[edit]Busbar Discussion, Please advise on my setup.

[Robert T]

I'm installing a 12v Quattro II 3000 with 4 12v LiFePo4 460Ah Epoch Essential batteries (200A continuous, 400A peak) in parallel. I'm planning on putting 250Amp MRBF fuses on each battery terminal. Based on Epoch's recommendations I'm going to use the busbar method using a Victron Lynx Power In, so now I'll have an additional blade fuse on each battery inside the Power In. Then I'm going to put a 400A T-Fuse (Blue Sea) for the AIC rating between the Power In and the Lynx Distributor.

Does this setup sound appropriate and maximally safe? Please advise.

I did do several MRBF and T-fuse searches and read a lot of good threads that confirmed that a MRBF on each battery and a T-Fuse on all 4 was a good idea but I couldn't find much info on combining them with the Lynx Power In, thank you!

 

[robbob2112]

Each fuse is at least 2 more connections, maybe 4 depending on the holder.

So, yes it can be to many in the end... but if they are all torqued correctly and you use no-ox-id special A on all contact surfaces the only issue is the wattage lost as current passes through them.

Were it me I would skip the Lynx and just use a pure copper bus bar with the appropriate number of studs...

These are the cheapest red/black with lots of studs... you can also get good ones from amazon by pike industries... the main thing is look for pure copper... if it doesn't say it is, then it is brass.

600A 12 Stud Busbars | Red & Black Kit

Manage high-current electrical connections efficiently with the 600A 12 Stud Busbars in a Red & Black Kit, ensuring organized and reliable power distribution in your electrical setup.

signaturesolar.com

 

[Robert T]

Exactly the information I was looking for! I had an itching suspicion the back of my mind that I should drop the Lynx and just do busbars, thank you!

 

[robbob2112]

One more note, speedymetals has 1/4 x 4 and 5 inch wide bar stock on sale for half price if you want to make your own. Raw stock, standoff, drill the holes and put bolts through from the bottom... you can nickle plate at home for around $20 in materials and a dc power supply.

Speedy Metals 1/4" x 4" 110 Copper Flat

Buy 110 Copper Flat from Speedy Metals, America's favorite online metal store with unsurpassed service, highest quality and best selection.

www.speedymetals.com

 

[Robert T]

I'm reluctant to make my own busbars because this is a mobile application and my lack of experience. I'm going to need 5 studs, my first choice would probably be the BEP Marinco 650A busbar, they seem to make really good products and I'm using their T fuse holder and master switch already, however I'm not happy about the price which seems overpriced ($100) and I'd need 2, $200 seems overpriced when the Power In was 140...

So I'm looking for cheaper option that very high quality, I discovered Daier which seems to make pretty solid products, considering this 400A solid copper busbar that goes for about $55 for both positive and negative, it has one more lug than I need but that doesn't matter. I'm a little worried that my lugs won't fit due to how tightly packed the lugs are.

400 Amp Solid Copper Busbar with 6×5/16" (M8) Stud Terminals

Upgrade your high-current system with this heavy-duty 400A solid copper busbar (8mm thick), featuring six 5/16" terminals and a protective cover for safe, reliable power distribution.

www.daierswitches.com

I just discovered that Epoch makes what looks like a pretty good busbar, I'm not sure the amp rating or the lug size, I'll have to message Epoch.

Parallel Busbar

www.epochbatteries.com

Finally, I'm considering going back to my original plan which was just linking all the batteries together in parallel using the halfway method, without MRBF fuses and just the T for all 4 batteries, which I discussed here:

R

Thread 'Halfway Parallel Wiring Method'

Dec 13, 2024

My first post! I hope this is appropriate for this forum, I considered using Beginner Corner, apologies if it should have been there.

I'm building a lifepo4 12v battery bank out of 4 Epoch 460Ah Essential batteries (powering a Quattro). I've read the options in Wiring Unlimited, searched the forums, and watched Will's videos on wiring configurations. And I'm still unclear on which method is I should use. It "sounds" like busbars is the technically the best but everyone seems to just use the Diagonal method for simplicity? So far I'm planning on using the Halfway configuration, using 4/0...

• Robert T
• Replies: 5
• Forum: General Battery Discussion

Open to further advice also

 

[robbob2112]

The epoch bar doesn't say what it is made from so I would ask before buying. The eaier bars look good to me. Bep makes good stuff, but they are pricey for what they are.

