diy solar

diy solar

Fuse

Ucatchmydrift

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Hi, im looking for a class t fuse for a 280ah eve 8s 2p lifepo4 diy bank that im building shortly.
I emailed fogstar.co.uk for the short circuit current for the above grade a cells and they said about 20,000 amps, so for me, presumably ill need a fuse with an interrupt capacity of 40,000 amps, which is crazy! , but anyway, they are not cheap, but ive found the following one at a good price, but it doesnt actually say its a class t fuse, but it looks like one, just wondering if you guys think it would be suitable?
Thanks ??

 
Hi, im looking for a class t fuse for a 280ah eve 8s 2p lifepo4 diy bank that im building shortly.
I emailed fogstar.co.uk for the short circuit current for the above grade a cells and they said about 20,000 amps, so for me, presumably ill need a fuse with an interrupt capacity of 40,000 amps, which is crazy! , but anyway, they are not cheap, but ive found the following one at a good price, but it doesnt actually say its a class t fuse, but it looks like one, just wondering if you guys think it would be suitable?
Thanks ??

Tmrf looks like it is a class T(mrf) fuse to me.
 
A proper holder for it is also recommended. Some just try to bolt them to their battery/cable lug.
Amps rating should be 125% of your max current draw. The linked one appears to be 335A - that's quite a lot of current at 24 volts.
 
The short circuit current for a battery is lower than for a cell because of the resistance of the interconnects between the cells.
Also the BMS and master fuse are usually considered part of the battery and also have non-trivial resistance.
BTW you could still have an un-protected short over 1 or more cells so physical security for the battery is a good idea.
 
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A proper holder for it is also recommended. Some just try to bolt them to their battery/cable lug.
Amps rating should be 125% of your max current draw. The linked one appears to be 335A - that's quite a lot of current at 24 volts.
Thanks.. The inverter is capable of 6000w (250amps) for a few seconds, and the bms is capable of 350amps peak also, but i wont be pulling any more than 3000w continuous. So i was thinking maybee even a 400amp fuse to cover the bms?
Whats the main reason for a good fuse holder over bolting to the wires to the fuse directly, placed inside a diy box? And less connections could be better also?
 
The short circuit current for a battery is lower than for a cell because of the resistance of the interconnects between the cells.
Also the BMS and master fuse are usually considered part of the battery and also have non-trivial resistance.
BTW you could still have an un-protected short over 1 or more cells so physical security for the battery is a good idea.
Thanks, im building a box for the cells with a temp controlled heating mat inside also. It will be stored in a metal shed outside with the inverter, so should be pretty safe (famous last words lol)
 
Thanks.. The inverter is capable of 6000w (250amps) for a few seconds, and the bms is capable of 350amps peak also, but i wont be pulling any more than 3000w continuous. So i was thinking maybee even a 400amp fuse to cover the bms?
Whats the main reason for a good fuse holder over bolting to the wires to the fuse directly, placed inside a diy box? And less connections could be better also?
That's a LOT of current. You'll need some heavy wire too.
Fuses aren't built to sustain the flex that wire is - a fuse holder covers that, and is a solid mount for it. Especially for ANL's, I really like the Spartan Power ones I got - used them for all the other fuse locations.

For Class-T, here's how I set mine up:

 
That's a LOT of current. You'll need some heavy wire too.
Fuses aren't built to sustain the flex that wire is - a fuse holder covers that, and is a solid mount for it. Especially for ANL's, I really like the Spartan Power ones I got - used them for all the other fuse locations.

For Class-T, here's how I set mine up:

Nice ?
Yes i agree its alot of current! I have some high quality 35mm2 battery cable doubled up to give 70mm2, so should cope ok unless a short occurs, but then thats what the fuse will be for.

Is the capacity controller on top of your bms part of the bms or a seperate unit? - do you use it to give a more accurate state of charge than the inverter or bms shows? Or maybe just to do a capacity test every so often?

And is that a shunt on the right hand side? - as thats something im considering if i cant get the (jk 200a) bms to show an accurate soc..

Im also considering fuseing each balance wire, im guessing there is no harm in this?

Really enjoying this whole solar system/battery building stuff, is an awsome project ????
 
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Nice ?
Yes i agree its alot of current! I have some high quality 35mm2 battery cable doubled up to give 70mm2, so should cope ok unless a short occurs, but then thats what the fuse will be for.

Is the capacity controller on top of your bms part of the bms or a seperate unit? - do you use it to give a more accurate state of charge than the inverter or bms shows? Or maybe just to do a capacity test every so often?

And is that a shunt on the right hand side? - as thats something im considering if i cant get the (jk 200a) bms to show an accurate soc..

Im also considering fuseing each balance wire, im guessing there is no harm in this?

Really enjoying this whole solar system/battery building stuff, is an awsome project ????

