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gregarious avatar image

Newbie Troubleshooting Questions

Hello,

About two months ago I had a system installed as itemized below and have read most of the manuals so far. I am not an installer and have no prior knowledge or skills in solar systems so please keep that in my mind when responding.

I am thankful for this forum and, like many users, will be consumer at first before I can contribute to others. If I don't thank you when you respond, please know that I do appreciate your responses.

Question 1
Often, when my battery bank is completely charged, I will turn on my inverter to run the air con for a couple hours or other power-hungry devices like the microwave or induction stovetop. Almost immediately after turning on the inverter, my Skylla-i Control GX unit will flash the red, "Low Battery" light then turn off the air con. Then, 10 seconds to a minute later, the light will go off and the air con will start back up. This process will repeat non-stop. Why does the "Low Battery" light come on when my 1,000AH battery bank is fully charged?

Question 2:
I read somewhere that it's not ideal for lithium batteries to always be topped off and in float mode between uses, as mine are. Is that true? Will the answer depend on whether you are full-timing or storing your RV?

Question 3
I read that one of the benefits of lithium batteries is that you can safely discharge them to at least 20%. However, my installer set the "Discharge floor" value to 48%. Does that seem reasonable or can I safely change that to 20% to reduce my costly and noisy generator use?

My 2021 Dynamax DX3 RV solar system the following key components:

- BMV-712 Smart Battery Monitor
- 6 x 200-watt solar panels
- 5 x 200 AH Victron Lithium Batteries
- Multiplus Inverter/Charger 12V / 3000VA / 120amp
- VE.bus BMS
- VE.Bus BMS Mains Dectector
- SmartSolar Charge Controller MPPT 150/100 \
- Tr VE.Can
- Skylla-i Control GX
- Magnum MS2812 Inverter/Charger

low battery warningdischarge level
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1 Answer
Alexandra avatar image
Alexandra answered ·

@Gregarious

1. Battery voltage may be sagging due to voltage drop under load possibly from the wiring configuration used or cable length and size. You can usually see this on the vrm data

The other possibility is the draw from the aircon is too high for the inverter. More spec on that will be needed.

2. Lithium cells do not like to be charged to 100% and discharged, this is true. However the battery manufacturer has already considered this and hover the cells in the battery in the correct voltage ranges. So when your battery is 100% it is at 100% of what you are allowed to use safely (not actually what the cells are fully able to take). No need for you to be concerned there. You have not built your own batteries.

You have a the bms protection listed there in your setup.


3. Cycling the batteries lower means lower cycle life. At 80% on the victron lithiums it is listed at 2500 cycles. So if you did this everyday then 6.8 years of that is the design life, but not necessarily the death of the bank, usually that refers to when you will notice capacity decrease down to 80% of original capacity. You can find their datasheet online.

https://www.victronenergy.com/upload/documents/Datasheet-12,8-&-25,6-Volt-lithium-iron-phosphate-batteries-Smart-EN.pdf

1 comment
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@Alexandra

Thank you for your thoughtful response!