Victron SCC odd behavior, scratching my head

[Riderice]

Putting my new 16s Overkill BMS through its paces with 200Ah 48V battery. Been a rocky start so far, several issues. Victron Quattro kept tripping the "short circuit" protection (I guess initial start-up current was too much?), and slow/buggy Bluetooth.

But the weirdest thing is how my trusty old Victron SmartSolar has been behaving. After hooking up the LiFePo4 battery to the rest of the system, then turn on the charger, it just sits there at like 5W...instead of 3000+ that it should be pumping out. This has happens regardless of BMS, or even total lack thereof (not a BMS issue at all).

Thankfully I've stumbled upon an "initiation sequence" that kick-starts the Victron into action...but I cant figure out WHY it works.

I've included a diagram of my setup, stick with me here! Red line is path from battery, to lower cutoff switch, to "distribution block" (shared stud), which branches to 1)breakers, then SCC and 2) upper cutoff switch, to fuse, to inverter.

So after hooking up battery, I turn ON lower cutoff and breakers. Now charger has power. Turn ON breakers to panels, then charger just sits there doing nothing. *THEN* I turn the upper cutoff switch to ON (inverter still switched off) and now charger is happily charging away at full power like normal. THEN if I turn the inverter cutoff switch back off, charger doesn't care, keeps charging.

Whyyyyyy would it matter what the cutoff switch to the interter branch is doing???? The battery-to-charger circuit is complete without the inverter branch. Anyone experienced this with their Victron SCC? Never had any weirdness like this with my AGMs, so, maybe a lithium thing...?

 

[Riderice]

Once the SmartCharge decided it was done (54.8V "absorbed" for 2hrs), it stopped charging (0W, vs a few watts to "float" my old AGM).

Now normally, with my old AGM battery, if a load came on the inverter, the solar charger would pick up its output to match (net current nearly zero), thereby keeping battery topped off while also providing power to inverter. But with this battery, the inverter starts pulling current and the charger does nothing. Even as the battery voltage drops below the "float" voltage setting in the charger.

I'm going to monitor and see if the charger ever kicks back on by itself...

 

[chrisski]

I can’t help you much, but I saw something similar. I am going through a restart sequence like yours.

On a small lithium 25 ah battery bank I have with the 75/15 Victron Smart SOlar Charger and 15 amp BMS, I noticed I had to dial my SCC back to 10 amps to prevent charging from shutting down. Reinitiating the charging sequence I do by disconnecting the solar panels and hooking them back up. Charging starts. I walked the max amps to 14 and 13, and charging still stopped. I went to 10 amps, and charging does not shut down.

I think its probably the BMS, but of courrse this tiny Daly BMS has no way to monitor.

With my SCC I am overpaneled for the 360 watt SCC with 600 watts of panels, so perhaps in my case, this overpaneling is causing an SCC to shutdown. A little overpaneling is OK, but I’m a bit more than a little overpaneled.

 

[Riderice]

Yeah, I posted this in the "BMS" section because initially I thought it was the BMS blocking charge. But then I removed it from the loop, and same behavior, so it must be the Victron being weird. It used to work perfectly with AGM, even totally over-paneled worked fine (3000w of panels but could only put 1000w into battery, 70A at 14.5V).

 

[chrisski]

What I noticed at first, was at 15 amp supply the Victron SCC stopped supplying the current. I saw it go to 15.1 amps, and no more current.

I wish I had checked for any error lights on the Victron. I’m setting this up again this weekend to look for those If it faults out again.

I do wonder if Victron has a built in protect where if the SCC gets to max charge and exceeds it by a certain set of parameters with seconds and amps, it shuts down charging until all current is removed from the PV side.

I do wish my small Daly BMS could be monitored, or at least an indication on over something, or at least instructions on how to reset it. None of those.

 

[Riderice]

Eventually the Victron decided to start charging again, once battery voltage dropped to 53.1V (float is 54V). No idea why it waited, maybe it's just not sensitive enough for the lithium flat curve? Luckily this morning it started charging as soon as sunlight was available. I'll keep an eye on the behavior over the coming days. Unfortunately now I've lost trust that it'll keep the battery topped until sunset. Once it finishes the big daily recharge, will it just go out to lunch and let the battery drop all afternoon...?

 

[Riderice]

@chrisski yeah the cheapo Daly units are frustrating because they do work, but you have no insight. My battery came with one of those, but I picked up an Overkill and a Chargery, to try those out. What is maybe happening with your battery is one of your lithium cells is running away and tripping the BMS overvoltage protection? Since you have a Victron charger, you can set the parameters to avoid that. Drop the Absorption and Float voltages way down below the standard LiFePo4 settings. Like my cells are happy at about 3.4V, full-ish charge. So for me, I set my Victron to absorb at 54.4V (3.4 x 16). That prevents the runaway ramp-up above 3.5V.

 

[Riderice]

Well if anyone's still reading/wondering, the Victron SCC finally settled into its normal routine, after it "woke up" it's been fine since. It charges until there's no light left in the evening, then starts up again the next morning at first light. Bulk for a while, then Absorption, then Float, and picks up additional loads when able to do so.

Still have no idea why it was being so weird at first, and I am actually scared to turn it off (like to disconnect and work on the battery), because I'm afraid it'll repeat the behavior...

