victronitnerd avatar image
victronitnerd asked

Class-T fuse question / Connecting Lynx Class-T Power In to a Lynx Distributor

So I already have 2 Lynx distributors and was planning to wire the multiplus 48/5000 into one of the fused connections followed by 2 MPPT into their own fused connection. Then the second lynx was going to have 1 Pylontech US5000 on each fused connection (4 in total).

However I hadnt planned any battery disconnects / isolators on them (or the multiplus), after further reading up on things it seems like Mega fuses might not be appropriate for the batteries and Class-T fuses should be used. So now I have a couple of options

1. Cut the pylontech cables shorter (2m currently) and terminate each of them into a Class-T fuse holder (and then possibly a disconnect switch), then onward to the Lynx Distributor with the mega fuses.

2. Replace one of the distributors with a lynx Class-T power in and create 2 banks of 2 US5000 batteries (again with or without a disconnect somewhere?)

Option 2 now has an issue of joining the Class-T power in to the distributor as the power in would be M10 and the distributor is M8. Putting the power in on the right would work as the hole is bigger than the M8 screw. But would this create a poor connection / resistance? Or not as long as things are tightened accordingly?

I feel like option 1 is the cleaner solution with more protection but maybe I've overlooked something? Adding battery disconnect switches can only be a good thing (as long as everything is tightened to minimize resistance)?

The same logic will be applied to fusing the mutiplus via a Class-T instead unless this is completley uneccesary as the short circuit current is nothing compared to LifePo4 batteries and the mega fuse will be sufficient.

Multiplus-IIlynx distributormegafuse
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2 Answers
pwfarnell avatar image
pwfarnell answered ·
I am not saying that connecting a busbar with an M10 hole to one with an M8 bolt is correct or not. I am making the observation that many suppliers of modular busbars such as BEP Pro Installer or TBS DCM have 600A connectors with M10 holes which sometimes connect to M8 bolts. They also have slotted holes to allow for some irregular spacing. Blue Sea also supply their battery terminal mounted MRBF fuse holders with only an M10 hole with most battery terminals being M8 or US equivalent.

If you consider a contact area of a 30mm wide busbar with a 30mm overlap onto a second bus bar with an M8 hole you have 900 - 50 = 850mm2 and if it is an M10 hole then the area is 900 - 79 = 822mm2. This is a small difference.

If you do this make sure that the M8 washers are large enough to transfer the clamping force to the outside of the M10 holes.

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victronitnerd avatar image
victronitnerd answered ·

Thanks @pwfarnell that does help give some confidence that option 2 wouldn't be as jacky as it sounded and is being done already. It might also work out cost effective compared to buying 4 Class-T fuse carriers. Would you think battery disconnects for each battery would be a good idea?

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pwfarnell avatar image pwfarnell commented ·
I have no idea on battery disconnects. I would need to know what the effect is of isolating a single battery within a bank of Pylontechs in parallel with comms cables linked. You usually see the Pylontechs connected together with a single fuse / isolator, often being a combined holder.
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victronitnerd avatar image victronitnerd pwfarnell commented ·
Good point, on the disconnects. Maybe best to have 2 x class-t power in's that each of the batteries will go directly to, then those connected to a lynx distributor (which have the MPPT's and inverter connected to).

I am short on space for 2 power in's directly connected to the distributor so my thought is 2 power ins (class-t) connected together via the bus bars, then 1m of 70mm2 cable connecting the power in's to the distributor which I believe should be sufficient for the expected current. This also solves the M8>M10 issue as I can just crimp the right sized lugs on the 70mm2 cable.
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