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Abay avatar image

Feature request: Allow 'DC input low restart' voltage values in VE Config closer to the 'DC input low shutdown' value

When programming 48V off grid systems with lithium batteries, I have found that the the 'DC input low restart' value's minimum 4V above the 'DC input low shutdown' voltage to be way too high.

My feeling is that this 4V margin is intended for lead-acid batteries, but it is not suitable for the much narrower operating voltage range that many lithium batteries have these days.

It is important to have low voltage shutdown set correctly to protect the batteries from over discharge, however, if this does occur the system won't restart again until the batteries are almost full!

I have also found this to be problematic in the event that a system is at a partial SOC (say 40% for example) and it is shut down manually for maintenance reasons. In the process of shutting the system down the inverter experiences a 'DC input low shutdown' voltage (momentarily before it dies). Then when the battery is reconnected the inverter won't turn on until it reaches the 'DC input low restart' voltage which corresponds to a SOC much higher than 40%.

~~~

Another feature that would be nice would be to be able to shut the inverter down on a set SOC outside of the ESS assistant. Or maybe this is already possible by way of virtual switch, which I haven't explored much yet??

feature request
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Completely agree. Thanks for writing this up.

8 Answers
Daniël Boekel (Victron Energy Staff) avatar image

Good news on the low voltage restart voltage, as Matthijs Vader posted on another topic:


mvader (Victron Energy Staff) answered · 7 hours ago ·

Hi all,

Good news! Last week we released a new version of VEConfigure. The minimum DC Low Restart has been lowered for 24V models from 21.8 to 20.6, and from 43.6 to 41.2 for 48V models. Unfortunately, we have not been able to reduce this minimum for 12V units, due to hardware limitations.


More information in this blogpost:

https://www.victronenergy.com/blog/2019/07/17/ve-bus-firmware-460-veconfigure-and-venus-os-v2-33/

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I installed the updated firmware on my quattro inverters and checked out the VEconfigure option to reduce the low voltage restart, unfortunately the restart still has the same 4 V offset from the shutdown voltage, this is what I need to change. My inverter shutdown battery voltage is 39.8V and I need a restart voltage about 1 Volt, or maximum 2 volts higher than the shutdown voltage.

For my 400 aH lithium 48V "volt" battery (12 cells in series vs 96 in series in the original volt configuration) operating from 3.3 to 4.025V , - (note for normal Lithium discharge curves and as confirmed by US DOE testing https://avt.inl.gov/sites/default/files/pdf/phev/battery2011volt0815.pdf my selected operating voltage range is in the mostly linear portion of the discharge curve) 4 volts of offset (on this 48 V nominal battery) prevents use of about 50% of the battery capacity or about 200 ah out of 400 ah total. I believe the offset will also be too high for users of other 48V systems and likely on tesla cell based systems as well.

So I am looking forward to a firmware update that allows for a reduced voltage offset between the shutdown and restart voltage for the 48V Quattro inverters.

Regards

Colin

Hi Colin, have you updated VEConfigure to the latest version?

Colin59 avatar image Colin59 Daniël Boekel (Victron Energy Staff) ♦♦ ·

Yes, running 90.04.213, as noted I can set restart voltage at 41.2 v but it keeps the 4 V offset from the shutdown voltage. 37.2 V works out to 3.1v per cell so is usable but I don't want to intentionally drop below 3.3 v/ cell. My bms has a cannet output capability so will investigate using the bms signal to shut down the inverter battery draw , until I can use the Victron software to do it.

Regards

Colin

Daniel, I tried reducing the restart voltage to 41.2 and the shutdown voltage to 37.2 V yesterday for testing. I saved and sent to both parallel quattros. This resulted in a quattro reset. When the quattro's restarted I received a low battery alarm and both quattro's stopped inverting. The battery was operating at about 48.05V at the time of the low battery alarm confirmed on my BMV 712. I verified on the color control that the switch was on but quattro was off AC disconnected. To troubleshoot I disconnected the color control and hooked in with VE configure, I verified the low battery shutoff was at 37.2V with DC ~ 48V. I turned on the virtual control panel and verified AC was available and low battery alarm was indicated with inverter off. I then used VE configure reloaded my previous values for low battery shutoff at 39.8V with the 4 V offset the restart voltage is 43.8V, when sending the files the quattro's reset, the low battery alarm cleared and the quattros inverted. It appears there is some fault in the firmware when the low battery shutoff is set to the minimum as above. Let me know if there's something I can adjust before retrying to reduce my restart voltage to 41.2V. It will be a week before I can get back to the system.

