M116A3 Build

[lfhoward]

Solar Update:

Nope, the Venus VRM never came back on today, so I had to reset things manually in person. The AUX solar controller load output can't be set to streetlight mode unless there is a solar panel telling the machine when dawn and dusk are. Live and learn.

On the other hand, I temporarily got my BMV712 battery monitor hooked up to the VRM and I love the additional info it provides on battery state and battery temperature. My USB cable is just out in the open, but I will hide it under the boards later, before our next camping trip.

It is hard to compare apples to apples on the new parking space, as I had no solar this morning due to my own screw up, but this afternoon it is 2 pm and I am still getting 20+ watts of solar. I would say that's a win compared to being parked next to the trees. Tomorrow I won't get max power in the morning because it will be cloudy, but it will be interesting to see what happens.

[lfhoward]

Thinking about adding timers to the load outputs for the solar charge controllers because streetlight mode doesn't really let you set devices to turn on during the day. I want the battery heater to be enabled during the day, for example, and not just before dawn. In order to keep it on past dawn I have to control it manually right now.

I have not found a satisfactory timer on Amazon or Ebay yet, because they are all either limited in what they can do, or are too big, or don't run on 12 volt. Here is a good option I found last night for a tiny, wifi-enabled timer that would potentially work great for what I want to do:

http://timers.shop



Edit: I ordered one and I’ll report back once I get it hooked up and working. One of the neat things about this device is that it not only has lots of timer modes, but that these can be started and stopped by voltage on a trigger wire. My idea is to program one of my Raspberry Pi’s to trigger the timer that enables the battery heater circuit. I could set up the Pi to trigger the heating circuit at the same time every day (like 6:30 am) and would be able to modify the time remotely if I wanted. Pretty cool.

[lfhoward]

This new parking spot away from the trees is officially better!



I have 90 watts coming in right now, which is 50% better than anything I got in the old location. 40 watts is going to loads (9 watts for the Victron equipment, 31 watts to the battery heater which is currently on). The other 50 watts is charging the battery. Nice!

The reason it’s doing so well at 10 am is the unobstructed position of the sun right now.

[lfhoward]

I am excited because the trailer’s solar system broke even today (and might get a little ahead by sunset). By broke even I mean that it made back the energy spent on 24 hours of VRM monitoring and warming the battery in the morning from 32°F up to 45°. Here are some screenshots from the VRM depicting the last 24 hours:

Production vs Consumption Summary:


Solar yield in Watts:


Battery amp hours status (0 Ah used at the top would be 100% full.):


^^^ The steady decline is the constant use of power for the battery monitoring system overnight. The trough to the right of that was power used to heat the battery this morning. The incline to the right is due to solar charging.

Finally, here is battery temperature for comparison:


^^^ The stepped decline is the battery cooling off overnight as the outside temperature dropped. The rise in temperature corresponds to the amp hour dip in the previous graph, when the battery heater was on. Apparently the battery temperature sensor has a resolution of 2°F, which is why the graph looks stepped.

Solar charging can only occur if the battery is at least 39°F the way I have it set up. (LiFePO4 can technically charge above 32° but I want a margin of safety.)

As the days get longer and the overnight lows get a bit warmer, I expect to have a net surplus of amp hours on average days. Today was mostly cloudy according to my weather app.

[featherliteCT1]

Good news and great data!

[lfhoward]

Good news and great data!

Thanks for following, Featherlite! I don’t know if anyone except you and me would be interested in the deep dive into data, but maybe someone considering setting up the VRM on their Victron system would be encouraged by seeing what it can do. I think the system is pretty cool.

Tomorrow morning’s low will only be 33° so it will be interesting to see if we can send more electrons into the battery tomorrow and fewer into the battery heater. As of 10 pm tonight the outside temperature is 35° and the battery is still hanging on at 43°. Tomorrow morning will be mostly cloudy like today, according to my weather app. High of 43°F predicted by mid day.

[lfhoward]

Today was a good day for charging. I made back all the energy used by 11:25 am. However, at this time the voltage of the battery hit 14.1, which I had set as the absorption voltage. At that point charging dipped as the controller changed modes. Two hours later it went into float mode, where it is now. In float mode, voltage is maintained at 13.5, and the controller is basically only offsetting current use. Because it didn't continue charging in bulk mode, the battery topped out at 92% at 11:25 am, when there was still tons of sunlight.

I think I had set the absorption voltage at 14.1 because I was trying to extend battery life. Victron's default is 14.2. I changed it back to that because I could probably get the battery up to 95% before it switches over. Float voltage is at 13.5 because that's Victron's default.

[lfhoward]

This morning the temperature dipped to 13°F. The battery heater kicked in as designed, and stayed on for 3.5 hours to get the battery temperature up to 45°. Solar generation this morning has been excellent. There will be no problem getting the charge back to where it was yesterday, and it’s almost there as of noon. Since I set the absorption voltage to 14.2 instead of 14.1, I will see whether the battery tops out above the 92% it has been doing. I’ll edit this post later to add this information.

