voltage fluctuations

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Hendo
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Joined: Tue May 04, 2021 2:58 pm

voltage fluctuations

Post by Hendo »

Hi,

We have installed a VFX2612EM into a vehicle, vehicle also has a cummins Onan 5.5kw gen. We also have 2 x 270Ah deep cycle batteries in there to power the inverter.
The vehicle came in today, batteries were flat (2.7v), this is because the customer had left their 12v fridge on for 2 weeks while at the panel beaters. when we restarted the generator to charge up the batteries, it took a while for the outback unit to start up, when it did we wildly fluctuating AC voltages at the power outlets inside fed from the HOT OUT of the Outback unit - from 170v - 274v.
Once the batteries were charging steadily the voltage fluctuation stopped and remained steady at approx 230v.

We turned off the gen and let the batteries go flat again (down to 9.3v) at the point the Outback turned off. we again started the gen and this time voltage remained steady at 230v.

Gen output remained steady throughout, so its an issue with the outback.

Any reason for this voltage fluctuation?
Hendo
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Joined: Tue May 04, 2021 2:58 pm

Re: voltage fluctuations

Post by Hendo »

Im in New Zealand
raysun
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My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: voltage fluctuations

Post by raysun »

I'm not sure about the fine details of the export models, but FX series inverters have a built-in Low Battery Cut Off of 10.5V for a 12V nominal battery. This is intended to keep the inverter from becoming unstable when too low a battery voltage is present.

The 12V @ 270AH battery blocks could not have been depleted to 2.7V by the inverter under normal circumstances.

I assume the refrigerator is a 12V parasitic load tied to the battery in parallel to the inverter?

During battery resuscitation (hard to call it recharge when its being brought back from the dead like that) the battery may have gotten to the Low Battery Cut In voltage, started the inverter, but had still been in such a depleted state that the battery fluctuations resulted in inverter output fluctuations.

For the sake of the inverter and the equipment it may be servicing, one may wish to assure the battery is fully brought back from the dead before applying power to the inverter.

I can't explain how the battery got to 9.3V before the inverter shut down, other than there is a time delay (IIRC 4 minutes) before LBCO activates, and draining the life out of the battery likely continued during that time, dropping the voltage from 10.5 to 9.3V

If all the above happened as outlined, then its less an Outback issue and more operational abuse of the equipment. I would suggest avoiding the scenario going forward.
Hendo
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Joined: Tue May 04, 2021 2:58 pm

Re: voltage fluctuations

Post by Hendo »

Thanks for the reply.

Yes, fridge was fed from from batteries.

We are fitting low voltage disconnect units to all units now.
bluespur
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My RE system: VFX3024x2
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Own built generator Kubota D600 engine, 7.5Kw gen head

Re: voltage fluctuations

Post by bluespur »

A further thought (from another Kiwi)
If there are parasitic loads using the battery directly and not going via the inverter, maybe they were pulling sufficient out of the battery to cause DC fluctuations such that the inverter was impacted, but not enough or for long enough to shut down. Is there any indication in the inverter logs of anything?
Cheers
Garth
raysun
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Posts: 4540
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: voltage fluctuations

Post by raysun »

We are fitting low voltage disconnect units to all units now.
That will help immeasurably. If the disconnects mirror the inverter's LBCO of 10.5V @ 4 minutes, the systems should experience faultless operation. (An inverter shutdown in this case not being a fault, rather a programmed feature.)
raysun
Forum Emperor
Posts: 4540
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: voltage fluctuations

Post by raysun »

A further thought (from another Kiwi)
If there are parasitic loads using the battery directly and not going via the inverter, maybe they were pulling sufficient out of the battery to cause DC fluctuations such that the inverter was impacted, but not enough or for long enough to shut down.
Its likely the recharge cycle got to the Low Battery Cut In voltage (IIRC 11.5V) but it was a "surface charge" voltage and drained off rather quickly when the inverter put a load on the battery. While the LBCO timer was counting down, the low (< 10.5V) battery voltage would have permitted the inverter to operate in a very unstable state.

That's very hard on the inverter's electronics, and possibly on the equipment connected to it.

As a safe operation rule of thumb, the inverter should be fully disconnected (via proper circuit breaker) from the battery when recharging same from such a depleted state. At the very least, the inverter should be switched to its OFF status until the battery is fully charged.
Hendo
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Joined: Tue May 04, 2021 2:58 pm

Re: voltage fluctuations

Post by Hendo »

Thanks all for the advice and help. its nice to get constructive answers from a forum!!
raysun
Forum Emperor
Posts: 4540
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: voltage fluctuations

Post by raysun »

It may be worthwhile to put a battery monitor of some sort on the system to help keep track of battery state.

Voltage is only a good indicator if the battery is fully at rest (no load) so isn't practical for a battery in use.

The "current counting" monitors work best overall for a system in use, as they track the amount of charge into and out of the battery dynamically.

A good example of a well-regarded monitor is the Victron BMV7xx series (700, 712). https://www.victronenergy.com/battery-monitors/bmv-700. The only problem with the Victrons is they cost US$150 - 250.

Looking around for some Chinese knockoffs to point to as "better than nothing" examples.

Victron clone on Amazon
https://www.amazon.com/CAMWAY-Voltmeter ... 088RG27LS/

Same thing on Alibaba (BW-TR16), half the cost of the clone on Amazon, but 10 pc. min order.
https://m.alibaba.com/amp/product/60734638385.html

There's a lots of "square faced" monitors with a thin 100A shunt out there for cheap, but they work in a strange and confusing way.

I recommend the "round face" Victron clones.
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