schnitzel avatar image

MultiPlus: Disable Charger based on battery temperature

I'm currently building an RV off-grid system based around a Lithium Tesla Battery and MultiPlus. In the system is also a BMV 702, BatteryProtect 220 and Color Control.

As the Lithium Battery really doesn't like to be charged below freezing temperature I'm planning to have an automated heating pad that keeps the battery warm, but I would like to have a fail safe which disables the MultiPlus Charger whenever the temperature of the Battery reaches 5°C

My current setup is to connect the BMV-702 Temperature Control Sensor to the Battery and then connected the BMV-702 Relay to the MultiPlus AUX1 which controls the Charger via the Charge Assistant. This works nicely, but I was wondering:

1. The MultiPlus already has a Temperature Sense Connector plus the Temperature Sensor shipped, when I measure the voltage of the Temperature sensor I get a reading of 2.6V at 25°C. Is there any datasheet of the Temperature Sensor that I could use to configure the MultiPlus Assistant for temperature? I would really like to not depend on the BMV for the temperature measuring and best have the MultiPlus measure the temperature directly.

2. I found the new Shared Temperature Sense feature of the Venus/ColorControl: which mentions:

the Venus-device will send the battery temperature to the connected Solar Chargers and Inverter/chargers.

But I don't see anything in the MultiPlus Configuration Screen to do anything with that Temperature or any other way that it actually receives the temperature form the Venus/ColorControl.

Plus just two other small questions:

1. Is there any way to see the current voltage reading on the MultiPlus AUX inputs? I'm having a bit a hard time to find the correct voltages to use in the Assistant

2. When I disable the Charger in the VEConfig all together, but then enable the Charger again via the Assistant based on the AUX1. The charger is actually running! That's a bit scary ;) Also which charge settings are used? I assume just the last settings of the charger before it was disabled all together?

Multiplus-IITemperature Sensortemperature
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3 Answers
mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi Schnitzel, welcome to the community; and sorry that this answer took a while.

1. Datasheet for the temp sensor: no we don’t have one available; sorry. Putting it in the freezer would perhaps be the most practical solution :-).

At some point we’ll add a feature in the inverter/charger itself so that you can configure it to stop charging at a certain temperature; just like our solar chargers already have.

For any other readers thinking about their lithiums:

- Victron VE.Bus BMS connected-, or BMS 12/200 connected-, Smart lithium batteries will stop charging; there the logic and temperature measurement is in the battery; and controls the connected equipment like the Multi. See recent Smart Lithium firmware update for details.

- same thing for CanbusBMS connected batteries like BYD or Freedomwon: the battery itself measures temperature and decides what to do by logic implemented by the battery manufacturer.

2. What does the Multi do with the temperature: it uses it to compensate the charge voltage. Only for lead batteries: lithium doesn’t need charge voltage compensation.

1-small: voltage reading on aux inputs: no; not available. Nice advanced feature though!

2-small: indeed. Last settings. Yes; its the issue with the Assistants:: gives you lots of power! :-)

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Hi @mvader (Victron Energy) - I'm working on a project with a small Multi and a non smart lithium battery.

At some point we’ll add a feature in the inverter/charger itself so that you can configure it to stop charging at a certain temperature; just like our solar chargers already have.

Has any progress been made on this?

Hi Warwick, not that was never made yet - sorry.

The number of systems where this is necessary (ie systems where there is no BMS installed that takes care of this) is so low that this change hasn't made it to the top of the list yet).

Warwick Bruce Chapman avatar image Warwick Bruce Chapman mvader (Victron Energy) ♦♦ ·

Ok, we have a very basic "Office Backup" solution with a 500VA multi and a lithium battery that has dumb BMS and we are looking for a way to limit charge current if below 0.

betz avatar image betz mvader (Victron Energy) ♦♦ ·

I also would love that feature. +1

durval avatar image durval Warwick Bruce Chapman ·
I just checked and on my Multiplus Compact 12/2000/80-30 230V updated to the latest firmware (2608485), there still seems to be no option for the Multiplus to control this (ie, disable its charger when its battery temperature sensor indicates the temperature is under a configured limit).

