Victron SCC odd behavior, scratching my head

[cinergi]

@cinergi this is what I sent tech support, when they asked to see that info.
View attachment 68751

@kgol you're right, that was a bad example I gave originally, since it appears like the re-bulk value was reached which is why it restarted. But in hours of testing since, it exhibits this behavior regardless of re-bulk (0.1V for example), and/or lower battery voltage. And, in Float mode, it's expected that the SCC pick up the slack when other loads are demanded, right? (eg maybe the battery needs 0W, but the inverter needs 1000W, so why is the Victron sitting there only providing 5W, letting 20A drain from the battery in full sun...)

So anyway, I have a pair of 150/70 SmartSolars for sale now...maybe a Quattro 5000/48/120 if you can pick it up, haha.

Rebulk = 0.6 .. 54 - 0.6 = 53.4 ... which is close enough to the 53.36v in the screenshot. In this instance, I'm not surprised about the behavior. How low does the battery voltage have to go before it restarts bulk?
Your voltage settings are a little conservative. You'll see better results with float at 54.4 and absorb at 56. You won't notice any difference in lifespan of LFP with those settings. You can't effectively balance at 3.4vpc, either.

 

[brb58]

@bruceb58 I removed BMS from the loop during troubleshooting, to rule it out. But fwiw, I think I set BMS to start balancing at 53.8v, and then SCC "absorbs" at 54.5 for a while so all the cells can even out to about 3.4V.

Seems like that won't even work. How can a BMS passively balance cells if you are actively putting a lot of current into them?

 

[Riderice]

How low does the battery voltage have to go before it restarts bulk?

It doesn't matter. Even when the SCC is in Bulk mode, it does nothing. When it's in Float, it's not *floating* at the specified voltage (54 in this case).

Your voltage settings are a little conservative.

That is intentional. I have no need to push them to their high or low limits. My understanding is that LFP cell lifespan is drastically improved (like, nearly infinitely) if you neither charge past "90%" full nor discharge below "25%"

How can a BMS passively balance cells if you are actively putting a lot of current into them?

My BMS (Overkill) has super weak balancing circuits (0.5A?), so your are correct it has no hope of balancing under high recharge rate. My concept with the "boost/bulk" is to shove a ton of kWh back into the batteries while the sun is shining mid-day, then spend the rest of the day "topping" the charge off with a more moderate CV/absorption taper. This gives the BMS a chance to "top balance" my cells to 3.4v each day. I'm not an expert obviously and maybe that plan is total BS, but it's been working fine for a few weeks. I guess in a year (or 5) if by cells are toast, then I'll know I was doing something wrong! Haha.

 

[cinergi]

It doesn't matter. Even when the SCC is in Bulk mode, it does nothing. When it's in Float, it's not *floating* at the specified voltage (54 in this case).

Ah, good point. Have you tried the built-in LiFePO4 profile? This is not how Victron SCC's normally behave - so something is wrong/broken.

That is intentional. I have no need to push them to their high or low limits. My understanding is that LFP cell lifespan is drastically improved (like, nearly infinitely) if you neither charge past "90%" full nor discharge below "25%"

Understood. But you're talking about 10+ years if you cycle the battery from 100 to 0 back to 100 every single day ... If you're cycling 100 to 50 to 100 every day, that's 20+ years of life.

My BMS (Overkill) has super weak balancing circuits (0.5A?), so your are correct it has no hope of balancing under high recharge rate. My concept with the "boost/bulk" is to shove a ton of kWh back into the batteries while the sun is shining mid-day, then spend the rest of the day "topping" the charge off with a more moderate CV/absorption taper. This gives the BMS a chance to "top balance" my cells to 3.4v each day. I'm not an expert obviously and maybe that plan is total BS, but it's been working fine for a few weeks. I guess in a year (or 5) if by cells are toast, then I'll know I was doing something wrong! Haha.

*no* balancing circuit can outpace a charger (unless your charger is only a few amps). The key is that none of your cells run away so much that charging to X voltage causes a cell to hit 3.65+ ... Targeting a VPC of 3.4 will not allow your cells to balance (you may actually cause them to go out of balance). A VPC of 3.5 will allow balance and gives you *plenty* of headroom for cells to be unbalanced at the top of the charge. This means a charge of 56v means you could have 15 cells at 3.49 and one at 3.65 - a 160mv difference: extremely unlikely to happen.

 

[Riderice]

@cinergi Agree with everything you said above. Although my cells were "matched and balanced" when I bought them, in initial charge-up tests I did, I had cells running away to 3.65 when the rest were around 3.5ish. I've been meaning to get a little 3.7V charger, so I can do a proper cell-by-cell top balance...but, just haven't gotten around to it. So in the meantime, I'm just limiting myself to about 3.4. Even with the self-limiting, I think 54V is over "90%" charged - I did one capacity test of the complete battery and drew 20A for almost 9hrs (206Ah cells) ?

 

[chrisski]

I've been meaning to get a little 3.7V charger, so I can do a proper cell-by-cell top balance...but, just haven't gotten around to it. So in the meantime, I'm just limiting myself to about 3.4.

What do you have in mind?

I’ve been using a 30 volt 10 amp charger, but would like to see something that can push more amps at a reasonable cost.

THis is what I use:

https://www.amazon.com/gp/product/B082HXVRNF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I think charging 8 of my 280 ah Cells at ten amps on the one I linked above will take between 9 and 10 days, so something with low volts and a bit more amperage would be nice.

 

[Riderice]

Wow that one looks pretty good and for a totally decent price.

Only ones I've found are surprisingly expensive... This is what I thought I'd probably end up getting. I'd charge up the battery pretty far with normal solar charger, like normal each day, then start each cell individually from there - then I only have the last 10-20ah to do on each (otherwise like you said it would take all freaking day at 10A, if you start with dead cells).

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[chrisski]

I'd charge up the battery pretty far with normal solar charger, like normal each day, then start each cell individually from there

I am starting that process tomorrow. The batteries will be hooked 8S to a 15 amp SCC, and should take 2 days to get close and I will move them over to the smaller charger.

Wow that one looks pretty good and for a totally decent price.

I got that off Will’s recommendation on his website. I did return have to return one because something was rattling inside and turned out to be a blown diode.

I’ve topbalanced two smaller battery packs with that and done some electroplating.