Victron charge controllers for lifepo4

[PNjunction]

RECHARGE time!

This time, I'm going to take it to 14.1v CV and do another discharge to compare to the previous charge at 13.8v with absorb.

Charge current is 0.3C, or in my case with the 40ah battery, 12A from the adjustable supply and current allowed to drop to C/20 (2A) being conservative.

Within a very short amount of time, all cells reached 3.45v and stayed there, with a current of approx 9A during the whole part of the flat part of the charge curve.

*** NOTE *** This procedure, of hitting your cells with the manufacturer's normal standard preferred charge current, may help identify what your cells think are the voltages it needs to actually recharge to full, given enough time. Either that, or identify problems early on! The cells are telling you something.

Huh? I'll bet you bottom dollar that had this been an A123 battery bank, that if hit with a decent amount of current, the cells would actually rise to 3.5V (if you set your CV to actually go that high per cell) instead of 3.45 like most other prismatics, like Winston, CALB, GBS and other do. A123 is different.

This might become part of my PM procedure. The cells are talking, so I'm going to listen and look for deviations from this baseline of cell voltages and current during the flat part of the curve.
***

At the very end of charge, here is the data:

VOLTAGE UNDER CHARGE 14.1v prior to termination (max delta .027v)

Total battery voltage:
3.517v
3.544
3.521
3.537

AFTER ONE HOUR RESTing voltages: (not enough for absolute values, but enough for me to see a trend) (max delta .006v)

3.390v
3.385
3.391
3.389

It will take a few days for me to get around to a discharge test to completion.

INTERESTING NOTE:
ALL my voltages are measured with the Fluke 87V at the battery / cell terminals. I do NOT rely solely upon anything else, including that of my supply!

For instance, once the cells all reached 3.45v and stayed there during the flat part of the charge curve, (13.8v at the battery terminals) guess what was showing on my supply? 14.1v for hours! WRONG. If one went by that only, they might make some errant conclusions. Only at the very end did the voltages between the supply display and that of my Fluke match. Cabling is short and beefy too!

Moral: ALWAYS vet the accuracy or behavior of your other gear with something like a reputable voltmeter directly at the terminals. At least once. They may or may not track, depending on a variety of things and you can either compensate, calibrate, or accept the difference if you know what is *really* happening at the battery terminals.

[PNjunction]

Discharge test over at 14.1v / cv absorb time to C/100. Sure enough, the same overall capacity if the end voltage is conservatively high near 3.1v under load lvd. Roughly 32ah with the 40ah bank.

This lines up with how I use it. Since manufacturer's capacity ratings are done by going to the dregs at the very bottom of the discharge knee, my desire to stop at around 3.1v at the high end of the discharge knee squares up with only 32ah usable for the so-called top-balance charge, be it at 3.45v per cell, or higher. Approximately 75% give or take.

Had I taken it to the bottom, or about 2.8v or so under load, then near 40ah would truly be available. But with my simplistic pack-level lvd, only a fool would go that low, knowing that each cell differs slightly in both capacity and IR.

What may be interesting to new users assembling their own cells, BARE NAKED with no vampire boards etc, is to simply CC/CV charge each cell to 3.6v, with .1 to .2C charge current, with an end current of C/100, and let it rest for 12 hours. Note the resting voltages of each cell for a baseline.

Discharge bank and watch for the runt who hits 3.0 / 3.1v under load first. Measure overall pack-level voltage for your lvd - for this simplistic conservative application. EV'ers, rc'ers and other high current applications may need to take entirely different measures.

Spend some quality time with your cells noting how they behave in the simplest of environments, before you wed them to the spaghetti nest nightmare. They may reveal things that the vampire boards or other circuitry is hiding from you, be it PRO or con.

Also quite forgotten is the quality of your cell-link structure. Did you clean the terminals with a non-metallic brillo pad, and apply a light-coating of anti-oxidant compound? Or did you just slam the parts together in excitement?

Now charge at your desired CV voltage based upon your needs. I'm taking the risk of course, but so far, as a first-owner of new cells, and with plenty of "human bms", I can deal with it. Your neighbor, most likely not...

