Renogy Rover Elite 20A with 12V Smart Battery Cold Weather setup

[sirloins]

Hi,

So I purchased these three items:

2 x 100W Renogy Solar Panels
Rover Elite 20A MPPT Charge Controller
Renogy 12V 100AH LiFePO4 with self-heating

I am planning to set this up at a remote location over the winter, hence the self-heating battery for those cold days (down to -30C perhaps). It will run a small camera, cellular hotspot, and raspberry pi. The cameras and raspberry pi can be remotely shut off if/when needed using some MOSFET switches.

I have a few questions that I can't seem to find answers on:

1. The battery and charge controller have a RJ45 communication port (RS485 I believe). Does anyone know if the battery and charge controller will talk to each other? I was hoping they would for battery charge % as well as temperature. The charge controller does have an external temp sensor, but I think reading from the battery directly would be more accurate than a temp sensor stuck outside the battery.

2. Does anyone know how the self-heating actually works? Will it only heat when it is being charged? I was hoping that during a week of cloudy weather it would not heat itself since it wouldn't be getting charged. The site basically says the battery will self-heat once it is below 5C, maybe I need to test this in my freezer for a few days?

3. Anything else I should think about running this setup remotely? I plan to have the battery and charge controller also wired up to a small microcontroller or the raspberry pi so I can collect data on it. I also saw reference to CAN protocol along with RS485 although I can't seem to find anything further about the CAN protocol.

Thanks!

 

[Wjm1964]

I can't help with Q1 but for Q2 I believe the battery heat only works under charge conditions. Putting your battery in the freezer will only result in a frozen battery.

 

[mikefitz]

You may have issues with this setup.
Self heating only occurs under charge with a continious charge current of over 4 amps, 50 watts. Heating will enable below 5 deg C and will not switch off until the battery temperature exceeds 10 deg C.
It's unlikely the other electric stuff, will be happy at -30, so this needs to be considered.
200 watts of solar in winter may not give you enough power for both heating and the application.

Under cold conditions the battery can deliver power down to - 20
It will accept power down to 0 deg C, then will disable the charge path, recovery at 5 deg C.

Renogy give no information that I can find on their product communication protocol.

 

[sirloins]

Thanks for the info on #2.

On #1, I am assuming that there is no communication from the Charge Controller to Battery via the RS485, they seem to both be "slaves" and they are meant to connect to the Renogy hub/controller they sell separately.


So what I have in my setup is a microcontroller (Particle Cellular one) that is connected to both the charge controller and battery, there are some open source examples of how to communicate with both the battery and charge controller. I used those as a reference as well as some documents I found that listed the different parameters to read/set.

I send the data over cellular and then into influxdb + grafana to view it. This is a subset of the data for the past 30 days. I am also logging individual cell voltage/temp and some other items. You can see on the 11th the battery got a bit lower than I'd like, so I remotely shut down some of the loads until we get some sunny days.

I appreciate the feedback as well about the whole setup under -30C not working right. This kind of setup has been something I've wanted to do for years, I decided last minute to just do it and see how it goes. As long as the solar panels and battery aren't destroyed by me this year then there are many things I will improve for next year. I am hoping that I can keep the inside junction box warm enough that it will never get to -30C (just by running the electronics continually). That said, the main electronics module that controls power to the other (consumer grade) devices is ok down to -20C.

 

[gerrys]

Just curious, and this is just a thought, i am more asking than suggesting:
Would it be possible that 5 or 6 lead acid batteries is a better choice for a location where it will continuously be freezing temperatures for much of the year? Five 100 amp-hr lead acid batteries (200 usable amp-hr at 40% depth of discharge if you want long battery life) can be bought for less than (60%?) the price of one good LFP with self heating. I know that LFP is sexy, but in this case it seems there is a practical side to lead acid. No worries about freezing temps, no worries about the super expensive LFP being ruined, can charge even if the battery goes dead from extended clouds etc. Thoughts?

