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trien019 avatar image
trien019 asked

Automatic fuse direction

I am planning out a new home storage installation with battery storage.

Will consist of 3x Multiplus-II (3 phase), 4 Smartsolar MPPT's and LiFePo battery,

At the moment i am defining the fuses. The LiFePo's will get a t-class like fuse each.

I have from previous projects some original Bussmann 187series automatic fuses. Only i am a little confused where and how i could use them.

They have a "batt" side and a "load" side. When i used them in a vehicle, this was easy. However, with the MPPT's, i am a little confused. See also this victron example, in the top right, the bat is connected to the "batt" side and the "load" side is connected to the input of the Orions. Compeletely logical.

When looking at the breakers in the middle of the example. There also the "bat" is connected to the battery, and the "load to the output of the mppt. This is not logical to me, because with this application, the battery effectively is the load, the mppt supplies power to this load.

If the fuses are directional, than the fuse should be connected reversed from the example.

If they are not directional, than they also could be used for the Multiplus? however in no example of Victron is see this. Only for Smartsolar and MPPT


Who has official information about the correct use of these fuses?


extra remark

- Various datasheets (bussmann/eaton) do not state any information about direction of connection.

- With the search function, i was not able to find an answer, only a remark from somebody stating that you should always connect the battery to the "batt" side, without a source of this informaton or a technical reason why.

MPPT SmartSolarfuses
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2 Answers
Justin Cook avatar image
Justin Cook answered ·

The side with the highest potential is always the side connected to the "batt" side when using breakers of this kind, to ensure that the magnetic arc suppression mechanism can function properly when opening the breaker under load. A battery will always have higher potential than a charge source, so battery still goes to "batt" regardless of whether what's on the other side is a load or a charger.

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Fideri avatar image Fideri commented ·

@Justin Cook

You could be right, but my understanding was slightly different. With polarized breakers (as opposed to the more expensive non-polarized type) usually labelled "line" and "load", the line side is the source of the power. The battery is unique in this case because it can be considered a "load" (when it's charging) or a "source" (when it's discharging). The breaker works depending on how you orientate it. In most (but not all) installations, you will give priority to the battery because, potentially, it carries more energy. One is discounting a situation where the chargers are feeding the loads. Fuses and non-polarized breakers avoid these headaches because they are typically bi-directional.

F.

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trien019 avatar image trien019 commented ·
Thanks, that makes very much sense and explains why it is that way in the original Victron drawings.


That means they are indeed bi-directional, what should be, since you can charge and discharge the battery when installed in a car.


This also means that they can be used for the DC side of the Multiplus if the Amperage is matched with the Victron recommended value.

Any reason why Victron doesn't use them in their drawings for the MP-II? They use Mega fuses.

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Fideri avatar image
Fideri answered ·

@Trien019

I couldn't open the link you posted but in general, mega fuses, like most fuses, are bi-directional. These should not be confused with "automatic fuses", a term that can mean different things.

F.

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trien019 avatar image trien019 commented ·

Hope the link works now, else at least the full link is visable now
https://www.victronenergy.nl/upload/documents/MultiPlus-3KW-230VAC-12VDC-600Ah-Li-Lynx-Smart-BMS-&-distributors-Cerbo-GX-touch-generator-MPPT-Orion-Tr-Smarts.pdf

No indeed, the mega is not "automatic fuse" by my definition.

What i mean with automatic fuse is the ones like the Bussman 187 i have, or the version (185 series i think) that is in the drawing in the link.

I find it interesting that de documentation of these fuses do not state what the use limits are regarding direction. There must be a reason Victron does not use them for the MPin the drawings.


Side note:, I just noticed that the breakers i have, state "line" and "load" on them. not "batt" and "load" like the one in the Victron drawing.

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Justin Cook avatar image Justin Cook ♦♦ trien019 commented ·
Surface-mount breakers like the Bussmann 187 or 285 series aren't available in high-enough current handling for most inverter/charger applications. A MultiPlus 12/3000, for instance, should be wired with 4/0 wire (or 2x2/0) and fused at 350-400A, but the highest current-handling ability of the Bussmann 187 breaker is 200A.
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Related Resources

MPPT product page

VictronConnect manual

PWM or MPPT

MPPT calculator

MPPT codes

Fuses & fuse holders Product Page.


Additional resources still need to be added for this topic