Allen Jackson

Chandrapal Mehula wrote:Nice build, and thanks for the detailed write-up. A few things from my experience with 4S LiFePO4 boxes of this size that might be worth a look before you close it up:

1. Short-circuit protection. A 314 Ah 4S pack can deliver well over 10,000 A into a dead short, and the BMS MOSFETs will not reliably save you from that. Many breakers and ANL or MRBF fuses are only rated to interrupt around 2 to 6 kA at DC. For the main battery lead, a Class T fuse (rated 20 kA or more) mounted as close to the positive terminal as practical is the usual answer. Size it to protect the wire, not the loads.
2. DC breakers must be DC-rated for the voltage, and polarity-sensitive ones must be wired the right way round. The 60 A breakers on the charge controller inputs are fine, but check the datasheet voltage rating against your PV array's open-circuit voltage in cold weather (Voc rises about 0.3 percent per degree C below 25 C).
3. Cell compression. EVE 314 Ah prismatic cells last noticeably longer with light, even compression (roughly 300 kgf for the pack is the common figure). A rigid fixture or end plates with a thin foam layer is better than loose foam blocks if the box will be carried around.
4. Terminal torque and bus bars. Torque the M6 terminals to the cell maker's spec (around 4 to 6 N·m) and recheck after the first few thermal cycles, since loose terminals are a common source of heat. Use clean, flat bus bars with a bit of anti-oxidant paste, particularly where aluminium meets copper.
5. Charging. Set the charge controllers to about 14.2 to 14.4 V absorption with a short absorption time, float around 13.5 V or off, and temperature compensation turned off for lithium. Don't charge below 0 C unless the BMS has a low-temperature cutoff, because lithium plating is permanent.
6. Cabling in a carried box. Secure the heavy cables so they can't pull on the lugs while you carry it, and use ferrules or properly crimped lugs only.

My position is that the fuse is the item people most often skip, so I'd put that first on your list.

Thanks for the observations and comments.

My box is no where close to being complete, in my view, but the timing of our trip and my outside workload dictated that I went with what I had, and had to make it work for the week, or we would have never made it out to Wheaton Labs, or even out on to our vacation.  It worked well enough to succeed at what we needed it to do, and we made it back home safely with it still running.

- I think I've mentioned a few times in the thread, that I still need to add lots of circuit protection.

- ALL of my breakers used in this build are at least said to be DC-rated, although I don't have any good way to test those claims, so I have to rely upon the labeling and marketing in some cases.

- Voc rating for my PV arrays isn't a big issue in my case, because I'm not anywhere close to pushing the limits - the charge controllers will fail before the breakers do - all of these charge controllers have a 100 Vdc max before they're toasted, and all the breakers that are installed or planned to be, exceed that rating.  I believe my Voc on these arrays was running under 48 Vdc, and that's a margin of safety of over 2x, but it is a very good point to illustrate, because exceeding that limit is a very expensive mistake.

- Cell compression is one of the most misunderstood concepts for prismatic cells.  Yes, compression has been shown in lab testing, to improve longevity, but NOT for the reasons most folks think, and it's NOT cut and dried, nor is it relevant for most folks common uses of these cells.

These cells are made up of a long thin flat ribbon sandwich of layers, that are folded/rolled up into their shape before being placed in the metal can.  This is done under vacuum, to extract as many of the gas bubbles from between the layers as possible, but due to the economics of manufacturing them perfect, vs. making them profitably, they probably DON'T get 100% of the bubbles out before packaging them.

What compression does, and ONLY in the early life-cycles of the cells, is to force more of the trapped gas bubbles to escape to the edges, due to the expansion while under pressure.  The reason why it probably doesn't matter for most folks, is if the cells weren't compressed from the very beginning, by the distributor, the vendor, and EVERYBODY, when testing or matching them up, and then the same compression wasn't followed by every middle-man in the chain prior to being put into service, it won't make a difference any more, to compress them later - the damage from such has already been done, and any additional gas bubbles that were going to be expelled, have already been, and those that weren't, will be cured in place, and they're not going anywhere now.

If the real/ultimate goal, is to increase the longevity of the cells, the longevity gains from limiting the charging voltages to a maximum of 3.5 or 3.45 Vdc/cell will by far, exceed any longevity gains one might be able to achieve by compression.  The trick is to charge slower for longer times, vs charging fast at high voltage, which does more to further cook the cell membranes - remember, these are still 3.2 Vdc cells, and charging them to 3.65 Vdc or charging them to 3.45 Vdc and letting them absorb for an extra hour at that voltage will get them just as charged, and if both were allowed to rest for a day, they'd both be back down to their resting voltage and they'd both be just as charged up/full, but the higher voltage charge will lower the capacity of the cell much faster...