[PNjunction]

Back to Victron for the moment --

Lurkers may notice that Victron's own LFP batteries have a spec of being charged up to 4.2v per cell. Normally, that voltage spec is reserved for NON-LFP chemistries, such as NMC, LICO etc (your typical 18650 laptop-type cell) which are the nominal 3.7v batteries, and not the nominal 3.2v LFP's.

Normally 4.2v would quickly destroy your typical GBS, Winston, CALB etc LiFeP04. How they get away with this is that the batteries have internal regulators to handle going beyond the normal 3.6v max voltage charge for LFP. This makes it more appealing to the "drop in replacement" crowd.

Moral - if you are doing your own thing, be SURE to get your NAKED CELL voltage specifications right, and don't always take marketing materials as the gospel truth for anything but their own product, which may have reasons for altering the standard specifications.

[Living Large]

This is fascinating. I go away for a year, come back and find PNj is testing LFPs in earnest, and Sunking and karrak are still... well, the same. It's not totally different than a soap opera - you don't have to see every episode. I'm confident that if one printed out these threads and studied them, they would be able to make an LFP system work for them, using one of a few of approaches. Lots of excellent information and experience here. The new format of the site looks great.

You may recall I lurked here for almost a year, arriving at the conclusion I could install an off-grid system with LFP batteries in the Adirondacks. It was at this very point Sunking finally said "WTH would you do that, if you can get power???" It has taken a year, but I and two partners have put in enough improvements to get 500' free each for a power line extension. It would have cost me $51,000 alone. With two more customers, the cost to the POCO is down to $7,000 divided between two of us. The three of us (mostly my two partners) put in improvements of about $20,000 (wells, sheds) to "demonstrate permanence", and trees should be cut by the power co in the next few months. Poles by spring hopefully. WTH was I considering solar I'll never figure, but it was a really fun exercise with the help of people here. I don't know now if I hadn't found my two partners that I would actually have jumped on the solar wagon. That water looks cold. Carry on!

[J.P.M.]

This is fascinating. I go away for a year, come back and find PNj is testing LFPs in earnest, and Sunking and karrak are still... well, the same. It's not totally different than a soap opera - you don't have to see every episode. I'm confident that if one printed out these threads and studied them, they would be able to make an LFP system work for them, using one of a few of approaches. Lots of excellent information and experience here. The new format of the site looks great.

You may recall I lurked here for almost a year, arriving at the conclusion I could install an off-grid system with LFP batteries in the Adirondacks. It was at this very point Sunking finally said "WTH would you do that, if you can get power???" It has taken a year, but I and two partners have put in enough improvements to get 500' free each for a power line extension. It would have cost me $51,000 alone. With two more customers, the cost to the POCO is down to $7,000 divided between two of us. The three of us (mostly my two partners) put in improvements of about $20,000 (wells, sheds) to "demonstrate permanence", and trees should be cut by the power co in the next few months. Poles by spring hopefully. WTH was I considering solar I'll never figure, but it was a really fun exercise with the help of people here. I don't know now if I hadn't found my two partners that I would actually have jumped on the solar wagon. That water looks cold. Carry on!

Wondered where ya' been.

You hunkered down 'til spring now ?

As for around here, 2 of many ways to see it:

1.) I guess the soaps are nothing if not consistent and predictable. Same for some aspects of this spellbinder. Characters come/go, but not much is new under the sun. Pretty much the same story lines.

2.) Or, one definition of insanity is doing the same thing over and over and expecting a different outcome for the same conditions and input. So it is with some parts/aspects of this operation.

Stay warm and remember that the number of daylight hours/day will be increasing for the next 6 months.

Regards,

[Sunking]

It was at this very point Sunking finally said "WTH would you do that, if you can get power???"

That sounds like a big THANK YOU. I saved you 10's of thousands of dollars Karrak, John, and Dan wanted you to waste. I might o fbeen tough on you, but in the end you learned a lot and found out who was full of crap.