Wednesday, May 27, 2020 at 13:17
"I suspected that the white wire/busbar was the negative. Jayco did seem to use white for negative and black for positive whilst Centurion used yellow for positive (sometimes!)"
There is nothing surprising about the wiring colours (or should I say colors) as the device originated in the old US of A. That is part of one of the colour codes used by the Yanks. There were a few other manufacturers over there that made them. They were primarily designed to supply a regulated 12 V supply from the mains. There was provision for a
battery connection with some charging to it incorporated in it. This was only provided for emergency use from the
battery , not the cyclic use that regular off power campers require. You will find a lot of these styles of devices in the imported 5th wheel vans that were popular here a few years back.
In their wisdom, Setec copied the design for their units so I can borrow the functional diagram from one of their handbooks. If you have a multimeter and are competent to use it, this diagram you can give you some ideas for chasing out your problem. I hope you can get something out of what I am saying.
Setec PSU
From what you have said any your pictures, it looks like previous owners have made a right hash of the electrics. Regarding the diode, it normally resides in the PSU case, I don't know why you have one externally. Perhaps the original failed and the replacement would not fit in the case. The diode in the diagram is the arrow pointing to a little bar in the wire from the terminal labelled "DC External Input." In the original wiring, there would have been one cable from the tugs
battery supplying the fridge and the PSU. The diode is there as Alan indicated to prevent the fridge from draining the
battery.
Do you have the new
battery charger handy? If so, I would suggest you junk the Centurion. Your
battery and
battery charger will do everything the Centurion will do for you. Clean up that pak-ah-pu ticket. Perhaps keep its front cover to plug the hole when you remove the rest of it. You will need a new block of fuses to replace those in the Centurion.
Regarding the 12 V to the fridge, leave it unconnected for now. If you connect it to the
battery and run the fridge whilst travelling then the current draw will rob a lot of charge from the
battery. If you connect it to the supply line from the tugs
battery there may be an excessive voltage drop that will mean that the charging system and fridge operation will be lacking.
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