Regards

Colin

I've tried it on my 10k Quattro, both firmware 459 and 460, and couldn't reproduce the low battery error.

Colin59 avatar image Colin59 Daniël Boekel (Victron Energy Staff) ♦♦ ·

Daniel, I have enabled VRM for my motorhome under Whale motorhome installation name, and the false low battery alarm was datalogged to assist in troubleshooting the potential firmware glitch described above.

ah yes I see them, looks like one of the units shut down.

how did you configure the units? by cable or through the venus?

Colin59 avatar image Colin59 Daniël Boekel (Victron Energy Staff) ♦♦ ·

UI used ve configure through the mk3 to the ethernet cable coming from the master to the color control(disconnected from the color control end)

Both inverters shut down when in parallel, maybe only one when in split phase....did this first...

Regards

Colin

Hi,

as written by Abay's feature request I cannot start my inverter even though the SOC is eg 50%.

This problem (feature?) persists already with the shown software version on my MultiPlus-II 48/3000/35-32 230V and newest VE configure from today.

This is because of the hardcoded (?) 4 V minimal delta between "DC input low shut-down" and "DC input low restart".


I have a 48 V LiFePo4 Pylontech US3000. If I try to set the "DC input low shut-down" to 44.5 V, the senseful value at which the Pylontech BMS will shut automatiocally down at 8 % SOC, the "DC input low restart" minimal value rises to 44.5 + 4.0 = 48.5 V which is about 50% SOC.

The workaround for me is to set the "DC input low shut-down" to eg 42.00 V, which is really protected by the external BMS in the lithium battery to 44.5 V. But this is no clean solution.

Therefore I'm sitting on a outlying alpine hut and cannot start my inverter at a SOC of 50% ...


--

Regards

Stefan


multiplus.png (29.7 KiB)

Hi @stefanhart

With CANbus controlled batteries like the Pylontech, the BMS will tell the system to shut-down when empty, and you can also use SOC as a factor (use 'shutdown on SOC')

So you can set the shutdown and restart voltages lower to suit your system.

stefanhart avatar image stefanhart Daniël Boekel (Victron Energy Staff) ♦♦ ·

Hi Daniel, thank you for your prompt answer.

This makes a lot of sense (more accurate SOC value over CAN than only measured voltage) and therefore the compatibility guide stated probably ... A GX-device is required, eg Color Control GX (CCGX) or Venus GX (VGX) ...

Hopefully the future Multiplus-Models will have a built-in CAN port.

And a Web-UI via Ethernet/IP/TCP/HTTP

And what about a 19"-Model?

are you saying you don't have a GX-device with the Pylontech battery?

there are now inverters with built-in GX devices, both Multiplus and easy-solar:

https://www.victronenergy.com/inverters-chargers/multiplus-ii%20gx

stefanhart avatar image stefanhart Daniël Boekel (Victron Energy Staff) ♦♦ ·

Oh! That is it! To my shame!

Yet I am not so familiar with the actual portfolio on this PV market - I come from the IT-world where almost all devices today have an ethernet socket.

I will try to replace with my distributor bosswerk.de the buyed Multiplus-II into a Multiplus-II GX. I hope on acceptance, because there could be some projects following.


Hi @stefanhart

I'd just ad a Venus GX or Color Control GX to your system.

Please read this manual about Pylontech batteries:

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

mvader (Victron Energy) avatar image

Hi all, an update on this hysteresis between DC input low shut-down and DC input low restart values. This is currently 1V for 12V, 2V for 24V and 4V for 48V models.

Within a few weeks from now, we'll be reducing that by factor four. The new values will be 0.25V for 12V systems, 0.5V for 24V systems and 1V for 48V systems.

This will allow to set the DC input low shutdown closer (= higher) to the lowest configurable DC input low restart level.

This change will not (further) reduce the lowest configurable DC input shutdown voltage (= 18.6 for a 24V model); also it will not reduce the lowest settable DC Low restart voltage (= 20.6 for a 24V model). The minimum DC Low Restart was lowered earlier, in July, for 24V models from 21.8 to 20.6, and for 48V models from 43.6 to 41.2. Unfortunately, we have not been able to reduce this minimum for 12V units, due to hardware limitations.

Now, if its a good idea to work with so low hysteresis will depend on the system, battery type, size, cabling etc. Up to the installer to pick the right values. When working with a too low hysteresis, the inverter/charger will be switching off -> on -> off -> on -> off, and so forth.


