I have a Smartsolar MPPT 100/20 connected to a LiFePO4 battery. From the battery datasheets it is approximately 70 percent charged when at 13.40v.
I have set a load output profile to come on above 13.40v and off below 13.35v. What I am trying to understand is how this is impacted by the voltage drop of the battery when under load - e.g. I can pull 10A and see the battery output voltage be 12.4v,presumably due to internal resistance. The Smartsolar load output remained on at this time.
My question is - is the Smartsolar unit accounting for battery voltage drop under load and my approach to maintain a minimum of 70% in the leisure battery works, or is there a complexity I am overlooking/configuration required in the Smartsolar?
All load output profiles except “Always on” and “Always off” have a two minute delay
Thanks however this far exceeded two minutes. I have removed any jumpers.
Then im not quite sure
My question is - is the Smartsolar unit accounting for battery voltage drop under load and my approach to maintain a minimum of 70% in the leisure battery works, or is there a complexity I am overlooking/configuration required in the Smartsolar?
It could use the Peukert exponent that you set in the battery settings to compensate for voltage sagging under load, but im not sure if thats actually the case.
Have you tried with a greater hysteresis, for example above 13.4V on and under 13.0V off? Or a predefined load output profile?
OK so that’s the SoC table for my battery and then 3 screenshots of my app setup.
I can certainly try with the lower threshold but I’m worried I’ll flatten the battery. The aim is to have my solar prioritise the caravan and then use the “extra” solar yield to top up the portable power station in the van.
I should note that whilst showing 12.71v under load, when the load disconnected the battery went straight back to rest of 13.4v.
I can certainly try with the lower threshold but I’m worried I’ll flatten the battery.
I mean just as a test, dont leave it at 13.0V forever
You do not state the Ah rating of your battery, which is critical info for voltage sag. Such a large sag appears high unless your battery is small.
The MPPT is measuring 12.7V at the MPPT terminals, that does not mean that the battery is at 12.7V, have you measured the battery terminal voltage. Also check the battery and load terminal voltages on the MPPT. This is to see if there is voltage drop in the system.
Thanks. It’s 100Ah,apologies for the omission.
I have a meter with me so I’ll drain the power station a bit later and hook it up again and get a meter on the terminals.
If I play out the two scenarios, either it’s a software offset issue, or it’s an MPPT reading inaccuracy.
If I got a smartshunt to monitor SoC could that be used instead of voltage levels to control the load output? Seems like that would be the answer for either issue if its possible…
I am pretty sure that a SmartShunt will not do anything to control the load output. The BMV712 Smart has a relay that can by controlled by SOC, but I do not know how to control the MPPT load output from that relay. Voltage is a real issue to try and control SOC with because the voltage curve is so flat and voltage sag can have a larger effect than resting voltage between 30% and 80% SOC.
You voltage sag looks too much, you are taking 7.5A from a 100Ah battery and dropping 0.7V, I can run a similar discharge rate (45A from my 600Ah) and see less than 0.2V drop, often less.
Thanks for the reply. Any suggestions on what could cause this?
I’m reading up on ve.direct at the minute and whilst SoC is something that can be read, I’ve no idea how to utilise it in the Smartsolar. Since the smartsolar is only acting as a relay anyways and the current draw partially comes from the battery then perhaps that shunt is the way to go, it doesn’t really matter if I control a relay on the MPPT or at the terminals.
I will get a load on it again though and check the voltages at the battery terminals and mppt terminals to see if I can get more insight into the voltage drop.
Feedback really appreciated, thank you.
Testing shows 13.22v at terminals under load, 12.58v at mppt.
Wiring looks about 10awg into soldered Anderson connectors. I have however found a bullet crimped connector on each of the two battery wires, presumably from a repair. I’ll cut that out and solder them when I get home. Can’t see anything else that might be the issue, it’s less than 50cm of cable from battery to mppt, screw terminals are good. Splicing inside is done with 32amp wagos.
0.6V drop at less than 10A is a significant voltage drop, something is amiss with your wiring, it is not the battery voltage sag.
