question

Al avatar image

MPPT not charging during Multiplus absorption (DVCC)

Should DVCC allow the MPPT to charge when sun is available, even when the Multiplus starts a charge due to low SOC early on a sunny day?

I've found the Multi will still be in absorption and the MPPT will go to float, but decides not to bother with any output, even though it could.

If i turn the MPPT charge off and on (in Victron Connect) it will try to charge for a few seconds but quickly cycle through Bulk-Absorption to float and give no output.. Only when the Multi goes to float does the MPPT start charging.

I'm using DVCC, + Ignore AC, both MPPT absorption and float voltages are higher than the Multi's

Could it be overheating? Today was hot and the batteries showed a peak of 37 Deg C, or maybe an incorrect setting, I.e. reduce the Ignore AC charge to end after bulk, but that's not ideal until we have more solar?

Or a symptom of the MPPT adaptive charge, either way i thought DVCC should tell them both what to do, as the Multi decided to use the AC In mains to charge when there was enough sun to cover the end of the absorption phase :( ..?

Thanks

VRM link:

https://vrm.victronenergy.com/installation/62545/share/c76c4bf6


MPPT - Solar Charge ControllerMultiPlus Quattro Inverter ChargerDVCC
mppt-not-charging.jpg (135.3 KiB)
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*Update 4th Sep 2020

Well my assumption it was a too low Abs voltage for the MPPT's making them go into float and not delivering any charge whilst the Multi took in the mains/ shore supply was misplaced.

I have again watched twice recently when the MPPT's go into float and don't deliver ANY current whilst it's sunny and the Multi is in a charge cycle. My 24v batteries: Multi Abs @ 28v.70v MPPT's Abs @ 28.80v Using all DVCC and all on Adaptive charge.


So My take away is:

If using DVCC + Ignore AC: DO NOT use Adaptive charge on the MPPT's as they are forced into float early and unable to give ANY output whilst in float + the Multi is in control of a charge cycle keeping Abs voltage up.

The Multi will keep the AC in on until its adaptive charge time is completed, even if the MPPT's could cover the charge load, which makes sense due to the variability of the sun, but also means the Multi will carry on and power the loads even if manually setting the MPPT's to Equalise to get them out of float and use some solar power.

Solution: I have kept the Abs 0.10v difference, but also set my MPPT's to fixed Abs plus kept the tail current setting at 3.5A per MPPT which equates to 2% of my old bank Ah to avoid overcharging.

Maybe DVCC / firmware's will be updated to allow MPPT's to work in the future, but they don't seem to for now with:

CCGX on Firmware v2.58

2 x MPPT 100/30 Firmware v1.50

SmartShunt Firmware v4.04

Multi 24/3000/70-16 Firmware 474


p.s. I'm not keen on the way these comments and questions / answers are not just automatically in chronological order, it makes it hard to make sense of updates over time.


@Al

I like the Adaptive mppt algorithm, and coincidentally have decided on 2% as well to drop into float.

At that point though I see absolutely no point charging with ac. Maybe you could look into Assistants to remove it under serious pv charge. Perhaps even early in Bulk stage of the pv day?

For me, I bring the genny on when the solar is done in the evening, just enough to ensure I never drop below 75% SOC at sunrise. I don't let the system determine that either, because it doesn't know my overnight plans.. :)

Update#2 04/03/21

It's happening again :(

I had previously got the Bluesolar MPPT's to keep charging by setting their Abs voltage 28.90v vs Multi's 28.80v + they HAVE to have a fixed Abs time! - Adaptive does not work with DVCC + AC Ignore. (The MPPT's will go into float with no output)

I have now upgraded to an 8k Quattro and am in the process of installing 2 x MPPT VE.CAN - Since installing the first Smartsolar VE.CAN MPPT (solar panels not connected yet though) the Bluesolars stop any output again around 5 hours after startup if the Quattro is using AC In to charge. Turning them off and on again resets the charge cycle, but is annoying to have to do to get any output from them.

I don't know why? All MPPT's are fixed Abs 8h .10v above the Quattro, everything latest firmware as of last week.

Maybe the VE.CAN MPPT talks differently in DVCC to the CCGX and it doesn't like the bluesolars as much.. possibly the current or voltage sense is prioritised differently, or the Bluesolars need a higher Abs voltage than the smartsolar VE.CAN even though it doesn't have solar panels connected yet?

Hopefully it will be irrelevant for me soon when all the new solar and a new 2000Ah FLA battery bank is installed in the next month or so, but this could be a bug in DVCC for others?

I have 24v:

8k Quattro (Temp + Vsense)

CCGX (DVCC + AC Ignore)

Smartshunt

Bluesolar 100/30 x2 (VeDirect) (1,600w solar)

SmartSolar 250/100 VE.CAN x1 (another on the way) (7,840w solar when all installed)

420Ah C5 FLA's (Upgrading to 2000Ah soon)



4 Answers
Al avatar image
Al answered ·

Update* 18/03/21

Everything seems to be working now! :)

There was an issue with SCS, which a patch has fixed and should be available from Venus 2.65

I also found with AC Ignore to end the Multi charge phase with SOC makes the most of solar input, I set it at 85% SOC rather than allow the Multi to finish Abs.