Charge fast, if you have limited time to charge, and deal with the results, but if you have the time, let it simmer on medium?

Check out Andy at the Off Grid Garage YouTube channel, where he has tested many of these common myths and misconceptions with real-world results.



- I always re-torque my terminals, and I only use copper or tin-plated copper bus bars.  Mixing copper and aluminum in power electrics can be done, is more complicated that staying with copper, and not worth the trouble most of the time, in my opinion.

- As explained above, setting absorption to 13.8 or 14 Vdc and letting it stay there for an extended time, will produce superior lifespan, and yield just as much capacity, but for many more years.  All my BMS have temperature compensation and protection to disable charging at or below 0 C.  They even have a heating enable relay contact, so I can turn on battery heating if I connect the battery heaters to said contact, although it's not an issue with this box, because my wife isn't compatible with temperatures that low, and she'll let me know long before a lithium battery problem arises.

-No cables should be pulling on lugs or terminals, whether being carried or not?  BTW, I have and use a hydraulic crimper, but your point is taken...

It occurs to me, that an inexpensive DC to DC boost converter, I can probably do in-vehicle charging just fine.

For example, if I get a 12 Vdc to 24 Vdc boost converter, like this one:  https://www.amazon.com/YRDZXG-19V10A190W-Converter-Regulated-Waterproof/dp/B0CTFJ8CGH

It's rated to supply up to 360 watts of power, and I can plug the high voltage output into a solar controller solar input, and as long as the input is at least 5 volts higher than the battery voltage, the mppt controller will charge from it. For my uses, I only need about 10 - 12 amps to trickle charge while running both my DC refrigerator/freezers, which by the numbers shouldn't use more than 120 watts, so the leftover surplus should top off the battery...

At any rate, the price is much easier to swallow, and I could conceivably use one on each solar controller for only $26/each, vs the nearly $300 for the really good looking Victron (but expensive) charger.

I'm not sure if this fits the theme of permies.com, but it's worth a try, primarily because I believe "Otis" would see value in renewing a piece of furniture, instead of tossing it out and replacing it. It's NOT press wood or particle board, it's a nice butcher block maple, nearly 2 inches thick, so I thought it worth saving.

My baby sister has a table in her kitchen that has a beautiful maple top, but it's unfinished, and she doesn't feel comfortable with her ability to effectively clean it... She's said she will toss it if I can't come up with a solution that she feels like she can reliably clean/sanitize.

All I can come up with that's reliable under her specific use, is the same kind of acrylic/polyurethane coating that they use on commercial bar tops.

I know it's not anywhere close to tung oil or ANY natural finish, but it's very durable and it saved this gorgeous real wood topped table a new lease on life.

First I sanded down the surface (and that's where I have the fewest pics, but a wheel on my shop vac broke, and I took pictures of it on the table - the vac was under warranty and I wanted to file a warranty claim on it).

I put the initial seal coat on, then I had to "tent" the table, to keep the cat off of the table for the 3-5 days recommended.

The table also need to be perfectly level for the next step, so there was lots of shimming with sometimes a sheet of newspaper at a time.

After the first coat had cured, it was sanded again, then I did the "pour" coat, which is where you literally pour a puddle on the middle of the table and encourage the puddle to spread out to the edges. It will end up dripping off the edges eventually, if you get it right (the bottom edge of the table, the trash bags are actually attached to the bottom of the table, so the edge is not covered up and available to be coated.

The product pool is self-leveling, so if you got the surface perfectly level beforehand, it won't drain off, it will puddle, for the most part, although there will still be some messy stuff on the edges to clean up a few days later.

After another week, it's no longer tacky to the touch, and it's safe to remove the tenting/cat guards. The edges were chiseled and sanded and then several more light brush coats were applied to the edges. The instructions say if there's any bubbling or imperfections in the surface, they can be sanded down and more can be applied. I found a few spots I wasn't perfectly happy with, but my sister was so thrilled with the table top, that she wouldn't let me make it "perfect"...

"Badge Bits from Heaven..."

Mike Haasl wrote:This is a badge bit (BB) that is part of the PEP curriculum.  Completing this BB is part of getting the straw badge in Electricity.

