diy solar

diy solar

Horsefly's New 160Ah Build

Horsefly

Solar Wizard
Joined
Dec 12, 2020
Messages
1,817
Location
Denver, mostly
Just finished my second LiFePO4 battery build. Actually this one is my fourth one, but two the previous two were not for me and so I didn't have as much latitude for the design.

My previous build (discussed here) is for our mountain cabin, and had lots of emphasis on insulation, heating elements and controls for them, and likely unattended operation for months at a time. That was was a 8S 230Ah battery.

This new one is in part just to have it, but also may be hooked in parallel to the cabin battery for heavy usage periods. It also is 8S, but this one is 160Ah cells that I bought from Jenny Wu @ Docan.

Here's a view of the box from the top on the black / negative side. The box made of 3/4" plywood is 20" (51cm) long and 8.5" (22cm) wide, not counting all the stuff mounted on the outside. All-in it weighs 66 lbs (30kg). I can carry it, but I would rather not make a habit of it.
IMG_20220418_085841364_HDR.jpg

I used the JK BMS this time (B2A8S20P). Thanks to other folks on this forum (especially @upnorthandpersonal) the transition after using JBD on the previous 3 builds was easy.


IMG_20220418_094710850.jpg

Here's the red / positive side of the box, including the fuse and disconnect switch, with a 10 ohm, 25 watt pre-charge resistor on the switch:

IMG_20220418_085906867.jpg
IMG_20220418_094614434_HDR.jpg

Someone else here had suggested using the toolbox liner foam (sorry I don't remember who) so I used that between the cells and on the ends of the pack. On one end I also capped the stack off with a piece of sheet metal, and used four 1/4" x 1" bolts to put just enough compression to keep the cells from shifting around in the box. The bolts are actually not quite finger tight. I'm not a fan of "compression fixtures" so I really just want to restrict movement.

I also topped the box with a 1/8" piece of Lexan to protect the cells from me dropping my wrench across cell terminals.

IMG_20220418_094527976.jpg
IMG_20220418_094547877_HDR.jpg

I put a 175A Anderson connector on to finish it off. I then have the corresponding 175A connectors on my cabin battery box, my bench power supply (for charging), and the small 24V inverter I have here at home.

IMG_20220418_085832280.jpg

All in all I think it turned out well.
 
Looks good! I love seeing peoples' different battery box builds.
Thanks! I don't have the skills that @RayfromTX does in building boxes, so I have to paint them up nice and pretty. ;) Building the box didn't take very long, but painting it and polyurethane over the top took way too long.
 
Last edited:
Looks good. Mine is gonna be an ugly box, I can't seem to make pretty things! Are those DIY bus bars? What size screw did you use for the balance leads?
 
I have a few questions, though.

What made you want to change away from JBD to JK BMS? I've been using the JBD's and I don't have any real strong complaints although I love the lug/bolt connections like are shown on your JK unit.

Do you feel like the black and red binding post/mini bus bar things that you used to attach your anderson connector leads are superior to single post units like the one shown here distribution post single stud.jpg
I've been using the single stud type shown, but mostly because they're cheaper.... IDK if there's really an upside or downside in terms of connection quality.


Also, what kind/brand/rating of disconnect switch is that?
 
Thanks! I don't have the skills that @RayfromTX in building boxes, so I have to paint them up nice and pretty. ;) Building the box didn't take very long, but painting it and polyurethane over the top took way too long.
This looks nice. Congratulations. I'm glad I'm here to get to see it. Keep up the good work!
 
I have a few questions, though.
I might have answers!
What made you want to change away from JBD to JK BMS?
I like the JBD, with the exception of a couple of things. First, because it only has passive balancing I ended up adding a Heltec capacitor-based active balancer to my first three builds. Unfortunately the balancer appears to be on all the time, instead of just balancing near the upper knee of the charge curve. Also, one of the active balancers failed while plugged into my cabin BMS, generating a ton of heat and throwing the cells way out of balance. Not good. The second thing that is a problem with the JBD BMS is the phone app, at least the one on Android. It's a bit quirky.

The JK BMS has active balancing built in, up to 2A in the model I got. You can tell it to only do balancing above a certain voltage, which is perfect. From what I can tell the app is really good.

I will admit though that this is a rapidly changing market, and it may well be that the JK is the "flavor of the month" and that JBD or someone else will leapfrog the JK at some point.
Do you feel like the black and red binding post/mini bus bar things that you used to attach your anderson connector leads are superior to single post units like the one shown here
I actually had several of the two-post and single post versions like you showed. I didn't feel strongly about it one way or the other. I actually picked the two post version thinking I was going to be changing what was connected to the battery, and figured I could just have that just be on one post. Then I decided to buy the Anderson connectors, which made that difference no longer matter.
Also, what kind/brand/rating of disconnect switch is that?
I had to go look at my Amazon history. It was this one: https://www.amazon.com/gp/product/B07HT44MP5 I don't remember how I decided, but this was smaller cells than the other three batteries I built, where I used beefier Perko switches.
 
