Let's Talk Shunts vs Battery Monitors

[teckersley]

Trying to get my head wrapped around the differences under load of a battery monitor just connected to the + and - terminals vs a shunt installation with the monitor. I am using a 48V and 72V lifepo4 cell pack in a golf cart application. When driving and under load, using just regular + and - connected monitor, the voltage and % SOC readings drop quite a bit. But once its at rest, things level out and its fairly accurate.

My question is, would a shunt plus the monitor alleviate this issue and show accurate readings while driving under load or is it just the way things work and the only advantage to a shunt would be amp readings????

Thanks in advance for the input.

 

[sunshine_eggo]

You're not using a battery monitor. You're using a voltage based SoC meter, which is mostly worthless and is almost never accurate. The only time it is accurate is when the battery has been at rest (no charge or discharge) for 20+ hours (for lead acid - maybe 30 minutes with LFP, but it may be based on lead acid voltages). Under very light loads and charges it might be somewhat accurate.

If you want accurate SoC, you use an actual battery monitor that uses either a shunt or a hall effect sensor that measures the Ah in and out of the battery to compute SoC based on the known battery capacity.

 

[teckersley]

You're not using a battery monitor. You're using a voltage based SoC meter, which is mostly worthless and is almost never accurate. The only time it is accurate is when the battery has been at rest (no charge or discharge) for 20+ hours. Under very light loads and charges is might be somewhat accurate.

If you want accurate SoC, you use an actual battery monitor that uses either a shunt or a hall effect sensor that measures the Ah in and out of the battery to compute SoC based on the known battery capacity.

Thanks. So that's a yes? the shunt should solve the issue and provide a more accurate voltage and SOC?

 

[Adam De Lay]

Yes, a shunt will be more accurate. Depending on what voltage you're at, you have the potential to see more fluctuations based on the load. The SOC should be fairly consistent and won't fluctuate based on the voltage.

 

[740GLE]

Yup as long as the shunt can meet the current needs of the load. if you have the choice try and go next size up as cheaper shunts at their rating burn a fair amount of heat.
Snag a 100a shunt if the max load of 50a, 2/300a is that much better.