Orion Smart 12/12/30 Fusing

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miksons asked Nov 15, '20

Orion Smart 12/12/30 Fusing

I just purchased a new Orion Tr-Smart 12/12/30 Isolated DC-DC charger to install in my RV. The installation is complete and the unit is operating properly, but I am confused by the fusing recommendation in the manual. It calls for a 60 amp fuse, but the charger is only a 30 amp charger so why are both the input and output rated for a 60 amp fuse. I would have thought that 40 or 45 amps would have been more appropriate.

I asked the vendor about it but they just replied that 60 amp was the maximum size for the fuse and I have never purchased equipment with a fusing requirement where the fuse size was not the minimum fuse size, not the maximum.

Any information would be helpful. Thank you.

Lithium Battery orion-tr smart

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Stefanie (Victron Energy Staff) answered · Nov 17, 2020 at 04:19 PM

Hi @miksons,

the fuse mentioned in the manual is related to the recommended cable gauge (10mm2 according to the manual).
The fuse is not protecting the Orion but the cable. Different cable sizes (and I should also mention length and environment) need different fuses.
You have to make sure to install a fuse appropriate to the cable size and cable size appropriate to the overall power of the device.

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miksons commented · Nov 17, 2020 at 05:03 PM

Hi @stefanie,

First, thank you for taking the time to respond, but your answer leaves me with a question.

The manual specifies different cables gauges for different lengths, up to 5 gauge wire for lengths in excess of 5 meters, but only recommends one fuse size. If the fuse size is based on the gauge why are there not multiple fuse recommendations, one for each specified gauge?

If the distance is short and I am only using 8 gauge wire, why should I be using the same size fuse as if the distance was 6 meters and I am using 5 gauge wire?

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philippe commented · Nov 17, 2020 at 05:10 PM

@Stefanie I want to comment your reply.
The manual states clearly the 60A (12V) to protect the device(s) [ and not the fuses protect your cable ].
The cable gauge is depended on the required current (60A) and the length of the cable (along with the accepted voltage drop, aim not bigger then 2,5%) . So the cable size must be appropriate to requirement of the device just like the the fuse.

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screenshot-2020-11-17-at-174948.png (317.5 KiB)

Stefanie (Victron Energy Staff) ♦♦ philippe commented · Nov 17, 2020 at 05:21 PM

Hi Philippe,

not sure where in the manual it states that the fuse is protecting the device. Maybe you can quote that part please.

However, you're right that the cable gauge must meet power requirements. But the fuse is there to protect the wire in case of big overload or short circuit.
I highly recommend reading Wiring Unlimted

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philippe Stefanie (Victron Energy Staff) ♦♦ commented · Nov 17, 2020 at 06:19 PM

@stefanie A fuse is a protection between the device and the cable. Cable size must be in function of the consumption, the voltage, the allowed voltage drop and the length. This is are principles. As such a cable is not intend to go faulty, but a device can !! Ether you have a short circuit and the fuse blow immediate, or a device goes in overload and not the cable, and then il blows also if it is correctly sized. I graduated as electrician.

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Answer 1 · 2020-11-17T15:43:33Z

philippe answered · Nov 17, 2020 at 03:43 PM

@miksons The specs provided in the manual is 60A. I assume it is based on the Short circuit output current that is 60A.

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miksons commented · Nov 17, 2020 at 05:14 PM

@philippe,

OK, but that leaves me with a couple of questions.

1) Is the intention to shut down any output if an internal short circuit occurs? If so, why 60A and not, say, 50A? Or is there some internal circuitry set for a maximum of 60A?

2) Assuming that is the reason for the 60A on the output side, why is it also 60A on the input side? If the output side opens due to a fuse blowing does not not also interrupt the input because the output falls to 0? Or am I misunderstanding what happens when there is a blown fuse?

Please understand that I am not trying to be difficult. I am only trying to understand.

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philippe miksons commented · Nov 17, 2020 at 06:27 PM

@miksons indeed the intention is to protect the remainder installation, so if the input side goes crazy, the fuse will protect your battery / alternator that provides the input, and if it goes wrong at the other side, the fuse will protect the installation / device beyond the DC/DC charger. This is a configuration example of my RV Bearbendum.pdf

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bearbendum.pdf (996.1 KiB)

Answer 2 · 2020-11-17T23:01:34Z

miksons answered · Nov 17, 2020 at 11:01 PM

@philippe Basically I guess I don't understand why there would be a difference between the short circuit current and what the fuse size would be, but based on both of your responses I will just leave the fuses as they are, 60 A, and stop worrying about it. In any case it is clear that the local company that sold me the 12/12/30 did not know why the fuse size was set as it was and that their response, that it was only the maximum fuse size, was completely off base. Thanks for the information.

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