[SOLVED] Low output from Inverter

[LAMB]

I have a 230VAC inverter that is only giving me about 197VAC with no load, and about the same voltage with load. on a three light voltage tester only the center light illuminates. Any ideas what controls the voltage output of inverters?

 

[WimRFP]

First check the voltage with another (true rms) instrument to make sure you measure what you see.

In case of a "modified sinewave" inverter (that is an inverter that generates a more or less square wave envelope instead of a true sinewave), some instruments may givve wrong readings.

Are you having problems with equiment connected to this inverter?

 

[LAMB]

No, the voltage is definitely low. Let us not question that, it is low on my Fluke meter, it is making a light bulb glow orange, and the voltage tester is only giving me one light output. The unit is a charger inverter. The charger works 100% no problem there. By the way it is 230VAC 50Hz.

 

[WimRFP]

Most lightweight inverters first convert the low voltage to a DC high voltage (isolated). For a "true sine wave" it should be around 350VDC as the peak of 230VAC is about 325V. This voltage feeds a full bridge (at least 4 power switches required) and this full bridge is PWM modulated with about 20 kHz or higher. The output is filtered to remove the 20 kHz or higher switching components and the 50 Hz passes to the socket. So if this DC bus voltage is too low, you will never get 230Vac output voltage.

"Modified sine wave" inverters use similar approach, however the full bridge is switched with 50 Hz with some dead time (instead of a PWM signal). During this dead time all switches are in the off position. This gives less transient current then square wave switching with very small dead time. This type of inverters can use somewhat less bus voltage, as the peak to RMS ratio is less (w.r.t. sinewave).

Pure sine wave inverters can stabilize the output voltage by changing the bus voltage and don't change the PWM signal that is fed to the full bridge driver. Other option is to keep the bus voltage at a constant level and change the PWM signal. At least there should be some voltage divider between the 230Vac output, or between one of the 230Vac wires and ground (so half the AC voltage is measured). This output is probably fed to an AD converter or rectified and then fed to an AD converter or other control circuit. There can be an (optical) isolation in between.

Modified sinewave inverters should control the bus voltage to regulate the AC output voltage.

You may post a request for a service manual for your inverter (maybe you did already somewhere on the Internet). Hope this helps you a bit.

 

[Raza]

Hi,
Can you please tell me the model number of the INVERTER if any?. Is this a PURE SINE WAVE or Modified Sine Wave or a square wave inverter?
If possible post a PICTURE of the control board.

 

[LAMB]

t is a Kipoint model K1-LTS-1000-12V. It is a pure sine wave inverter.

 

[WimRFP]

Hello,

I downloaded the manual for the K1-LTS series, the default setting may be 200V. You may read page 28 (english manual). You can change the output voltage via the installation/operation menu.

 

[LAMB]

The problem with that is, I already did that, but the actual output from the inverter is reading 187.1 volts even with the reading on the inverter LCD shows 240VAC

 

[WimRFP]

Does the output voltage drop when you program 200V instead of 230V? Did you try to contact the manufacturer/supplier regarding this problem?

 

[LAMB]

I did not check to see if the output dropped, but I did raise it from the menu to 240VAC and the output was still 187.1 Volt. Yes I am in contact with the manufacturer, but the response has been very slow.

 

[LAMB]

Just want to say, the problem has been solved. It was a pot adjustment on the board that somehow or the other was tampered with, new adjustments were made, and the voltage is now easily up to 240 Volts. Let me say how grateful I am to all you guys who so willingly tried to help me, it is much appreciated, I hope that some day I will be able to reciprocate. What a delightful forum.

 

[WimRFP]

¡Good to hear that everything is fine now!

Wim

 

[vimalkhanna]

Actually , the manufacturer should be taken to task on this rather than treat the case as solved .
Why was the LCD display showing 240VAC when the load output was 187VAC ?
Shows that the output was not the actually across the terminals .
If not so, why the supplier is capable of giving an incorrect improper equipment and getting away with it ?
Why should the consumer keep mum and take it in his stride ?
Is the manufacturer not fooling the public ?