cgabay avatar image

DVCC vs Smart Network in order to sync two mppts.

Hi all,

After reading manuals still I am little bit confused about which one to use.

My installation as follows on our sailboat.

A non victron inverter/charger combi

4x160 agm non victron service batteries

280watts solar array charging service batteries via victron mppt smart 100/20

340watts solar array charging same battery bank via victron mppt smart 100/30

A bmv 712 monitor

a venus gx have connection to 100/20, 100/30 and 712 with cables.

my problem is two mppts are

ok and works fine in bulk phase,

then they are ok passing to and work in parallel in absorb phase

afterwards they are ok passing to float phase. however in some shady days 100/30 stays in float which is normal, 100/20 turns back to bulk mode which is not normal.

manuals says do not use smart battery sense or smart networking between mppts if there is a gx product in the system. Do I have to use dvcc in order to get two mppts synced. Or can I use smart networking while dvcc is off.

thanks in advance

smart solar set-up helpDVCCSmart Battery SenseVE.Smart Network
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1 Answer
JohnC avatar image
JohnC answered ·

Hi C. DVCC can't sync them, and unless you have some specific reason to use it, perhaps best left off anyway.

This 'syncing' seems to be something that people 'crave', but all can live without.

Seeing one mppt in float and the other return to Bulk state might conceivably result from beginning their solar day at different times, maybe locking in things like Abs time and temp compensation at slightly different levels. Maybe one might decide to do a short 'reAbsorb', and the other hasn't picked up the need to do that?

In the washup, what happens over the course of a day with your batt V's is the important thing. If it's doing what you want, then rest easy.

If you have VRM, perhaps post up screenshot(s) of the relevant stuff, and we can take a look.

I don't know how far this 'syncing' thing needs to be taken. Some endusers may well have (say) 4x mppt's, a wind genny, hydro, grid & generator, even conceivably all running together. To sync them is impractical (meaningless?), and 'priority' is usually the issue anyway then. That can all be managed with kit/settings, but at the end of the day what the batts get is the target.

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Thanks for the answer.

The thing is one of the mppts stays in float state. That is ok. However the second one starts to fluctuate between 13.8 and 14.4V as lt is in bulk state It cannot go to absorb and float state as it has not enough power for charge and supply the load. I am little bit disturbed about over voltage till sun drops. I am curious whether I am damaging batteries within these hours.

Yeh, I can understand why you may be concerned, but it's not necessarily an issue.

Make sure your units are set to exactly the same charge algorithm. I think the newer firmware can be set to a fixed Abs time rather than an adaptive one, so both will experience that together.

If you were pushing into very small batts, maybe an issue, but you're not. With even all your panels at full spec you're not even 0.1C (Ah). With one mppt falling away, you're well less. So what defines 'overcharging'?

It's hard to explain, and subject to personal preference too. Airy-fairy it is. As an example, in poor winter weather my own system may spend all of the day in Bulk mode, never reaching Abs, but most of the day above Float level. After dark I can see how well they're charged by the V they settle to, and usually fall just that little bit short. So all day they've been 'chasing' the chemical reaction within the batts, rather than 'forcing' it at Vabs. I don't call that overcharging. Personal view, I can wear any dissent, ha.

Some people, even on this forum, demand Victron provide a longer Bulk phase. Personal preference again, and that's usually achievable by limiting Amps.

So the Science can become a bit of an Art. It's why I love my VRM graphs so fondly, don't use SOC much, nor auto genny start to top up after a bad solar day.

Hope this drivel makes some sense. Hard to explain Artistry.. :-)

In the absence of a “Like” button on replies.

Thanks again for answer with artistry. :)

I clearly understand your explanations and really appreciated.

Well I think overcharging meaning differs in different situations. If a battery is hungry with the 55% SOC 0.25C is not overcharging. On the other hand, if SOC is 100% and you are still pushing with 14.20V lets say with 0.03C it is overcharging. Am I wrong?

@Cgabay "not enough power for charge and supply the load"

100/30 has no load output.
100/20 you have a DC load going via load output?

Assuming thats the case If you remove the load form 100/20 and have it go direct to the battery then you will undoubtedly see the two perform in a more similar way. If you would like it to work that way get a battery protect.

The higher voltage you see is most likely supplying the load and when the load pulls more than the PV supplies its pulling the voltage down to 13.8v when current is pulled form the battery / other MPPTs float current so that is why you are seeing it jump.

If when you see the voltage on the 100/20 rise to 14.4V it is not equally rising on the 100/30 then the battery is not being over charged. You may want to possibly lower the float voltage on the 100/30 as a slight offset but i am certainly not telling you to do that. I don't know the specifics of your batteries.

To understand the significance of the non rising voltage seen on the 100/30 check out how the flexcharge energy state taper charge works

"however in some shady days"

I missed that bit. the PV voltage may be falling low causing the charge cycle to start over. that was a known issue that was meant to be fixed in firmware update.

Thanks for the answer the firmware is the latest.

"I think overcharging meaning differs in different situations. If a battery is hungry with the 55% SOC 0.25C is not overcharging. On the other hand, if SOC is 100% and you are still pushing with 14.20V lets say with 0.03C it is overcharging. Am I wrong?"

It depends (again personal views)..

Any pb charging at 0.25C would likely be condemned by their maker as overcharging. Most can't manage that anyway, as the V-rise will dominate and put an end to such high A. I don't get excited if, after a heavy load has been applied, the charger responds with a return to Abs and quite high A. Maybe only for a few minutes, and I think that's a clever algorithm.

The 'tail' current (as described in the BMV manual) is a good guide as to whether they're charged, and a low and stable tail in Float mode is really suggesting there's no value in pushing harder - that would be overcharging.

Batt temp can also be an indicator too. High temp isn't welcome, and if apparent, maybe suggests something is being pushed too hard.

So there's a few factors and situations to consider. Maybe akin to learning how to treat a spouse? Batts are easier though.. :-)

John C, This thread became very good by your information and the view of yours not only for me but for the community. Thanks again.

I definitilely stop worrying about my problem.

What about to use smart battery sense and create among two mppts while dvcc off? Manuals says dont do that. Do you think I will get any trouble with that?

Hi c,

You can already create a smart network between your 712 and mppts, no need for a SBS.

It might be interesting to find out how well a smart network works, compared to DVCC with venus control. Plz report back.