 

[sirloins]

I did weigh those options, the reason I went for the LFP with heating was that if I did discharge the lead acid too far it would freeze, and then I could never charge it until it thawed (I had this happen to a car battery once). I am also monitoring the "charge cycles" of this battery through the BMS, so far I have only used what it claims is ~3 cycles, this was a concern for me as well initially.. but based on only using 3 cycles in 1 month it seems like a non-issue.

If I had more confidence in not bringing the charge below 40% say (or whatever is required to not freeze at say -30) then I might have opted for that route.

 

[sirloins]

Alright, the first day of sun in a week or so!

I just wanted to say that the description of the heater/charging from SolarShed is spot on: https://diysolarforum.com/threads/renogy-smart-lithium-battery-with-self-heating.25782/post-355513

My battery hasn't been charging for a few days and I can see it is due to the low temperature (as expected).



On some days, I see many spikes of battery usage around 3-4A. This is when the battery is receiving some solar, and attempts to turn on the heater but there is not enough solar power to run the heater so it shuts back off. Below pic is of a day where the cell temp is below 0C.





The battery heater seems to require 60W of solar to remain on. If there isn't enough solar then it will kick off and try again later.

It is actually interesting, because there is some power available, I can turn on some small loads (a few watts) and they will not consume battery power. So say my battery is low, as long as I have a few watts of solar, I can turn on a few of the items I have during the day.


Here are some graphs from today, again you can see the large current spikes from the battery before the solar is able to provide a consistent 60W. Then once the cell temp gets above 5C it will feed power to the battery (and intermittently use the heater as necessary).





I am able to remotely query the BMS via modbus and I checked the two battery temperature settings:

Charge Low Temperature Limit = 5.0C
Charge Under Temperature Limit = 0.0C

I could also adjust these if I wanted, obviously they are set to safe values and will leave them for now.

The discharge numbers are also important.

Discharge Low Temperature Limit = -10.0C
Discharge Under Temperature Limit = -25.0C

So I suspect some current limiting below -10.0C, although nothing I have would hit this. Max I draw is ~10-15 Watts.

The -25.0C might become an issue though, if the battery gets this cold I believe it will disconnect output power completely. This might be something I remotely adjust to allow the battery to remain functional (again with no load on it except the charge controller) below -25.0C.

I don't know if much damage to the battery could occur with just the charge controller drawing power during the night. The charge controller also states to not have it connected without a battery, so I don't know what is worse.

 

[HRTKD]

While I sympathize with your system's inability to charge due to low temperatures, I will point out that I made a conscious decision to keep my batteries above 35°F so they could take a charge as soon as the solar charge controller (or whatever) is able to send current to the batteries.

As you've seen, a battery that is allowed to get colder than 32°F can take hours to heat up, wasting valuable solar production.

With an internal heating solution (heat before charge), there isn't much you can do. However, insulating the battery (on all sides) works very well. I don't track the amount of time my warming pads are actually on. That would be a very good metric to have, but I don't have that level of detail. What I can say is that my system doesn't seem to use many watts to warm the batteries. I use R-7 insulation on the long sides of each battery and R-10 on top.

 

[sirloins]

Thanks for the input, I think the suggestions for insulating the battery are great. Definitely something I will do next winter. I suspect once it is fully buried in snow that will help a bit with insulation (it is in a plastic battery box as well, but that isn't insulating).

I didn't research it enough beforehand. I figured the battery heater would just use as much power as I gave it, I didn't realize it required 60W or it wouldn't even heat. I thought maybe if I was getting ~20W that would slowly warm the batteries up. Another option that would be good, is if I knew that it would be a sunny day, it would be nice to warm the batteries using internal power so that I don't lose any of that solar power while I wait for it to reach 60W and then heat the batteries.

Update: Below is a graph of the battery cell temp (from BMS) over the past 7 days. The first few days were cloudy and was not able to get 60W from solar, so the battery did not charge or heat. The last two days were sunny and the heater was able to get the battery up to temperature fairly quickly and begin charging.

