This is more of a question for the product developers - Can we add an option to reset smart shunt SOC to 100% when a connected MPPT charge controller enters the float stage? I know this wouldn't apply to all systems, but when all your devices are connected using VE Direct with a GX device (Cerbo in my case) all the information is there.
It should be possible to do this already. On the proviso that you use the 'Tail' function in the mppt to terminate Absorb (which to my liking is a far superior way to do it). You'd then just set the sync Tail in the Shunt to the same value.
Of course your Cerbo would need to be networked to the shunt using DVCC (SCS) and the % Tail setting in the shunt made to match the Amp Tail in the mppt (I don't know why they're expressed differently?). Maybe too you'd need to ensure the Charged Voltage in the shunt is lower than the mppt Float setpoint.
But that's a great idea, and for me would be even better if the auto-sync wasn't restricted to 100% only, but selectable to a lower value - as can be done now manually only. Now that would really be something..
Thanks for the reply @JohnC,
Yeah, I've already set them up to run quite well this way, it would just be a neater and simpler setup if the SOC reset was linked explicitly to the MPPT.
Thanks again!
Just an update on this, one of my systems is located in an area with a pretty warm climate, it's been 35-40°C for the last few days, as such, the MPPT is dropping the voltage setpoints a fair bit due to temperature compensation, so this has led the smart shunt to not hit it's 100% charged point, even though the MPPT has sat in float almost all day. This highlights why an SOC reset triggered by float stage in a connected MPPT would be really nice. (I've actually got an alarm on this site now due to 'Time since last full charge' greater than 3 days, even though it's been in float since mid morning each day.
You should still sync the shunt to 100% if you've been in Float for that long. In practical terms that's as close to full as you'll ever see, and rolling on without syncing is inviting continual and magnifying drift away from the true SOC if the drift is downwards.
You blame the Temp Comp, but that's adjustable. At 35-40C pb's become very reactive, and you don't need a high V to charge fully.
I too see a 'seasonal' drift in SOC, but that's largely due to drawing down more in winter, and the recharge is more efficient at lower SOC. So I tweak the CE setting to give a better SOC result in line with the Tail I expect to see.
I understand your response, but I have set my charge controllers up using the recommended settings for the batteries I use - Concorde SunXtenders, which have a temp compensation of -64.8 mV/°C. Given that we have had batteries destroyed by being overcharged in high temperatures, I am not keen to change the temp compensation.
my settings are as follows:
MPPT:
V Absorption: 57.6V
V Float: 53.6V
Tail Current: 1.0A
Temp compensation: -64.8 mV/°C
Shunt:
Bat cap: 306Ah
Charged voltage: 53.5V
Tail Current 1% (3.06A)
Charged detection time: 5min
The issue is that when the battery temps get up above 35 degrees, the float voltage in the MPPT drops down by about 650mV, which in turn stops the shunt from recognising that the batteries are fully charged.
I guess I'm trying to walk the fine line between over and underestimating the battery capacity.
