Acceptable high current draw load voltage?

[ericfx1984]

What is an acceptable voltage for high current draw? Where should this voltage be measured? At the battery bank? At the inverter? For instance the inverter might see 11.6 under heavy draw, while the bank reads 12.2... of course recovering to 12.7-12.9 shortly after the draw is complete...

by heavy draw I mean the invert is pumping out around 1700 watts on the AC side... I dont often do this, but from time to time I like to use the electric tea kettle for heat my water for coffee in the morning...

 

[sunshine_eggo]

12.2V @ bank with 11.6V @ inverter means you have a substantial voltage drop. This may be typical given the very high current you're pulling from a 12V system. It's worth checking your wire gauge and connections.

There's no absolute answer to your question, but the resting rebound voltage is a good estimate. If it rebounds to 12.2V or higher after a couple of hours of no-load/no-charge, you can be confident the battery is above 50% SoC.

Easy mode is a Victron BMV or smartshunt that takes the Peukert effect into consideration and reports SoC based on the load, capacity and temperature - far more accurate than voltage.

The situation you describe is a good example of why it's generally a bad idea to adjust inverter cut-off to 12.2V/50% or so because it's easy to drop below that voltage level even when the battery is at a high state of charge.

 

[ericfx1984]

12.2V @ bank with 11.6V @ inverter means you have a substantial voltage drop. This may be typical given the very high current you're pulling from a 12V system. It's worth checking your wire gauge and connections.

There's no absolute answer to your question, but the resting rebound voltage is a good estimate. If it rebounds to 12.2V or higher after a couple of hours of no-load/no-charge, you can be confident the battery is above 50% SoC.

Easy mode is a Victron BMV or smartshunt that takes the Peukert effect into consideration and reports SoC based on the load, capacity and temperature - far more accurate than voltage.

The situation you describe is a good example of why it's generally a bad idea to adjust inverter cut-off to 12.2V/50% or so because it's easy to drop below that voltage level even when the battery is at a high state of charge.

I agree the voltage drop is a bit much... I questions weather one reading or the other is wrong(or both lol)

as for wiring, 4 runs of 1/0 (2+ and 2-) both runs are equal length and all all cable terminations are made with a proper crimper

as for the rebound its almost right away, within seconds for the most part and a few minutes to fully rebound

 

[sunshine_eggo]

I agree the voltage drop is a bit much... I questions weather one reading or the other is wrong(or both lol)

Use a separate meter to measure each in turn.

as for wiring, 4 runs of 1/0 (2+ and 2-) both runs are equal length and all all cable terminations are made with a proper crimper

Should be fine provided your connections are properly torqued.

as for the rebound its almost right away, within seconds for the most part and a few minutes to fully rebound

Probably nothing to worry about then, BUT a BMV or smartshunt removes all doubt. It's almost magical knowing your battery's true state of charge to a high degree of accuracy...

 

[ericfx1984]

Use a separate meter to measure each in turn.



Should be fine provided your connections are properly torqued.



Probably nothing to worry about then, BUT a BMV or smartshunt removes all doubt. It's almost magical knowing your battery's true state of charge to a high degree of accuracy...

I was thinking about using the same meter and just tanking the reading while under load...

they are torqued well

I wish I could justify the expense on the smart shunt

 

[sunshine_eggo]

IMHO, it or a similar device is critical. Not optional.

Without it you can never truly know your state of charge.