I would buy the eaier from the ones you listed.

As far as experince making bus bars - there is really nothing to it... but most don't want to DIY them.... For mobile application it is probably simpler to stick with pre-made.

The 1/4" x 4" copper bar is good to 1250amps.... so if you ordered 2 pieces 2 inches wide you could drill and tap them... there are nylon standoffs ... but then you would have to make a cover....

 

[LakeHouse]

it has one more lug than I need but that doesn't matter.

There's no downside to extra connections on your bus bar. You will find a use for it, probably sooner than you think. And then soon after that you'll wish you had one more.

 

[robbob2112]

I have to almost agree - the downside can be size when you are installing in confined space.

 

[Drizzt321]

There's no downside to extra connections on your bus bar. You will find a use for it, probably sooner than you think. And then soon after that you'll wish you had one more.

Totally agreed with this. One extra spot, unless you literally can't fit it, is what I'd consider a bonus.

And avoid ANY Amazon bus bars for high current stuff like this. There are some on Amazon that look like the the Daiers one, but are likely not pure copper underneath the nickel.

If I understand right, you're doing a MRBF at each battery, and then after the Lynx Power In bus bars, a Class-T between it and the rest of the system?

I suspect in a dead short situation you'll have the MRBFs pop before the Class-T, which means the Class-T won't do anything. Although I suppose can't hurt to have a backup in case one of the MRBFs fail and keeps arcing, the Class-T will then blow.

Isn't the usual recommendation just a MRBF/Class-T at each battery, and then a disconnect between the combined batteries and the rest of the system? I could be wrong, haven't ever done a larger battery setup like this myself before.

 

[Robert T]

Totally agreed with this. One extra spot, unless you literally can't fit it, is what I'd consider a bonus.

And avoid ANY Amazon bus bars for high current stuff like this. There are some on Amazon that look like the the Daiers one, but are likely not pure copper underneath the nickel.

If I understand right, you're doing a MRBF at each battery, and then after the Lynx Power In bus bars, a Class-T between it and the rest of the system?

I suspect in a dead short situation you'll have the MRBFs pop before the Class-T, which means the Class-T won't do anything. Although I suppose can't hurt to have a backup in case one of the MRBFs fail and keeps arcing, the Class-T will then blow.

Isn't the usual recommendation just a MRBF/Class-T at each battery, and then a disconnect between the combined batteries and the rest of the system? I could be wrong, haven't ever done a larger battery setup like this myself before.

Correct me if I'm wrong but I believe the Class-T fuse is required because of the AIC rating, while MRBF fuses have a 10k rating, this could be too little in a worst case scenario. Also Victron recommends a 400A class-t before the Quattro. Perhaps the ideal setup would be a class-t on each battery?

After doing some research on the exact amount of lost wattage due to resistance through the fuses (totally insignificant for my setup, 1-2watts) I have decided to go with the Lynx Power In with a class-t between the Lynx and the Inverter. I may STILL put MRBF fuses on the terminals as well, I haven't decided. The reason why is that I feel like the Power In is the best bet for the busbar and I feel like I "must" have a high AIC class-t on the entire setup. I could just use the Mega fuses on the Power In and the class-t but then I don't have protection on the actual terminals, which I like, so I may add the MRBFs as well.

 

[Rocketman]

Victron now has a Lynx class T bussbar- two slots in with class T’s on them. So you could forgo the MBRF Fuses. Just one more idea.

 

[Robert T]

Victron now has a Lynx class T bussbar- two slots in with class T’s on them. So you could forgo the MBRF Fuses. Just one more idea.

I definitely would have went with the Lynx class-t but it only holds 2 class-t fuses and I have 4 batteries so I would need 2 of them, excellent suggestion though.

 

[Drizzt321]

Correct me if I'm wrong but I believe the Class-T fuse is required because of the AIC rating, while MRBF fuses have a 10k rating, this could be too little in a worst case scenario. Also Victron recommends a 400A class-t before the Quattro. Perhaps the ideal setup would be a class-t on each battery?

After doing some research on the exact amount of lost wattage due to resistance through the fuses (totally insignificant for my setup, 1-2watts) I have decided to go with the Lynx Power In with a class-t between the Lynx and the Inverter. I may STILL put MRBF fuses on the terminals as well, I haven't decided. The reason why is that I feel like the Power In is the best bet for the busbar and I feel like I "must" have a high AIC class-t on the entire setup. I could just use the Mega fuses on the Power In and the class-t but then I don't have protection on the actual terminals, which I like, so I may add the MRBFs as well.