Yes, was a very fun project, a whole power system upgrade for the Winnebago. Started out with wifey, "Can we get something to charge my laptop?" A couple of grand later we can surely charge the laptop. LOL

The digital meter is just that, a charge meter that I have since removed. I had not had experience with the BT apps everything comes with now, and that does a way better job anyway. Plus, where the battery ended up it's hidden anyway. I was also advised that copper lugs on alumium posts was a big no-no, so new primary cables were made with tinned lugs. That's when cleaned up the balance leads and took the meter off.

Yes, a smart-shunt on the right side, a master cut-off switch on the left side. The BT sending unit just above the smart-shunt. I took a chance when the Junctek smart meters were introduced, for a fraction of the cost of a victron, and turned out to work just dandy. Everything got moved from the original entry-step battery tray open to the outside, to indoors under the sofa. There's no acid venting with LFP like there is for flooded lead acid.

This is a 125A JBD (overkill solar) bms. My inverter is 600W, so the most I would possibly see for draw is about 75A. Once everything got hooked up I turned everything on that I could and checked everything with a laser thermometer. Nothing more than ten degrees above ambient. The BMS has a very nice app too, and both ambient and battery-mounted temp sensors.

You don't need to fuse balance wires - they are just sense wires, that's why they're generally about 24 gauge.

A bms is just okay for SOC. The problem is they report such by battery voltage, which can be all over the place, and they don't really coulomb count (although I've heard some say they do). Anyway, a smart meter is going to be WAY more accurate. For $50 or so the Junctek has been phenomenal, and it has a nice BT app as well.

More battery pics, and the smart meter in action. I have 430W of solar on the roof, and another 160W potable I can set out at camp. We only use about 100Ah or so per day/overnight, so this replaced a pair of golf cart lead-acid batteries. I have also replaced the 12V converter-charger with a smart LFP 120VAC charger from Meanwell. There is also a Victron Orion DC-to-DC charger that switches on when the engine runs.







Smart-meter app:

 
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Ahh ok ?. The junctek looks like something i may go for as it will be handy to have an accurate soc so i can compare it to the inverter soc and the bms soc,, then i should be able to set all the settings more accurately, seems like they still sell them at a reasonable price.. How good is the bluetooth reception? (on the junktek) , as i would need it to penetrate through a metal shed wall, about 20 foot to the house, then through the house wall to the living room! - not sure it would reach that far which would be annoying!

Your setup looks a nice neat one ? i would like to build myself a campervan (rv) install one day too, when i can afford it ???

My setup is a small house system, 3kw of 12 panels on workshop and shed roofs, going into house powering a seperate off grid set of sockets in each room. Inverter is an all in one epever 3kw. The solar and wiring side is all done now and up and running all successfully, just the Battery bank to build which will be about 7.2kw 24v, expanding to 14.4kw in the near future..

20221008_133713.jpg
The two old car batteries are just there to test and for me to get used to all the inverter settings, which im pretty confident with now (famous last words).

20221008_133654.jpg
Got a 200amp mccb breaker for the battery bank all ready (ill double up the other leads soon). Ordered the class t fuse last night!

And the jk bms (200a) arrived the other day too ?
IMG-545de30598a05c2f9a870366c3f59445-V.jpg

But like i said, great project ??
 
That's a great way to do off-grid solar. What I plan for the next house - will more than likely move when I retire a year from now, and why I've not opted for a grid-tie system here in so-Cal.

The BT signal on the junctek isn't nearly as good as the JBD bms. The RV parks next to the house, and my phone will reach it inside, thru two walls and a solid core door, but not more than about 15' away. The bms on the other hand, will reach all over the house, at least 30' away.

So I dunno, and not sure about a repeater either, or if there's an extension for either the sending unit to the shunt, or the connection to the meter - IIRC someone asked about that and they said no. There's a couple of threads here on the junctek, and a member that seems to be affiliated with them somehow, is very technically savvy on them.
 
That's a great way to do off-grid solar. What I plan for the next house - will more than likely move when I retire a year from now, and why I've not opted for a grid-tie system here in so-Cal.

The BT signal on the junctek isn't nearly as good as the JBD bms. The RV parks next to the house, and my phone will reach it inside, thru two walls and a solid core door, but not more than about 15' away. The bms on the other hand, will reach all over the house, at least 30' away.

So I dunno, and not sure about a repeater either, or if there's an extension for either the sending unit to the shunt, or the connection to the meter - IIRC someone asked about that and they said no. There's a couple of threads here on the junctek, and a member that seems to be affiliated with them somehow, is very technically savvy on them.
Ok, sounds like the bluetooth might just reach, as being at work atm im just guessing at 20', it may well be more like 10-15', ill check later. But thanks for the advice, i shall dig up some info on this forum about the junctek and others, se what i can find.. Plus, i expect ill find a way being a bit of a tekky geek lol.

