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OutdoorAcorn avatar image
OutdoorAcorn asked

Isolated Orion-Tr negative wire thickness with both batteries grounded to chassis

Hi,

The starter battery negative terminal is connected to my van's chassis (as per usual) and my leisure battery negative terminal is connected to the chassis via a 20mm2 wire. I have just ordered an Orion-Tr Smart 12/12-18 Isolated DC/DC Charger; I didn't need the isolated version as my batteries are already bonded via the chassis but it was cheaper than the 30A non-isolated version. I will connect the starter and leisure batterie's positive terminals to the Orion-Tr via 20mm2 wire.

My question is, given that the two batteries negative terminals are already connected via 20mm2 wire and the vehicle chassis, can I connect the negative input and output of the Orion-Tr to the chassis/battery negative with thinner wire (say 6mm2 or even 2.5mm2)?

From my limited understanding of electrics, I would think that the Orion-Tr just needs the negative wire to be able to power itself and sense the voltage of the two batteries and the current path will be through the vehicle chassis as that will be lower resistance.

I have attached a Wiring Diagram.jpg for clarity.

Thanks

battery chargingorion-tr smartOrion DC-DC Converters not smartGrounding
wiring-diagram.jpg (58.0 KiB)
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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

As the input and output voltages are similar, the negative wire will carry the diference in current between the two positive cables as well as the internal supply current and for voltage sensing. There will also be some ripple current in this wire from the switching function. Using too thin a wire would allow this ripple current to cause an offset in the voltage measuring function of the unit -so I would use at least 10mm, or use 2 x 6mm, one to each battery to isolate any voltages caused by external currents.

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Hi Mike,

Thanks for your quick reply.

Would it be okay to run 2 x 6mm² cables, one from each negative terminal of the Orion-Tr, both to the chassis/leisure battery negative? I would like to avoid having to run another wire to the starter battery as that would require more wire and drilling another hole in the van.

Alternatively, if I were to use 10mm² cable from the negative output of the Orion-Tr to the chassis/leisure battery negative, would a 6mm² cable between the negative input and the negative output of the Orion-Tr be okay?

Thanks

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