Multiplus ignores AC input when battery is too low

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jasonsele asked Apr 4, '21

Multiplus ignores AC input when battery is too low

I have two multiplus 24/3000/70-50 and two MPPT 250/60 with 300amps of 24v lithium batteries and a color control . It's a 50amp RV with a each multiplus connected on L1 and L2. I have an issue that only happens when I am connected to shore power and run the batteries too low.

A few times I've overloaded the AC input by running too many appliances including air conditioners and that trips the shore power breaker. This usually happens when I am on 30amp shore power, even if I set the input current limit to 30amp max. Because the system works so well it switches over to my batteries and I sometimes don't notice. It eventually drains the batteries and shuts off the system with the low power alarms. Once this happens I can't get the shore power to charge the batteries any more. I reset the breaker so that there is power AC in 1 but the multiplus won't accept the power input. At this point usually the multiplus is off and the switch for "on/off/charger only" won't do anything. I have to use a jumper cable on the terminals of the multiplus to power it back on. Once it is on it still does not accept the AC shore power input to charge the batteries and I have to wait until the solar panels charges them enough that it will allow AC in again. Even with both multiplus on, resetting the switches, and seeing main on, the color control still shows AC input at 0 and state is off. However, the solar input works fine and once the batteries get recharged to a certain level it accepts the AC input again.

I assume that the batteries have to be restored enough for the system to return to normal but why would it accept solar in and not shore power in to charge them? Obviously this creates a problem when it happens at night because I have to wait until the sun comes up in the morning to charge the batteries. Shore power, generator or any input on AC in 1 will not work until the batteries recover.

So two things I'd love to fix. 1. How can I get the multiplus to stay on when I have shore power but batteries are low? Why would I need to jump it? 2. How can I get the multiplus to accept AC input when the batteries are dead? Shouldn't AC input work all the time?

MultiPlus Quattro Inverter Charger Generator low battery warning

2 |3000

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Answer 1 · 2021-04-04T16:28:56Z

Daniël Boekel (Victron Energy Staff) answered · Apr 04, 2021 at 04:28 PM

Hi @jasonsele

what kind of batteries are you using? (brand / type / bms?)

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2 |3000

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jasonsele commented · Apr 04, 2021 at 04:35 PM

I have 6 X Battle Born 24v 50amp batteries with BMS

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Daniël Boekel (Victron Energy Staff) ♦♦ jasonsele commented · Apr 05, 2021 at 09:23 AM

Hi @jasonsele

If you have AC on both inverters, do they start up?

(just a hunch, when batteries are at 0V due to BMS disconnecting, a multi-phase system might not be able wake up on a single phase input)

I am assuming a bit here: is it a split-phase system?
and what do you mean by: 'I have to use a jumper cable on the terminals of the multiplus to power it back on '

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jasonsele Daniël Boekel (Victron Energy Staff) ♦♦ commented · Apr 05, 2021 at 04:36 PM

It's a split-phase. When the batteries are too low I actually put 12v on the multiplus terminals where the battery input comes in and that is enough to fire up the multiplus and feed the color control so I can get to the menu. What I don't understand is why the multiplus would not function with AC input still active. Should the AC on both inverters keep them running?

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Daniël Boekel (Victron Energy Staff) ♦♦ jasonsele commented · Apr 07, 2021 at 10:58 PM

Hi @jasonsele

is there AC input on both inverters? or just one?

I think you need input on both inverters on a battery that is at 0 volt (due to BMS disconnected)...

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jasonsele Daniël Boekel (Victron Energy Staff) ♦♦ commented · Apr 08, 2021 at 03:43 AM

I'll check. I believe it is.

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Answer 2 · 2022-06-16T08:21:18Z

I think this is caused by a bug in the Multiplus firmware, I am experiencing the exact same issue with similar setup, two Multiplus 24/3000/70, 24v lithium batteries (8 of 5.2KWh tesla s battery modules balanced by their own original tesla BMS, BMS is not connected to / does not talk to Victron equipment and BMS is a standalone system that can balance the modules and take any of the modules offline if anything is out of range, e.g. any cell < 3v or cell temperature < 0 c) setup as Split Phase 180 degrees, wired as it should, everything works fine no matter what is my battery voltage when i connect to 50A RV outlet (which is Split Phase 180 degrees So 240v between L1 and L2, 120v between L1 and Neutral / L2 and Neutral), Now when i connect a 30A RV outlet or a generator to my 50A inlet with the help of a adaptor that simply connects L1 to L2 (another words: Single Phase 120v So 0v between L1 and L2, 120v between L1 and Neutral / L2 and Neutral) then two Multiplus will not accept the AC input because its not Split Phase 180 degrees, so i use "VE.Bus System Configurator" to disable switch as group, now two Multiplus accepts AC input on L1, uses it to charge the battery and inverts from the battery to serve the L2. Problem starts when the battery is low! In my setting I have "DC input low-shutdown=18.90V , DC input low restart=20.60V", If my battery voltage is bellow 20.60V and there was an invertor shutdown (either manual or because batteries got bellow 18.90V) Multiplus does not accepts AC input no matter what. If my battery voltage is above 20.60V Multiplus accepts AC input on L1 and starts charging the battery.

When i was in the situation of low battery and multiplus refusing to accept 30A 120v input and no sun, I solved it by reconfiguring two Multiplus as parallel, then they accepted the input, charge the batteries to over 20.60V then reconfiguring them back to Split Phase 180 degrees.

So what i want to see happen is that two multiplus configured as Split Phase 180 degrees with no switch as group, accept AC input on L1 for charging as long as battery voltage is above 18.00V

I have 2 questions:

1) how / should we submit a bug report to Victron?

2) Is their anyway to persuade Victron to allow lower than 20.60V for "DC input low restart" on future firmware updates? (in my case i have a pretty large 24V battery system, that can go as low as 18V without damaging the batteries, I have my "DC input low-shutdown=18.90V" to be safe, there is no reason why i shouldn't be able to set my "DC input low restart=19..10V")

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