All charge controllers are set to adaptive, but still I keep the MPPT's @ 28.90v vs the Multi/Quattro @ 28.80v and everything seems happy.

Thanks Victron.

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JohnC avatar image
JohnC answered ·

@Al

Don't apologize. My fault not sticking to the question. :)

How hard you push Absorb settings is something to consider too. Solar needs to get heavy handed with peaky days that are often very short in winter. But they do work up slowly to it, so much is already done before they hit their peak, and if pv is sized well, the solar insolation bell-curve will be tapering at much the same time as the batt current demands taper too. Seasons and weather invariably foul that theory in practice, and a balance is needed.

Shore supply is 'man made', and you get to choose how hard you push. If it's on-call it doesn't need a heavy Abs V or current, and the batts will likely appreciate being treated more gently. A generator might have different needs, to reduce running time in particular.

I too use the Adaptive setting on both charge methods, but I'm not so sure about how it works with the Multi.. just dunno/suspicious, maybe not quite like the mppt?..

With on-call shore, I'd still suggest lower target V settings, but it's your choice.

Got my own hands on a Smartshunt just recently after a long wait, and it's better at rating my batts than I am, even with it's default settings. And I could often easily push aside the Multi's SOC, I know my batts well.




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@JohnC

'And I could often easily push aside the Multi's SOC.. '

Ha, yes, I've played with our Multi's SOC settings for over 7 years.. but that's why we originally got a SmartGauge and for it's SOC triggerable relay outputs, which is now a moot point as the assistants can be so flexible combined with a GX device and BMV of some sort.

I'm not sure if it's right, but my understanding of charging Tubular plate 2v FLA's was that they need to get up to absorption voltage to start gassing a little and mix the electrolyte, I guess an alternative to be gentler on them is to reduce the Multi's max charge current, which for years without solar but with shore power and just using the Multi for assisting higher loads I kept at 30A charge rate but now we do have solar and using ignore AC to maximise it I figured 70A = 15% of C20 was reasonable for forklift type cells. They allow a nominal C5/5 discharge rate so 83A for our 420Ah C/5

I guess with both yours on adaptive you've never seen a period where the MPPT output stopped whilst your multi was charging? Which might scupper my thoughts on the MPPT going into float and stopping, assuming you use DVCC?


I'm looking forward to finally getting a SmartShunt though :)

@Al

You seem experienced, and know your batts too, that's good. Probably little we can 'argue' about, most will be personal opinion, and then much of that perhaps derived from differing circumstances.

Sure I've seen my mppt overwhelmed by the Multi. Just had a couple of foul solar days, and given this discussion, I did some testing for the benefit of us both while I had to run my genny (which gets the full monty settings cos I don't like running it).

With all charge settings the same (adaptive too), DVCC (all functions), the Multi pushes the mppt to zero once Abs is reached.

Raise the mppt Abs by 0.05V (@48V), the mppt comes back. It's a bit 'mushy' deciding, but seems to settle happily as the dominator.

Raise to 0.10V above and it's clear-cut, decisive. But then the mppt doesn't reach Abs state, as it doesn't have enough grunt to reach it alone. So it's rolling on in Bulk with only 0.1V stopping it from registering Abs. Today it took 14 minutes before a 'spike' must've registered it was at Abs. Then it will lock in Abs.

This 'unknown Abs' situation isn't really an issue for me as on the days I use the genny I'm aware of where I am. But it may be an issue for others, perhaps you too? Maybe one day we might see GX sync them?

I've always used Tail Current (at whatever V) to determine my batt status, and the Multi's SOC doesn't do that. You get a feel for it. But the BMV and Smartshunt do use Tail, also eliminate dc & ac loads from consideration, and together that's a quantum leap ahead for me .


JohnC avatar image
JohnC answered ·

Hi @Al

DVCC won't prioritise pv over shore, unless you have a Charge Current Limit set. Then that'll maybe only apply in the time that limit is being applied, ie before Abs is reached and current has tapered anyway. I've found that just a 0.05V raise (@ 48V) in the mppt setpoints will allow the mppt to dominate then. That's using default temp compensation setpoints, and if you've fooled with those then you may need a wider span to see that effect.

Permit me some observations and possible suggestions you could consider (ta for those graphs, the 'thousand words' thing):

1. The Multi and mppt aren't synced, so you run the risk of doubling-up on the charge programme, like 2x Absorb cycles in the same day. Without any idea of your loads, but presuming fairly constant, your charge current has flattened-off around the 16:00 mark, suggesting your batts are close to fully charged. And maybe the Multi's Abs cycle is too long..

