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Keith Arnold avatar image
Keith Arnold asked

Why am i getting voltage spikes on DC bus?

My system is multi 48/5000, ccgx, mppt 250/70, 4 kw fronius on output 1. Huawei ESM 48100 li-ion x2.

1. Getting dc voltage spikes now and then, why.
2. Also each day the soc increases gradually and at some stage jumps from say 50 % to 95%. Do i have some wrong settings in ess. Battery is 100 Ah x 2. Charge volts 53.5 ideal charge current 20 A each float 51 V. Not found the setting on smartsolar to set the charge volts, on network on ccgx device shows charge volts 57.5 ? Not found where i can change that?

battery charging
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Murray van Graan avatar image Murray van Graan commented ·

I’m my experience, a lithium with an unsupported BMS- check that’s its not the BMS the momentarily disconnect the battery.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

The most likely cause of battery voltage spikes, low battery current absorption, and incorrect state of charge readings is a bad DC wiring connection, half blown or poorly seated fuse, wire, or dodgy battery cell. In that order.

Run through the system with a multimeter when it is under large loads and charge currents to and from the battery. With a notebook recording the results, test the voltage at each step where there is a connection.

Start at the battery terminals themselves, then to both sides of the battery fuse, then to the DC bus, then to both sides of the Multi fuse, then to the Multi terminals, and look for unexpected drops or rises.

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Keith Arnold avatar image Keith Arnold commented ·

I looked at some vrm detail. Each time there is a change from bulk to absorption, this is when the voltage spike happens. Dunno if this helps the analysis? It returns to normal soon.


any ideas on the soc jump?

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ Keith Arnold commented ·

Did you run through the troubleshooting steps above? What were the voltages at each of the points?

Some photos of the installation might also help.

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Keith Arnold avatar image Keith Arnold Guy Stewart (Victron Community Manager) ♦♦ commented ·

Yes. Checked volt drops at charge current around 50 A. On positive 130 mV. I have 100 A fuse on each charger (multi and mppt). 200 A fuse on battery. Negative cable is more direct so has less volt drop, 53 mV.

On vrm data the spike occurs when the multi changes from bulk to absorption.

Not sure it is normal but the mppt history shows that it only does bulk? It is slave.

Pic. Left db is all AC right db has all DC.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ Keith Arnold commented ·

I can't see anything connected to the MPPT PV terminals, is this a current photo?

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Keith Arnold avatar image Keith Arnold Guy Stewart (Victron Community Manager) ♦♦ commented ·

Lol, yes, I see it was a photo before I connected the PV. I have 8x370 Wp on it, 2 strings of 4.

in the dc dB I have pv surge arrestors and a pair of fuses. PV wire is 6 mm sq.

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