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tanglewood · 05-01-2019, 12:56

Quote:

Originally Posted by john61ct

How about 2/0 or so fine-stranded, as flexible as possible? long enough to allow for some movement, adding spacers later if needed, etc

I've built up a bunch of short cables using 2/0 and 4/0 with crimped lugs. Flexible is not a work I word use for them. Anything less than around 6" just doesn't want to move other than a slight side to side. To bridge adjacent cells, regardless of the gap size, you would have to make a big swept U.

I'll just track down so sort of manufactured strap.

Those CALB straps absolutely look like solid bar stock, and I had installed and removed a bunch of them before I realized they are actually a stack-up of sheet copper. It's actually quite an effective way to make a flexible jumper.

john61ct · 05-01-2019, 13:21

I think long-enough to get flexible-enough would be OK, long as they're all matched to avoid imbalance.

But the welding cable stock is **lots** bendier, maybe OK long as you compensated for the lack of tinning.

Montanan · 05-01-2019, 13:57

Quote:

Originally Posted by nebster

I don't have any great insight for you, but I have a few related observations and opinions:

2. Given that there is a whole class of LFP cells that use no compression support at all, my theory is that the compression recommendation of yesteryear is basically outdated advice. If someone is at the point where compression has a chance at stopping a bulge and therefore holds the electrodes in a mechnically more stable orientation during a stress event, they've probably already messed up electrically by allowing the cells to get out of range in the first place. At that point you have questionable cells that you probably don't want to count on in the future.

Bulging batteries means an inappropriate buildup of gas inside. The gases are produced due to electrochemical oxidation of the electrolyte. Such oxidation occurs usually due to overcharging of the battery due to a faulty battery, or faulty charging electronics. Any swollen batteries should be replaced and the cause of such discerned and resolved so as to not happen yet again.

Checkswrecks · 05-01-2019, 14:33

Something occurred to me that may be answered if you Google for broken or dissected cells like yours.

Jumper batteries are sold in hard casings contain pouch cells. The casings are made big enough for the pouches to swell and contract with charge/discharge cycles. It may possibly perhaps be that your CALB prismatics are actually just housings for pouch cells. If so and IF they have provided growth space in the plastic case, you could stack these side to side.

The photo below shows a jumper battery containing several pouches, probably after somebody got the polarity backward. I'm attaching it so you can see what I mean by the hard plastic case holding internal pouch cells.

nebster · 05-01-2019, 14:41

Quote:

Originally Posted by Montanan

Bulging batteries means an inappropriate buildup of gas inside. The gases are produced due to electrochemical oxidation of the electrolyte. Such oxidation occurs usually due to overcharging of the battery due to a faulty battery, or faulty charging electronics. Any swollen batteries should be replaced and the cause of such discerned and resolved so as to not happen yet again.

I completely agree. I haven't seen any evidence of prismatic LFP cells swelling under normal, modern charge management.

Oops, correction: looks like the cobalt chemistries do exhibit something like 0.1% dimensional swelling at sub-C rates and normal temperatures, see http://www-personal.umich.edu/~siege...p_Swelling.pdf. That probably means the iron phosphate chemistries do, too. There is enough room inside the prismatics to accommodate this, for sure. I don't think we can see that from the outside of the box.

When placed under abnormal conditions, of course, the chemistry can produce lots of gas then a lot of swelling. It may be possible to continue to use a swollen cell for a while, but it will be structurally compromised inside and more likely to spontaneously fail. And perhaps in an exciting way.

nebster · 05-01-2019, 14:42

Quote:

Originally Posted by tanglewood

That's right, my "practice" bank, which will power my house, by the way, is a top loaded battery box with good access. And I have the cells stacked immediately adjacent to each other, but not bound together in any way.

Oh, just your house, eh? Hehe.

hellosailor · 05-01-2019, 14:45

As nebster said, there's now some thinking that when you pack cells together, that's going to make the center cells run hotter than the outer cells, creating accelerated wear and shorter life. But packing cells together is still supposed to give them extra support and prevent bulging from overheating.

So a reasonable compromise might be to pack them together, but either put 1/4" aluminum plate in between them, serving as a heat sink, or to use some type of aluminum extrusion (or a tall stack of 1/4" to 3/8" aluminum box tubes perhaps) so there's a rigid support plus a good airflow maintained between them.

IIRC the CALB aluminum cased batteries are supposed to have something like a 5x longer potential life, so some type of heat sinking and cooling on the plastic ones seems like a reasonable investment.

nebster · 05-01-2019, 22:40

Quote:

Originally Posted by tanglewood

I appreciate the heating and cooling issues, but the feedback I'm getting is that operating in the .5C and lower range creates negligible heating. So I haven't been too worried about it, but better cooling would be, well, better.