In this Badge Bit, you will fix an electrical appliance.  Fridge not working quite right?  Toaster only toasts on one side?  Let's fix that appliance!

There are youtube videos for nearly any type of appliance issue and repair so do some digging to figure out what is wrong, what parts you may need and how to do the job.

To complete this BB, the minimum requirements are:
  - fix a problem with an electrical appliance
  - more complicated that replacing a light bulb
  - must be an electrical issue for this BB

Electrical points earned vary from 1/2 to 4 points
 - the points awarded are up to the certifier based on the challenge of the troubleshooting and the complexity of the repair
 - replacing a heat element is likely to be low on the range
 - replacing circuit boards and motors and rat eaten wires is likely to be high on the range

To show you've completed this Badge Bit, provide proof of the following as pics or video (less than two minutes):
  - the broken appliance before you start your project
  - explanation of what was broken, how you troubleshot it and how you fixed it
  - the parts you bought (if applicable)
  - the parts you replaced (if applicable)
  - the appliance at maximum point of disassembly
  - the appliance reassembled

"Honey, the washing machine isn't filling up with water..."

We recently made a pilgrimage to Wheaton Labs, as SEPPers. The prep for the trip was challenging in many ways, with the least of it being that the washing machine stopped working, the week prior, & I was covered up with work, just trying to get out of town. I did the basic troubleshooting to hopefully ID the problem, but didn't order replacement parts until we were headed back home, so they wouldn't be stuck on the front porch for a week.

Got back home, got mostly recovered from the long drive, and started digging out from the mountain of work that piled up while we were gone, and shortly after, my wife presented me with a box, recently delivered... "Can you please take a look at the washing machine, now? I think this is the part."

OK. The symptoms are no water flowing, when it's on/supposed to be.

First step, make sure the water is on & available at the inlets! (Duh?  I guess they have to say that?)

Next, verify that the inlet screens are not clogged.

If none of those has yielded improvement, take it apart and replace the inlet valve.

Re-assemble and test.

There was water from the hoses, and the inlet screens were pristine.
This is the scariest part of the journey - the manuals and YouTube videos all said to slide a plastic putty knife into the joints to release them.
I literally don't know how much force to apply, and I really don't want to make it broken worse than it already is...
Slowly ramping up the force, and it did open up the top control section. Removing the back screws was comparatively easy.
There's only 2 screws and an electrical connector to remove the part at this point.
Swapping the part, and reassembling was simple and straightforward.

Reconnect the hoses & check for leaks - ok.
Plug it in, and turn it on.
It at least sprays water now, but it's going to need to be leveled again (a bit of a pain).

That's a separate problem...

Mike Haasl wrote:This is a badge bit (BB) that is part of the PEP curriculum.  Completing this BB is part of getting the sand badge in Electricity.

In this Badge Bit, you will label an electrical panel.  Don't you hate it when you're trying to install a garbage disposal in your guest bathroom and you can't figure out which breaker to turn off?  Let's get that panel labeled!

To complete this BB, the minimum requirements are:
  - accurately label an electrical panel

To show you've completed this Badge Bit, provide proof of the following as pics or video (less than two minutes):
   - the poorly labeled panel you're starting with
   - the wonderfully and accurately labeled panel once you're done

I installed all these, and I figure I should probably label them, for anyone who has to follow in my wake, and even better, before I forget which ones are which!

In the installation of the powerwall, I installed to adjacent breaker panels. One is for the supply side of the entire server room, and the other is for the individual branch circuits in the server room, fed by the inverters & battery backup of the powerwall, or directly by the utility/grid, if the interter system is bypassed for maintenance.

I don't think this would count as 2 separate panel-labeling tasks, as the panels are adjacent to each other and the branch circuit panel feeds off of the supply one, either indirectly via the inverters, or directly, when in bypass mode, so I'm submitting them as one BB.

r ransom wrote:

Allen Jackson wrote:Is this the thread I should have posted in for my correction of the BB in question?:
https://permies.com/wiki/140481/pep-electricity/Charge-Carry-lithium-battery-power

There's a technical error in the BB requirements as listed, because the 30 amp RV outlet in question isn't 220 Vac, and even in the YouTube video example presented, Jehu Garcia didn't use a 220 Vac outlet (or an inverter capable of producing 220 Vac).  He did clarify that in the comments later, as someone asked about it.

I've asked the SKIP team to review this.  It's not a fast process, especially on a holiday weekend.

