Multiple shunts for loads?

[Acercanto]

Hi all,

I am a ham radio operator working on making a radio trailer for camping and such. I have 200AH prismatic cells, and 400w of solar. On the load side, I have "small" loads like lights, the radios (~20 amps), and stuff that normally will never get above 50 amps TOPS. I also have a 2kw peak inverter for AC loads.

Is there any way to hook up my SBMS0 with 2 separate shunts, one for the small loads, and a bigger one for the inverter? I've read the GitHub manual by Bdlow, as well as the pdf manual and a bunch of the threads on here, and don't think I saw any setups like that.

Any advice on shunt setups/locations for the best resolution/accuracy?

Thanks,

Acercanto

[Bernd]

I´m using SBMS0 with 24V 150Ah with a 2KW inverter, with 2 100A 75mV shunts. I never had the feeling to need 2 different shunts for the load side.

I´m running typicall loads of 30-40watts and up to 1,5KW for a coffee :-) for a few seconds.

Why do you want to have 2 shunts for the loads?

Greetings from off-grid-germany 

Bernd

[Dacian Todea]

Acercanto,

The SBMS0 has only inputs for two current shunts one will measure the battery current and the other will measure the PV current and based on this two the Load current is also calculated.  I see no reason why you will want to see the inverter current separate form the DC loads.

I guess this will be a 12V system with 4 of those 200Ah cells in series and I guess those 400W of PV solar is made up of 4x 100W 36cell panels.

[Acercanto]

My thinking was that I could get better accuracy by having a smaller shunt (50A or so) for the smaller loads, and a 200A one for the inverter. 90% of the time, the only loads would be lights and usb chargers, so amps in the single digits. It would also simplify the wiring a bit, but not by much.

Yes, it's a 4S LiFePO4 setup, and the panels are 2 of these 200watt panels in parallel.

I plan on putting a shunt on the PV side as well.

Acercanto

[Dacian Todea]

The accuracy will be plenty good with a 200A shunt.

If you want best accuracy get a 200A 100mV shunt  that will be able to display current in the range of plus minus 180A and with the 16bit ADC resolution on the SBMS0 you have 15bit (32768) resolution in one direction.

180A / 32768 = 5.5mA is the smallest current step that SBMS0 can measure that is 0.005A and so good enough resolution to measure very small loads fairly accurately.
Even with a 75 or 50mV shunt you can still see a 10mA change in current and even that is more than sufficient for small loads even those in the mW range.

[Acercanto]

Ok, thanks for the numbers! I read your shunt selection post from a while back, and it was very helpful. I guess I'm just overthinking things. I'll be sure to post pictures once I get everything installed and running.

Acercanto