To conclude, a warning: for a Tesla lithium battery, and any other lithium battery, you should not rely on the shutdown setting in the Multi to stop discharging. Instead, to make for a safe system, you need to have a BMS that measures voltages at cell level, and act on that. And not only that, you also need a BMS that, in case for some reason discharge continues, or at the other end of the spectrum, charge continuous while it should not, has an independent disconnect switch, breaker or contactor. I explained this in more detail here: https://community.victronenergy.com/questions/5217/tesla-model-s-battery-multiplus-can-not-turn-on-in.html?childToView=26433#comment-26433 .


I'll post a comment here once the release is done. Have a good night! Matthijs

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Hi all, last Thursday we released the update of VEConfigure allowing a 0.25V hysteresis (for 12V, its 0.5 for 24V and 1 for 48V) between the DC input low shutdown setting and the DC input low restart level. See above for details.

(note that VictronConnect has not yet been updated for this; which means you'll have to manually download the 465 firmware from Victron professional; and update your system to that. And then use VEConfigure for setting it up)

Guy Stewart (Victron Community Manager) avatar image

Thanks for taking the time to write out the suggestion.

I agree with you, and have had to do a delicate dance myself before between battery BMS shut down, inverter shut down and restart voltage with a narrow band lithium battery.

I have passed it on the dev team, and expect some adjustment during an upcoming release.


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That's great to hear.

A related issue is that it would be very helpful to have the dynamic voltage/current curve feature that is only available in ESS also available as a configuration option in the normal mode. I have asked about this before, and I believe I was told that it would happen one day.

I am begging for similar functionality as well for use in my 24v system. I am using a Tesla Model S- battery which has usable voltage from around 19v to 25v. The "DC input low restart" function will not allow settings below 21.8 which means that once my battery falls below 60%, the inverter can not be turned until the battery is recharged above 60%.



Please help make this a reality, thankyou Guy!

same here but with 2 x Tesla in series. 43.6 Volts is the minimum restart voltage settings, which is way to high.

Jens

Boekel avatar image

It would be very nice to have this, also because of the blinking 'low battery' LED when 40% left in the batteries.

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Ilie3000 avatar image

The difference between low input shutdown and restart mine is bigger than 4v, i set 37.2 (shutdown), minimum restart is write on VE config between 41.2 and ..., but when i put 41.2 it automaticaly adjust to 43.6.

We wait the new release so we can adjust values with our needs. Thanks.

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Guy Stewart (Victron Community Manager) avatar image

To be clear, this may come in a future release, not the next next release.

There are software development reasons for this which will become clear soon, but not yet public.

I will continue to advocate for the change.

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Very unpleasant "software development reasons", especially for flooded batteries. If you do not want to discharge below 30% "DC input low restart" should be over 51v ... usually in the middle of the night.

Sirs, in my case when shore power tripped while away from the motorhome, my battery was drained below the restart minimum, there should be a way that for example charger only inverter switch position could override this or AC1 inout generator can override. With my lithium battery, specification (Chevrolet Volt) minimum cutoff is 40.0 V but it means I can only use solar power to recharge until above the reset voltage.

Until the firmware update, or in the interim, I would Also like some additional low voltage alarm or shore power tripped alarms to be able to take action before I lose inverter capability to charge and operate.

Regards

Colin

Hi @Colin59

I don't understand, the 'charge only' setting does just what you ask doesn't it?

Also, with relatively small batteries, that can drain from just powering things like a Venus device, bms, inverter in 'off' position, etc. you really need a way that the bms can disconnect the battery (like a shunt-trip or a bi-stable contacter)

Colin59 avatar image Colin59 Daniël Boekel (Victron Energy Staff) ♦♦ ·

I wanted to "charge only"with voltage less than 43.8 v the current minimum reset, I thought it might be easier for Victron to provide this as a limited software patch. Our lithium batteries have 400 ah at 48v, so even raining we get enough solar to discharge with the base loads. Regards Colin

if you select that voltage as lower discharge limit, you effectively do the same as selecting 'charge only'

Colin59 avatar image Colin59 Daniël Boekel (Victron Energy Staff) ♦♦ ·

My goal is to find an interim measure (until victron updates the firmware) toovercome the minimum 43.8 Volts setting... to use the inverter to charge from 39.8 v to 43.8 when I put the inverter back on normal....Again my lithium batteries operate between 40 and 48.3 Volts....currently this reset limit reduces my battery capacity by half. I can only use my solar through my 150/70 smart solar to get above 43.8 V. Thanks in advance for your support.

Regards Colin

Colin59 avatar image Colin59 Daniël Boekel (Victron Energy Staff) ♦♦ ·

Even if the inverter was enabled for pass through power, tat would help keep the motorhome going until the inverter is reenabled....

