Can someone explain voltage drop to me

agboett · Sep 16, 2022

Can someone explain voltage drop to me. I have (2) 100aH Li batteries that my battery monitor shows while discharging is at 90% but running high draw devices i.e. 800w microwave -- the voltage can drop fast to 11V & trigger the low voltage shutdown -- I have 14.3V full w/ these 2 batteries wired in parallel

The voltage comes back quickly w/ my 800w solar array however I'm trying to understand why voltage drops quickly & why for example if I had (4) batteries that would mitigate this issue ?

Thanks for the consideration

sunshine_eggo · Sep 16, 2022

99% of the time, this is loose connection(s), thin wires, or an improper bank configuration.

800W output microwave uses closer to 1300W input.

1300W/12.8V/.85 (efficiency) = 119A

You're pulling 120A total between the two batteries. If your bank is configured and connected optimally, the batteries should share that equally within reason. If you haven't configured it properly, one of the batteries could support most of it and potentially trigger over-current protection.

Are your battery terminal connections high quality and properly torqued?
Is your battery cable of sufficient gauge?
Are your crimps of high quality?
Do you have any shrink pinched between the ring terminals and the battery terminals?
Is your bank configured optimally (see Victron Wiring Unlimited in my signature)?

Bob B · Sep 16, 2022

What @sunshine_eggo said .... probably a bad connection .... could be too small a wire. The resistance will be the total resistance of fuses, wire, shunts, connection resistance, etc in the circuit.

The formula to calculate voltage drop would be E=IR .... where E is the voltage drop, I is the current, and R is the amount of resistance. So.... as the current increases the voltage drop increases.

As an example if you have .1 ohms of resistance and 100 amps of current the voltage drop would be 10 Volts .... so, as you can see as the current goes up it doesn't take much resistance to cause a lot of voltage drop.

I would do an internet search for Ohms Law and read explanations till you fully understand it.

agboett · Sep 16, 2022

sunshine_eggo said:
99% of the time, this is loose connection(s), thin wires, or an improper bank configuration.

800W output microwave uses closer to 1300W input.

1300W/12.8V/.85 (efficiency) = 119A

You're pulling 120A total between the two batteries. If your bank is configured and connected optimally, the batteries should share that equally within reason. If you haven't configured it properly, one of the batteries could support most of it and potentially trigger over-current protection.

Are your battery terminal connections high quality and properly torqued?
Is your battery cable of sufficient gauge?
Are your crimps of high quality?
Do you have any shrink pinched between the ring terminals and the battery terminals?
Is your bank configured optimally (see Victron Wiring Unlimited in my signature)?

Thank you

DThames · Sep 16, 2022

If you put a volt meter at the battery and see 11v, you are seeing the battery's internal effective resistance causing this. If you put a volt meter at the inverter's terminals and it says 11v but measured right on the battery terminals you see (say) 12.3v, then your "drop" is in your wiring. In the case where you see the 11v right at the battery, yes more battery should improve the situation.

McKravitts · Mar 25, 2024

It would be helpful to know where exactly you are measuring the 11 volts.
Is it at the battery terminals, the inverter input, or elsewhere.

Can someone explain voltage drop to me

agboett

New Member

sunshine_eggo

Happy Breffast!

Bob B

Emperor Of Solar

agboett

New Member

DThames

Solar Wizard

McKravitts

Solar Enthusiast

Similar threads