Battery Temp monitoring for external devices (charger, BMS, etc.)

Waterskier1

New Member
Joined
Aug 23, 2021
Messages
5
I'm building a 4S 12 Volt battery with EVE 280 AHr cells. I plan to heat, and possibly cool them inside a Group 27 Marine Battery Case. I'll be replacing 4 6-volt, 150 AHr AGM batteries. While I was considering options for temp sensing for the heating pads in the bottom of the battery case, I got to thinking that my current AGM batteries in my motorhome have three separate battery temperature monitors on the batteries. There are two "stick on" pads, one of which I think went to the old inverter/charge which was replaced before I bought the coach with a Victron 3000KW MultiPlus. I think the Victron MultiPlus temperature sensor is currently bolted on the Negative terminal of the battery bank. I'm not sure what the 3-rd temp sensor goes to yet (2nd stick on sensor). I know I'll want to move the Victron Temp Sensor to somewhere it can get useful battery temperature. I'm not planning on the BMS being the sole control for my system. I will have 3/8" Battery Terminals mounted through the plastic battery box lid, but mounting the sensor to that will not work. That terminal is thermally insulated from the batteries and won't reflect battery temperature. So, I'm sure this isn't a unique situation so I'm curious what others have done. I would prefer a solution that doesn't require me to take the top off after the batteries are in place, just to connect a temp probe. I'm considering a multiconductor connector mounted on the battery lid. I'll want to pick up ground after the Victron Shunt which is bolted to the wall in the battery compartment. I want to do this so I can measure the battery consumption of the heaters and have a more accurate SOC on my Victron BMV.
 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
129
Tape the Victron to the batteries directly. Current models are wireless, but if necessary just drill through the case.

I have no idea how you’d use that to control a heater. I do believe they make products with built in thermostats.

Victron controllers will cut off even without a temp sensor, using the LiFePo4 profile. The default is set at 5 Celsius to compensate for the controller based default measurement.
 

Waterskier1

New Member
Joined
Aug 23, 2021
Messages
5
I must not have been clear. I want to use the Victron temp sensor to control the Victron units. I have 180 Amp charging capacity (between the MultiPlus and 2) 100/50 MPPT Controllers. It's my understanding that Victron uses battery temp as an input to maximize charging.

I will have separate Temp Controllers mounted inside the box which will turn on & off the silicon heating pads. I'm also considering a fan with it's own Temp Controller to keep the high temp in control.

My statement that I wasn't using the BMS as the primary management system to control the batteries may have confused the issue. My intent was to say that I want to turn on or off heat, voltage and current externally to the BMS, such that it should never have to shut down the battery. It will be only used if all else fails.

I can tape the Victron temp sensor to the battery. I could also bolt it to the negative terminal on the BMS, but I expect the BMS will be at a different temp than the batteries, especially under heavy charge/discharge.

I haven't seen anyone mention this in their battery builds, so was curious how it was handled or if it was just ignored. My Victron Equipment will be in another bay, several feet away from the battery, so it's temperature won't be related to the battery at all.
 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
129
LiFePo4 does not use temperature adjusted charging. Take a look at the (editable) LiFePo4 Victron charge profile.
 

DLTooley

Solar Enthusiast
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Jan 12, 2020
Messages
129
This JBD on AliExpress says something about a heating function, but that is something I know little about specifically or generally. I do believe some folks have heating pads with completely separate thermostats.

The simplest solution of all is to keep the batteries in your living space.
US $91.63 30% Off | JBD 4S 200A BMS Lifepo4 Battery 3S 12V Li-Ion Battery Smart Balance Protection Board With Bluetooth Uart
 

mikefitz

Solar Addict
Joined
May 28, 2020
Messages
859
Victron controllers will cut off even without a temp sensor, using the LiFePo4 profile.
No.
Although you can set the temperature in the controller, it needs info on the battery temperature from an additional Victron device like: Smart shunt, BMV712, Smart Battery Sense, Multiplus. It will not cut off at the programmed temperature based on its internal sensor.
This makes sense since the Solar Controller internal sensor could be at a very different temperature to the battery.

Mike
 

Waterskier1

New Member
Joined
Aug 23, 2021
Messages
5
LiFePo4 does not use temperature adjusted charging. Take a look at the (editable) LiFePo4 Victron charge profile.
Understood. I am not looking for temp compensation charging, I am looking to turn off all charging below a specified temp.
 

