Off Grid Parallel Multiplus II's not charging batteries correctly - Temperature Sense Issue?

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vward asked Dec 20, '23

Off Grid Parallel Multiplus II's not charging batteries correctly - Temperature Sense Issue?

Our parallel Multipluses are not charging our batteries from the generator correctly. Our SOC is 76% and yesterday, when the generator started, it went straight into absorption (according to the VE Bus summary) and after an hour it went into float drawing minimally from our generator. The voltage during the absorption was only about 55v instead of the usual 58v. Today it didn’t even do absorption but went straight to float at just under 54v with the current dropping gradually from 30a to 11a over a 4 hour period.

Last year early in the ‘generator season’ (winter) our multipluses gave an error/alarm - the temperature sensor had failed. We replaced it this summer, but battery temperature widget shows no data has not shown any data since then.

The VRM VE Bus summary widget says that battery temperature is 50C, which is NOT the case! MPPT’s say the battery temperature is 7 C and that seems likely.

The Multipluses temperature compensation is set to -64.8 mV / deg C. Could temperature compensation be messing up the Multipluses and preventing them from proper bulk or absorb charging?

This is the third year with our Victron Off Grid System that runs our home. We have a lot of solar, but it’s winter now and need to use the generator to charge batteries.

Multiplus firmware v. 506 recent upgrade

Batteries are Flooded Lead Acid

Multiplus-II battery charging Temperature Sensor lead-acid

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klim8skeptic ♦ commented · Dec 20, 2023 at 06:52 PM

@VWard what gx device do you have?

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vward klim8skeptic ♦ commented · Dec 20, 2023 at 07:27 PM

Color GX. And we have a Smart Shunt.

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vward answered · Dec 23, 2023 at 06:49 PM

We removed the Temperature Sensor from the Multi's, used VE Configure to change Temperature Compensation to 0.

But also, we had done a software upgrade to the Multi's before this all started and it seems that there is an issue where you need to switch the Multi's off and use a 3.5mm headphone plug in the Current Sense port, to plug in and out around 10 times. It was Victron themselves who advised me to do this years ago to clear an issue with multi's not accepting current from my AC-in which is my generator. (see below)

So we've done that too and today generator is on and charging our batteries, along with PV, as I would expect.

I can't help but wonder, could this current sense port problem (that it is making bad contacts internally) be part of my multi's issues? How many years will wiggling a headphone jack in that port work to persuade my multi's to accept AC-IN and charge my batteries? Will that fault get worse? Is it connected in any way to the Multi's Temperature Sensor port failing?

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Answer 1 · 2023-12-20T19:33:30Z

vward answered · Dec 20, 2023 at 07:33 PM

And some more information - we have a LOT of solar and found synchronisation issues with our Smart Shunt in the summer. So we followed these instructions from the manual. Which means the Smart Shunt thinks our fully charged Voltage is 58 volts.

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Answer 2 · 2023-12-21T03:55:26Z

JohnC answered · Dec 21, 2023 at 03:55 AM

@VWard

It appears that your Multi's T-sense has failed. The 50deg shown is likely a fail-safe injected value, and you're running in a limp-home mode. Indeed it could mean a ~3V drop in Charge V with that Temp Comp.

I can't verify this, but your RS mppt seems to have a T probe, and you could try passing that across to the Multis via DVCC. That's a setting in the CCGX, and the STS selection should show the RS option. It should work..

Until you sort something, best disable Temp Comp altogether and use manual charge settings for your Multis.

The Smartshunt Charged V you can set wherever you want. My own is set below Float level because that's where I want it to sync.

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vward commented · Dec 21, 2023 at 09:32 AM

Thank you so much for this.

Can you tell me how to disable Temp Comp? Just set the -64.8 to 0?

And use manual charge settings? How to do this?

We are actually wondering if our batteries are fully charged, based on:

1. Multi's went into Storage mode, but were showing SOC as 78%

2. When Multis went into Storage mode the graph was this, showing a clear tail current:

It was dark by then, so we switched off the generator and did a voltage check on each battery. our 48V FLA bank was at 2.11 volts per cell, or 50.64V.

A few weeks ago we had a day of sun all day and the SmartShunt didn't synchronise: If I do a guesstimate of voltages based on that day being 100%, not 89%, (I record every day, along with loads and weather), our batteries should have been at around 97%.

Does that voltage and the fact that our batteries won't accept charge possibly mean we are full? Or something else?

Thank you again

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JohnC ♦ vward commented · Dec 21, 2023 at 11:10 AM

@VWard

Yes, just set TC to zero. The standard Absorb setting for fla's is like 57.6V, and this would suffice. Far better than your <54V. Don't worry too much about Float level, by then the genset isn't worth running.

VEConfigure via VRM I use. I note on other posts you have Apple stuff, so you'll need to sort that.

The Smartshunt wont sync unless it's set up to use the low V's. So may have drifted over time. The Tail current is useful, but you'll need to get the V up to real levels to make serious estimates. I'm only guessing, maybe in your pic it's got to 95-97%? But I don't even know your batt size.

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vward JohnC ♦ commented · Dec 21, 2023 at 12:13 PM

Thank you so much for this. I can use VE Configure on my Mac, so I'll be OK for setting TC to zero.

Absorb in VE configure (the multis) is set to 58V, which is what the battery manufacturer had recommended. I've just changed the SmartShunt 'charged value' to 53.9 from 58. You helped us with our tail current last year and we feel pretty confident about it. Things got a lot better when Victron upgraded MPPTs and we were able to put the tail current up in those too.

I suspect it is going to be a while before I see an absorb voltage on those charts because either the batteries are not accepting charge any more, or they are full? The voltages on the batteries last night, resting, was around 2.11 volts per cell, (our battery bank is 2000 aH at a C20 rate. 2x 24 in series batteries, in parallel)

We took Hydrometer readings this morning and around 19 of the batteries are between 1210 and 1225,( most of those 19 are 1225). The other 29 are between 1230 and 1265, the majority being around 1240.

There is a lot of mixed info on which SG means charged or not for FLAs. Hope we're right to think this is pretty full?

The last time I saw 57 volts on a chart was during a generator charge 2 days ago and the VRM said it was doing an absorb charge (on the dashboard). Yesterday during a generator charge it started as float on the dashboard and showed the graph you see above which started as 54 volts. When it got down to around 12 amps the Dashboard changed to say 'Storage' and the generator was throttled back even further!

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