Low voltage alarm and full battery. Is my inverter broken?

[natdak]

The low voltage alarm on both my inverter and charge controller are triggered whenever I try to use anything high powered (around 750w or 1000w)
It is a 2000w off-grid inverter, that until now has handled these loads regularly without a problem. The battery is full, 13.4v, I have gone over all the connections and there is nothing loose, I have tried a different battery (a slightly smaller one) only to get the same result. I have even reconnected it with new battery cables, straight from the battery to the inverter and I tried that with 2 different batteries. I checked fuses, I looked inside the inverter, nothing appeared burnt.
During the surge the voltage goes as low as 9.8 volts then is constant between 11.8v and 12.2v before sounding the alarm about 5-10 seconds after switching it on.
Interestingly the voltage on the charge controller screen reads 12.2v battery voltage under no load when it reads 13.4v at the battery terminals and the terminals of the charge controller. Tests where done on the inverter with the charge controller switched off and it made no difference to the inverter.
And interestingly when the inverter was switched on without the load plugged in the voltage actually rose to 14.3v! My inverter draws about 20w continuously.
Please let me know what you think!
Big thanks,
Nathan

 

[Horsefly]

That sounds like the 1000w load is simply more than the battery can handle. If it used to be able to handle that size load, it probably means your battery is at end of life. From what you've described, I don't think it is anything wrong with the inverter.

How big (Ah) is the battery?

 

[time2roll]

What make/model inverter? What type of battery do you have? Next you need to use your multimeter to verify these voltages.
Get readings at the controller, battery and inverter. Right on the terminals, not the wire or connectors.
Then apply the load to the inverter and take the same readings to compare.

Post the results.

 

[sunshine]

The low voltage alarm on both my inverter and charge controller are triggered whenever I try to use anything high powered

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[circus]

Wire gauge, length or resistance somewhere. In a wire as amps go up so does resistance and the voltage drops.

 

[natdak]

That sounds like the 1000w load is simply more than the battery can handle. If it used to be able to handle that size load, it probably means your battery is at end of life. From what you've described, I don't think it is anything wrong with the inverter.

How big (Ah) is the battery?

It's 2 100ah truck batteries in parallel. But I somehow don't think the problem is what you suggested because they were working great until a week ago then suddenly gave problems. It got suddenly bad then gradually worse. Before it was handling 1500w continuous and the pump at 750w for a long time. The batteries are 1 year old of regular use, never taken below 12.46v.

 

[natdak]

What make/model inverter? What type of battery do you have? Next you need to use your multimeter to verify these voltages.
Get readings at the controller, battery and inverter. Right on the terminals, not the wire or connectors.
Then apply the load to the inverter and take the same readings to compare.

Post the results.

Will post results soon. It's a photonic universe 2000w, 4000w surge. Batteries are 2 100ah truck batteries that are one year old with regular use and never taken below 12.46v. The inverter does a buzzing/zapping noise on start up. Like the sound of the current streaming in

 

[Rednecktek]

The inverter does a buzzing/zapping noise on start up. Like the sound of the current streaming in

umm.. yeah... that's not right. I'd probe the voltages right at the battery as recommended and if those aren't bottoming out I'd look at replacing that inverter. Noise is usually a precursor to magic orange smoke.

 

[natdak]

The tests with loads were all separate tests and therefore vary a bit. The figures were taken with a multimeter.

 

[Rednecktek]

Ouch!! Yup, at least one of the batteries is dead and dragging down the other one. Worst case it's both batteries dead. You can repeat the experiment with each battery independently and see if it's just 1 battery or both that have given up the ghost.

I'm guessing you've already done the basics like check the water? Your starting voltage looks OK but it shouldn't drop anywhere near that much once there's a load.

 

[natdak]

And now the sun is out, and boosting the voltage to 14.6v so I tried again. This time it worked and I was able to run the pump continuously!! There showed no surge voltage drop just directly to 13.6v and gradually decreasing to 13.2v. We have had it dark and rainy the last fews day. Is this indicative of a bad battery? Can it also be the lugs?

 

[Rednecktek]

Yup, I bet if you had a shunt or a DC amp clamp around the SCC wires you'd see the SCC ramping all the way up to pick up the slack.

Do you have a hydrometer you can poke in there and get the specific gravity readings on each cell? Any auto parts store should have them cheap. I doubt it's the lugs but those are easy to clean, sounds like the batteries are just pushing up the daisies. Check the SG and water, throw a battery charger on there in the sun to help out the SCC, then try the load experiment again with each battery individually.

 

[time2roll]

Batteries seem to be close to inadequate or shot. Really should have 4 to 6+ batteries to drive this inverter. Unless they are 8D size then maybe 2 is ok.

 

[Horsefly]

Do you have a DC clamp meter? An easy check would be to measure the current out of each of the two batteries during a load. I had 4 12V batteries in a 2S2P 24V setup in my system, and similar issues 2 years ago: Suddenly the battery bank seemed to drop faster than before. I put a 40A load on the bank, and measured 38A out of one of the two strings, and 2A out of the other. I did some testing with different combinations of single 2S strings, and quickly found the bad battery.

 

[natdak]

After a full day in the sun the batteries are 15.2v! Even when the sun has gone down. I have been able to use it normally for some days now without problems. It appears that the voltage of 13.6v that I had when I was getting the alarm is now the new empty, 15.2v is full and its usually running in the 14v range. Bit weird huh? Why the hell has it done that? Maybe its bad for other components?
The batteries are still both 15.2v when isolated

 

[Horsefly]

15.2V is very high. You said your batteries were "truck" batteries. I assume that means they are flooded lead acid. The battery manufacturer should tell you for sure, but I would bet the bulk / absorption charging for those batteries is not above 14.6V. Of course I don't recognize that meter, so it may be completely inaccurate too.

 

[time2roll]

Replace the battery in your meter. Meter will tend to read high with a depleted battery.

 

[natdak]

Solved: I replaced the battery in the meter and the readings are back to normal. That thing made me discharge my batteries hard, but at least its not them that are broken. I was thinking it was be impossible to increase the voltage like that! Thanks for all the help guys.