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freesurfer avatar image
freesurfer asked

Can an MPPT controller cause an overvoltage if the battery connection fails?

If I have a battery bank connected to positive/negative busbars, with an MPPT controller (with a relatively higher PV voltage than battery voltage), an inverter and other devices connected on the same busbars.

Normally the battery should "regulate" the voltage. But what happens if the connection between the battery and the busbars gets broken, leaving the busbars with the loads in a floating state, while the solar power going in is greater than the loads?

Will the MPPT controller immediately detect this and cut out as soon as it reaches 14.4V/28.8V/57.6V?, or is there a chance it can overshoot or leave the system with a voltage out of control where it can damage the loads on the busbars?

In my case I have the SmartSolar MPPT 150/35, which I want to use with about 1400W of PV @ 80V, with a 48V battery bank and a Multiplus II 48/3000.

MPPT Controllers
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5 Answers
wkirby avatar image
wkirby answered ·

I did try this experiment once.
The battery is essentially just another load to the MPPT.
With other loads on, I never did see any overshoot above the Voltage setpoint for the current stage.
With a very light load, the MPPT did shoot over the current Voltage setpoint for a few mS when the battery was suddenly disconnected. The duration of the overshoot depends upon the size of the load. A heavier load can absorb and dissipate the overshoot quicly until the load is heavy enough that the MPPT can react quickly enough that no evershoot is observed.
When absolutely no other loads are present with the battery suddenly disconnected the overshoot will be sustained at the higher Voltage until the excess Voltage is bled away. However, if there are no loads present, then nobody cares about Voltage overshoot.

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airtime avatar image airtime commented ·
I know this is an old post... what was the maximum voltage overshoot when battery was disconnected with no load?
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freesurfer avatar image
freesurfer answered ·

"worst case" here will be something like the MPPT charging at max current (1800W of PV), and with the multiplus II in either the "0" position or idle with little load. The capacitors should probably catch some of the overshot if any. Maybe I am overthinking, and maybe Victron have already thought of this

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johnsmith avatar image
johnsmith answered ·

Any answer's from Victron?

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matrixrat avatar image
matrixrat answered ·

Short answer is don't let it happen. Two dead MPPT 150 100 on my bench are testimony of previous owner's fumbling.

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zeroco2 avatar image
zeroco2 answered ·

How to protect from this (impact on the MPPTs of a battery disconnection while there is little or no load) ?

I have circuit breakers (C60H-DC - 63A - curve C, model A9N61519) between the Lynx (and fuzes) and the MPPTs, but those wouldn't be of any help in this case ? (nor the ones between the PV part and the MPPTs).

A permanent load in the DC distribution (resistor/dissipator ?) or a in the residential part then ?

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