boondox
Chief Engineer, RedNeckTech Industries
- Joined
- Mar 1, 2020
- Messages
- 788
Ha! The 16 Crown batteries that I will be replacing shortly weigh around 1000 pounds! So 16 LFP is as light as a feather!
RV DIY battery box: plywood vs acrylic vs FR4 vs something else?
- Thread starter biisty
- Start date
chrisski
Solar Boondocker
- Joined
- Aug 14, 2020
- Messages
- 5,170
Nope I have not; however, when I see a vendor advertising his product outside the corporate section, I feel it’s wise for someone to check on his own whether it’s a reasonable price.so... in other words... you have not bought any
Not even Will Prowse pushes his affiliates and this is his site.
If I do another build, I will use pre-made battery boxes. Plywood and hardware has gotten a bit more expensive over the last year. Something to be said for the time saved also.
Pic below of my steel framed boxes with compression. Lishen 272 cells with overkill bms's. HDPE strips as hold downs on the tops, black hex plywood with phenolic resin coating for the panels. All the compression is basically with captive nuts and grub screws. Materials are pretty cheap, but time consuming to design and build.
Installed in my van:
Installed in my van:
Nice build!
I see you have Blue Systems block fuses on each battery directly on positive terminal - do you have additional Class T fuse down the line after batteries are connectes in parallel?
No, just the terminal fuses. Debated using a class T, but there is very little going on between the battery and lynx distributer (which is where a class T would make the most sense). If something went wrong on that stretch, I've got the mrbf terminal fuses and also the battery BMS short detection that offer layers of protection. The terminal fuses do have the possibility of blowing to a closed state, but I've still got the BMS protection and I thought it was a reasonable trade off to allow individual fusing internal to the batteries without the complexity/cost of individual class t's. You can get crazy trying to protect for every situation, my general approach is to eliminate complexity (points of failure) where possible and focus on the highest risk areas. There are other compromises in my system for sure.
^^Analyzed and decided.
I would have utilized a ANL block at the battery, but lots of clamoring here about a class-T. Being an electrical dunce, I followed along.
Then, does it go before or after the master cutoff...EVERYTHING I could find said before. Then someone comes along and says it's supposed to come after.
I would have utilized a ANL block at the battery, but lots of clamoring here about a class-T. Being an electrical dunce, I followed along.
Then, does it go before or after the master cutoff...EVERYTHING I could find said before. Then someone comes along and says it's supposed to come after.
You can make make the case to fuse almost every component and every wire at both ends if you think about every possible mode of failure. There are things you absolutely should do, things you absolutely shouldn't do, and a bunch of opinions and judgement calls in between. Also, remember that every point that you add a fuse or breaker is another point of possible failure. Fuses/breakers do great at protecting against short circuits, but they can also result in increased risk of a high resistance situations (more lugs and connections). Heating/burning wires probably happen more through resistance than short circuits, the fuse often doesn't blow unless the wire cover completely melts off and shorts against something. I'm not saying fuses are bad, just saying they don't remove all wiring risk and can actually increase risk in some cases.
How did you attach the sides to the bottom?
Pilot drilled and used #6 x 2” construction screw with glue. The pilot holes were drilled on a horizontal boring machine for a nice straight hole. Baltic Birch is very strong and the 1/2” that I use has 9 plys.
Has anyone used fiberglass to add a little compression to the cells? Start with the cells at 50% charge, wrap in a few layers of fiberglass, let it harden and then recharge. Not as fancy as the spring compression options, but it should keep the cells from swelling and limit movement. Would heat be an issue in this case?
Adding to the plywood crowd here. Building a 2p4s battery out of 230AHr cells, and the overall container will be made out of marine ply (it was the easiest to cut to the shape of the boat's hull, then epoxy down). The cells themselves will be in a fixture made from HDPE cutting boards (end caps) stainless threaded rod, and thin HDPE flexible cutting sheets between the pairs of cells for extra electrical insulation. The whole thing will then be covered in plexiglass to protect the battery tops/terminals.
Building a 2p4s battery out of 230AHr cells, and the overall container will be made out of marine ply (it was the easiest to cut to the shape of the boat's hull, then epoxy down). The cells themselves will be in a fixture made from HDPE cutting boards (end caps) stainless threaded rod, and thin HDPE flexible cutting sheets between the pairs of cells for extra electrical insulation. The whole thing will then be covered in plexiglass to protect the battery tops/terminals.What thickness are you using for the end caps? Any links for where you got your sheets?Adding to the plywood crowd here.
I think it's 3/8" HDPE for the end caps. My boat partner's girlfriend picked up a couple of cheap HDPE cutting boards at Costco that we used to fabricate them. That said, the end caps aren't taking the whole strain. We're using aluminum angle iron to actually apply the force from the threaded rods. Once we have it completely built I'll take some pictures and post it.
You're not worried about the terminal fuses with regard to vibrations, given that they extend quite a bit from the terminal screw itself? Are these m6 or m8 terminal screws?
As for the rest: they sure look good.
The issue boils down to the insanely low internal resistance of many LiFePO4 batteries, and the Amp Interrupting Capacity of the fuse in question. If a wrench gets dropped across the bus bars, what happens?
For a moment, at least, you have a dead short. A battery pack like the 430AHr, 2p4s I’m building could temporarily drive upwards of 12,000A through the short. The only reasonably available fuse that can stop that is a Class T. With other fuses (MEGA, AMI, there’sa reasonable chance that when the fuse blows the resulting arc will continue to conduct through the plasma channel.
So, as such, you always need to select the proper fuse based on the design.
if a wrench dropped across the bus bars, a fuse further down the line won't help you
Yes, which is why my Class T is directly connected to the battery, on as short of a cable as was practical. The bus bars, and other gear, are downstream of the fuse.if a wrench dropped across the bus bars, a fuse further down the line won't help you
Sorry, I have no idea what this means. Can you post a picture?
I think he meant the bus bars connecting the cells together.
Ahh, I think we're confused about which bus bars we're talking about. I'm referring to system bus bars that the battery, and other loads, are connected to, rather than bus bars used to inter-connect the cells in the battery.
