematics be used to discuss this?