MPPT-Voltage or SmartShunt-Voltage used?

Q&A and troubleshooting
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1

Which voltage is used for Battery and Load On/Off?

Config:

BlueSolar with VE.Direct Bluetooth Smart Dongle (7 years old),

now new additional:

SmartShunt 300A

SmartBatterySense.

  • all updates made.

Network installed, in Config it says MPPT is using voltage from Shunt and temp from BatterySense.

So far so good, but…

due to some change in my system I made experimental tests of the operations.

First thing i recognized was strange behavior of the load-output. My setting for for the test is Load On >13.00 and OFF <12.90 Volt

No i have two voltages applied 13.20 to Batt of the Mppt and (Batt MPPT reduced by 0.50V) 12,70V to the shunt.

After 2 Minutes (Some hysterese-time) the output switches On !!. (Eventhough it should not! with voltage below 12.90V given by shunt)

if i open the apple Victron App it shows all network devices. There i can see MPPT with 13,2xV and Smartshunt with 12.7xV

Load output still On!! (MPPT shows 13.2V instead of 12.7V what it should be, using the voltage from Shunt.)

If i lower voltage MPPT to 12.8V (shunt at 12.3V) then the output switches off.

Opposite direction same result: I increase MPPT Batt to 13.2V (Shunt at 12.7V) Output switches On. Which is wrong again.

This shows me that at least for the load output the shunt-voltage is not reference.

But what is with Battery-Loading setting voltages? Is it taken from shunt or MPPT?

It should take reference from the shunt, but after my small experiment, i am not really sure….

Thanks for your opinions.

2

For starters smartbattery sense will give you both temp and voltage. Also it should be installed right on the battery. So it should have very accurate voltage. I would remove the shunt from the network and see what happens. Your system is simple enough that the sharing of the battery current with the mppt wont be very relevant. I would simplify your potential for communication errors and just use the data from the smartbattery sense.

I’m pretty sure the load output is using the MPPT voltage. Not sure how the shared voltage of the other devices interacts with it. It would make sense that if you are sharing the voltage from the shunt or battery sense it would use that voltage. It definitely uses the shared voltage to regulate the charge algorithm.

On another note, are you using lead acid batteries? If you are using LFP with BMS with low temp cut off then you don’t really need the temp function of the smartbattery sense. Which means you don’t really need the smartbattery sense because the shunt can transmit voltage.

3

Thanks,

here some detailed information:

first: i am using 12.8V LFP with internal BMS. Not from Victron.

second: i need the reading of Current and estimated SOC in the Victron Network.

as i dont have the additional temp-wire for the shunt, i am using SmartBatterySense for temp.

so it does not make sense to me to only use the SmartBatterySense.

The load disconnect should use the battery-voltage. nothing else is important, due to voltage-drops

on the way to the mppt. I am planning to keep the battery between 40 to 60% SOC specialy in wintertime.

that is only possible if voltage is measured directly, and precised at the battery.

Do to informatoion of Victron it should work that way.

Okay, i will do some more testing, and check if voltage for charging is taken from shunt or from MPPT.

4

Why do you need the temp? LFP doesn’t need temperature compensation for the charging algorithm and your BMS should have temp sensors for low temp charging disconnect. If this is all true you actually don’t need the smartbattery sense at all.

5

Please believe me what i say.

I need Temp to evaluate to turn of Loading at cold temps. You should know that below 5° C Charging is bad for lifePo4.

That has nothing to do with the problem that Victron network does not behave as told by Victron.

THAT is the problem. (Victron says: MPPT takes voltage from the shunt)

funfact: if you select and open the MPPT in the network-list , voltage drops to the voltage of the shunt (12,62V) , if you exit the MPPT-Details and go back to the startlist of networkpartners, voltage is taken from MPPT again!! (13,32V) This is great bug in software!

6

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7

explanation found :+1:

it seems that the MPPT is only connecting (Reading voltage) from shunt, if PV delivers energy.

As soon there ist some input from solar, the MPPT switches from internal Voltage to the voltage from the shunt.

In this case also the load-Output is using the right voltage.

So the worries about wrong voltage are gone, and things are clear now.

just to let you know.:+1:

8

That is helpful information.

9

I guess it’s just a measure to reduce battery-drainige for networktraffic when it makes no sense. (no PV energy)

thanks for your input anyway TherealKT. :grinning_face: