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timzim asked

Easysolar battery voltage drops during fridge start up

I installed a 24/1600/40 Easysolar with two 220Ah Victron Gel batteries six months ago into a small residence. The unit powers lights, refrigerator, WiFi and tv. The system has functioned well until about a week ago when it started going into “alarm” mode - red led on - about 3 to 4 hours after sundown. Closely watching the battery monitor it appears that when the battery SOC is below 85% and the fridge turns on, the inrush current of the fridge is dropping the battery voltage to around 18V (the battery current as registered on the BMV700 is in the region of 50 amps during inrush) The inverter registers low DC voltage and disconnects. This “alarm” is not a problem when the solar is active - in that case the battery voltage hardly drops at all and the registered BMV current is around 30 amps. Is this normal, or is there something wrong with the batteries? I have used the default settings on the Easysolar as delivered by Victron which, looking at the settings, appear to me to be optimal for the configuration.

EasySolar All-in-One
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JohnC answered ·

Hi Tim.

I'd call it unusual if the 'fridge' is responsible, despite there being a few other small loads on at the same time.

I'd look first to the fridge. They're usually quite low powered, and pretty well tuned to avoid serious spikes. Maybe it has a start capacitor which is faulty, and that might do it.

The Victron kit will surely measure a spike down to milliseconds and react accordingly and unwaveringly.

See if you can find the cause of that spike before venturing further..

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timzim answered ·

Thanks John. I will check the fridge as a first port of call.

Does the fact that the system works fine while solar is available not indicate that the appliance is possibly okay?

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JohnC avatar image JohnC ♦ commented ·

Coming off a higher base while solar is on, may be getting it by. I just think that a fridge start causing this is a little unusual. Unless the fridge is a walk-in coolroom. :-)

Just a start point. This could be any number of things, from wire size/length or even a dicky wire terminal or isolator restricting current from the batts.

I get this sort of thing myself, but never reaches trip stage (bigger inverter/loads). I didn't even know about it until I let VRM email me, and the 'fault' is so short that the email announcing that it's cleared sometimes arrives before the one saying it's there. My issue is a 1000W pump starting, but that's much, much more of a load than my 40W fridge compressor.

Spikes are difficult to measure, but you may be able to simulate a wiring/contactor issue with a heavy resistive load (like a toaster or radiator), and measuring any V loss between the inverter and batt terminals.

Such is troubleshooting. I wish you well with it.



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timzim answered ·

Thanks again John. I do suspect it is something on the house wiring or a problem with the fridge. As you say "such is troubleshooting".

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klim8skeptic avatar image klim8skeptic ♦ commented ·

Hi guys,

One thing you have missed, is that the output power is similar for both voltage states.

26v (?) x 30a = 780w for the battery being charged by mppt.

18v x 50a = 900w for the slightly discharged battery.

Once the battery voltage drops, the inverter has to draw more current to provide the same output power. Also once the batt voltage drops, inverter efficiency drops off a cliff, making thing worse.

I know my fridge draws over 1000w peak during start.

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timzim answered ·

Hi Klim. I wasn't sure on start-up power draw on fridges - I thought 1000W was a bit high for a fridge so thanks for putting me right on that score. Looking at other installations I have, the initial start-up on a fridge is only for a fraction of a second and then the current drops off rapidly as the compressor reaches running speed. On this problem installation the fridge start-up seems to take at least a couple of seconds, resulting in the DC voltage dropping and the inverter disconnecting. If the start up was rapid I believe the inverter would handle okay. To me this indicates a potential problem with the fridge compressor - as John suggested, possibly a faulty start capacitor. I'm not sure if poor wiring on the house plug circuit could cause a similar problem, but I think it could as the mains voltage the fridge is seeing at start-up may be low if the wiring is poor, causing a similar sympton.

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