One hiccup I’ve been noticing is that the VRM keeps losing connectivity with the battery monitor and one of the charge controllers this morning. Connectivity will disappear and come back. Rebooting the GX device (RPi) did not solve it. I suspect the low temperatures are interfering with the cheap Ebay cables I got to connect the devices to the raspberry pi. Looking online, I see that non-Victron cables van cause strange issues like this, so today I sprung for the expensive Victron VE.Direct to USB cables, which are beefier construction and shielded.



I used the DIY5 code at ContinuousResources.com for 5% off. Every little bit helps.

EDIT: at 12:05 the battery voltage reached 14.2 and the charger went into absorption mode. At that time, the amps used from 156 were about 16, so the battery was at 90%. The battery monitor decided to do a synchronization at that point and call the battery full at 100%. So, from now on 100% means 100% of usable, but 90% of actual battery capacity. I am ok with this, as charging to 90% of capacity is supposed to minimize cell degradation and extend battery life. It will also simplify things for family members who might be looking at the battery monitor to know when charging will be complete.

EDIT: Now that the outside temperature is above 20° the VRM stopped having its connectivity issues. The low tomorrow morning will be 11°. We will see if they return.

[John61CT]

Can you change the definition of 100% SoC?

Hitting any setpoint over 13.8V is fine especially if it is holding CV / Absorption stage.

Not saying 14.1V is "overcharging" per se but really anything higher than the minimum required to get to 3.33-3.35Vpc is just unnecessary stress, does not significantly add to actual usable capacity, aka "surface charge"

That is for normal usage cycling

maintenance protocols for occasional balancing, SoH benchmarking can go higher, even to max spec voltage if desired

[lfhoward]

Can you change the definition of 100% SoC?

Hitting any setpoint over 13.8V is fine especially if it is holding CV / Absorption stage.

Not saying 14.1V is "overcharging" per se but really anything higher than the minimum required to get to 3.33-3.35Vpc is just unnecessary stress, does not significantly add to actual usable capacity, aka "surface charge"

That is for normal usage cycling

maintenance protocols for occasional balancing, SoH benchmarking can go higher, even to max spec voltage if desired

The battery monitor automatically synchronizes the charge level to 100% on its own. I can synchronize it manually back to 90% yes, but don't really mind, since 90% is for my purposes, "full."

I hear what you're saying about 13.8 volts being sufficient to charge the battery without undue stress. I think that's what Andy from the Off Grid Garage has his absorption charge set to. I may play around with it and move the number back to 13.8 to see how it goes. Andy also uses 15 minutes for absorption time rather than the default 2 hours. I am not sure what the difference would really be in regards to charging, but the voltage would not be held at the max for as long every day, possibly leading to less degradation. On the other hand, since cell balancing at the BMS is most effective when the voltage is higher, I would guess it is good to have at least some time during the day with the battery up at absorption voltage.



^^^ Here is the record of amp hour status of the battery over the last 24 hours. You can see the steady drain by the Venus GX (Raspberry Pi's) during the night, the chasm of battery heating in the morning, and the steady rise during morning charging. At about 12:00 PM you can see the vertical up, which is when the battery monitor resynchronized itself to 100%.



^^^ John, looking at the difference in 13.8 vs. 14.2 volts-- The difference today was literally only a difference of 9 minutes of charging (11:51 am for 13.8 volts, 12:00 pm for 14.2 volts). During those 9 minutes the battery only added 0.4 amp hours, using data from the previous graph. Seems like you and Andy are probably right. Those 0.4 amp hours are not worth the extra degradation that would occur over a lifetime of use at a set point of 14.2 volts vs. 13.8 volts. I'll set my absorption voltage to 13.8 and see how it goes tomorrow.

[featherliteCT1]

You go, brother!

[lfhoward]

You go, brother!

Thanks!

[John61CT]

You got it, less is more at that top end, avoiding the shoulders can extend lifespan a lot.

Balancing should only be needed occasionally, say 4x a year, let it go higher / longer specifically for that

Can you see the per cell/group voltages?

[lfhoward]

Can you see the per cell/group voltages?

I can, but not remotely. It is a bluetooth connection with the Overkill BMS. Last I checked a few days ago when the battery hit 92%, the cell voltages were still nearly identical with no need for balancing.

[John61CT]

So long as you can pretty easily get them back to say 20-30 mV then you can let the delta get to say 70-80mV between rebalancing sessions

In case the BMS does not let you drop the Start Balance voltage lower than your usual charge termination CV setpoint.

Then when you want to balance, bring V up over that threshold and hold, ideally at a current rate just enough for balancing, until you get to your target delta.

In a healthy pack kept from the shoulders both top and bottom that might be needed only a few times per year.