DIY 12V Battery Chaining – Need Help with SmartShunt Setup

Ben Nichols
Thu, 19 Sep 2024 01:53:25 +0000
DIY

Hi everyone,

I’m working on a custom DIY battery box and using a SmartShunt IP65 Battery Monitor (500A) to track the state of charge. However, I’m not getting consistent or accurate readings, and I’m hoping someone can point out what I might be doing wrong.

Current Setup:

2 x 12V batteries chained together (parallel).

Negative from the battery chain is connected to the SmartShunt input, then output.

Temp monitor connected (though I’m unsure if it’s necessary for me anymore so I can remove)

Positive to battery positive.

Aux to battery negative for the temp sensor

I followed the diagram for the temp sensor, except I’m chaining two batteries instead of using just one.

App Settings:

Capacity: 210AH.

Charged Voltage: 13V (measured after a full charge and waiting overnight).

Synchronize SOC to 100% when batteries were at full charge.

All other app settings are default.

Issues:

The app reads voltage and output values correctly, but the time remaining never seems accurate.

After a night of discharge, SOC shows 70%, but if I disconnect/reconnect the batteries (power cycling the shunt), the SOC resets to 100%.

Questions:

1. Does the SmartShunt need to stay connected at all times, even during charging?

2. Are my app settings incorrect for this setup?

3. Can the SmartShunt be turned off when not in use? (I’m using this for astrophotography equipment, so it’s not always needed but could stay hooked up in a car if that’s okay.)

Future Plans:
I’m planning to add two more batteries and want to ensure I set everything up correctly. Below is my planned setup:

Chain 4 x 12V batteries in parallel.

Negative from Battery 4 connects to SmartShunt input, then SmartShunt output splits into two negatives.

Positive aux links to Battery 4’s positive, which also splits into two positives.

The split is intended to minimize voltage drop over a 50ft run (from my car trunk to equipment in the field). I can’t keep lugging 60lb battery boxes back and forth!

Each positive line is fused and fed into separate DC-DC 0-36V in / 12V out stabilizers (I haven’t tested these yet but hope they help reduce voltage drop). The outputs from the stabilizers are linked back into a single line that goes to the equipment, so voltage and SOC should still match.

Concerns:

Is my setup feasible?

Would moving the SmartShunt to the end, after the DC-DC stabilizers, impact its ability to track accurately due to voltage drops?

Battery Specs (if relevant):
EverStart Maxx Marine Battery, Group Size 29DC
12V, 845 CCA, 114AH

Pictures Included:

2 app screenshots: settings and summary (100% SOC after a quick power cycle; it was at 70% before overnight discharge).

2 wiring diagrams: one with my planned setup and one blank, in case anyone wants to suggest the correct linking.

Thanks for any advice or thoughts! If this is the wrong category, let me know, and I’ll move it.

19 posts - 6 participants