When there is AC available on the input (input 1 for Quattro's) the inverter starts up at any voltage.

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Ilie3000 avatar image

Any news with this feature? It past three months... thanks

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Oxy- avatar image

Autumn is here, which means low battery voltages for solar installations too. I tried the latest VEConfigure version and still can't set the restart voltage closer than the restricted +4V delta. Needed settings for a 2S Tesla pack:

  • Low voltage disconnect - 39V
  • Low voltage restart - 40V -> can only set to 43V currently (which is +4V from 39V)
  • Low voltage warning - 40V

In this pack we're talking more than 12kWh in these artificially induced 3V!

Are you planning to fix this? Why is it hard @mvader (Victron Energy Staff) and @Guy Stewart (Victron Community Manager) ? Thanks!

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Hi @Oxy- we did lower the hysteresis, ie we did make it possible to set the restart closer to the disconnect. Its 0.25V minimal difference for 12V systems, 0.5V for 24V and 1V for 48V systems.


And, as also mentioned above, the minimum configurable restart is 41.2 Volts.


Please check again.


Oxy- avatar image Oxy- mvader (Victron Energy) ♦♦ ·

I tried this with latest VEConfigure version on Quattro 48/10000 and MultiPlus 48/5000 - both did not allow to set it lower than +4V delta.

Do I need to update FW on inverters (it did not sound needed)? How to force it out of this +4V constraint?

BTW, the blog above is not saying a word about delta reduction.

Sorry, but I dont know if you need to update firmware, and I dont want to disturb the developers either: so lets apply the standard victron rule: in case of issues: first update to last fw version.

Ps: I dont know what batteries you are using, but why dont you set the dc low disconnect super low? For lithium, you need to use a BMS for disconnect / stop discharge on battery empty. An inverter cant do it by himself since it doesnt measure cell voltage.

Oxy- avatar image Oxy- mvader (Victron Energy) ♦♦ ·

I’m not putting a weak link (contactor) for a reason here. These are Tesla batteries with OEM BMS balancers enabled. This pack never reaches more than 10mV delta between the max/min cells on discharge. Then I have a genset + charger kick-in at 39.3V, so inverter’s cut-off is to be reached only if genset fails. Of course, VRM will send a warning before that. 39V cut-off is still about 18% for Tesla batteries, so plenty of safety margin. Temperature is non issue for this pack - batteries don’t even react to a 250A charge, while environment doesn’t get to freezing. Though I do have BMS setup to send temp. warnings through VRM. All in all, I can rely on inverter’s cut-off for that rare low voltage event (unless it has other issues?).

However, if it does shutdown, to charge the pack from 39V to 43V will take many many many hours with a genset, so I need ability to set this delta to lower than these artificial 4V.

All reasonable lithium packs stay stable until they don't. Cell-based disconnect protects you if a cell goes bad along the way.

It definitely happens: I had to replace one sheet of cells in my Tesla many years ago.

It's okay to do what you're doing (I happen to use a similar approach), but the typical user concerned about protecting the rest of his pack should probably use a contactor wired to a BMS with cell-level monitoring. A good contactor is not a very "weak link."

Hi Oxy, here the official text:

To make for a safe lithium system; there must be a mechanism in place that automatically disconnects the battery from the rest of the system on cell under-voltage, over voltage and also on cell-temperature issues as well as other adverse conditions. This means that the voltage on each cell needs to be measured individually. And also temperature needs to be measured and monitored; preferably at cell level, but usually it is also OK to measure it for a certain number of cells together.

Those measurements must be taken care of by a BMS. At Victron we do make BMS-es, but they are only to be used with our own batteries. We do not make general purpose BMS-es. Also, the under voltage lockout of an inverter, and the over voltage protection in a battery charger can *not* substitute a BMS: both only measure total battery voltage, rather than the required individual cell voltages, and temperatures. Finally, the BMS must control a contactor, that disconnects the battery from the rest of the system.

Please take this seriously, any Tesla or other cell over and under voltage can lead to explosive fires and other severe issues.

For which at Victron we take zero responsibility and also accept no liability at all. It’s the responsibility of a BMS to disconnect the battery in case of issues; not of the Victron equipment.


And unofficially: really, you need a contactor. If you choose not to, you're on your own. Your current solution does not protect against an issue at cell level. Its no joke, and its not me shying away or deflecting the conversation.

Back to the 4V minimim difference: this was fixed (changed to 1V minimum) per firmware version 464.


all the best, Matthijs


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