I’m running some SmartSolar 75/10 MPPT charge controllers powered by 100W panels.
The connected 12.8V 12Ah LiFePO4s are drained downto 10.4V by the bluetooth module when no power is coming in from the panels. I think that’s a bit low, right? Is there any parameter in the settings to control the voltage when the bluetooth module switches-off. I can only find the limits for the load connected.
Best, Daniel.
How long does it take to drain the battery?
It takes around 3 days. I’m still testing in a lab setup with no input at all during this time, which is not really comparable to a real world setup. I’m still concerned for the battery packs.
If the minimum battery voltage that drives the bluetooth module can’t be set in the parameters, can you please tell me the default.
I’m not aware of a setting that does that.
My system will sit for a couple weeks with the solar panels off before the battery even gets to 60% and that’s running an RPi and other hardware for 8 hours a day. With no load apart from the MPPT is should last for months.
Do you have anything else apart from the MPPT connected?
If not then something is wrong in the hardware.
Another thought
If you are only charging the battery to 12.8v then it’s flat before you start. My LifePo4 is charged to 14.2 and after half hour at that voltage drops back to “float” at 13.5v. Looking back through Smart Shunt history the lowest voltage I’ve seen is 12.73v.
Wow, for weeks with a pi connected! Your right, I’m also charging my battery to 14.2V and the draining time of three days was only from 12.0V to 10.4V. I should’ve mentioned that.
I have no other load connected directly to the battery, but maybe the voltage source, that i use to simulate the pv panel draws something when it’s off. I’ll try that. Thank you very much for your thoughts.
What is the capacity of the battery’s? You are saying that you are running “some smartsolar modules”. Is that two? Here’s the calculation and what you notice MIGHT be what you could expect. The Smartsolar uses around 0.20A itself. So, that’s around 0.5Ah per day. That would be 1.5Ah in three days. If you are running two, double that.
Furthermore, if the battery is only 12.0V (cells are 3V), it’s not at 9% of it’s capacity, but more around 4%. Depending on your capacity, you only have a few Ah left then. E.g. a 314Ah LiFePO4 cel only has around 10Ah left if at 3V. So, that’s not a lot. And at 10.4 the cell is at 2.6 and is almost at 0%. Long story short; there is not a lot of Ah left between 12.8
This table might help you and is quite accurate:
Hope this helps!
OMG, thank you, you’re absolutely right. Should’ve looked at the discharge curve.
Thank you very much for the clarification.
No, i run a few 75/10s, but in separate systems in parallel. The capacity of the battery is only 12Ah. I calculated with a current drain of the modules of 10mA. I thought i read that in the datasheet. But if its 200 I probably mis-chose the part.
But of course Julian and you are absolutely right. I didn’t really look at the discharge curve.
But still, independent from the time it takes to discharge, i think the lowest voltage that still runs the bluetooth module should be adjustable to protect the battery.
I’m mistyping. It’s 20mA according to Victron, so, around 0,5Ah a day. And, with that, your experience is totally as expected. With around 3 or 4% SOC, with a 12 Ah battery you only have around 0,5Ah left in the battery if at 12V. So 3 days is exceptional and it might be that the SmartSolar lowers it’s standby current if no power for a longer time? Anyway; works as expected.
And thank you for that great graph!
And, bluetooth can only be switched on and off by hand. However, the SmartSolar in total can be controlled externally, if you are looking for that.
NoNo thank you. I was just looking for a parameter to adjust the minimum battery voltage that drives the bt module. Because the system seems to drain it down to 10.4V. Which is of course not catastrophically low. But I would like to set it a bit higher, since that can happen quite frequently in my system.
Damn, what a great and helpful forum!
Are you guys with Victron?
Although I live next to them, I’m not. I’m just a small independent LiFePO4 maritime battery manufacturer. But of course I work with Victron stuff for the rest of the chain.