 

[Riderice]

...aaaaand the weirdness continues! The Victron just won't work properly for this setup, or battery, or who knows what... I can "trick" it to work, for a few days, but it eventually just randomly stops providing any power.

In the meantime I got a Schneider Conext MPPT to try, and it works perfectly. So, no idea why that works, and the Victron is being weird. I don't have the equipment or expertise to solve the mystery. I drank the Victron koolaid, but this has made me rethink... And unfortunately I just got a Victron inverter, now I wish I had the Schneider, since the mixed brands can't network together...

Victron warranty and tech support from Pike Industries (Amazon seller) has been amazing though, I must say! (Won't get that with the Schneider probably...) Pike actually sent me a replacement SmartSolar to try, assuming the first one was just defective somehow.

 

[cinergi]

All I can say given the information at hand is that this is not normal. Victron equipment is indeed very good and should not be behaving like this. Can you post a screenshot of your SCC config (e.g. VictronConnect settings page on your mobile device)?

 

[kgol]

[...] Eventually the Victron decided to start charging again, once battery voltage dropped to 53.1V (float is 54V). No idea why it waited, maybe it's just not sensitive enough for the lithium flat curve? [...]

In the Victron SCC settings in the Bluetooth app, at what voltage do you have set the "Re-bulk voltage offset" (enable "Expert Mode")?
The default value for the Victron LFP profile is 0.2 V per 12 V, so in your case 0.8 V. This more or less matches with your observation that the SCC restarts the charge sequence at 53.1 V, which is 0.9 V below the float voltage.

 

[Riderice]

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


@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.

 

[chrisski]

I wonder if Victron has something built in that will not allow high wattage consumption on a full battery and for float to deliver the power. A glitch in the software.

I saw my thing again last week where there was no charge current delivered to the batteries. I added a second Battery with a BMS, so I find it odd that with a 15 amp cutoff, both BMS would shut off if the SCC could only deliver 14 amps. THat should be 7.5 amps to each BMS. I’m starting to think this is a problem with the SCC.

Perhaps the Scheider has better firmware.

When I shut my VIctron off, there was new firmware which I downloaded, and I’ll see how it goes today.

 

[tim0shel]

I've been having issues with mine. 100 watt panel I would always get 30+ watts and almost 98 at times. Lately or last 5 days now in full sun only seen it max out at 13 watts and .8 amps. Trying to think if it had an update lately that might be buggy. Checked cables unplugged for 10min then back. Getting frustrated with it. By the way it's a victron 100/30. The low voltages seen is the days I disconnected it.
By the way it's on a car AGM battery

 

[kgol]

@cinergi this is what I sent tech support, when they asked to see that info.
[screenshot of SCC settings]
@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.

So, to wrap up:
- there is plenty of sun and the panels are not shaded whatsoever
- the battery voltage measured by the SCC is lower than the float voltage minus the re-bulk voltage
- the above is continuously true for several minutes (the SCC decision making algorithms have some strong low pass filters on them)
- you run recent firmware on the SCC
?

 

[Riderice]

So, to wrap up:
- there is plenty of sun and the panels are not shaded whatsoever
- the battery voltage measured by the SCC is lower than the float voltage minus the re-bulk voltage
- the above is continuously true for several minutes (the SCC decision making algorithms have some strong low pass filters on them)
- you run recent firmware on the SCC
?

Yes, that's about it.

...except all the other stuff, haha! That I could "kick start" it into functioning, which I randomly discovered, by throwing open the disconnect to the turned-off inverter branch...but even then the SCC would only function normally for a few days then eventually revert to doing nothing. And this was experienced on TWO separate Victron units, but not at all with another brand unit?‍ (and never on my prior setup, with smaller Victron SCC, basically same config but with AGM batteries)

 

[Riderice]

So, to wrap up:
- there is plenty of sun and the panels are not shaded whatsoever
- the battery voltage measured by the SCC is lower than the float voltage minus the re-bulk voltage
- the above is continuously true for several minutes (the SCC decision making algorithms have some strong low pass filters on them)
- you run recent firmware on the SCC
?

I should've said: yes, plus your bullets 2 and 3 are N/A because I get the same no-power (5-12W) even with SCC in Bulk mode w/full sun.

 

[brb58]

Out of curiosity, at what voltage does the BMS top balance at?

 

[kgol]

I should've said: yes, plus your bullets 2 and 3 are N/A because I get the same no-power (5-12W) even with SCC in Bulk mode w/full sun.

This makes it even weirder. If you don't mind more questions: does the issue occur only in bulk, only in float or in both?

I've the impression it occurs only in the bulk phase (and not in float) in the case of tim0shel?

 

[Riderice]

@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.

@kgol Happens in both Float and Bulk. In the screen shots above it thinks it's Floating, but isn't even trying to maintain the float V. When it thinks it's Bulking, it's doing nothing either.

I will miss the snazzy Victron bluetooth app interface, but (besides the fact it's my only option at the moment...) I actually prefer the scheme of the Schneider - it has a bulk boost voltage setting that it'll hold for 1hr (for a rapid charge-up), then whatever slightly lower absorption V for however long you want (for cell balancing), then down to Float.

 

[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) ?