So no Class-T between batteries? Just between Power In (non-fused) and the Inverter? So no fuses on each battery? Bad idea.

I'd use at _least_ MRBF for each battery. A ton better than nothing. And then a Class-T between the Lynx Power In & the rest of the system (not just the Quattro).

You also will definitely want a pre-charge circuit, so you don't pop any fuses due to in-rush current on the Quattro capacitors.

 

[Robert T]

So no Class-T between batteries? Just between Power In (non-fused) and the Inverter? So no fuses on each battery? Bad idea.

I'd use at _least_ MRBF for each battery. A ton better than nothing. And then a Class-T between the Lynx Power In & the rest of the system (not just the Quattro).

You also will definitely want a pre-charge circuit, so you don't pop any fuses due to in-rush current on the Quattro capacitors.

The current choices I am considering are:

10" wire run from the battery to the Lynx Power In busbar, where each battery will have it's only mega fuse then the class-t fuse between the power in and the Lynx distributor. My main power switch will be directly after the class-t and before the Lynx distributor. I think this covers what you mean by the "pre-charge" circuit?

OR, the same as above plus an MRBF fuse on each battery.

In the first scenario each battery is protected by a mega fuse 10" from the terminal, mega fuses have terrible AIC ratings but in the event of catastrophic mega fuse failure the class-t would still protect the rest of the system. Please correct me if I'm wrong but fusing within 10" of the terminals seems technically adequate.

In the second one I protect the 10" of wire from the battery to the power in busbar with the terminal MRBF fuses, the 10k AIC rating of the MRBF fuse would *probably* be enough and the class-t would be backup just in case. The mega fuses in this case become rather pointless as far as I can tell, but they allow me to use the power in busbar, which is worth it to me and it does add some (maybe pointless) redundancy.

Tangent: I'm annoyed the MRBF fuses are M10 and my battery terminals are M8 but as I understand it this technical incompatibility is frequently done without issues. My MRBFs are M10 to M8 (they were provided to me for free) but I've searched and M8 to M8 MRBFs don't seem to exist so...

 

[Drizzt321]

I think this covers what you mean by the "pre-charge" circuit?

Nope, not at all correct. Pre-charge circuit is connecting the inverter to the battery through a very large resistor (both ohms and power dissipation capacity) in order to allow only a relatively tiny bit of current through to charge up the capacitors. Because capacitors, when near empty, can sink tremendous amounts of currently extremely fast they can pop fuses or cause battery damage or LFP BMSes to shut off.

I think this link is the general explanation/concept and one way to build a shutoff with a pre-charge circuit as part of it.

Inverter Disconnect Switch with Precharge

Jun 4, 2020

Inverter Disconnect with Precharge

• FilterGuy
• Inverter's

MRBF fuses are better than MEGA AFAIK, so I'd go for MRBF fuses. And since your fuses on each battery will be lower than the Class-T, those are more likely (in general) to probably pop first. And the Lynx Distributor is the one with MEGA fuses, the Lynx Power In is just the bus-bars. Although with some nuts and bolts you can effectively turn it into a Distributor without fuse monitoring.

Distributor (with fuses) https://www.victronenergy.com/dc-distribution-systems/lynx-distributor
Power In (no fuses) https://www.victronenergy.com/dc-distribution-systems/lynx-power-in

As for M8 -> M10 MRBF holder, you probably could get a short chunk of pure copper, drill an M8 hole, and then an M10 hole, and mount to your terminal and then the MRBF to the M10 on the copper. Not sure the thickness/size you should get, I haven't done this.

You'll also want to check the blow curves and peak current that can be drawn by the Quattro with it's surge, and make sure that the parallel (so 4 batteries, so 1/4 of the total) can be handled by the MRBF on each battery. So the blow curve/time on a 400A Class-T, make sure the total of 4x of the MRBF you choose closely matches that blow time for the same total % overage.

https://diysolarforum.com/threads/class-t-fuse-mrbf-on-individual-parallel-batteries-x4.96301/ might also be inspiration for MRBF mounting

 

[LakeHouse]

capacitors, when near empty, can sink tremendous amounts of currently extremely fast they can pop fuses or cause battery damage or LFP BMSes to shut off.