The BMS seems to attempt to turn on the heaters every 10 minutes while it has solar power available. It turns on the heater, and if the solar is enough (~60W) then it will keep them on. If it detects there is not enough solar and that the heater is drawing from the battery, it will shut the heater off and try again in 10 minutes. I would love an option in the BMS settings to allow the heater to function and draw power from the battery. This would let me use the increasing solar power in the morning to warm up the battery so that it isn't wasting any solar power.

 

[sirloins]

I wanted to add an update after speaking with Renogy regarding the modbus communication and the battery heater. I mentioned to them that I wanted to know if there were any configuration options via modbus to allow the battery heater to function using internal battery power.

So they did reply with the following:

The starting conditions of our RBT100LFP12SH-US battery self-heating function: When the voltage difference between the external charging device voltage and the battery voltage is greater than 0.5V, and the battery charging current is greater than 4A, the internal temperature of the battery is lower than 41°F (5°C) , the battery self-heating function starts to work, and when the internal temperature of the battery reaches 50°F (10°C), the battery self-heating function will stop; the heating film in the RBT100LFP12SH-US battery consumes the power provided by the external charging device and will not Drains battery power; there is no mechanism to drain power from the battery to allow the heating film in the battery to work.

There were two parameters in the modbus datasheet I thought would let me adjust when the heater turned on/off.



I was a bit too hopeful, I now believe that the heater on/off temperature is basically hard-coded at the above mentioned temperatures. I believe these two configurable temperature limits just tell the BMS to not charge below the "Under temperature limit" and will charge at a some reduced current rate below the "low temperature limit". I haven't really been able to prove this, but that is what it seems. I did try setting my battery to allow charging at -1C with the above parameters, but it didn't seem to work.

 

[Northernchateau]

Let me speak from 5 years of experience with 2 unit shown below which is:
175w panel,
Renogy Rover 20a,
2 110ah deep cycle Walmart FLA Batteries in small vented coolers
TP link router w/ Verizon air card
Foscam or Microseven webcam uploading a pic every 5 mins. ( both cams have IR for night pictures)

In the summer 1/2 the time that will make enough power to go into "float mode"during the day.
If the panel does not get snow covered this unit has functions no problem down to -30 deg F.
If the panel gets snow covered I get approx 3 days before I have it low voltage shut down @ 11.5 VDC (per battery)
If the unit low voltage shuts down it will take several days to charge enough to reset. (12.7 volts)
For that reason I will be upgrading both units next year with 300 watt panels .

My suggestion based on the low temps, go to FLA and go to bigger or more solar panels.

 

[sirloins]

Nice setup! Thanks for sharing!

Yeah, that sounds like a good way to go for me next year. More FLA capacity and keep it charged enough to not freeze.

What mechanism do you use to do the low-voltage shutdown? I see you mentioned the Renogy Rover and not the Elite, I believe that has a "load" output that will handle this for you correct? On the "Rover elite" that I have it does not control the load from the battery, so it might be worthwhile for me if I switch to FLA batteries to ensure they don't drain too far.

 

[Northernchateau]

Nice setup! Thanks for sharing!

Thank you

Yeah, that sounds like a good way to go for me next year. More FLA capacity and keep it charged enough to not freeze.

Agreed as I am sure once you start you will want to start adding other things.

What mechanism do you use to do the low-voltage shutdown? I see you mentioned the Renogy Rover and not the Elite, I believe that has a "load" output that will handle this for you correct? On the "Rover elite" that I have it does not control the load from the battery, so it might be worthwhile for me if I switch to FLA batteries to ensure they don't drain too far.

I have 4 cams running on solar and all had, the unit in the picture below to avoid killing a battery because if low voltage when first put into service.
Two of the systems now have Renogy Rover or Rich Solar SCC and they have a low voltage output disconnect built in.

 

[sirloins]

Oh awesome, thanks! I didn't know those existed.