grantiegrant avatar image
grantiegrant asked

Smart Shunt & Battery voltage under load

Hi all,

Busy learning as I go here in load shedding South Africa so any help would be much apricate:)

I will try keep things as simple as possible so here goes:

I have a Gel battery with a 200 ah capacity hooked up to a 1600w pure sine wave inverter. I bought a 500a smart shunt in order to regulate my usage and monitor the vaults.

The question I have regards the voltage reading of the battery dipping substantiality when I apply a load of around 300w. Fully charged I have the battery reading around 13.61v without a power draw exceeding 20w. When the load increases to around 250w the battery takes 30 or so minutes to drop below 12.1 (at which point I cut the load to ensure I don't drain it past dod) just to have the battery jump back up to a range of 12.5v without a load and no charge applied

Am I doing my battery harm by dropping the vaults so low under load?

What is the lowest voltage I should allow under full load?

The vaults have never dropped below 12.3v while no load is being applied? Would it be safe for me to keep using the system under load if I know when i cut the load it returns to thee "safe" operation vaults of the gel battery?

Any help would be appreciated,

Kind regards,


batteryvoltage drop
2 |3000

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ingo21 avatar image ingo21 commented ·
how old is your battery??

your 250watt load is about 20Ampere the battery is 200ah which in theory is from full charged battery to empty (200ah/20amp) 10 hours of discharge.

the battery should not drop that much in 30sec.

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grantiegrant avatar image grantiegrant ingo21 commented ·
Thanks for the response:) The battery was bought brand new from supplier and I have had it for a couple of weeks, making sure not to drop the voltage to low. The battery percentage calculated by the Victron app gets down to about 85% but while still under load the vaults read around 12.15 then when I cut the load the vaults jump back up the around 12.5 again with battery charge still stating 85%
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ingo21 avatar image ingo21 grantiegrant commented ·

"around 250w the battery takes 30 or so minutes"

sorry i did read this wrong i took it for 30sec...

i am still surprised that it almost 0.4V under a relatively low/medium load.

i would stop discharge the battery at about 11.8 volts which is about 40% of charge. that give you longer battery life but also you using only 60% of your 200ah which is 120ah

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