Waterskier1

New Member
Joined
Aug 23, 2021
Messages
5
This JBD on AliExpress says something about a heating function, but that is something I know little about specifically or generally. I do believe some folks have heating pads with completely separate thermostats.

The simplest solution of all is to keep the batteries in your living space.
US $91.63 30% Off | JBD 4S 200A BMS Lifepo4 Battery 3S 12V Li-Ion Battery Smart Balance Protection Board With Bluetooth Uart
I plan on using that BMS, but I want to stop charging before the BMS has to do it. The way I look at it, if the BMS has to shut down on over voltage, under voltage, low temp, high current, your design was poor, or a component in the design failed. To me, the BMS is a last lifeline before destruction. I know others have a different philosophy.
 

Waterskier1

New Member
Joined
Aug 23, 2021
Messages
5
No.
Although you can set the temperature in the controller, it needs info on the battery temperature from an additional Victron device like: Smart shunt, BMV712, Smart Battery Sense, Multiplus. It will not cut off at the programmed temperature based on its internal sensor.
This makes sense since the Solar Controller internal sensor could be at a very different temperature to the battery.

Mike
I believe, after further study, that ONLY MPPT controller can shut down on low temperatures. It appears that Victron as specifically addressed this issue, and has prohibited (in software) that function in MultiPlus type devices, believing that should only be handled at the cell level. Curious that the MPPT doesn't follow that philosophy.

There are some work-arounds, but none are very elegant. I'll look further into using Assistants later, my main question is where are people sensing their battery temps, and it seem that most don't (other than internal by the BMS).
 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
129
Both of my Victron’s claim to do it and the setting is accessible to the user in the LiFePo4 charge profile. I presume the battery sense will override the controller thermostat. I have tested none of it.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
5,957
Location
Somewhere South of Denver
I have two Victron MPPT 100/50 and a Victron BMV-712, networked together. I also have two Overkill Solar (aka JBD) BMS.

I have my solar charge controllers and the BMS set to cut off charging at around 32° F. The cutoff for the solar charge controllers is slightly higher than the BMS. I use a 3rd party thermostat with heating pads on the batteries to maintain the battery temperature at 35° F to 45° F. I created a thread for my install of the battery heating solution, which can be found here.

I have three temperatures probes/sensors.
Probes for the BMS and the thermostat are co-located on the top/center of the battery with a small piece of foam insulation on top of them.
The BMV-712 is attached to the post of one of the end cells.

All three probes report almost identical numbers.
 

Philtao

Sailor, EE & Designer of the TAO BMS
Joined
Jun 10, 2021
Messages
28
Location
New Zealand
My statement that I wasn't using the BMS as the primary management system to control the batteries may have confused the issue. My intent was to say that I want to turn on or off heat, voltage and current externally to the BMS, such that it should never have to shut down the battery. It will be only used if all else fails.
I fully agree with you that the BMS should shut down the battery only if all other warnings and corrective measures have failed... and give a lot of warning before it does. Instead of using multiple external systems, you can use a BMS that can do all of that on top of the basic protection / shutdown capabilities. The TAO BMS has been designed for that purpose. It has 6 outputs that can be used to:
  • command charge, load (or shutdown) relays (these are the last resort actions if all else fails)
  • remote control equipment like Victron MPPT / Multiplus (can also do it with CANbus) - usually done well before a battery shutdown is required
  • turn on/off heating and cooling
  • parallel the lead-acid battery before the lithium battery is shutdown
  • pre-charge inverter and charger capacitors...
Each of these outputs can be activated by one or more triggers. For example if you use one output to remote control the chargers, it can command the OFF state of the chargers if either of these conditions happen:
  • a cell voltage is above a set value (if charge voltage is 3.45vpc, you can set to cut charge at 3.55vpc) - can also set a visual / audible alarm in your living quarter
  • a cell temperature is less than 5°C
  • the SOC reaches 100% (based on parameters set in the BMS)
  • .....
You can set triggers based on cell voltage, cell temperature or SOC%. It can be a high value, a low value or a maximum differential between cells (one cable / lug per cell to measure both voltage and temperature). Each trigger has its own reset value (hysteresis)
There is also a charge management feature that is used to remote control the chargers by stopping charge when SOC reaches a set value and restarting the charge when it falls below another value... with a periodic full charge to re-calibrate SOC. For example, when the motorhome is not used but fridges are on, the solar can cycle the battery between 40 and 60%, with a full charge every month.
 
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