@mvader (Victron Energy) I have a reasonably smart battery (a Pylontech RV12100) with a BMS that protects it from almost anything (excessive charging, discharging beyond a certain voltage, overcurrent, etc), but as far as I can see, it has no temperature control, so I really need this feature -- specially given that the BMV will seemingly not energize its relay on such a condition, only sound the buzzer (see the answer I just posted to the OP).

And even if the battery BMS did it and the BMV supported it, the correct place to control this would be in the charger itself, just like the competition does.

So, can you please move the priority for this a bit up in your list? Pretty please? ;-) Seriously, the Multiplus is an amazing piece of equipment and not having this really detracts from it.

Thanks in advance,

-- Durval.

Hi Durval and all, yes noted. Its pretty high up on the list; I expect that we have this taken care of in the coming few months, ie before northern hemisphere winter.
durval avatar image durval mvader (Victron Energy) ♦♦ ·
Thanks for the update, @mvader (Victron Energy). Definitely looking forward to the firmware version with this implemented. will let me sleep much easier at night! ;-)
durval avatar image durval mvader (Victron Energy) ♦♦ ·
@mvader (Victron Energy) please let us know back here when the firmware version with this feature is released, will make it much easier for me (and all the folks watching this) to be alerted and then apply the update. Thanks in advance!
Hi @durval , I'll try. I'd love to have some process for this in place, but currently we don't.
durval avatar image durval mvader (Victron Energy) ♦♦ ·
No prob, @mvader (Victron Energy), your efforts are greatly appreciated. I will try and keep an eye on the firmware changelog anyway, I just hope I'm able to understand it when it comes up :-)
Hello Durvan,

Till the option from Victron is availible you can use a programmeble fridge thermostaat, programmed at 5 degrees for example you can switch off the Multi from charging.

Have the switch from the thermostat wired to the Multi aux or other contact,

Program the "2 way BMS" assistant, to stop charging.

Hi @BenM, good tip. I in fact have such a thermostat, but I'm not very sure of its precision/exactitude. And as always, it's one more thing to fail / worry about / etc.

As winter is just ending here, and in a few more days/weeks I plan on heading with my motorhome to the beach, I don't think I will be experimenting negative temperatures in the next few months, so (by @mvader (Victron Energy) 's estimate), we should all get the new firmware with charging-disabled-on-low-temps capability -- I think I will just wait till then (but with an eye on the thermometer anyway).

Thanks for the tip anyway!

Hi @BenM
There is a problem with sending a signal "do not charge" from BMS or that "Fridge thermostat", because MP does not know if this signal was sent because of the battery is full or temperature is to low.

MP assumes that the battery is full and sets the SOC to 90%.

That reaction of MP can be disabled in "2 signal BMS assistant" but not in "ESS assistant".

First priority is always protecting the battery. It is correct that with many BMS it is not visible the reason that charge is disable.

With the thermostat you can see temperature is too low, maybe you can feel also that it is cold:) or adding a extra warning LED would be easy.

You can program in assistant what you like to do if a external contact is activated by low temperature.

I can not review at the moment, but I think you can force the charge to float.

With a good system the charge is never disable by BMS with a full battery. When battery is full charger goes to a lower, safe, float voltage.

With the Victron update, the Victron battery tempsensor notice a low temperature, I hope that they also add a LED fault code on the Multi.

Without this fault code we can not see why charge is stopped.

It would be nice if the new function can OR switch the charge off, OR switch the charger to float.

johanneshovda avatar image
johanneshovda answered ·

I would like to do a similar variation of this, to restrict max charge current to 10% of the battery capacity if the temperature is at or below freezing.

Can I achieve that on the Multiplus using the Multiplus Temperature Sensor (for ambient temperature sensing) and an assistant? In other words, not an on-off relay function, but rather a dynamic config change?

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durval avatar image
durval answered ·

Hi @Schnitzel long time since you posted, but I hope you are still around and the following is useful to you.

I just found this on the BMV manual PDF (p.29 in the file and p.27 in the paper manual):

45. Low temperature alarm -702 and -712 only

When the temperature falls below this value for more than 10 seconds, the alarm will be activated. This is a visual and audible alarm. It does not energise the relay.

Sorry if you are already aware of that, and/or if I'm missing something.

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