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donb asked

Low Voltage light on for 24V/3000 Multi II; how high does the battery voltage need to be to get it to go off and turn on the inverter?

A few days ago I completed my design and build of our off-grid RV power system using the Tesla Model S battery module and a 24/3000 Multi II (along with an MPPT 100/20, BVM 712, and 2 back to back BP220's). From the start the Low Voltage LED was on. The MPPT appears to charge OK, but not much solar power available here, so I tried the generator and watched it supply 50A+ for a couple of hours, but I shut down at 25V for fear of causing damage. Then the Low Voltage LED was blinking and now it will not even charge. I tried adjusting a few of the settings, particularly the low voltage shut-down and restart, which I have set at the minimums of 18.6/19 and also tried higher voltages for the heck of it. Then I tried resetting all of the settings back to default and lost the blinking LED. But it still will not charge from the generator, though the 712 says it is taking about 2A from the solar, the present voltage is 23.17 and the low cutoff and restart are 18.6 and 21.8 (minimums) and the low voltage LED is still steady on. If I can find out what voltage I need to be at to get it to start, maybe I could add some temporary cells to get there and then switch them out?

Multiplus-IIlow battery warning
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Tod Kinsley avatar image Tod Kinsley commented ·

DonB,

I have a similar setup with tesla battery. Based on Don Morton's schematic. If Victron does not have an inverter charger that will work, have you found an alternate competitive inverter charger?




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Rob Duthie answered ·

Hi

How many cells are in series? Min is 7 cells in series for the inverter to work properly.

This has being mention on this forum and has being put to rest because of this issue not using the correct cell combination.

I run nissan leaf batteries in a 48 volt configuration 7 series with no problems at all. Except you must set then absorption and float voltage correctly.

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donb avatar image donb commented ·

I provided a lot of background information I the description that appears to have clouded the issue. Yes I am very familiar with all of the well discussed issues about the Tesla Battery modules 6s issue and that the Victron CEO considers the case to be closed. My issue here is that even at 25 V, well above the restart threshold of 21.8, it still will not start.


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boekel avatar image boekel ♦ donb commented ·

Sorry DonB, your text is very hard to read, and even harder to understand.


If you connect the Multi to a computer (with the MK3 cable) you can see the values the multi is reading (AC / DC / etc) this gives valuable information so we might be able to help you.

Als use a multimeter at the terminals to make sure what voltage arrives at the Multi, maybe a fuse has blown / BMS has cut connection / etc.

using 6s is no problem (apart from not starting at low SOC), I've been using 6s and 12s (48v) systems for more than a year with no problems.

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donb avatar image donb boekel ♦ commented ·

Are saying that 2 Tesla battery modules in series would work on the Multi Plus 24/3000/70?

Yes I had a computer hooked up through the MK3 and that is where I obtained the voltage readings from, which were confirmed with the 712 and a voltmeter.

I have also mothballed the Tesla battery module and the battery protection circuit for now as we were supposed to leave this week with a working off-grid power system for our fifth wheel. I have replaced it with two 12V 105AH AGM's to get us by for now.


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boekel avatar image boekel ♦ donb commented ·

I read something in your post about Battery Protects in your system 'back to back' if it's done as I think it is: this doesn't work! and no BP should be between battery and inverter.

Please have your system checked by an experienced installer


about the tesla modules, not in series: parallel for 24 volt, in series for 48 volt

Please make sure you have a proper BMS on the tesla modules (like SimpBMS) and don't overload them (they need cooling if used hard). and they -will- catch fire if charged to 'normal 24 volt' voltages.

Also note that on offgrid installations, a 6s lithium ion battery (like the Tesla Modules) has a very low voltage for a 24V system, and as a result the inverter cannot start if the battery is below (about) 30%-40% SOC If you don't turn off the inverter it will run just fine. It -should- start with AC present though.

So for off-grid: a 6s battery might nog be the best choice. A battery with a higher voltage will work better.

the minimum startup voltage is about 21,8 volts I think.


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donb avatar image donb boekel ♦ commented ·

@Boekel I thought I replied, but it's not showing here, so apologies if this turns into a double post.

As to the BP, I have found a lot of discussion about that also. I will just leave it at that for now though as BP is not what I attempting to resolve. It would sure help though if Victron would be more forthcoming with technical information about its products.

In order to ensure that was not the issue here, I temporary bypassed the battery protection system and connected directly to the multi plus terminals and measured the voltage at 24.5 which confirmed what the multi saw. I also had AC power applied and I was able to charge to 25 V in "charge only" mode, In my mind, if 21.8 is the minimum startup voltage then anything over that should allow it to start, but then what do I know? In addition, I did hook up my two 12V AGM batteries in series and it turned on (25.6V).

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boekel avatar image boekel ♦ donb commented ·

If you have 2x battery protect (one in reverse) you cannot cuttoff anything, but as you still don't provide a diagram, I might understand you wrong.

Can you provide a diagram of your system? and also (screenshots of) the settings?

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donb avatar image
donb answered ·

@Boeklel,

Thanks much for your help and I am sorry, but I do not have formal complete drawings. Just a note pad with many sketches; and as I mentioned in earlier replies, the Tesla battery system is no longer installed (it is now in storage at 22V) and I am in the middle of rewiring my power system for two series 12V AGM batteries bypassing the Tesla BP system. I expect the two 12V 105AH batteries in series will get us going, since that worked, but think of it as a temporary solution; and, I need to complete this today, so I don't really have time to draw up something more formal at the moment.

As for this particular question it is rather simple though as I did try it with a direct connection between the Battery + to the 24/3000/70 Battery + terminal and the same for the negative side, thus bypassing all of the BP circuitry and eliminating that as a potential source of the problem. It did not work at 24V or 25V, but it did work at 25.6 volts with two 12V AGM batteries in series.

I have not completed installing the two 12V AGM's yet, so there is a possibility it might not work either, since when I tried it I just used some jumper cables to see if it would work.

BTW, I have 20 years of experience installing, operating testing, repairing, and troubleshooting new designs of advanced military and commercial electro/mechanical and electronic research projects, and if anything, experience has taught me humility so I do apologize if this comes off sounding otherwise. I also suspect that many in your community have even more, but I do know a few things...

It just seems rather interesting that after Victron said they would not support the lower voltage configuration of the Tesla's, that my just activated system will not turn on without a voltage that would theoretically fry a Tesla battery, particularly since it has worked for so many, for so long even with the 18V/19.6 cutoffs, which still allowed 70% of the capacity and most appear to have been using less than 60%.


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boekel avatar image boekel ♦ commented ·

Hi @DonB, don't worry, if you still experience problems with the AGM batteries, or later with the Tesla modules, please report back.

I've never experienced units that didn't switch on with 24 volts so very interested in the settings in the unit. And of course there is always the possibility of a defect.

ps. a diagram can be a simple sketch :)

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