Prismatic Battery Thread | Van & RV Living Forum

I'm in the process of accumulating the makings for a 280ah prismatic cell battery. I already have in my possession everything but the cells themselves and possibly a cable or three to connect the finished product to other things. These cells were ordered from Will Prowse's current favorite provider of 280's, and ought to arrive any day now if all goes well. (Which doesn't by any means always happen. This is very much a high-risk purchase.) Since I already have a working watt off-grid system at my home base, I bought this stuff mostly to learn the new (to me) skill of building batteries, something I've never done before. If everything goes well, in addition to gaining experience I hope to end up with a large, useful LiFePO4 battery easily capable of supporting many people's van-life needs all by itself (and probably able to handle significantly more) for about $650 (including a BMS that in theory can safely support a watt inverter off of that one single large battery, though I'll probably never push it that hard and suspect nobody else probably should either). My goal is to try and accomplish this safely, but also without spending a ton of money on specialized tools I'd only need once (like stuff for initial cell-balancing) which would defeat the entire purpose of "going prismatic" in the first place. I haven't done all the research yet, and in the end may well have to break down and buy more tools. It won't break me if that happens. But I'm going to make a serious effort not to.

I've been seeing mentions scattered here and there of building from prismatics as a means of saving serious money for as long as I've been on this forum, but never a lot of details about the nitty-gritty of the process. And triply so from a complete novice's point of view. Will Prowse's videos are generally excellent, and will serve as my primary resource. He's handicapped, however, in that he's not a complete idiot/newbie like I am, and therefore sometimes tends to "talk over" some people's heads without meaning to. (Like my own personal head, as one example.) So... Would anyone be interested in me continuing this thread in order to document my learning process, including possible complete failure and all the enormously stupid mistakes I'm certain to make along the way? It'll be significant extra work, so if no one sees potential benefit there'd be no point. keep us posted please. I have just built a 100 AH LiFePO4 pack for my van to replace the existing Lead acid GC2. I'm actually pretty well versed in this stuff and having some fun learning a bit more about the characteristics of these packs. It's amazing to see them drop down to 3.3 volts per cell or so under high load and then just keep cranking out the amps with nearly a change.

Just as a small short list...I have the 4 module battery pack that was built using cells, each module has 20 cells.
Assembled in series as a 14.6V pack now.

Installed a Victron Orion DC-DC 12vdc 18A converter/charger. Since I had previously had the GC2s I had a 2 gauge run from the alternator, through a solenoid switched manually back to the GC2s, I took that line and brought it in to the DC-DC charger.
Foot note, run a fan on that charger!

Installed a cheapo battery Monitor from China that measures voltage and current through a shunt. Basically same as Victron but much less expensive and good enough for me. 

I've got an moderately inexpensive BMS on the way from Battery hookup. rated 100 amps, has low temp cut off and bluetooth RS485 capable. 

So feel free to ask away. 

Mike R I found out building the battery is the easy part.

The following Is what I learn from trial and error of trying to run a lifepo4 system with solar.
1. The bms I recommend to use with solar is the chargery bms8t, its in 110 dollar range, it uses contactors/relays to shutoff charging/discharging so it can handle as many amps as the contactor can handle. I've had the chargery on my 220ah lifepo4 for the past 2 years running 24/7 and has been very reliable. Using contactors will prevent voltage surges that happened when using the cheaper bms that use mosfets. Voltage surges will destroy any 12 volt devices connected to the battery especially fans and lights.

2. If you plan to charge at high amps, you need active balancers. I use the qnbbm balancers (cost in the 100 dollar range) you can find at the electriccarpartscompany website. Without active balancers the bms will always shutoff early before the battery gets a full charge. Even if you have a good matched cells, they always drift in voltage when they are almost full. The qnbbm balancers can balance at up to 6 amps per cell which means it will keep up when fast charging.

3. Use a coulombmeter to measure the SOC of the battery. I recommend the tk15 (30 dollars) its cheap and does the job.

4. Get a solar controller that can be used with lithium and will not produce surges when the cheaper bms activates. The only one that I seen that actually advertises that it can handle bms activation is the makeskyblue mppt 50 and 60 amp models ( in the 130 dollar range). I bought one but never tested the feature since I use the chargery bms. One other thing the makeskyblue also has is the ability to calibrate the voltage to the controller with the actual voltage that you have on the battery terminals. this feature I tested and works excellent. Every controller I used had voltage drop, so this feature is a must have.