I hope I haven't been one to contribute to that understanding. I have a data point for you:

I took a string of 16 100Ah aluminum skin cells, arranged in an 8x2 array that ends up occupying almost exactly one cubic foot, with the 3/32" spacing between each imposed by the dividers, in a large open room stable at roughly 75F, sitting idle for several days and so also at 75F. This string started at 37% SOC and charged at 0.3C (~1600W) for 65 minutes. At the end of the charge, the SOC was 69%.

At this point, the batteries themselves measured roughly 89F on the outside edges and 91F in the center of the cube. The terminals were at ~105F.

All of that heating does not include very much of the additional ambient rise from the ohmic losses in any wiring and fuses that might apply in a small space. So I think, depending on the enclosure's insulation and venting properties, heating should definitely be a consideration. (Maybe not for your situation specifically, but just speaking generally.)

SailRedemption · 06-01-2019, 03:14

We have the CALB 180s and have a post on it on our blog..

https://redemptiverepair.com/2016/07...cal-fun-vol-3/

tanglewood · 06-01-2019, 09:18

Quote:

Originally Posted by nebster

I hope I haven't been one to contribute to that understanding. I have a data point for you:

I took a string of 16 100Ah aluminum skin cells, arranged in an 8x2 array that ends up occupying almost exactly one cubic foot, with the 3/32" spacing between each imposed by the dividers, in a large open room stable at roughly 75F, sitting idle for several days and so also at 75F. This string started at 37% SOC and charged at 0.3C (~1600W) for 65 minutes. At the end of the charge, the SOC was 69%.

At this point, the batteries themselves measured roughly 89F on the outside edges and 91F in the center of the cube. The terminals were at ~105F.

All of that heating does not include very much of the additional ambient rise from the ohmic losses in any wiring and fuses that might apply in a small space. So I think, depending on the enclosure's insulation and venting properties, heating should definitely be a consideration. (Maybe not for your situation specifically, but just speaking generally.)

Thanks, that's a very helpful data point - one with actual data as opposed to "seems to stay cool".

It's also interesting that the terminal was the hotest part. How much do you think that's because it's effectively conducting internal heat, vs it's ohmic heating? I ask because I have been exploring different attachment/sense points for temp sensing, and you results suggest the terminals might be a good point. They are certainly the easiest to attach too.

nebster · 06-01-2019, 13:56

Quote:

Originally Posted by tanglewood

It's also interesting that the terminal was the hotest part. How much do you think that's because it's effectively conducting internal heat, vs it's ohmic heating? I ask because I have been exploring different attachment/sense points for temp sensing, and you results suggest the terminals might be a good point. They are certainly the easiest to attach too.

Good question. I don't actually remember which terminals I measured (I have a FLIR camera, so I usually just kind of "look at" all of them at once, and they were pretty close), but I do know that the point at the end of the string, where the terminal fuse block sits and the positive wire comes off, get LOTS hotter. The fuse and the extra connections there definitely make tons of heat.

So I would hazard a guess that most of it is just the connection?

nebster · 06-01-2019, 14:53

Oh, I forgot to write something I was thinking about earlier. In the scenario where the BMV drops out and the MPPT has to revert to its own DC wires for the voltage measurement... don't you end up kind of automatically degrading gracefully there? In the sense that the voltage reading will yield a more conservative charge profile.

tanglewood · 06-01-2019, 18:07

Quote:

Originally Posted by nebster

Oh, I forgot to write something I was thinking about earlier. In the scenario where the BMV drops out and the MPPT has to revert to its own DC wires for the voltage measurement... don't you end up kind of automatically degrading gracefully there? In the sense that the voltage reading will yield a more conservative charge profile.

Yes, it fails in a favorable direction. That's good.

I can probably locate the MPPTs right near the main DC buss bars and get acceptable sensing with fat wires. I think it was you who said your solar makes up for power consumption, but isn't really big enough to charge the batteries. Mine will be the same on the boat, so end-of-charge is kind of a moot thing. At the house where the solar is the main source of power, the MPPT controllers get their remote voltage sense of the network from a common sense point (it's a Schneider Conext system). Outback supports it too. Hook up one temp and voltage sense point, and the results are networked to all devices. I would just expect something similar from Victron.

A blue tooth device just doesn't cut it for me, especially if the connection and operation is not supervised and alarmed. Operation would be un-deterministic with no way to know which voltage sense the MPPTs were using. And I have found bluetooth to be flaky at best.

But we are getting off the topic of bundling/strapping cells....

nebster · 06-01-2019, 21:46

Quote:

Originally Posted by tanglewood

A blue tooth device just doesn't cut it for me, especially if the connection and operation is not supervised and alarmed. Operation would be un-deterministic with no way to know which voltage sense the MPPTs were using. And I have found bluetooth to be flaky at best.

Yeah, radio is a non-starter for me, too.

I'll let you corral your own thread back on track.