Trip a BMS, yes that's entirely possible and is the reason to use a precharge circuit.
The amount of power involved is not enough to blow a fuse or damage a battery unless there are serious other design flaws in the system, like maybe a drastically undersized fuse.

battery through a very large resistor (both ohms and power dissipation capacity)

The resistor need not be 'very large' in terms of resistance (I use a 15 Ohm resistor), or power dissipation (I use 5W).
I precharge a 3.5kW 48V inverter with that resistor. With a battery at 53V and a 15 Ohm resistor, it would draw just under 200W.
How exactly does a 5W resistor survive 200W, you might wonder? It's only there for a fraction of a second and the current tapers off very rapidly to zero as the capacitors charge. There isn't enough time for any significant heat to build up.

 

[Drizzt321]

How exactly does a 5W resistor survive 200W, you might wonder? It's only there for a fraction of a second and the current tapers off very rapidly to zero as the capacitors charge. There isn't enough time for any significant heat to build up.

One thing to note is that without this resistor, it otherwise is SIGNIFICANTLY higher current than with a resistor, and long enough (several microseconds) to cause issues with BMSes, and potentially with fuses if you aren't quite doing it right. And it's long enough and high enough it actually can, potentially, cause permanent damage to the BMS without doing a pre-charge.

And while it doesn't heat up _too_ much, it the resistor will still heat up quite a bit for the faction of a second, and then tapers off pretty substantially in a second or two which allows the heat to dissipate. Just don't use crazy tiny wiring for the resistor. Like, 24awg is way too small. Not sure, 18 awg should be fine? 14 awg I expect is way more than enough.

 

[HRTKD]

And since your fuses on each battery will be lower than the Class-T, those are more likely (in general) to probably pop first.

Please clarify what you mean by "will be lower". In what? AIC? Amperage?

I can tell you that my 175 amp Class T fuse blew instead of my 80 amp MEGA fuse. Probably because the Class T was a fast blow fuse.

 

[Drizzt321]

Please clarify what you mean by "will be lower". In what? AIC? Amperage?

I can tell you that my 175 amp Class T fuse blew instead of my 80 amp MEGA fuse. Probably because the Class T was a fast blow fuse.

Lower in current rating. So you won't fuse all 4 of the batteries each with a 400a fuse. Probably more like 100-150a for each MRBF.

And that's interesting that your Class-T blew before Mega.

Looking at the Class-T charge (400a from BlueSea)

and MRBF 90, 100, 125, 150a chart from BlueSea

I think at moderate over load (say, 200%) which is ~800a, the MRBF will blow first for a 100a, somewhere around 2.5-3-ish seconds. While the Class-T will take 50-200 seconds to blow.

However, when talking worst case dead short past the Class-T, I think you're right, the Class-T will below in at or under 0.01s, while the MRBF likely won't, even at it's fastest possible bounds, it's approaching, maybe, what the Class-T would do.

So yeah, you're right, most times for dead short/high overcurrent the Class-T will blow first. But on moderate overcurrent, the MRBF will blow first.

Which that level of moderate overcurrent is unlikely to happen, unless he's also got a decent amount of other 12v loads and the Quattro II is outputting is max peak (500W, ~458A https://www.victronenergy.com/upload/documents/Datasheet-Quattro-II-3kVA-2x120V-EN.pdf). So providing the MRBF is ~100a or so, maybe 125a, I think OP is quite safe from blowing any fuses, while protecting really well from a dead short on the system side of the Class-T, and decently protected on each battery before the bus-bars.

Yay! It's fun to have something pointed out to make me think and actually run some numbers and figure out, based on specs, that it backs up the real experience someone has

EDIT: Adding in the MEGA curve

Looks like it'll blow faster than the Class-T at moderate overload (200%), but high current or dead short it has a terrible blow time. Ugh. Absolutely horrible, makes me really never want to work with them.

ANL only seems to be a bit better, but still not all that fast for high current or dead short.

Heck, ATO fuses seems to blow better, from that perspective. Although of course they can't handle that high level of current in general, so not very applicable for moderate or larger system protection.

Unfortunately BlueSea doesn't seem to have a chart for AMI/MIDI fuses

But for MAXI, seems OK, closer in comparison to MRBF, but not as good as Class-T.

 

[HRTKD]

My Class T fuse is from Littelfuse. It is model number JLLN175.XXP. The graph below is from the Littelfuse datasheet. There are different versions of Class T fuse. I don't know if the Blue Seas product is the same as the Littelfuse product.