picture of qnbbm active balancers I use

Attachments

• active balancers.jpg

The Mission Statement--
 
I built my first solar power system for a 6x10 cargo trailer, with _much_ help from several members of this forum. (Thanks again!) It was very successful, so much so that I built another larger one for my home base partly using leftover components. (Fiddling with it is currently my favorite pastime.) I've since sold the 6x10 and replaced it with an 8.5x20, but I've had so many difficulties with both the trailer itself and my health that I'm still reluctant to mount expensive panels on it at this time. So my current plan is to build a large battery (as described above) out of Lishen cells to act as a stopgap. On a temporary basis I can recharge it from shore power or generator as needed, or so the theory goes. Plus, as a second-level stopgap, I can deploy ground-panels. Since LiFePO4 batteries don't need to be bought all at nearly the same time, like lead-acids do, I can add more batteries later if I ever feel the need. (I probably will. Not because I'll actually require them, but because I so love playing with this stuff.) My plan is to somehow (exact means still unknown, but likely to include either a hand cart or milk carton or both) physically attach it to a -watt pure-sine inverter I already have on hand, plus a Victron battery charger identical to one I already own and like very much. So, with luck I should end up with a highly-capable "non-solar generator" perfect for supporting travel and other odd jobs that, if I choose, I can add a solar controller to any time I please.

Besides, as stated above, I want to do this for the sheer joy of it. And to learn how.

My next post, in a day or so, should be on component selection-- why I picked what I did. To keep these posts short-- and to kill time as well, since I have at least one component on order that may well not arrive for over a month, I'll probably limit discussion to one buying-choice at a time. Selecting Components-- The Cells, Part 1

(This post's length will easily exceed forum limits, and so will be broken up into multiple pieces.)

Background Information

Do-it-yourself prismatic batteries are sold in the form of individual cells-- the "prisms" that give them their name, though pretty much everyone just calls them "cells". The operating voltages of these cells are defined by chemistry and the laws of physics (this is too complicated to go into here), and is generally quite low. So, in order to obtain a useful voltage-- in this case the correct amount to operate standardized 12-volt items like inverters and car-type plug-in chargers, you have to "stack" multiple cells together into one large battery. (Lead-acid batteries operate on the same basic principle.) I'll go into much more detail on this in future postings, but for now all you need to know is that a set of four prismatic LiFePO4 cells is required to make a functional 12 volt battery. There's no dodging this, period. Because science.

Sizing one's battery is a complex subject worthy of a thread all its own and will not be discussed in detail here. In my case, I chose to go larger than most people would due to the fact that I'm sort of improvising my way along with my trailer, and because I just like this sort of thing to begin with. Besides, the 280ah cells currently available (if they're of good quality, which they at least appear to be but is still uncertain) are a screaming bargain. So I'll suffice it to say that based on what I've read here about other people's setups and a very small amount of personal experience, one single battery of this type will probably handle the needs of most people. It will _not_ support an air conditioner; few setups will. But most people here seem to function well on a lot less effective power storage. Your personal situation may vary, and likely will. Again, battery sizing is _complicated_, and will not be dealt with further here. There are multiple other threads on the issue on this forum. Good ones. Selecting Components-- The Cells, Part 2

The cells are the heart of any battery, and I'm going to go on at great length about them because they're also the most expensive and probably the easiest component to get ripped off on. I know this will irritate some people here, but I've come to trust Will Prowse and his forum.   (I've had good experiences there many times over, almost as often as I have here.) So I frequently checked in there while shopping and researching, and watched Prowse's videos. A few months back people started buying these for about $375 (the price varies over time-- I paid $419 and they've mostly been significantly higher since) for a set of four. Even accounting for the cost of other components, this is roughly _half_ of what the cheapest "drop-in" batteries on the market cost per unit of power storage, and much less than any other non-completely-shady source of "build your own" cells that I've yet found. Prowse made a video about them that I recommend highly. This video is what, after long and hard consideration and deep reluctance to buy from anything even distantly related to AliBaba, eventually sold me. I still don't have these cells in my hands yet-- it's entirely possible I may yet get completely ripped off. But he who will not risk cannot win. One non-obvious but notable risk that needs to be taken into account is that no seems to have firmly established yet whether these are actually "A" or "B" cells. (Prowse calls them "B"'s in his video, but on the forums other expert buyers seem far less certain of this. Even Prowse notes that the terminals on his are unworn and seem never to have been used. While I've been unable to find an exact, precise definition of "A" and "B", "B" cells are often used, with part of their working lifespan consumed. I've been unable to determine if "B" perhaps also means "manufacturing seconds". Caveat Emptor very much applies here. I'm taking a calculated risk.) Because this product is made in China, the details of this product's provenance are murky and uncertain. Nearly all cells are delivering full "A" level capacity when tested, and appear 100% newly manufactured with none of the common indicators of "B" status, like defaced UPC codes and scratched terminals. But at least one buyer of a set of four has received mismatched cells. (Two were of a slightly different color and had different-style UPC codes, clearly from a different manufacturing batch. And matching cells are important-- I'll try to remember to explain why later.) Even these, however, gave him something like 97% of the promised capacity, and he was (given the low price) completely happy with "close enough".

There's a near-identical product on the market, also recommended by Prowse, also made in China by another company, Eve. Supposedly there's little to choose between the Eves and the Lishens I bought, save that the (still less than excellent, see the vid recommended above) terminals are slightly worse. On the day I bought, the Lishens were cheaper as well. So, I chose them over Eve.

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