I appreciate the info! I'm going to look into the JK bms some more; as I said the JBD units are working for me, but I'd like it if they had a better app, better balancing, and more robust terminal/connections for the power leads.
 
I appreciate the info! I'm going to look into the JK bms some more; as I said the JBD units are working for me, but I'd like it if they had a better app, better balancing, and more robust terminal/connections for the power leads.
Just so you know, there are JBD's with the screw terminal lugs. I used these on my previous two builds, available here: https://www.aliexpress.com/item/1005002338673024.html
Screenshot 2022-04-18 150751.jpg

The terminals are threaded for M5 (instead of M6 like the JK), but that's not a big issue. I have leftover M5 hex bolts for you. ;)
 
nice work, looks great! wonderful utilitarian style. dig the connector, t-class fuse and precharge! interesting to see JK BMS in a new build; have read lots of good stuff about that company BMS operation. nice carrying straps, looks easier to carry with two people, hehe.

???
 
Looks great, it looks like you have replaced the original buss bars that are supplied with the batteries.
 
nice work, looks great! wonderful utilitarian style. dig the connector, t-class fuse and precharge! interesting to see JK BMS in a new build; have read lots of good stuff about that company BMS operation. nice carrying straps, looks easier to carry with two people, hehe.

???
Ah, the carrying straps. I knew kinda what I wanted, but didn't know what to look for. I eventually found a general category of "kayak carrying straps" (who knew?), and found lots of choices I liked. As for two people... My wife looked at it and said it looked nice, and when I said it was 66 lbs she basically said "Great! You don't need my help!" and walked away. :oops:
 
Looks great, it looks like you have replaced the original buss bars that are supplied with the batteries.
This works out to be a bit of a strange story. My main cabin battery (my first build) was 230Ah Eve cells. Turns out, they are the same width and thickness as the 160Ah, but taller. So the same bus bars work on both. When I bought the 230Ah cells the bus bars they came with were good 3mm zinc/nickel plated copper, but had oval holes made for M8 bolts. That seemed like too big holes for the little M6 studs. I decided to make my own plated copper bus bars. When I started making this battery, I realized three things: (1) the bus bars from Docan were no good, (2) I wasn't sure I wanted to cut, drill, and plate more homemade bars, and (3) the ones I rejected before suddenly looked more acceptable!

I just had to drill and tap the M4 holes in the middle of them for the sense leads, put my 1/4" aluminum washers under them (which mostly overcame the issue of the larger holes), and rolled with it.
 
I almost forgot to mention the corner protectors shown here. After mostly finishing the build, one of the bottom corners got dented a bit while moving the box around. I got on Amazon again (they love me by the way) and found these little guys. They only provide a little bit of protection, but they make the box look a bit like my grandmother's old cedar chest. Kinda cool.

IMG_20220418_202753353_HDR.jpg
 
Very, Very nice!
Although I thought I heard that the JK-B2A8S20P wasn't able to be used for a 24 volt setup without a DC Booster.
 
Very, Very nice!
Although I thought I heard that the JK-B2A8S20P wasn't able to be used for a 24 volt setup without a DC Booster.
Nope, that was true with many / most of the older JK / Heltec BMS's, but this one runs directly off the 8S battery itself. I think if you want to use any of the current JK BMS's on a 4S 12V battery you would still need a buck converter, but I'm not sure. Supposedly they are coming out with a BMS designed for 4S 12V, which would not require a >12V power source.

It does have an annoying "kick-start" requirement though. To start the BMS when power is first applied, you have to either (1) use the optional little LCD device, and press the button to start, or (2) bypass the LCD button and rig together a resistor and push-button connected to two of the pins where the LCD would connect to the BMS (@upnorthandpersonal figured this one out), or (3) apply a relatively small voltage across the B- to the P- connectors a moment (apparently a 9V battery will do). You only have to do this the first time, or if you ever actually turn off the BMS. I went ahead and bought the LCD with mine (it was cheap), but I may only connect if/when I need to start the BMS.
 
I also forgot to mention that I put four of these little rubber feet on the bottom of the box. They were on Amazon (like I said, Amazon loves me), and were marketed as feet to put under a wooden cutting board.

IMG_20220419_082910627_HDR.jpg
 
Back
Top