Was there any resolution on this?  I'm working on building one, and I'd like to know how to adjust for compatibility with both the BB requirements and my actual use cases.

At the very least, can the requirements be corrected to remove the "220 volt" part?  That's the part that's both impossible with the original parts used in the example given, and not even accurate to the what the visible components are.

My explanation is here:
https://permies.com/t/320/210060/skills-inherit-property/BB-clarification-thread#3759092

And I have other questions about the same BB - can such a device be made to be modular and break down into smaller components for travel/ease of transport by folk with less physical strength, or does it have to be all in the same container?

If we don't have or plan to ever get an RV that uses a 30 amp travel trailer plug, can we substitute a different 30 amp outlet, or skip it entirely?

Yes, that 4S2P arrangement would work much better and as long as you didn't slam the system very hard, or at least hard enough to go over 200 amps for long, it should work.

Keep in mind, with the battery packs being different, they won't likely all quit at the same time, & as soon as the first one (the weakest one in the group) goes into protection mode, it will immediately shut down that series string, and the overload on the remaining string should shut down that string shortly thereafter.

John Weiland wrote:
As an aside, the weekend's project will be to remove 6 X 6V legacy (=HEAVY!) lead acid batteries from my farm-yard golf cart...one or more seem wonky or underperforming and it's a good time of year to do some testing. In the meantime, I'm going to try replacing them with 3 and 4 LiFePO4 batteries (100Ah each) to provide the stock 36V or alternatively an upped 48V to the system.  Good rumor has it that the better quality carts of yester-year had components built like a tank....hence motors and controllers that can handle the increased voltage to 48V (power draw is the same....just a slight reduction in current).  The one component I did invest in is the solenoid which some say is best to keep at the same voltage as the battery pack.  The experiment:  Can these "non-locomotion" 12V batteries (100 amp BMS) power the cart at either 36V or 48V?  Because of the current demand at 36V, the BMS might be tripped.....but if the potentially 200-250A draw is distributed *equally* across all 3 batteries, it might be okay--especially as start-up and cruising amps range from ~50 - 150A.  It also could be a complete bust....but that's the excitement of experimentation!   Fun!!......

I typed out a detailed reply to this, and it disappeared... Round 2?

The current drawn is exactly equal in all the cells of a series stack, and your BMS shouldn't allow you to abuse your batteries for very long under those conditions.

For that application, you'll be much better off, with something like the 280 Ah cells and a 200 amp BMS.

I'm struggling with the choice to build something to my needs, vs build to the BB requirements...

As I contemplate building a better version of the "Charge and Carry" lithium battery box BB (because having AC available would be really nice), I realize that I can build to the posted minimum requirements, or I can build something that would be truly useful in a field/off grid/camping experience.

The conundrum comes down to weight/capacity. My biggest issue with my DC 12 volt system, is that it's uncomfortably heavy, especially for that cheap plastic toolbox. Unfortunately, my calculations suggest that for camping with family (not solo), I probably want to have 8 KWh of energy stored, for the various electric appliances/cooking apparatus I'd love to have available to use. The DC box is close to 60+ lbs and the weight would more than double if I made a system with double the battery capacity AND also had an inverter, plus all the AC outlets/breakers, etc.

I suspect that a 150 lb box of anything won't qualify for the BB, and it would surely be a challenge to carry or transport too, so I'm contemplating if making it modular would disqualify it for that BB, or worst-case scenario, I buy some more 105 Ah cells, and build a much lower capacity, but lighter box that only had 2560 Wh (2.5 KWh), but weighed less than the 12 DC system...

If I go the modular route, I can wire it so that the BMS power is disabled until both battery modules are connected, and the BMS automatically measures the resistance of the balancing wires, so I don't have to worry about those either. The AC side would also have to be a separate module too. At what point does it stop qualifying for the BB?

If I just build with 105 Ah cells, I'll need to pony up another wad of cash, to get more of those, because I only have 4 right now, but I expect I'll have to find a new use for them after the BB is completed, because I don't think I'm willing to live with a 2.5 KWh energy cap - isn't that why hand trucks exist???

I'll try asking for guidance in the BB clarification thread, and see where that goes, even though they have not answered my last question about the same BB - where I'd pointed out that the 220 volt requirement was an error - none of the examples they gave can support or provide 220 VAC. (It's a 120 Vac 30 amp RV outlet, NOT a 220 volt outlet)