Hopefully the jk bms will also have a good range on the bkuetooth. - one thing that was worrying me a bit about the jk bms is the two 7awg wires on each side are a bit of a bottleneck in my system, but after reading another thread on here, it seems that being silicone sleeved with many strands, they should cope with 200amps ok. Still, would have rather added my own thicker cables. I may get the thermometer out on those wires when pulling a hefty load!
 
Hmmm, yeah, my 125A bms said use three times 8-10awg. I would have to look again to be sure, but I think I used two times 4awg. Or maybe it was 6. I even ordered in some colored jacket wire to match the diagram, which provides a little more clarity when hooking everything up. Overkill options their bms with soldered lead wires, or blank, or screw terminals. I chose the latter so I could make up my own leads. At the time I wasn't sure how I was going to configure the pack, nor where the bms would actually go, so lengths were in question. I would have to dig thru my build thread to confirm what I ended up using for lead wire gauge.

The main leads are 2awg - everything is a little oversized for the current it carries to reduce heat from resistance, and voltage drop. When you're making up your own stuff the additional costs for upgrades are marginal.

EDIT: Found it, post 19 here. I was going to use a single 4awg, then thought the better option would be two-times 6awg:

 
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Hmmm, yeah, my 125A bms said use three times 8-10awg. I would have to look again to be sure, but I think I used two times 4awg. Or maybe it was 6. I even ordered in some colored jacket wire to match the diagram, which provides a little more clarity when hooking everything up. Overkill options their bms with soldered lead wires, or blank, or screw terminals. I chose the latter so I could make up my own leads. At the time I wasn't sure how I was going to configure the pack, nor where the bms would actually go, so lengths were in question. I would have to dig thru my build thread to confirm what I ended up using for lead wire gauge.

The main leads are 2awg - everything is a little oversized for the current it carries to reduce heat from resistance, and voltage drop. When you're making up your own stuff the additional costs for upgrades are marginal.

EDIT: Found it, post 19 here. I was going to use a single 4awg, then thought the better option would be two-times 6awg:

Strangely the lower amperage jk bms has bolt holes like your overkill bms, which personally i would have preferred. But i Dont fancy soldering on big cables inside the bms incase i heat up the circuitry too much. So ill see how it goes.
I just had a quick look at your build thread, think ill probably copy how you have the balance leads tapped into the busbars ?. Unless there is enough room on top of the battery posts to put the balance leads with a second nut, which there probably wont be at a guess.
Handy forum this ?
 
I never liked the idea of the balance lead ring terminal being under the nut for the bus bars. It just complicates things there.
Someone here suggested I drill and tap the bus bars, and I didn't really think that was possible because they're so thin. But low and behold, worked out perfectly. I had a couple of spares so one got sacrificed - cut in half and used on the main cable terminals.

The bars they give you with the batteries are two copper layers, tinned, and heat-shrinked together. I'm sure they're adequate for 125A or less - for more current I think I would opt for something else/more. There's a chart somewhere that gives ampacity for copper bar by dimensions. Frankly, for these cells with the aluminum posts, I think aluminum bars would be better than copper. The galvanic corrosion incidence with copper to aluminum is one of the highest on the chart. So tinned at a minimum, and apply no-lox or ox-gard to everything.

I really don't plan to take it apart any time soon, but I supposed it would be worth inspecting and cleaning after a few years. We have a really dry environment here, especially indoors.
 
I never liked the idea of the balance lead ring terminal being under the nut for the bus bars. It just complicates things there.
Someone here suggested I drill and tap the bus bars, and I didn't really think that was possible because they're so thin. But low and behold, worked out perfectly. I had a couple of spares so one got sacrificed - cut in half and used on the main cable terminals.

The bars they give you with the batteries are two copper layers, tinned, and heat-shrinked together. I'm sure they're adequate for 125A or less - for more current I think I would opt for something else/more. There's a chart somewhere that gives ampacity for copper bar by dimensions. Frankly, for these cells with the aluminum posts, I think aluminum bars would be better than copper. The galvanic corrosion incidence with copper to aluminum is one of the highest on the chart. So tinned at a minimum, and apply no-lox or ox-gard to everything.

I really don't plan to take it apart any time soon, but I supposed it would be worth inspecting and cleaning after a few years. We have a really dry environment here, especially indoors.
Lolks like i may be getting slightly different fitments on the cells to yours. Hopefully they will be good quality and handle plenty of current. Having two studs at each end may be a good design with any luck, and hopefully the busbars will be nice and thick too.
Might need some of that ox guard you mention though as it can be pretty damp around here in the winter, and being outside in a metal shed too?
Should be arriving in a week or so i hope ?

Theese are the cells:
 
Very happy with my Eve cells. I’ve done quite a bit of manual balancing at high knee though, even after a perfect top balance pre-assembly.

Seems a common thread for use is to not try to push them past 98%, or about 3.5Vpc. Some even say 3.45Vpc.
 
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