 

[Drizzt321]

When I visit my trailer I'll have to see the specific brand they sell, might be LF, not sure. But I think the graph is saying similar things, just in different ways.

 

[robbob2112]

My Class T fuse is from Littelfuse. It is model number JLLN175.XXP. The graph below is from the Littelfuse datasheet. There are different versions of Class T fuse. I don't know if the Blue Seas product is the same as the Littelfuse product.

View attachment 286227

Blue sea generally uses Littelfuse for their class T -- I have a half dozen of them and they are all littelfuse or bussman

 

[Robert T]

Nope, not at all correct. Pre-charge circuit is connecting the inverter to the battery through a very large resistor (both ohms and power dissipation capacity) in order to allow only a relatively tiny bit of current through to charge up the capacitors. Because capacitors, when near empty, can sink tremendous amounts of currently extremely fast they can pop fuses or cause battery damage or LFP BMSes to shut off.

I think this link is the general explanation/concept and one way to build a shutoff with a pre-charge circuit as part of it.

Inverter Disconnect Switch with Precharge

Jun 4, 2020

Inverter Disconnect with Precharge

• FilterGuy
• Inverter's

MRBF fuses are better than MEGA AFAIK, so I'd go for MRBF fuses. And since your fuses on each battery will be lower than the Class-T, those are more likely (in general) to probably pop first. And the Lynx Distributor is the one with MEGA fuses, the Lynx Power In is just the bus-bars. Although with some nuts and bolts you can effectively turn it into a Distributor without fuse monitoring.

Distributor (with fuses) https://www.victronenergy.com/dc-distribution-systems/lynx-distributor
Power In (no fuses) https://www.victronenergy.com/dc-distribution-systems/lynx-power-in

As for M8 -> M10 MRBF holder, you probably could get a short chunk of pure copper, drill an M8 hole, and then an M10 hole, and mount to your terminal and then the MRBF to the M10 on the copper. Not sure the thickness/size you should get, I haven't done this.

You'll also want to check the blow curves and peak current that can be drawn by the Quattro with it's surge, and make sure that the parallel (so 4 batteries, so 1/4 of the total) can be handled by the MRBF on each battery. So the blow curve/time on a 400A Class-T, make sure the total of 4x of the MRBF you choose closely matches that blow time for the same total % overage.

https://diysolarforum.com/threads/class-t-fuse-mrbf-on-individual-parallel-batteries-x4.96301/ might also be inspiration for MRBF mounting

I totally get the pre-charge now, great info, thank you!

I don't know why was thinking about mega fuses on the Power In, of course it's just 2 busbars, don't know why I got that confused, MRBFs+Class-T is what I'll be going with!

That MRBF mounting thread is perfect, ordering copper washers now.

 

[HRTKD]

That MRBF mounting thread is perfect, ordering copper washers now.

If you need a copper washer to complete the circuit then something is wrong. All the power flow should be at the mating surface of the busbar and the MRBF mount. If power is flowing through the washer then perhaps there is resistance at the mating surface or too much current is being run through that fuse. That said, if you want copper washers, it won't hurt anything other than your wallet.

 

[Robert T]

If you need a copper washer to complete the circuit then something is wrong. All the power flow should be at the mating surface of the busbar and the MRBF mount. If power is flowing through the washer then perhaps there is resistance at the mating surface or too much current is being run through that fuse. That said, if you want copper washers, it won't hurt anything other than your wallet.

I was going to add the copper washers based on this thread that was linked above:

S

Thread 'Class T fuse + MRBF on individual parallel batteries (x4)?'

Dec 17, 2024

I am upgrading our sailboats housebank from lead-acid to LiFePo4.

New batteries will be 4 x drop in Litime 100ah, group 24,100a BMS, bluetooth versions.

I understand a Class-T fuse is required. I'll be upgrading our old ANL version to a Blue Sea Class T fuse (300amp) in their Blue Sea fuse holder. This is positioned after the batteries are combined in parallel.

My question is regarding before the batteries are in parallel - for the fuse on each individual battery. I have heard a rumor that an MRBF is sufficient for individual LFP batteries in this circumstance. Any insight...

• SailSolar
• Replies: 9
• Forum: Beginners Corner and Safety Check

But I checked and my lugs are wider than I thought and I guess I won't need it.

This thread has been super helpful, thank you everyone for the excellent input!