2. Presuming (again) you're using shore mains and not a generator (And Pb batts).. I don't have that luxury, but if I did I'd consider just a 'Storage' level charge set on the Multi, maybe down as low as 26V. Then the batts would still charge, but much more slowly, giving your solar a free run.

3. Your SOC (where's that derived from?) has reached 100%, yet you're still on mains. The 100 may not be correct (it isn't), but that suggests the work is largely done before the solar gets a chance to finish it.

4. Yeh, you need more panels. But you know this already.

Please pardon me my critique. But maybe it'll help.

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Thanks for your thoughts @JohnC

I do have a 70a charge current limit for my batteries, I've seen the solar helping the Multi actually get to and hold the 70a limit in bulk which a 3k multi isn't normally able to do.

Both Multi and MPPT have the same default Temp compensation: 32.4mv/deg

1. The Multi is set to Adaptive / 5 hour max Abs + Tubular plate (although charge cycle doesn't bring the voltage up at the end anymore as it's meant to, minor point though)

2. We have shore power although will move moorings soon, so i'm seeing how self sustainable we can be. I prefer the idea of getting a proper charge cycle @ 28.8v from the Multi when SOC drops to 50% whilst we only have 720w of solar. This happens roughly every 2 days with our loads at the moment.

3. SOC is from the Multi, and yes both the Multi and smartguage seem optimistic when hitting 100% SOC, but could still be leaving Abs on longer than necessary. I'm waiting 6 weeks for a SmartShunt to be delivered.. but I have a SmartGuage battery monitor, which I've been using to adjust the Multi to get it as close as possible to a more realistic SOC

It's a shame the algorithm isn't that smart like the SmartGuage which doesn't use a shunt but is well regarded for SOC readings. For anyone without a BMV I also wish there was more / some / any!? info on adjusting the SOC settings in VeConfig 'Enable Battery Monitor', but if anyone else with FLA batteries reads this maybe it will help as a starting point:

Note* My pre-used 8 year old Pb forklift bank with a C5 of 420Ah was probably 530Ah C20 when new, (their C20 rate isn't published)

I found these settings are very close to the SmartGuage:

State of charge when Bulk finished: 84%

Battery Capacity: (Victron uses C20) 470Ah *See note above

Charge Efficiency: 0.81

These settings help get me to the 50% SOC point at the same time for both Multi + SmartGauge, but they deviate during discharge and charge by up to 7% although the 50% SOC recharge point is of more interest anyway.

4. I'm currently wiring up another 900w of solar, which should cover our loads June / July, but I'm hoping to have 5Kw of solar and 1200Ah C20 of battery in the future to be self sufficient as we use 6-10Kwh/Day

I'm still none the wiser of why DVCC did not allow the solar to be used for a few hours whilst shore power was charging the batteries.

My suspicion is the MPPT was set to adaptive as was the Multi, and this needs to be turned off in the MPPT, as I'm guessing if an MPPT goes into float based on battery voltage then it can no longer give any current to the batteries whilst they're being held at absobtion voltage by another charge source... Which surely means DVCC needs a change to documentation or software, or my reading of it?

Sorry for the long post, I'll update if the MPPT fixed Abs helps when the Multi next charges on a sunny day, or if indeed it was overheating.

Al avatar image
Al answered ·

Many thanks to @JohnC for having a play with your similar system and last comment to update findings, which I would accept as the expert answer if possible, I think the minimal voltage difference was the main reason my system had no MPPT output during the Multi's Absorption phase. See below:

From JohnC's test:

"With all charge settings the same (adaptive too), DVCC (all functions), the Multi pushes the mppt to zero once Abs is reached.

Raise the mppt Abs by 0.05V (@48V), the mppt comes back. It's a bit 'mushy' deciding, but seems to settle happily as the dominator.

Raise to 0.10V above and it's clear-cut, decisive. But then the mppt doesn't reach Abs state, as it doesn't have enough grunt to reach it alone. So it's rolling on in Bulk with only 0.1V stopping it from registering Abs. Today it took 14 minutes before a 'spike' must've registered it was at Abs. Then it will lock in Abs."

I also found by changing Adptive charge on the MPPT to Fixed this also allowed the MPPT to go back into Bulk after the Multi finished its Abs, rather than the MPPT hitting float early and the Multi's Abs voltage being too high for any MPPT output.

So there are two ways around this, but obviously having both charge sources on adaptive is preferable.

As JohnC mentioned the voltage difference is the critical factor, looking back I think I'd only played with up to a 0.04v difference for Abs I.E. 27.76v = Multi + 28.00v = MPPT a safer bet is to have 27.70v = Multi and 28.00v = MPPT / 28.00v + 28.10v or equivalent 0.10 voltage difference depending on charge and system preferences, but like JohnC I'll wait until the next time a charge cyccle starts so I can test at which point on my 24v system the voltage difference starts to work, and report back.

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Good work @Al Be interested to hear how you go.

Take care with the Adaptive algorithms when running two charge sources, as they assume they're doing it alone. As long as you get what you want at the end of the day, hey..

Good luck with it.