We’ve deployed 8 IOT agricultural sensor stations having following main components:
Solar charge controller: Victron Energy 75/10 MPPT (model: A074, part number: SCC075010060R, firmware: v1.66, bluetooth firmware v2.53, bootloader v1.18.)
Solar panel: Victron Energy BlueSolar 4a 20W (model: SPM040201200)
Battery: ECO-WORTHY LiFePO4 12V 8Ah
Load: IOT Lora agricultural sensor at 12V / 70-160mA
Controllers are configured to “User Defined Algorithm” operation mode to connect the load on 12.0V and to disconnect it at 11.8V. (All jumpers have been removed.)
OUR DEPLOYMENT ISSUE:
When being packed & shipped batteries are drained below 11.8V and they disconnect the load as configured - this is expected;
When installed in the field and solar panel is connected it charges battery above 12V in 5-10 minutes and most of the stations connect their loads as configured - this was expected behaviour, BUT:
Several charge controllers (unrelated to their battery power state) DO NOT connect the load as configured by “User Defined Algorithm” even battery voltage reaches above 12.0V (load remains disconnected and OFF).
To revive those stations our customers have to manually connect to their charge controllers via Bluetooth using Victron smartphone app with which they have to change operation mode to “Always On” which forcably connects the load and then change it back to “User defined algorithm” which then again works as configured (Until next bug).
We have conducted testing stations powering on after entering LVD (low-voltage disconnect) and we observe this bug is consistently appearing. Victron Energy 75/10 MPPT controller doesn’t automatically re-enable the load even though the “load on” threshold is satisfied. The load control logic doesn’t always re-trigger after battery reconnection or very low voltage shutdown unless the internal state machine is “nudged” by temporarily switching it to “Always On”.
We’ve tried:
updating firmware
modifying thresholds to 11.9V/12.1V or 12.0V/12.2V
Therefore we have advised customers to switch to Always-On on all stations.
But now we have new station design with new battery type which is not “forgiving” and robust as LiFePO4 and also we have pre-orders for hundreds of such stations, so now we are sincerely hoping to see firmware update that fixes this “User Defined Algorithm” operation mode bug or we will be forced to switch to some other brand/supplier.
I don’t fully understand why this happens, but I know it can occur. On my installs, I use a BatteryProtect in series with the load to help protect the equipment. It safeguards against over-discharge and over-voltage, and in case of a fault, it helps isolate the load from the charge controller.
We are limited with both physical space and budget envelope per station. BatteryProtect 65A is total overkill for a 0.1A load.
Now we are looking into alternative BMS solutions which is pitty considering SmartSolar has it all and we have great collaboration with our local Victron distributor.
12V is a good discharge floor for lithium. What do you mean you are looking at a different BMS? The 12V 8AH ECO-WORTHY is pretty small. To be honest, the only battery I have failed was an ECO-WORTHY 20AH, and after some testing, I found the BMS was letting cells reach 14.8V before disabling charge. But I do have 2x 8AH in a UPS in a 24V configuration without a balancer and have been in there for 4 years. It’s for a PC that is not that important, but I hear it does the test every day to check the battery, and it passes. I do have a set of AGMs that I am going to put in.
The BMS in the 20AH was the size of a matchbox. I dont know what the 8Ahr will be like. The cells in the 20AH were pouch cells 2P4S. Are you looking are build your own battery? You could if you want, with a BMS and adjust the discharge floor. I did replace the pouch cells in the failed ECO-WORTHY with cylindrical 20AH C40 cells and a JBD BMS. There is a cylindrical cell called an A123 that is 4AH and quite small. You could build your own 2P4S 12V battery and pick the BMS you want so you can program it. Something like this is very small. I have used them, and they are very good.
Considering 0.1A IOT sensor is the main load, 8AH LiFePO4 turns out also to be an overkill. then physically it all goes into metal chassis which needs to go into lower part of pole because of center of weight. So then we need much more cabling and the installation becomes problematic.
So we went for 4x 18650 2900mAh Li-Ion (11.6Ah) and then we need reliable BMS that considers also temperature conditions (stops charging below 0C and starts above 5C).
We don’t have budget to build own battery pack for now, but we’ll go with generic casings (hoping that users won’t reverse polarity).
I’m deciding between XJ and KLS BMS on Alibaba. JBDs are, again, overkill (20A and up)
Interesting. I have a couple of UPS setups for RPI using 3V 1300mAh Sodium Ion Batteries 18650. They still have >0 deg charging but will go down to 0 volts. That might be an option with a much higher usable voltage range and much safer chemistry. When I say I make your own battery, what I mean is you shuck the existing one and replace the cells and BMS with what you want to use, like I did with the 20AH.
Very interesting but currently our power parts partner doesn’t offer Na-ion batteries and the voltage range is too low for 4 pcs and too high for 5 pcs without additional circuitry but it is definitely interesting to be considered in future reviosions. Thank you for your suggestion.
4S is nearly 16V 3.95V per a cell. They work fine on a Li-on profile you just lose ~ 1/2 the capacity with 3S BMS. Being able to let to them go 0V is the crazy part. If you can find a BMS that you can program and is not overkill should be a good fit.
I am using them for RPIs running Venus OS. They 100% all the time, and if there is an error, they go to 0%. Li-ion does not tolerate that, but Na-ion does. Just doing some research and chatting to people, the Li-ion will only last a year used like this, but the Na-ion have been there for 2 years now and seem fine.
Have you looked at a small DC-DC converter? 12-12 or 12-14V for example? They usually have a voltage cutoff that is reliable, and they are cheap.
Talk to the PWOD or GENISH on aliexpress. I have bought from both I think GENISH re-sells PWOD. I am using a Li-ion BMS its provides enough backup power for me to do firmware upgrades and get alerts. That is all I need.
Yes, it certainly does. Does not fully charge it either. That’s why I said you only get 50% using a Li-ion BMS, so a 1300 will only give you 650, for example. I have 2 of them on a PI 3 B plus get about 20 minutes at 14-15W. That was 2 years ago, there might be better options. I dont need capacity, I want longevity, avoid the thermal runaway risk, and if I run them flat for a long time will not damage them. There might be BMS options, but I dont think you will need one. I think from my experience, an active balancer will work due to the linear charge - discharge curve and no risk of over-/ under-charge. I haven’t looked at building anything greater than a 18650 UPS, so you will have to do some research.
We were unable to reproduce this behavior. What you could try is whether this also occurs when there is no load connected. Perhaps the load (inrush) current influences the load output behavior.
Thank you for your feedback Thiemo,
due to above documented uncertainties we’ve decided to develop
our own Na-Ion charger/BMS so we end up with reliable product.
We’ll be still ordering Victron Energy solar panels.
