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I need some help regarding the transformer in the battery charger unit. The lightning struck my house, and sadly the mobile home was connected to 230V outlet. Among other things that needed to be repaired or replaced in the house I have noticed that my batteries in the mobile home are not chraging.

After quick inspection I have found a fuse than was blown out. I have replaced the fuse but as soon as I connect charger to the 230V outlet the fuse blows out. I guess there is a short circuit in the transformer ? I did quite a lot of project with microcontrolers and stuf like that, but I only know basic principles how transformers work.

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The unit is EBL 264-3 it has 12V logic. (Picture is for the 264-7 model but the specifications are practicly the same)

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So, I guess the transformer is 230V - 12V, why are there 3 output wires ?

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Here are a couple of pictures, as you were interested where the output wires go.

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Marked wires : enter image description here

Two wires (D,E) are going directly to the circuit on the right (I presume D is ground and E is +12). On the board is connected to the bridge rectifier (B40C800). By the looks of it, this is the board that switches things on and off from the control panel (couple of relays and so on). This is probably the power for the realy switching. (B40C800 - output current 0.8A, I guess ? )

The recomended input voltage for B40C800 is 40V. is there anyway I could figure it out how much was the transformers output ?

Picture of the circuit board above the transformer :

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I have removed the transformer from the box :

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I have found the scheme of the battery charger (the resolution is low, but this is directly from the manufacturer's site)

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  • \$\begingroup\$ Can you show us more of where those output wires go? Some systems use two secondaries: one for charging the batteries and one for powering the control electronics. \$\endgroup\$ – DrFriedParts Jul 3 '18 at 8:42
  • \$\begingroup\$ The voltage has been changed from 220 V AC to 230 V many years ago. It is written on the front of the charger. If an overvoltage caused by the lightning found a way to the transformer, the primary winding isolation may be damaged. If there is a short from one winding to another, the transformer should be replaced. Replacing the winding may be done by a "Trafowickler" but will be more expensive than a replacement. \$\endgroup\$ – Uwe Jul 3 '18 at 9:44
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    \$\begingroup\$ There is plenty of testing you can do with a multimeter before powering this on again. I would strongly urge you to probe before you power it on again. Measure the resistance between all combinations of transform pins, and make a table. You can also use the diode test setting to check the diode bridge works as expected. \$\endgroup\$ – Oliver Jul 3 '18 at 15:27
  • \$\begingroup\$ Sorry Oliver but I did not see your post soon enough :(, so I tested it again without anything connected to the secondary coil. The fuse blew instantly... So I presume this means there is something wrong with the primary coil ? And by the way I really appreciate all your help, thank you \$\endgroup\$ – Bob Bobovski Jul 3 '18 at 16:53
  • \$\begingroup\$ The test "I tested it again without anything connected to the secondary coil. The fuse blew instantly." is an indication for a short circuit in the primary winding of the transformer. The short may be caused by an overvoltage induced by the lightning. \$\endgroup\$ – Uwe Jul 3 '18 at 20:36
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As an alternative to Andy's answer, it is also possible that this circuit arrangement is used:

enter image description here

This uses only 2 diodes but needs a transformer with a "centertap" output (the middle connection, which is grounded). You can recognize that centertap by the fact that it has two wires connected to it instead of one like the other two pins.

I think this is more likely what is used as a symmetrical supply isn't needed for 12 V battery chargers.

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  • \$\begingroup\$ Yes, most likely that is the use of three wires. Lookingat photos though, it looks like there are TWO heatsinked 3-pin devices. They are likely thyristors, so I would think they are instead of the diodes in the Bimpelrekkie's schematics. \$\endgroup\$ – EmbeddedGuy Jun 2 at 17:16
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why are there 3 output wires ?

Quite often a split secondary is used like this: -

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This configuration produces plus and minus DC voltages and a mid-point 0 volts.

Regards fixing the charger, I would consider that the transformer to be more likely to have not failed and maybe something like a bridge rectifier (as shown in the four diodes above) to be more vulnerable. Try disconnecting all secondary wires and seeing if the fuse blows.

If it still blows then you can be sure it's the transformer. If it doesn't blow then it might be the rectifier bridge.

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