24v 2000w wrong input voltage readout

[Wonko]

I'm having some trouble with my Giandel 24v 2000w inverter. The input voltage readout (on the LED panel on the front of the inverter) is not reporting the correct voltage and is consistently lower than the actual voltage. The system was working great for about 5 days of operation but then this problem started happening. I had run the batteries down to 19v during the first few days and the lo power cut off worked great, now it is cutting off the power at 24.5 volts which is obviously not good.

The system is shutting down due to a low power alarm while there is plenty of charge in the batteries.

Symptoms: The input voltage on the inverter consistently reads a voltage under the actual input voltage.

Here is the troubleshooting I've tried.
All the supplied voltages are being tested with a power supply and double checked at the input terminals with a trusted multimeter. Input voltage ("when I supply") is from the power supply. "input voltage reads" is from the LED screen on the front of the inverter.
When I supply 26.5V the input voltage reads 25.8V.
When I supply 26.0V the input voltage reads 24.0V
When I supply 25.5V the input voltage reads 21.5V
When I supply 25.2V the input voltage reads 19.5V and the low power alert starts beeping.
When I supply 25.0V the low power cutt off activates with the LED screen displaying LO and the buzzer is on consistently until the system is turned off.

Is there anything to do to re-calibrate the voltage reader? What could cause this issue?

The only thing that I can think of that could do damage to the system is I have a 12v water pump running on a circuit behind a 24v to 12v step down. It's also possible the inverter is just bad.

Anyone else experience this? Suggestions on what to do?

 

[mopat]

Not sure what was the purpose of the troubleshooting you've tried?

What is (supposed to be) charging the batteries?

 

[Wonko]

I have taken the batteries out of the equation by using a power supply (an adjustable power supply where the voltage can be changed and it will be kept constant).

Basically I'm simulating the batteries at different levels. I hope this helps.

 

[rmaddy]

What size wires do you have to the inverter from the battery? Are the wires getting warm?

Maybe you have real voltage loss. Use a voltmeter and measure the actual voltage at the inverter DC connections. How do those voltages correspond to the voltages at the battery terminals/power supply?

And what kind of batteries do you have (what chemistry)? If you have a 24V nominal setup then I would consider a battery voltage of 24.0V as being below 10% SOC for LiFePO4. At 19V you've drained the batteries dry. If you have LA then it is likely different. But then you shouldn't go below 50% SOC.

 

[Bud Martin]

The more current you draw from the batteries the more Voltage drops on the wires to the batteries so you will see less Voltage at the inverter meter, you can also have Vdrops on poor connections too. Most inverter built-in V meter does have high tolerance, typical 2 ~3% range
Do you have clamp-on DCA meter to check the current draws feeding the inverter?

How much current is the inverter drawing in the test below?
When I supply 26.5V the input voltage reads 25.8V.
When I supply 26.0V the input voltage reads 24.0V
When I supply 25.5V the input voltage reads 21.5V

 

[tazmann]

I have the same inverter and when it is under a pretty good load it always shows about .5 volts less. The one time I had problem it turned out my batteries were a lot lower charged than I thought

 

[Wonko]

Thank you all for your replies. I'm sorry if my post was not clear, I have now made a video of the problem (at the request of Giandel) for more clarification.

https://photos.app.goo.gl/MMXfWEc3XSAEfSpm9

@rmaddy I have tested with large and small wires, I've ruled out that possibility. As you can see in the video the multi meter is directly connected to the input terminals of the inverter. I've also taken the batteries out of consideration as the problem because I'm using a power supply.

@Bud Martin I hope the video above can answer that question, from what I see I am drawing about 0.26 amps through all of the voltage levels.

@tazmann I've definitely had that problem before I really like using a power supply any time I'm dealing with batteries or some sort of untrustworthy voltage source so I can rule out battery problems.

Thank you all again, this is my first post and I wasn't expecting such great and awesome help. I'm going to send the inverter back to Giandel for a replacement. I am mostly interested if someone knows what could cause this problem (assuming I started out with a good inverter) because I want to make sure I make changes to my system before ruining another inverter.

Thanks again! Aloha, Dusty

 

[tazmann]

Yep something wrong with it. I have 24 to 12 step down also no issues there. I have run mine hot an heavy with no problems , I did pull it out of cabinet and mount on wall for better cooling. the original battery cables that came with it would get pretty warm so I swapped them out for 2/0.
When its hot ambient temps in the rv I will put a fan on blowing to the housing of the inverter which helps because 100F temps and heavy load that housing gets hot