how to add an additional temp sensor?

[RV14_TD]

I'm in the process of transitioning to a lithium battery and I though it would be a good idea to monitor the battery temperature. Q: is there a sensor that I could purchase and connect to one of available general inputs in EMS?

 

[Bob Y]

The EarthX temperature sensor is wired to GP10 on my RV-12iS.

 

[RV14_TD]

My battery doesn’t have a temp sensor
I need to get one and connect it to EMS

 

[CanardMulti]

Lithium batteries do indeed need to be monitored, preferably by an integrated BMS (battery monitoring system).

To be precise, that wire from the EarthX battery does not send numerical temperature data.. The wire coming from the battery is a way for the BMS circuit board that is part of the battery assembly to indicate that one of several problems may exist. The flashing of the LED refers to the LED on the battery. I think (but I'm not certain) it also refers to a remote LED that builders can install on their panel. If the fault alert wire is instead connected to the EMS 220/221 per the diagram, how a fault alert is presented via SkyView beyond just a simple 'battery warning' is not clear to me yet. From the EarthX manual:

 

[Rhino]

The battery discrete fault output does not indicate an actual temperature, but it does indicate an overtemp fault by fast flashing ( 2 seconds on/2 seconds off). That can go to an LED, or to the Skyview where you could configure a widget to display it. This is a notification only. There is no action required by the user because the BMS automatically shuts the battery down whenever there's an overtemp. I know of no way to put an additional temperature sensor on an EarthX battery. I suppose you could ask them if it's possible to piggyback off the built in sensor, but it isn't really necessary with the BMS already monitoring it. It might also void the warranty.

 

[RV14_TD]

Just to clarify, I'm NOT using an earthx battery. All I need is a temp sensor which could be attached to the battery box in front of firewall.

 

[Rhino]

A temp sensor in the box is much less than an ideal solution. The internal battery temperature is what matters, and an external sensor won't help much with that, other than to make a wild a$$ guess ever so slightly less wild. Does your battery have a Battery Management System? Most advanced BMS will be set up with internal temperature sensors to monitor temperature within a cell or cells. An external temperature sensor can be used, but it doesn't give an accurate indication of the temperature within the battery. So, BMS systems with external sensors have specialized circuitry and algorithms to estimate the internal temperature. It's not as accurate as the internal sensor, but it's far better than a simple temperature probe on the outside. If your battery has a BMS, it's possible you might be able to tie in to a non-discrete connection somewhere to get a temperature reading a Skyview could interpret. If you're wanting to do this without a BMS, your chance of getting a reliable reading is very low. To determine what sensor you could use would require knowing the external temp range of your battery, how it corresponds to internal temperature, where a limit should be, and correlating that to a five volt range for the Skyview. I wouldn't know where to begin doing that. The range and limit would depend on your specific battery chemistry (see https://batteryuniversity.com/article/bu-409-charging-lithium-ion), and those are based on charging temps, not cranking temps. How to determine that from outside the battery is a challenge I simply would not undertake. But if you ever do figure it out, please come back and let us know.

 

[RV14_TD]

Thanks for all comments. My battery doesn't have a BMS. I'm very aware of pros and cons, as well as operational limitations. There are two corner conditions that I want to monitor: low tem and high temp. Meaning respectively 40 and 170 deg. I'm OK with attaching the sensor to battery case.

 

[CanardMulti]

Do you mind sharing which battery you are considering? Is it Li-FePO4 or Li-something else? Since it has no BMS, how do you plan to keep the individual cells balanced and protected from deep discharge? I'm genuinely curious.

 

[RV14_TD]

Shorai LFX18A1-BS12, it's a very robust Li-FePO4 battery. Cell balancing is done using an external charger