For weird personal reasons, I want to be able to power a SmartShunt monitoring a 24V house battery from a variety of sources, including a 12V starter battery, through a diode-OR.
Is it acceptable to power a SmartShunt from a much lower voltage source than is being monitored?
As the smartshunt works from 12 to 66v, i see no problems.
But if the house battery is empty, why do you need the Smartshunt ?
There are two 24V packs, selected through a relay (long story, not subject to revision) and a 12V starter battery. There’s a SmartShunt on each 24V pack. I’d like the SmartShunts (and some other devices, like the Cerbo) to keep running even if the 24V packs go into low-SoC shutdown.
I’m not sure how you’d manage that - its power source has to be the bank it’s monitoring, that’s part of the monitoring.
Hmm…need to think about that. The SoC algorithm includes voltage, it doesn’t just integrate current over time?
I think if he feeds the voltage through diodes as proposed it will work.
It measures coulombs in and out, but has a 100% charge voltage reset and 0% voltage. The Coulomb count is often crude and inaccurate compared to a good quality clamp meter. If you get a low voltage disconnect and the battery disables discharge, the shunt shuts down, it will remember it’s at 0% when you repower. It will be offline in the Cerbo.
Thanks for that.
It’s probably sufficient, on further analysis, to power the individual shunts from their respective packs, and to power the Cerbo from the diode-OR (including the starter).
That’s as long as the Cerbo doesn’t care if the attached SmartShunts power down while connected. Any ideas on that?
I’m not sure. I’ve only used the MultiPlus with a shunt. Because the system has a low SOC shutdown, the inverter stops discharging before the battery gets close to disabling charge. I no longer use a shunt and instead rely on the MultiPlus to estimate the SOC.
If you have a DC-only system, a shunt is the only way to estimate SOC. I found that even at 0% SOC, there was still a decent amount of charge left in the battery. The only way to fully deplete it was to run it down to low voltage.
Yeah, the battery has a low-voltage cutoff point in the BMS that will stop it supplying any current if the cell voltage falls too low.
That will happen if you dont have a device like a multiplus to stop discharging before it gets too low. Have you looked at using a battery protect to disconnect the loads before the battery turns off?
Yes, but eventually the battery turns off, either by its own BMS or an external device like a Protect. Then if the Cerbo is powered from the starter battery, it is still on and connected to the powered-off Shunt. Then what?
It will just alarm until its powerup again. Maybe with a low battery warning.
If you go from the battery to the shunt then battery protect to the loads the battery protect will stop discharge and the shunt will remain powered. If you can figure out how long the system needs to be powered and leave a little in there to cover the load of the shunt and battery protect it will always remain on.
A smartshunt has nothing in common with a coulomb counter.
Power the shunts with the diodes, no problem.
What? A Victron SmartShunt operates as a Coulomb counter because it monitors charge and discharge through current measurements obtained from a shunt.
A Coulomb counter functions by integrating current over time Amp-hours in and out, and this is precisely what the SmartShunt accomplishes. It utilizes a shunt to measure current, subsequently calculating the state of charge, power, and energy flow, which aligns with the definition of a Coulomb counter. All be it a crude one.
Yes, it work like one but it isn’t.
A true coulomb counter does not have a shunt.
With a coulomb counter you can even measure the charge of a piezocrystal or a 1nf capacitor.
The Victron SmartShunt is a Coulomb counter that uses a shunt to measure current.
Some Coulomb counters may use other sensing methods, but many battery monitors rely on shunts.
Measuring tiny charge movements like in capacitors is a different application of Coulomb counting, unrelated to battery SOC tracking.
If you want the shunt to synchronize to 100% Soc when the battery has fully
saturated, your needing to know the battery (being charged) voltage.